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Control and readout electronics for miniaturized temperature sensors integrated with an organ-on-a-chip

Abstract

De acordo com um estudo realizado pelo instituto de biomateriais e engenharia biomédica da Universidade de Toronto nos Estados Unidos da América, 4 em cada 1000 pacientes sofreram de efeitos adversos provocados por fármacos. Este problema surge devido ao facto de o teste de fármacos serem realizados em animais e, posteriormente em humanos. A utilização dos organ-on-a-chip aumentam a eficácia quando se inicia os testes em humanos porque são mais representiativos do que os testes em animais. A tecnologia organ-on-a-chip (OOC) surgiu com o objetivo de ser possível replicar aspetos importantes da fisiologia humana e deste modo poder superar as limitações dos procedimentos tradicionais, aumentando assim a segurança e eficácia de quem os toma. Apesar da tecnologia OOC fornecer uma série de vantagens comparativamente com as técnicas convencionais, esta ainda carece de sistemas para monitorização de multiparâmetros capazes de fornecer informações à microescala durante os testes de cultura de células bem como na testagem de novos fármacos. Neste sentido, torna-se muito importante o desenvolvimento de microssensores integrados em sistemas microfluídicos para monitorizar os diversos parâmetros celulares de modo a perceber que efeitos os fármacos provocam nas células. Parâmetros como temperatura, oxigénio, pH, nível de nutrientes, entre outros, são variáveis de interesse para a perceção global do metabolismo criado pela combinação de fármacos com células de múltiplos órgãos. Assim, o trabalho desenvolvido nesta dissertação tem como objetivo estudar e desenvolver a eletrónica de leitura e atuação de um microssensor de temperatura, baseado em resistance temperature detector (RTD), que será integrado na tecnologia OOC. O sistema desenvolvido para além de fornecer portabilidade e baixo custo, permite realizar leitura de vários microssensores com uma sensibilidade de 15mV/0.1°C. Foi também implementada uma componente gráfica que permite ao utilizador selecionar o sensor e acompanhar os resultados em tempo real.

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Control and readout electronics for miniaturized temperature sensors integrated with an organ-on-a-chip

Author: Oliveira, Carlos Manuel Lima
Year: 2022
Source: https://repositorium.uminho.pt/bitstreams/9695516d-26bc-4ec0-b142-bc784f464103/download
Uni e sidade do Minho
Escola de Engenha ia
Ca los Manuel Lima Oli ei a
Con ol and eadou elec onics o
minia u ized empe a u e senso s
in eg a ed wi h an o gan-on-a-chip
Ma ço de 2022
UMinho | 2022 Ca los Oli ei a Con ol and eadou elec onics o
minia u ized empe a u e senso s
in eg a ed wi h an o gan-on-a-chip
Ca los Manuel Lima Oli ei a
Con ol and eadou elec onics o
minia u ized empe a u e senso s in eg a ed
wi h an o gan-on-a-chip
Ma ço de 2022
Ca los Manuel Lima Oli ei a
Con ol and eadou elec onics o
minia u ized empe a u e senso s in eg a ed
wi h an o gan-on-a-chip
Disse ação subme ida na Uni e sidade do Minho pa a
ob enção do g au de
Mes e em Engenha ia Ele ónica Indus ial e de
compu ado es
T abalho e e uado sob a o ien ação do(s)
P o esso a D .ª G aça Minas e D .° Paulo Sousa
Ma ço de 2022
iii
DIREITOS DE AUTOR E CONDIÇÕES DE UTILIZAÇÃO DO TRABALHO POR TERCEIROS
Es e é um abalho académico que pode se u ilizado po e cei os desde que espei adas as
eg as e boas p á icas in e nacionalmen e acei es, no que conce ne aos di ei os de au o e
di ei os conexos.
Assim, o p esen e abalho pode se u ilizado nos e mos p e is os na licença abaixo indicada.
Caso o u ilizado necessi e de pe missão pa a pode aze um uso do abalho em condições
não p e is as no licenciamen o indicado, de e á con ac a o au o , a a és do Reposi ó iUM
da Uni e sidade do Minho.
Licença concedida aos u ilizado es des e abalho
A ibuição-NãoCome cial-SemDe i ações
CC BY-NC-ND
h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0/
i
ACKNOWLEDGEMENTS
I would like o hank P o esso G aça Minas o he good o ien a ion and oppo uni y
o be a pa o his p ojec .
To P o esso Paulo Sousa, a big hanks o all he guidance, knowledge, disponibili y,
and dedica ion o his o ien a ion.
Also, hank Tiago Ma os o all he suppo in he elec onics and assembling o he
ci cui and all he pa ien and disponibili y ha you had h oughou his p ojec .
To my pa en s, hanks o allowing me o ha e an educa ion and o all he pa ience
on his ough pa h, all I achie ed un il now, and wha I am se o achie e in he u u e is all
hanks o you e o s and ad ice.
To my sis e , hank you o all he ad ice and o being always he e o me when I
needed i . You a e an example o me, someone o look up o.
To Ma ga ida, hank you o all he help, ad ice and o always being he e o me.
To all my iends, all he gang, you know who you a e, hanks o all he help you ga e
me in hese se en yea s, I could no ha e made i wi hou you all. I is a pleasu e o call you
amily, we wen h ough e e y hing oge he and we made i , le s celeb a e.
To all he Re ood gang, he olun ee wo k con ibu ed di ec ly o wha I am oday and
b ough he mos awesome people o my li e, hank you all, le s keep going.
Thank you o all o he unnamed pe sons who somehow con ibu ed o wha I am
oday.
Finally, a big hank you o you B uno. I am hank ul ou pa h came oge he . Wha e e
you a e, you a e my s eng h and he ligh ha guides me h ough my pa h, his one is o you
dude.

This wo k esul s pa ially o he p ojec NORTE-01-0145-FEDER-029394, RTChip4The anos ics, suppo ed by
P og ama Ope acional Regional do No e - No e Po ugal Regional Ope a ional P og amme (NORTE 2020),
unde he PORTUGAL 2020 Pa ne ship Ag eemen , h ough he Eu opean Regional De elopmen Fund (ERDF)
and by Fundação pa a a Ciência e Tecnologia (FCT), IP, p ojec e e ence PTDC/EMD-EMD/29394/2017.
i
DECLARAÇÃO DE INTEGRIDADE
Decla o e a uado com in eg idade na elabo ação do p esen e abalho académico e
con i mo que não eco i à p á ica de plágio nem a qualque o ma de u ilização inde ida ou
alsi icação de in o mações ou esul ados em nenhuma das e apas conducen e à sua
elabo ação.
Mais decla o que conheço e que espei ei o Código de Condu a É ica da Uni e sidade do
Minho.
ii
RESUMO
De aco do com um es udo ealizado pelo ins i u o de bioma e iais e engenha ia
biomédica da Uni e sidade de To on o nos Es ados Unidos da Amé ica, 4 em cada 1000
pacien es so e am de e ei os ad e sos p o ocados po á macos. Es e p oblema su ge de ido
ao ac o de o es e de á macos se em ealizados em animais e, pos e io men e em humanos.
A u ilização dos o gan-on-a-chip aumen am a e icácia quando se inicia os es es em humanos
po que são mais ep esen ia i os do que os es es em animais. A ecnologia o gan-on-a-chip
(OOC) su giu com o obje i o de se possí el eplica aspe os impo an es da isiologia humana
e des e modo pode supe a as limi ações dos p ocedimen os adicionais, aumen ando assim
a segu ança e e icácia de quem os oma. Apesa da ecnologia OOC o nece uma sé ie de
an agens compa a i amen e com as écnicas con encionais, es a ainda ca ece de sis emas
pa a moni o ização de mul ipa âme os capazes de o nece in o mações à mic oescala
du an e os es es de cul u a de células bem como na es agem de no os á macos. Nes e
sen ido, o na-se mui o impo an e o desen ol imen o de mic ossenso es in eg ados em
sis emas mic o luídicos pa a moni o iza os di e sos pa âme os celula es de modo a
pe cebe que e ei os os á macos p o ocam nas células. Pa âme os como empe a u a,
oxigénio, pH, ní el de nu ien es, en e ou os, são a iá eis de in e esse pa a a pe ceção
global do me abolismo c iado pela combinação de á macos com células de múl iplos ó gãos.
Assim, o abalho desen ol ido nes a disse ação em como obje i o es uda e
desen ol e a ele ónica de lei u a e a uação de um mic ossenso de empe a u a, baseado
em esis ance empe a u e de ec o (RTD), que se á in eg ado na ecnologia OOC. O sis ema
desen ol ido pa a além de o nece po abilidade e baixo cus o, pe mi e ealiza lei u a de
á ios mic ossenso es com uma sensibilidade de 15mV/0.1°C. Foi ambém implemen ada
uma componen e g á ica que pe mi e ao u ilizado seleciona o senso e acompanha os
esul ados em empo eal.
Pala as-Cha e: Mic ossenso es de empe a u a, O gan-on-a-chip, esis ance empe a u e
de e o , sis emas mic o luídicos.
iii
ABSTRACT
Acco ding o a s udy conduc ed by he Ins i u e o Bioma e ials and Biomedical
Enginee ing a he Uni e si y o To on o in he Uni ed S a es o Ame ica, 4 ou o e e y 1,000
pa ien s su e ed om d ug- ela ed ad e se e ec s. This p oblem a ises because he d ug es
mos ly pe o med on animals and, he e o e, does no ai h ully ques ion he phenomena ha
occu a he le el o he human being. Thus, he use o hese d ugs can lead o complica ions
o humans as well as damage o he pha maceu ical indus y. O gan-on-a-chip (OOC)
echnology has eme ged wi h he aim o eplica ing impo an aspec s o human physiology
and hus being able o o e come he limi a ions o adi ional p ocedu es, he eby inc easing
he sa e y and e icacy o hose who ake hem. Al hough OOC echnology p o ides se e al
ad an ages compa ed o con en ional echniques, i s ill lacks mul ipa ame e moni o ing
sys ems capable o p o iding mic oscale in o ma ion du ing cell cul u e es ing as well as
es ing o new d ugs. In his sense, i is e y impo an o de elop mic osenso s in eg a ed in
mic o luidic sys ems o moni o he a ious cellula pa ame e s in o de o unde s and wha
e ec s he d ugs ha e on cells. Pa ame e s such as empe a u e, oxygen, pH, numbe o
nu ien s, among o he s, a e a iables o in e es o he o e all pe cep ion o me abolism
c ea ed by he combina ion o d ugs wi h mul iple o gan cells.
Thus, he wo k de eloped his disse a ion aims o s udy and de elop he elec onic
eading and ac ua ion o a mic o empe a u e senso , based on esis ance empe a u e
de ec o (RTD), which will be in eg a ed in o OOC echnology. The sys em de eloped in
addi ion o p o iding po abili y and low cos , allows o pe o m eading o se e al mic o
senso s wi h a sensi i i y o 15mV/0.1°C. A g aphical componen has also been implemen ed
ha allows he use o selec he senso and ack he esul s in eal ime.
Keywo ds: Tempe a u e mic osenso s, O gan-on-a-chip, esis ance empe a u e de ec o ,
mic o luidic sys ems.
15
1. INTRODUCTION
In his chap e , i will be made a con ex ualiza ion o he subjec , ollowed by he
mo i a ions and objec i es o his disse a ion. When i comes o con ex ualiza ion, i aims a
gi ing a li le unde s anding o o gan-on-a-chip (OOC) echnology and he need o senso s o
moni o hem. In he ollow-up, he mo i a ion o he de elopmen o his p ojec will be
p esen ed, ealizing he eason o choosing his heme. The objec i es o his disse a ion will
be p esen ed and desc ibed in de ail, suppo ed by he expec ed esul s o each objec i e.
Finally, he s uc u e o he disse a ion will be p esen ed.
1.1 Con ex ualiza ion
Acco ding o a s udy by he Ins i u e o Bioma e ials and Biomedical Enginee ing a he
Uni e si y o To on o, 20% o enal diseases acqui ed a e hospi al admissions a e di ec ly
ela ed o oxici y om e ec s no o eseen in clinical examina ions o hese d ugs. To
unde s and he e ec s o a ious d ugs and inc ease he sa e y and e icacy o hose who use
hem, OOC echnology is eme ging o simula e impo an aspec s o human physiology when
new d ugs a e being de eloped. This echnology allows ec ea ing h ee undamen al aspec s
o human physiology: (1) he mul icellula o epi helial ascula in e aces o o gans, in he
case o a blood essel, lung o bowel ne wo ks, which unc ion as ba ie s in issues; (2) he
o ganiza ion a he le el o he issue o pa enchymal cells, such as li e , hea , muscle
skele on o umou s, which a e esponsible o impo an unc ions o he o gan; and (3)
sys ema ic in e ac ion be ween o gans, allowing o, mo e accu a ely, pe cei e all he
mechanisms in ol ed in he human physiology [1,2].
OOC echnology no only inco po a es a ious ypes o cells, bu also enginee ing
aspec s, such as he inco po a ion o di e en ypes o senso s and mic o luidic channels [3].
Tempe a u e measu emen s a e ex emely necessa y o mos biological and chemical
p ocesses. This measu emen mus be e ec i e and accu a e, howe e , when he samples a e
in mic o o e en nano o de , his ask becomes qui e di icul [4]. RTDs a e highly linea and
sensi i e senso s, wi h a e y wide empe a u e ange be ween -200°C and 850°C, always
depending on he ma e ial om which i is ab ica ed, and a e he e o e mos ly used o

16
minia u ized empe a u e measu emen sys ems especially due o hei educed dimensions
[4,5].
This disse a ion will explo e solu ions o empe a u e mic osenso s in eg a ed in o
mic o luidic pla o ms o in i o es ing ocusing on he OOC echnology, in i s his o y and
wo k al eady de eloped. The choice o RTD as a empe a u e senso o his wo k compa ed
o o he senso s o he same pu pose, i s a chi ec u e, ab ica ion, measu emen echniques,
and i s ole in OOC echnology will also be analysed.
1.2 Mo i a ion and obje i es
Science and echnology ha accu a ely s udies and manipula es mic oscale luids a e
called mic o luidic, and OOC is a subca ego y o hese whose main objec i e is o simula e he
physiological aspec s o he human o gan. OOC echnology was conside ed one o he op 10
eme ging echnologies o 2016 a he Wo ld Economic Fo um [6].
Since his is an eme ging echnology, al hough al eady widely used and de eloped, is
s ill in an emb yonic s a e and so he e a e s ill some sho comings in i s implemen a ion.
One o he s ands o his echnology ha s ill lacks wo k is he enginee ing a ound
echnology, in a mo e conc e e case, he in eg a ed senso s. This is a echnology ha o be
unc ional equi es senso s ha allow use s o moni o he en i onmen al pa ame e s o he
cell, such as pH, oxygen le els, nu ien le els, empe a u e, among o he s. The main
mo i a ion o his disse a ion is o s udy and de elop a sys em o con ol and eading o
empe a u e mic osenso s in eg a ed on OOC o o e come he ac ual limi a ions. These
mic osenso s we e de eloped in he labo a o y o Mic o/Nano echnologies and Biomedical
Applica ions o he Cen e o Mic oEle oMechanical Sys ems (CMEMS) o Minho Uni e si y.
The main objec i e is he de elopmen o elec onic ci cui s o inc ease he eading esolu ion
o hese senso s, using low noise ci cui s and po able sys ems. This sys em mus be able o
p ecisely and accu a ely ead wi h a esolu ion o 0.1°C in he ange o 35°C o 45° o co e ing
he op imal empe a u e o he human body. Besides, i is also aimed o de elop a g aphical
applica ion ha allows he use o iew he empe a u e da a in eal- ime and change
be ween he a ious senso s ha can be connec ed o he ci cui .
To accomplish his goal, some asks mus be done:
17
• De elopmen o a cu en sou ce o RTD exci a ion
The RTD is a empe a u e senso ha uses an exci a ion cu en , known and
cons an , o p oduce a ol age in i s e minals, esul an om he combina ion o he
known cu en and i s a iable esis ance alue a he poin o measu emen (Ohm
law). This cu en alue mus be he maximum cu en ha gi es he bes esolu ion
and a he same ime p e en s he senso om sel -hea ing.
• De elopmen o low noise and po able con ol and eadou ci cui
To p o ide low noise, he powe sou ce o he ci cui mus be independen o
he powe g id and his is only possible wi h ba e ies, allowing no only low noise bu
po abili y o he sys em. The ci cui mus be in eg a ed in o a PCB o con ibu e also
o educing he noise om wi es and he elec onic componen s ha compose i , all
mus be low noise.
• De elopmen o a g aphical in e ace
To see he changes in empe a u e and esul s o mul iple senso s, i is
necessa y o ha e an use - iendly in e ace ha can display he alues o empe a u e
om an RTD ha is connec ed o he sys em. Also, he use mus be capable o
selec ing which senso wan s o ead and sa e he alues on a ile.
1.3 Disse a ion s uc u e
This disse a ion is s uc u ed in he ollowing way:
• Chap e 1 con ains he in oduc ion, a sho con ex ualiza ion and he mo i a ions
and objec i es o his disse a ion.
• Chap e 2 p esen he s a e o a , highligh ing he esea ch abou heo e ical
subjec s and wo k done in mic o luidic de ices, OOC and empe a u e senso s.
• Chap e 3 p esen s he adop ed me hodology o sys em de elopmen .
• Chap e 4 con ains he implemen a ion o he de eloped sys em, which ollows he
me hodology ou lined in he p e ious chap e .
• Chap e 5 add esses all he expe imen al esul s ob ained in he es s made as well
as i s analysis and discussion. Some imp o emen s o he de eloped sys em a e
also p esen ed.
18
• Chap e 6 p esen s he conclusions d awn om he de elopmen and alida ion o
he sys em. Mo eo e , his chap e p oposes u u e wo k o imp o e he sys em.
19
2. STATE OF ART
In his chap e , he heo e ical componen o his disse a ion will be p esen ed. Fi s ly,
he mic o luidic de ices will be add essed, ollowed by a deepe ocus on he OOC. A e hese
opics i will be in oduced he mos common empe a u e senso s used o hese
applica ions, dedica ing a sub-chap e o he RTD, he senso ha was chosen o his p ojec .
2.1 Mic o luidic sys ems
Mic o luidics is he science and echnology ha p ocess o manipula e small amoun s
o luids, using channels wi h dimensions o ens o hund eds o mic ome es. These sys ems
in ol e se e al ields: biode ence, mic o echnology, molecula analysis, and molecula
biology, among o he s [8].
2.1.1 His o y
A lo o di icul ies and p oblems in a ious ields con ibu ed o he de elopmen and
g ow h o mic o luidics. A e he end o he cold wa , mic o luidic sys ems we e impo an
o de ec chemical and biological h ea s since his h ea was a majo conce n in his e a.
Then, ano he ac o was he big necessi y o mic oanalysis, in he 1980s, in he ield o
molecula biology, mainly on high- h oughpu DNA sequencing. This p ocess came wi h he
neediness o sys ems wi h mus highe h oughpu , highe sensi i i y, and esolu ion.
Mic o luidics o e came hese p oblems. A las , ano he majo con ibu ion o he
de elopmen and g ow h o mic o luidics came wi h mic oelec onics. Pho oli hog aphy and
associa ed echnologies a e success ully implemen ed in silicon mic oelec onics and MEMS
ab ica ion. The objec i e was o ex end his ab ica ion o mic o luidics. This ype o
ab ica ion con ibu ed di ec ly o he educ ion o he size o hese sys ems. Howe e , silicon
and glass used in he i s wo ks we e apidly eplaced by polyme s because hey a e
expensi e and in addi ion o ha he ab ica ion o he mic ochannels is mo e complex and
expensi e. Also, he silicon is opaque which b ings p oblems o op ical applica ions. Thus,
mic o luidic apidly s a ed o be ab ica ed in polyme ic ma e ials like polydime hylsiloxane
(PDMS) [8].
20
2.1.2 The impo ance o mic o luidic sys ems
Mic o luidic sys ems a e low-cos and minia u ized de ices wi h a sho eac ion ime
and high h oughpu using a small olume o eagen s/samples which allows he de ice o
ope a e nea i s wo king en i onmen . Fu he mo e, hese de ices a e ab ica ed by easy and
well-es ablished p ocesses. Ope a ing close o he en i onmen allows high pe o mance as
hey a e highly accu a e and e ec i e [9].
These ad an ages ha e eased he selec i e and e ec i e es ing o chemicals in cellula
en i onmen s, he e o e addi ionally pe mi ing o obse e in eal- ime he changes ha his
has a he physiological le el o he cell, which was p e iously p ac ically impossible. I is a
echnology wi h a lo o po en ials ha may gi e dis inc i e oppo uni ies, o ins ance, o
a e ci cula ing umou cell isola ion and de ec ion om he blood o pa ien s, which u he s
he esea ch o cance s em cell bioma ke s and expands he unde s anding o he biology o
me as asis [10].
2.1.3 Physics o mic o luidics
Di e en p ope ies a e shown in he luid low o mic o luidics [9]:
Lamina low
The eloci y a luid s eam is called lamina low. Due o he small size o
mic ochannels, he low is almos always lamina . Lamina low can be desc ibed by Reynolds
numbe ,𝑅𝑒, which is de ined by he equa ion,
𝑅𝑒 = 𝜌𝑣𝐷ℎ
𝑢
whe e 𝜌 is he densi y o he low, 𝑣 is he low eloci y, 𝐷ℎ is he hyd aulic diame e o he
mic ochannel and 𝑢 is he iscosi y o he low.
Di usion
Di usion is esponsible o mixing he di e en luid lows ha a e in con ac bu ne e
mix due o he muddy low. This can be desc ibed by he equa ion,
𝑡 = 𝑙2
2𝐷

21
whe e 𝑡 is he di usion ime o he molecule o di use o e he dis ance 𝑙 and 𝐷 is he
di usion coe icien o he molecule in solu ion.
Capilla y numbe
This mic o luidics physics is exclusi e o d ople mic o luidics. The con inuous phase
low ha de o ms he d ople is de ined by he capilla y numbe ,
𝐶𝑎. I is de ined by he
ollowing equa ion,
𝐶𝑎 = 𝜂𝑐 𝑣𝑐
𝛶
whe e 𝜂𝑐 is he iscosi y o he con inuous phase, 𝑣𝑐 is he eloci y o he con inuous phase,
and 𝛶 is he in e acial ension be ween he oil and wa e phases.
Webe numbe
Webe numbe is he esul o mul iplying he Reynolds numbe and he capilla y
numbe and cha ac e izes he in e acial ension, equen ly used o pa ame ize d ople
b eakup p ocesses.
𝑊𝑒 = 𝑅𝑒 × 𝐶𝑎
Bond numbe
Bond numbe cha ac e izes he ela i e impo ance o g a i y and in e acial ension.
I 's de ined by he equa ion,
Bo = ∆𝜌𝑔𝑤2
𝛶
whe e ∆𝜌 is he densi y di e ence be ween he wo immiscible luids, 𝑔 is he accele a ion
o g a i y,
w
is he cha ac e is ic leng h scale, and 𝛶 is he in e acial ension be ween he oil
and wa e phases.
2.1.4 Types o mic o luidics
Mic o luidics can be di ided in o wo ypes [9]:
Con inuous- low mic o luidics
This ype o mic o luidics is based on a single-phase luid in he chip. This has he
objec i e o educing he consump ion o eagen s and samples, which leads o g ea e speed
and ep oduc ion compa ed o adi ional expe imen s. Whoe e , his ype has some
disad an ages, like (1) he was e o luid de i a ed om he o e low in he channel, (2) he
22
slowness in achie ing uni o m mixing due o he lamina low, (3) he channel easily
con amina es he luid and he eagen , (4) he size o he de ices inc eases wi h he
inc easing o he numbe o pa allel expe imen s. This echnique can be seen in igu e 1 [11].
D ople mic o luidics
D ople mic o luidics is based on, a he han ha ing a cons an low o luid, only
disc e e d ople s a e eleased using immiscible phases. The eac ion o each d ople can be
handled wi hou he in e e ence o eagen s o he sample. Also, his ype o mic o luidics
has a highe h oughpu and p o ides a pla o m o pe o m many eac ions. The e a e h ee
main echniques used in his sys em: (1) co- lowing, (2) T-junc ion and (3) low- ocusing ( igu e
2) [9].
Figu e 1 – Schema ic ep esen a ion o a con inuous low. Adap ed om [11].
(1) Capilla y
(2) T-Junc ion
(3) Flow ocusing
Aqueous
Oil
Aqueous
Oil
Aqueous
Oil
Figu e 2 - Types o mic o luidics echniques o d ople s gene a ion. Adap ed om [8].
23
2.1.5 Ma e ials o mic o luidic de ices
The mic o luidic de ices ha e been widely ab ica ed by PDMS-based so li hog aphy
since his ma e ial is easily ab ica ed and easily bond h ough plasma ea men .
Fu he mo e, he PDMS is a low-cos ma e ial, biocompa ible wi h high op ical anspa ency
and has good gas pe meabili y and high he mal s abili y. I also eplica es nanome ic
cha ac e is ics om moulds ab ica ed by UV pho oli hog aphy, which can be eused se e al
imes, ensu ing ep oducibili y. As i has supe icial ea men me hods well de ined enables
he unc ionaliza ion o he de elopmen o biosenso s [12].
Howe e , he moulding o hese ma e ials in ol es a la gely manual p ocess, which
makes he manu ac u ing p ocess di icul o au oma e and consequen ly expensi e [13].
The moplas ics, like polys y ene, PMMA, polyu e hane, among o he s, a e used o
ab ica e mic o luidic de ices, enabling high- h oughpu bu compa ed o he PDMS, does no
allow ab ica ion wi h high-quali y. This ype o ma e ial will bend a ound 1000 imes less han
he PDMS because i s Young’s Modulus is h ee imes la ge han he PDMS, which in some
applica ions can be an ad an age [14].
Finally, in 2008, a s udy p oposed c ea ing de ices in pape o sol e he p oblems o
cos s and he equi emen o pumps. Pape is an inexpensi e ma e ial ha can pump he luid
i sel wi hou he need o pumps, by is wicking ac ion, and i is accessible o anyone ha has
a simple wax p in e . Howe e , i has i s disad an ages, namely, i is no a good ma e ial o
cell manipula ion because i abso bs biomolecules which can di icul he de ec ion o some
analy es, especially when hey a e in lowe concen a ions. Fo now, i is no an ideal solu ion
o be used in bio echnology [10].
In conclusion, he e is a need o imp o e he ab ica ion p ocesses o educe he o al
cos s. I is needed o de ices o be made o a ma e ial ha can be apidly p o o yped, like
PDMS o pape , ab ica ed o a low cos pe uni , and whe e he low can be ully con olled,
s opped, and e-s a ed.
24
2.2 O gan-on-a-chip
OOC is a mic o luidic de ice specialized in mimicking he unc ions o human o gans in
i o. I can ec ea e he en i e cellula en i onmen , he connec ions be ween cells and hei
in e ac ions. I allows o p ecisely egula e he condi ions whe e cells a e g owing and adap
hei ope a ion wi hin he en i onmen ha is being ec ea ed. Thus, egula es all pa ame e s
and op imizes he cell cul u e mic oen i onmen [16].
P elimina y es ing o d ugs be o e hey a e a ailable o humans is he mos impo an
p ocess, bo h on he consume side, o ensu e ha hey do no su e om se ious side
e ec s, as well as on he pha maceu ical indus ies side, as hese es s incu high cos s and i
is impe a i e o assu e he sa e y o he consume .
The de elopmen o new d ugs goes h ough a s age o animal es ing, which
some imes p oduces a high ailu e a e because hey do no eplica e human physiology e y
accu a ely. In addi ion, hey a e ime-consuming p ocesses and ha e e hical issues ha g ea ly
limi hei use. So, he es in animals has been complemen ed by 2D cell cul u es in i o [1,3].
Howe e , in i o models, e eal one majo disad an age compa ed o he in i o me hods,
hey canno , mos o he ime simula e he complex cell-cell and cell-ma ix in e ac ions
c ucial o egula ing cell beha iou in i o. Despi e ha , hey a e use ul o s udying he
molecula basis o physiological and pa hological esponses. The p oblems wi h es ing in 2D
models o animal-based models ha e gene a ed sizeable in e es in he sea ch o human-
based issue-like cons uc s o imp o ing he disease modelling and d ug and chemical
es ing, inc easing hei e ec i eness and educing economic losses om he lack o
e ec i eness [17].
Since he 90s, se e al mic o luidic echnologies ha e been applied o in i o sys ems.
Mic o echnology has opened doo s o OOC echnology o se e al easons: he ac ha
makes i possible o implemen small elec ic and luidic ci cui s o be in eg a ed in o
minia u ized de ices. They also allow g ea e p ecision and acili a e he deli e y o essen ial
nu ien s o cell g ow h, due o hei lamina na u e, so he g adien s a e o high
concen a ion due o a sho e di usion leng h. Finally, as he las ad an age, he shea s ess
applied o he cells can be con olled and minimized. In a way, all hese ad an ages allow he
c ea ion o a well-con olled en i onmen in he in i o cul u es wi hin OOCs, and hus
31
hand ha e a nonlinea esponse, small sensi i i y, small ou pu ol age, equi e cold junc ion
compensa ion and a e leas s able. The he mis o is a as esponse senso , has a high ou pu
and minimal lead esis ance bu needs an ex e nal powe o ol age sou ce, is non-linea , e y
agile and su e s om sel -hea ing e o s. The RTD is he mos s able wi h good linea i y and
accu acy (0,01°C) bu has low sensi i i y, a ound 0,00385 Ω/Ω/°C o pla inum senso s, i is
also ex e nally powe ed wi h a cu en sou ce, i is mo e expensi e, has a small ou pu
esis ance and also su e s om sel -hea ing e o s. Howe e , he RTD a e easie o
minia u ize and ab ica e in o he mic o luidic de ices and wi h sui able ampli ica ion and
il a ion elec onic ci cui s, a high sensi i i y esponse can be ob ained [31,36].
In he de elopmen o a senso , i is impo an o ake in o accoun ce ain
cha ac e is ics app op ia e o he desi ed applica ion [32]:
Ope a ion in e al
In he ope a ion in e al, he empe a u e limi s ha he senso eads, lowe and
uppe , a e de ined. A longe in e al can some imes p o ide a lowe senso 's linea i y and
sensi i i y.
Linea i y
Is he capabili y o he senso o espond linea ly o all he changes o empe a u e
h ough all he ope a ion ange.
Sensi i i y
I is said ha a senso is mo e o less sensi i e depending on he change in i s ou pu
alue when he empe a u e changes, ha is, wi h a small empe a u e change, he mo e
a iabili y he e is in he ou pu alue, he mo e sensi i e i is he senso .
Response ime
When a empe a u e change occu s, he ime i akes o he senso ou pu o change
i s alue is gi en wi h he esponse ime o he senso .
S abili y
This cha ac e is ic is de ined by he senso 's abili y o main ain he same esul a he
ou pu when i is unde a s able empe a u e.

32
E icacy
The e ec i eness o he senso is gi en by he en i onmen ha su ounds i and he
ci cui s whe e i is implemen ed. To be mo e e ec i e i is no mally needed good wi ing, good
g ounding h oughou all ci cui s, noise il a ion, among o he s.
Du abili y
The du abili y o he senso is he capabili y o he senso o ope a e in he same
en i onmen o some ime, no mally decided by he manu ac u e . This cha ac e is ic is
usually ela ed o he ma e ial ha composes he senso and i s encapsula ion.
Requi emen s o condi ioning signal
All senso s will ha e a ious signal condi ioning equi emen s such as ampli ica ion,
cold-junc ion compensa ion ( he mocouples), il e s, exci a ion (RTD and he mis o s), o se
e o adjus men , scaling o empe a u e uni s, lead esis ance co ec ion, channel- o-channel
isola ion, open he mocouple de ec ion ( he mocouples only).
Cos s
In all p ojec s, i is impo an o deno e he cos s, some imes a cheape senso will
sa is y he needs o he p ojec , as i will p obably need less su ounding ma e ial like wi ing,
signal condi ioning o e en assembly cos s. Howe e , some applica ions need mo e complex
senso s and hus op imized manu ac u ing, which can inc ease he inal cos . Ne e heless,
he le el o in eg a ion o he sensi i i y equi ed may jus i y a highe cos .
2.4 Tempe a u e measu emen in mic o luidic de ices
Se e al wo ks abou empe a u e measu emen s in mic o luidic sys ems ha e been
s udied and implemen ed. In he i s example, i is p esen ed a nanoneedle o measu e he
empe a u e o single cells. This sys em s udies he possibili y o a low o wa e o mo e he
cells agains he nanoneedle wi h enough amoun o o ce o pe mi he nanoneedle o
pene a e he cell wi hou damage. An elec ical ol age is applied o he nanoneedle and i is
measu ed he ou pu cu en o he con e sion o empe a u e, howe e , he s udy was only
simula ed and no implemen ed, he esul s we e p omising [38].
I is inc easingly impo an o analyse he beha iou o cells, bu i is also necessa y o
be ca e ul o no damage hem. The e a e cells om diseases such as cance , which e eal an
33
inc ease in empe a u e which makes i impo an o s udy in e cellula empe a u e. To
measu e cell empe a u e, many a emp s we e made, success ully and wi h high le els o
sensi i i y, bu he ma e ials used in hese measu emen sys ems p o ed o be a c i ical
disad an age because o hei high oxici y wi hin he cell in luencing hei de elopmen .
These phenomena occu ed when empe a u e sensi i e-ma e ials we e used o measu e he
empe a u e o cells, such as quan um do s, ha a e used as nano he mome e s [39],
nanopa icles, ha a e connec ed wi h o he nanopa icles and oge he ac as a molecula
sp ing and wi h he a ia ion o he empe a u e i s ex ension changes and ha ex ension is
used o measu e he empe a u e [40], and he mosensi i e ma e ials [41].
Nanoneedles ollowed, accompanied by ma e ial wi h p ope ies ha a e a ec ed by
empe a u e change. In he s udy o Binsilm e al. [38], a nanoneedle mic o luidic sys em was
p esen ed. The based ma e ial used in i s ab ica ion was he ungs en and he senso showed
o ha e a posi i e empe a u e coe icien o empe a u e (TCR) wi h he inc ease o
empe a u e. Fab ica ed in Y shape allowed he nanoneedle pene a ion in he cell o cause
minimal damage o he cell. The ou pu o his senso is gi en in he cu en o m, and i was
ob ained a esolu ion o 0.02°C which ansla es in a ia ions o 50nA.
In a s udy by Chunyan Li e al. [42], is p esen ed he de elopmen o a sma
mic oca he e wi h se e al in eg a ed mic osenso s, such as a empe a u e senso (RTD), low
a e senso (ho - ilm anemome y) and glucose biosenso (ampe ome ic senso ). The
empe a u e senso was ab ica ed in i anium gold (Ti/Au) deposi ed in a polyme ic and
lexible subs a e. A p ecise and linea esponse conce ning empe a u e was demons a ed
using he ab ica ed RTD. Fu he mo e, he au ho s showed ha he ab ica ion p ocess o
mic oca he e wi h in eg a ed mic osenso s is e y simple and sui able o low-cos mass
p oduc ion.
Ano he app oach o empe a u e senso s in he mic o luidic sys em was ela ed by
Naoki Inoma a, e al. [43]. This app oach was based on a pico calo ime e ha uses a esona o
o de ec he empe a u e a ia ion in he sample by equency acking o he esona o . The
sys em has a hea guide ha conduc s he hea o he sample and he esona o is kep in
acuum. The change o empe a u e makes he esona o ib a e and ha ib a ion equency
was ansla ed in he a ia ion o empe a u e in he mic o luidic channel. Was achie ed a
esolu ion o 5.2 pJ in he ab ica ed senso .
34
Mic o luidic de ices a e no only used in medical expe imen s. In he wo ks o Schmi
e al. [44] was p oposed he implemen a ion o an in elligen mic o luidic empe a u e
indica o o p ecisely p edic he expi ing da e o he ood on he package. The idea goes
h ough a sma package wi h passi e senso s ha , based on he empe a u e and ime ha
ood is packaged, demons a es a mo e eal expi a ion da e han con en ional ones p in ed
a he ime o packaging ha is es ima i e. Senso s ha al eady exis a e usually on he ou side
o he package and use ead ci cui s ha do no make i e y easy o ead. This s udy p oposed
a senso wi h wi eless eading. The senso is composed o a capilla y wi h a ec angula c oss-
sec ion wi h wo elec odes placed in opposi e walls o ob ain a pla ed capaci a o . Non- oxic
luid is used wi h high iscosi y ha will mel , educing he iscosi y, wi h he inc ease o
empe a u e, en e ing he mic ocapilla y, and inc ease i s iscosi y wi h he dec ease o
empe a u e, decele a ing he luid and s opping i . The dis ance ha he luid a elled will
be ela ed o he capaci y be ween he wo elec odes, which inc eases p opo ionally wi h
he inc ease in empe a u e.
Finally, an RTD senso was bonded oge he o he su ace o a PDMS based
he moelec ic coole in a wo k o Oile e al. [45] o a he oscle osis s udies. As he p e ious
wo ks ha used ho -wi e anemome e s, al hough ha ing high sensi i i y and being obus ,
had a limi a ion in low p ope ies measu emen a cell le el because i was p o en ha
damages he cells. I is impo an o unde s and he blood low in a he oscle osis s udies
because his disease a ec s di ec ly he blood essels bi u ca ions and i is de ec ed by
s udying he shea s ess ha is di ec ly co ela ed wi h he low a e. The he moelec ic
coole was ab ica ed in PDMS and he RTD was bonded o he su ace o he de ice, his
allowed each ime ha he low was inc eased, he empe a u e senso de ec ed ha inc ease
by changing i s alue o empe a u e. This p o es ha i is possible o use he RTD in a
he moelec ically coole o measu e he low a e o blood.
2.5 Tempe a u e mic osenso s based on RTD
Measu ing empe a u e wi h con en ional senso s such as he mocouples and
he mis o s a e success ul in samples in he o de o millime es, bu when ad ancing o
smalle samples hese senso s a e mo e di icul o in eg a e, as an example, in o mic o luidic
de ices. Se e al app oaches o cell cul u e empe a u e sensing ha e been explo ed in
35
p e ious wo ks such as comme cial PT-100 RTDs [46], luo escen polyme ic he mome e s
[47] and comme cial T- ype he mocouples [48]. Howe e , hese solu ions a e no e y
compac o in eg a ion in mic o luidic de ices o p esen a poo esolu ion. The ad ances in
mic o echnology ha e allowed he de elopmen o minia u ized empe a u e senso s based
on RTDs which can be in eg a ed wi hin mic o luidic de ices, as p oposed in his disse a ion
[4].
2.5.1 Cha ac e is ics
To cha ac e ize he RTD's, some de ails abou i should be speci ied [49]:
Type o esis i e ma e ial
Mos RTD is ab ica ed wi h pla inum, al hough o he ma e ials as nickel, aluminium,
coppe can be used. Pla inum is he p e e ed ma e ial since has highe linea i y and
sensibili y.
Tempe a u e coe icien
To con e he senso ou pu alues o empe a u e, i is necessa y o pa ame e ize
he empe a u e coe icien which ep esen s he change o esis ance pe uni o he
empe a u e o he esis i e ma e ial om 0°C o 100°C ( eezing and boiling empe a u es o
he wa e , espec i ely). The empe a u e coe icien decla ed by he IEC (In e na ional
Elec o echnical Commission) in 1983 o he pla inum was 0.00385 ohms pe ohm deg ee
cen ig ade. This alue is accep ed wo ldwide when using pla inum RTDs.
Nominal esis ance
This ea u e is he empe a u e ha should be expec ed o a ious empe a u e
alues. 100 ohms is he s anda d IEC a 0°C o PT100 bu he e a e o he nominal esis ances
a ailable (PT500, PT 1000, and o he s).
Tempe a u e ange o ope a ion
As i s name implies, i is he empe a u e ange whe e he senso ope a es. This
alue a ies wi h i s con igu a ion and ab ica ion me hods.
Dimensions and size es ic ions
The esis i e elemen mus i inside i s p o ec i e encapsula ion, so i s mos
impo an dimension is he ou e diame e . In his case, he RTD a e easy o minia u ize
acili a ing i s in eg a ion.
36
P ecision
This speci ica ion is gi en acco ding o he IEC 751 o pla inum RTD's as we can see
in able 1, di ided by wo classes (class A and class B) ollowing DIN 43760 equi emen s o
accu acy.
Response ime
I is he ime ha he senso akes o espond o a change o empe a u e and p o ide
a s able alue.
Sel -hea ing
This is a pa ame e ha is e y impo an o be awa e o because i ansla es in
pe u ba ions on he alues on he eading. As hese senso s need a cu en o exci a ion o
ope a e, ha alue mus be chosen and pa ame e ized so he senso ne e en e s in sel -
hea ing. This e o is ansla ed in o °C/mW.
Wi e con igu a ion
The elec ical connec ions o he exci a ion and eading o he RTD senso s add
elec ical esis ance ha is summed up o he esis ance o he senso . In his way, when
Tempe a u e °C
Class A
Class B
De ia ion
De ia ion
Ohms
°C
Ohms
°C
-200
±0.24
±0.55
±0.56
±1.3
-100
±0.14
±0.35
±0.32
±0.80
0
±0.06
±0.15
±0.12
±0.30
100
±0.13
±0.35
±0.30
±0.80
200
±0.20
±0.55
±0.48
±1.30
300
±0.27
±0.75
±0.64
±1.80
400
±0.33
±0.95
±0.79
±2.30
500
±0.38
±1.15
±0.93
±2.80
600
±0.43
±1.35
±1.06
±3.30
650
±0.46
±1.45
±1.13
±3.6
Table 1 - Pe missible de ia ions om heo e ical pla inum RTD alues. Adap ed om [34].

37
accu acy is impo an , he wi e con igu a ion needs o be conside ed o minimize ha
in luence.
2.5.2 Fab ica ion
The e a e RTD's ab ica ed wi h conduc i e wi e w apped in a glass o ce amic co e,
howe e , he minia u ized RTD's a e usually based on esis i e hin- ilm o pla inum, nickel,
o aluminium. Pla inum RTD's a e he mos accu a e because hey demons a e g ea e
s abili y o e ime. Tempe a u es can be measu ed in a ange o -189°C o +962°C wi h a
maximum accu acy o 0.001°C [36]. The hin p o ile o he RTD allows i o be ab ica ed in a
plane wall wi h a hickness o ew nanome e s and hus, can be easily in eg a ed in o
mic o luidic de ices. Usually, glass o PDMS a e used o close he mic o luidic channels and
RTD can be di ec ly ab ica ed on o his subs a e. The RTD is ab ica ed by hin ilm acuum
deposi ion echniques and hei s anda diza ion is ca ied ou by pho oli hog aphy echniques
and li -o p ocess [44,45].
Fi s , i is necessa y o ealize ha he ab ica ion o nanoma e ials and nanos uc u es
is pe o med in an ex emely clean en i onmen called a clean oom, in which he e a e ew
pa icles and specialized equipmen o h ee basic unc ions: (1) Thin ilm deposi ion; (2)
Pa e ning; (3) E ching.
The hin ilm deposi ion equi es a acuum en i onmen in he o de o 10−6 o o
1.3 × 10−4 Pa o ensu e ha any impu i ies o con aminan s a e no p esen in he deposi ion
chambe . The ma e ials o be deposi ed mus be o high pu i y, ypically 99.9999% o highe .
The h ee mos common hin ilm acuum deposi ion echniques a e:
The mal e apo a ion
The mal e apo a ion uses hea o e apo a e he sou ce ma e ial o high pu i y om
solid ma e ial o gas. The gas a oms a el h ough he acuum inside he chambe and when
hese a oms each he sub ac , hey condense and o m a hin ilm on he su ace. Me als
and dielec ics can be deposi ed using his echnique bu a e mos commonly used o deposi
me als because hei boiling poin is much lowe and hei deposi ion a es a e mo e s able.
This p ocess is comple ely au oma ized, a compu e con ols he empe a u e inside he
chambe and he hickness o he hin ilm, i jus needs he use o inse a he beginning o
he p ocess he hickness desi ed and he limi o empe a u e [52].
38
Elec on beam e apo a ion
Elec on beam e apo a ion is simila o he mal e apo a ion. I also uses hea o make
he e apo a ion o he high pu i y ma e ial and is pe o med inside a acuum chambe . The
majo di e ence is he sou ce o hea . A beam o elec ons is esponsible o hea ing and
consequen e apo a ion o he ma e ial o be deposi ed [53].
The elec on beam allows he hea ing o a me al ilamen un il abou 2500°C. A his
empe a u e, he elec ons a e e y ene ge ic and some o hem lea e he su ace o he
ilamen and a e accele a ed in di ec ion o he sou ce ma e ial wi h he help o a high ol age
elec ode. A g oup o magne s lead he elec on and ocus he beam o he sou ce ma e ial
[53].
One o he ad an ages o his echnique is ha i allows being deposi ed di e en
ma e ials on he subs a e wi hou opening he chambe because he elec on beam is well
con ined in space, i hea s only a small a ea o he sou ce ma e ial allowing o he sou ce
ma e ials o be in he chambe o be e apo a ed sequen ially. The sou ce ma e ial is pu inside
he chambe on he c ucible [53].
Sys ems ha hold ou ma e ials a e e y common and hey a e called he ou -pocke
hea h. Fou c ucibles i in o he hea h, and each c ucible can hold a di e en sou ce
ma e ial. So ha i can ha e up o ou laye s o di e en ma e ials deposi ed wi hou
b eaking he acuum. The hea h is a o a ed holde o coppe which is wa e -cooled. The
wa e cooling p e en s he c ucible ma e ial om mel ing and mixing wi h he sou ce ma e ial
o wi h he hea h i sel [53].
Spu e ing deposi ion
Spu e ing is a di e en p ocess compa ed o he o he wo ypes because i does no
use e apo a ion. Ins ead, uses ene gized a oms ha each he sou ce ma e ial ( a ge ) o be
deposi ed on he subs a e. These ene ge ic a oms hi he a ge and p opel he a oms o he
sou ce ma e ial ou o he a ge and in o he acuum sys em. Some o hese a oms each he
subs a e ha is a anged on he op o he acuum chambe and deposi . These ene ge ic
a oms used in he p ocess a e c ea ed by plasma. The a gon is he gas used o o m plasma
because i is an ine gas and will no esul in unwan ed chemical eac ions du ing he p ocess
[54].
39
When he gas is in he chambe , a high elec ical ol age is applied o he a ge . This
high ol age is s ong enough o emo e an elec on om he a gon a oms causing i o
become ionized and as he sou ce ma e ial is nega i ely cha ged, he a gon a oms will eac
wi h hese a oms indi idually by emo ing hem om he a ge ma e ial and peppe ing hem
in a ious di ec ions, including owa d he subs a e [54].
Pho oli hog aphy
Pho oli hog aphy is an indispensable s ep in he ab ica ion o hin ilm-based RTD. This
echnique is esponsible o ans e he desi ed pa e n o he senso o a pho o esis ma e ial
which is used o p o ec selec ed a eas du ing subsequen e ching o deposi ion p ocesses. I
uses ul a iole ligh o ans e he geome ic pa e n om an op ical mask o a pho o esis
deposi ed on he subs a e [55].
40
3. METHODOLOGY
In his chap e is p esen ed he me hods and he alida ion o a empe a u e senso based
on RTD. All he p ocedu es inhe en o he de elopmen o hese sys ems a e de ined. The
gene al equi emen s will be po ayed in he ollowing.
• Reading esolu ion o 0.1°C, in he ange o 35°C o 45°C;
• Low noise ci cui ;
• Real- ime and in si u moni o ing;
• Display he collec ed da a in g aphical o m;
• Compac size;
• Po able sys em;
• Capabili y o ead mo e han one senso .
The main goal o his disse a ion is he de elopmen o a sys em o measu e
empe a u e changes in OOC wi h a esolu ion o 0.1°C in a ange o 35°C and 45° C. This ange
o empe a u e alues co e s he ypical human body empe a u e, a ound 37°C, whe e he
human cells ypically g ow and i also can be used in s udies o hypo (35°C) o hype he mia
(42°C). To achie e his goal, he noise in he ci cui mus be minimum because in low signal
sys ems like his, e e y pe u ba ion, e en i i is minimal, is going o ha e a big impac on he
signal and, consequen ly on he alues ha a e ead and con e ed. A las , he alues ha
a e ead and con e ed a e going o be displayed in g aphical o m o be easy o he use o
ollow he empe a u e ansi ions o he en i onmen whe e he senso s a e inse ed. A
esolu ion o 0.1°C is c ucial o de ec ing, as an example, an exo he mic eac ion esul ing
om he in e ac ion o he cells wi h d ugs. Fu he mo e, he sys em mus be po able and
compac wi h he capabili y o eading mul iple senso s. The po abili y and he educed size
will allow he sys em o ope a e inside o equipmen wi h small dimensions, like incuba o s
whe e he le els o oxygen and ca bon dioxide a e con olled. The RTD senso s will be
in eg a ed in o mic o luidic de ices, and hus, he de eloped sys em mus be able o pe o m
au oma ic, eal- ime and in si u empe a u e measu emen s.
The con ol and he eading sys em de eloped in his disse a ion was di ided in o
di e en pa s o a be e unde s anding o he sys em. Fu he mo e, i simpli ied
oubleshoo ing i some hing is no wo king o needs o be imp o ed/changed.
47
In [58] an ins alla ion o a senso using he ou -wi e con igu a ion o geo he mal
s udies was add essed. Since i is an applica ion whe e he senso is ins alled a abou 100m
dep h, his makes i impossible o he senso ou pu alues o be ead on si e. I is necessa y
o use conduc i e wi es o he alues o be ead emo ely. These wi es will ha e a esis ance
ha is associa ed wi h hem wha causes he esul s o be changed and a e no eal, so he
ou -wi e con igu a ion o his applica ion was chosen. As expec ed, i was concluded ha
he e we e no luc ua ions o measu emen e o s de i ed om he esis ance o he lead
wi es and all he alues ead on he senso we e he eal ones.
3.1.2 Fab ica ed RTD
The empe a u e mic osenso s used in his disse a ion we e de eloped in p e ious
wo ks o some esea che s in he labo a o y o Mic o/Nano echnologies and Biomedical
Applica ions o he Cen e o Mic oElec oMechanical Sys ems (CMEMS) in pa ne ship wi h
he In e na ional Ibe ian Nano echnology Labo a o y (INL) whe e hey we e ab ica ed. Mo e
de ail abou he ab ica ion p ocess and cha ac e iza ion o he empe a u e RTD
mic osenso s a e desc ibed in [59].
A e some compa ison s udies, pla inum was selec ed o ab ica e he RTD, since i was
he one ha ga e be e esul s in e ms o sensi i i y. Fu he mo e, he ab ica ion p ocess
is well es ablished p o iding good ep oducibili y. The pa e ning o he senso s was made ia
li -o p ocesses and pho oli hog aphy echniques, wi h a se pen ine geome y ha ga e he
maximum leng h in a educed a ea allowing he senso o ha e mo e elec ical esis ance and
consequen ly mo e sensi i i y. The geome y o he RTD used consis s o meande -shaped
wi h 24 windings o a 200 nm pla inum hin ilm (deposi ed by spu e ing, as desc ibed in
sec ion 2.5.2) wi h a line wid h and spacing o 10 µm. These senso s we e designed in a ou -
wi e con igu a ion, o ensu e high accu acy and an ou pu ol age di ec ly p opo ional o he
RTD esis ance only.

48
In igu e 10, i can be seen a wa e wi h a ious and in igu e 11 senso s de ailed
pho og aphy o one ab ica ed senso .
These senso s ope a e wi h an exci a ion cu en and i was impe a i e o know how
he senso esponds o e e y alue o cu en o ind he maximum alue o cu en ha he
senso can ope a e wi hou sel -hea ing. P e ious wo ks [59] showed ha 100µA p o ides a
negligible sel -hea ing (0.008 °C), and hus, was selec ed o he ollowing es s.
In he inal pa o he p ojec , he de eloped sys em will be in eg a ed in o a
mic o luidic de ice wi h ou empe a u e mic osenso s and a mic o hea ing sys em. The main
objec i e o his in eg a ed sys em is o p o ide empe a u e op imal condi ions o cul u e
cells g ow h in OOC. The in o ma ion collec ed by he senso s will be c ucial o ac ua e he
hea ing sys em and keep he en i onmen a a empe a u e ha he use wan s.
Figu e 10 – Pho og aphy o he ab ica ed RTD.
Figu e 11 – Wa e wi h a ious aluminium senso s wi h he same geome y bu di e en windings.
49
3.1.3 Calib a ion echniques
To achie e high senso e ec i eness, se e al calib a ions a e equi ed. Depending on
he e ec i eness equi ed, calib a ion me hods may be mo e expensi e, i.e., he cos o
calib a ion ope a ion inc eases as senso e ec i eness inc eases. Typically, a he indus y
le el whe e RTD is used, he empe a u e anges used a e small and his makes i s calib a ion
simple [36]. The highe accu acy o a he mome e he mo e expensi e he calib a ion
echnique is demanded. Howe e , o some indus ial-g ade RTDs, i is possible o pe o m a
simpli ied calib a ion echnique because o he na ow empe a u e anges hey a e used
o e . I is also essen ial ha he calib a ion echnique should d aw less ope a o a en ion and
op imize calib a ion ime. In he publica ion o V. V. Gu eye e al. [36], a e sa ile
semiau oma ic me hod o calib a ing indus ial RTDs was p esen ed wi h he use o he
compa ison me hod, compa ing he esponse o he RTD o an indus ial he mome e . The e
a e wo calib a ion me hods:
Fixed poin calib a ion
This calib a ion me hod is e y p ecise, i can each calib a ion close o 0.0001°C and
consis s o ixing he senso o be calib a ed inside a chambe wi h a limi ed numbe o ixed
hea ing poin s a di e en empe a u es bu each main ains a i s cons an empe a u e
du ing he p ocess. These empe a u e alues a e known and selec ed h ough he
In e na ional Tempe a u e Scale o 1990(ITS-90) o selec he minimum numbe o poin s. The
poin s ha a e in ITS-90 ha e been documen ed and accep ed by he global communi y [60].
Compa ison me hod
In his calib a ion me hod, he senso is compa ed o o he s ha al eady ha e been
calib a ed and i s esponse is compa ed wi hin an en i onmen and he empe a u e is known
and con olled. The e a e se e al ad an ages o using his me hod in compa ison o he ixed
poin me hod. Fi s ly, his me hod allows a a ie y o empe a u es, a he han ixed
empe a u es and on a limi ed numbe . Ano he ad an age is ha hese calib a ion sys ems
a e easy o use and allow calib a ion o mul iple senso s a he same ime and in an au oma ed
manne . This me hod is he mos used o calib a e RTD's o indus ial applica ions. Howe e ,
i is necessa y o pay maximum a en ion and ensu e ha he empe a u e o he he mos a
is s able and uni o m o a oid a lack o calib a ion e ec i eness [36].
50
This me hod was used o he RTD calib a ion using a ho pla e (P äzi he m ype PZ28-2,
1100 W) wi h a esolu ion o 0.1°C which has a come cial senso in eg a ed which i was used
o alida ion o he RTD senso used.
51
4. SYSTEM DEVELOPMENT
A e he me hodology is de ined, he elec onic ci cui o con ol and ac ua e he RTD
will be de eloped. This sys em should be capable o measu ing empe a u e changes, wi h a
esolu ion o 0.1°C.
4.1 Con ol & ac ua ion ci cui
This is he mos impo an pa o he sys em since a ec di ec ly he pe o mance o
he senso s. A sui able cu en sou ce and, ampli ica ion and il e ing ci cui s a e essen ial o
ensu e p ope unc ioning. E e y hing has o be well chosen and implemen ed o low noise
and accu a e measu emen s.
4.1.1 Powe sou ce
The supply o he ci cui was pe o med by ba e ies o assu ing he independence o
he powe supply and po abili y. Two ol age egula o s (L7805CV and L7905CV) we e used
o supply he ci cui wi h 5V and -5V o powe all he o he componen s o he ci cui - These
supply alues we e chosen because he cu en sou ce ope a es wi h 5V, and hus, o be easie
o in eg a e and design o he ci cui , all he o he elemen s we e also supplied wi h 5V and -
5V.In igu e 12, can be seen he designed powe ci cui . The capaci o s mus be all elec oly ic
and hei alues a e acco ding o he ecommenda ions o he manu ac u e o he egula o s
[40,41].
Figu e 12 – Powe sou ce ci cui wi h ol age egula ion and p o ec ions.
52
4.1.2 Cu en sou ce
The RTD needs an exci a ion cu en o ope a e and any luc ua ion o he exci a ion
cu en will o igina e a change in he elec ical po en ial o he senso s, and consequen ly, will
p o ide inaccu a e empe a u e alues. So, an adjus able cu en sou ce (LM134 om Texas
Ins umen s, Dallas, TX, USA) was used o p o ide a s able cu en o 100 µA. This de ice was
chosen because i allows a cu en adjus men om 1 µA o 10 mA, wi h high accu acy and
low noise.
In igu e 13, i can be seen he implemen a ion o he cu en sou ce. This
implemen a ion is ecommended by he manu ac u e o his ype o ci cui ha is
empe a u e sensi i e. The addi ion o a diode (1N457) and a second esis ance (R2) cancels
he empe a u e-dependen cha ac e is ic o he LM134 [63].
To p o ide a s able cu en o 100 µA, he alues o R1 and R2 mus be calcula ed using
he ollowing equa ions:
𝐼𝑠𝑒𝑡 ≈ 0.134𝑉
𝑅1
𝑅2 = 10𝑅1
Figu e 13 - Cu en sou ce ci cui o powe he RTD.
(11)
(12)

53
Finally, wi h he alue o 100 µA in Ise , i was ob ained a alue o 1.34kΩ o R1 and
13.4 kΩ o R2, bo h esis ance used a e p ecision esis ances wi h an 1% ola ance. The
expe imen al alue o he cu en measu ed wi h he implemen ed ci cui can be seen in
igu e 14.
4.1.3 Mul iplexe s
To selec he senso o ead, i was chosen he mul iplexe 4:1 (TMUX1104) since his
componen allows o ead up o ou senso s. This componen is a low noise p ecision
mul iplexe ha has a ail- o- ail logic, ha enables ope a ion in all anges om GND o VDD,
ul a-low leakage cu en , ul a-low cha ge injec ion and a ail-sa e logic ha allows he
analogue pins o ope a e up o 5.5V ega dless o he ol age in he supply pin [64]. In able
3, he u h able o he componen is p esen ed.
Table 3 -T u h able o TMUX1104. Adap ed om [64].
EN
A1
A0
Selec ed inpu o D ain(D) Pin
0
𝑋∗
𝑋∗
All channels a e o
1
0
0
S1
1
0
1
S2
1
1
0
S3
1
1
1
S4
Figu e 14 – Expe imen al exci a ion cu en using he implemen ed cu en sou ce ci cui .
*X deno es don’ ca e
54
Fo he selec ion o be done success ully, he sys em mus ha e wo mul iplexe s, one
o each g oup o wi es (RTDXWIRE2 and RTDXWIRE3). The signal channels (A0 and A1) o he
mul iplexe will be connec ed and oge he connec ed o he wo signal pins o he
mic ocon olle , hus ensu ing ha he co ec wi es o he RTD a e chosen simul aneously.
4.1.4 Ampli ica ion
Fo he ampli ica ion, i was chosen he high accu acy ins umen a ion ampli ie
AD620. Like is impe a i e h ough all he ci cui s is also a low noise componen wi h an
excellen DC pe o mance, i has a gain ange om 1 o 10 000 wi h high accu acy and low
cos . I 's ideal o his sys em as i has also a low powe consump ion [65]. AD620 has i s gain
p og ammed by a esis o (Rg) o o he impedance. The equa ion o calcula e he Rg is he
ollowing:
𝑅𝑔 =49,4𝑘Ω
𝐺 − 1
The ou pu ol age o he empe a u e senso s used in his disse a ion shows high
linea i y be ween empe a u e and elec ical po en ial, anging om 163.5 mV o 167.5 mV
when he empe a u e is inc eased om 35 o 45°C. The ADC has a maximum inpu ol age
s a ed a 3.3 V, so, a gain o 16 was de ined, in his phase, allowing he ou pu o he senso
o ange om a ound 2.53 V o 2.6 V. Applying he o mula, he alue o he Rg is a ound
3.3kΩ.
(13)
55
Finally, he ci cui esponsible o he selec ion and ampli ica ion o he signal can be
seen in igu e 15
4.1.5 Fil e ing
The ampli ica ion sys em is low noise bu he e was a need o a enua e he signal
be o e i en e s he ADC o be e eading. I was implemen ed a i s -o de low pass il e
wi h a cu ing equency o a ound 106 kHz. This equency gi es he be e a enua ion o he
signal. Wi h he alue o he equency, he alues o he esis ance and he capaci o ha
ake pa in he il e can be calcula ed wi h he ollowing o mula:
𝐹𝑐 =1
2𝜋𝑅𝐶
whe e Fc is he cu ing equency (Hz), R he esis ance (Ω) and C he alue o he capaci o
(F). The alue o he esis ance calcula ed was 15 Ω and he capaci o was 100 nF.
In addi ion o ha , an inpu il e was also implemen ed o p e en adio equency
ec i ica ions e o s in ins umen a ion ampli ica ion. This ype o e o appea s as a small dc
ol age o se and no mally occu s because all ins umen a ion ampli ie s ec i y small ou o
band signals. The inpu signal is limi ed by he il e acco ding o he ollowing wo equa ions
[65]:
𝐹𝑖𝑙𝑡𝑒𝑟𝐹𝑟𝑒𝑞𝐷𝐼𝐹𝐹 = 1
2𝜋𝑅(2𝐶𝑑+ 𝐶𝑐)
Figu e 15 - Ampli ica ion ci cui wi h he mul iplexe .
(14)
(15)
56
𝐹𝑖𝑙𝑡𝑒𝑟𝐹𝑟𝑒𝑞𝐶𝑀 = 1
2𝜋𝑅𝐶𝑐
whe e, 𝐶𝑑>10𝐶𝑐.
The schema ic o he ci cui is shown in igu e 16.
The inal e sion o he eading ci cui can be seen in igu e 17.
Figu e 17 – Schema ic ep esen a ion o he inal ci cui .
Figu e 16 – Inpu il e ha p e en s RF ampli ica ion e o s and low pass- il e .
(16)
63
As can be seen in igu e 28 his g aphical in e ace is e y simple and use - iendly.
Ini ially, i opens he i s window o he de ini ion o a iables and RTD selec ion. I was also
added some ins uc ions o help he use unde s and how o use i . On he i s window, he
use connec s he boa d, chooses he senso ha wan s o ead, inse s and sa es he
a iables ha will be used in he con e sion and s a s he eading. A e his selec ion, a
second window is open o show he empe a u e da a ha was con e ed and whe e he use
can s op he eading and disconnec he boa d.
Figu e 27 - S a e machine o he sys em.
Figu e 28 - Implemen ed g aphical in e ace o choose and p esen he RTD esponse.

64
The sys em s a s, as ese mode, in a s a e called “Disconnec ed” whe e he
mic ocon olle is no eading alues and is no connec ed o he compu e The connec ion
be ween he compu e and he mic ocon olle is ob ained by p essing he bu on “connec ”.
I he boa d is no connec ed co ec ly, an e o message will appea and he sys em will s ay
in a s a e o disconnec ion. On o he hand, i he connec ion is success ul, a message will
appea o in o m ha he connec ion was co ec ly pe o med ( igu e 29).
Once he connec ion is made wi h success, he nex s ep o he use is o choose he
senso o ead and se he a iables ha will ake pa in he con e sion o he ol age alues
o empe a u e. The use canno s a he eading wi hou inse ing alues ha a e nume ic
and di e en om ze o, as i shows an e o message ( igu e 30 a). When he a iables a e all
se , he use p esses he sa e bu on o sa e he alues o he a iables and o send he
numbe o he RTD ha is going o be ead by he mic ocon olle .
As he a iables a e success ully sa ed, a con i ma ion message will appea on he
sc een ( igu e 30 b). To ese he a iables inse ed, he use mus p ess he ese bu on o
e ase he p e ious alues and inse he new ones. Once he connec ion is made wi h success,
he nex s ep o he use is o choose he senso o ead and se he a iables ha will ake
pa in he con e sion o he ol age alues o empe a u e. The use canno s a he eading
wi hou inse ing alues ha a e nume ic and di e en om ze o, as i shows an e o
message ( igu e 30 a). When he a iables a e all se , he use p ess he sa e bu on o sa e
Figu e 30 - Wa nings ela ed o a iables inse ion.
Figu e 29 - Connec ion wa nings.
a
b
65
he alues o he a iables and o send he numbe o he RTD ha is going o be ead by he
mic ocon olle .
P essing s a , he mic ocon olle ini ia es he eading and sends he alues ia UART.
The p og am ecei es he ol age alues which a e con e ed o empe a u e and hen a e
displayed in a g aphical o m and on a digi al LCD. These con e ed alues a e also sa ed in a
ex ile. Each senso has a ex ile o ol age and empe a u e. The use can dele e all he
iles by p essing he “dele e iles” bu on, o he wise, e e y eading is s o ed in he same ex
ile o he p e ious eading. The use s ill has he possibili y o see he empe a u e o he ou
senso s using he “All senso s” mode. This mode will change he senso ha is being ead
e e y 30 sec and sa e all he con e ed da a in di e en iles, one o each senso .
Finally, he use has wo op ions: 1) p ess s op and he sys em only s ops eading and
con e ing alues o 2) disconnec all he sys em going back o he ese s a e o he sys em,
by p essing he disconnec bu on.
4.3.2 Liquid C ys al Display (LCD)
As p e iously men ioned, he sys em has a ious s a es and allow selec he RTD ha
is being ead. This in o ma ion will be displayed on an LCD. Fo his pu pose, he LCD DFR0063
16x02 wi h communica ion ia I2C p o ocol was used. The I2C p o ocol uses 2 wi es, SCL
(Se ial Clock) and SDA (Se ial Da a) o communica e be ween he mas e , in his case, he
mic ocon olle and he sla e, in his case, he LCD. Fi s ly, he mas e sends a s a condi ion
ollowed by eigh bi s whe e se en a e he sla e add ess and he eigh h bi is he mode ha
he communica ion is going o ope a e, 0 is o w i e and 1 o ead om he sla e. I wai s o
he acknowledge signal om he sla e ha he connec ion was made success ully. Then he
mas e sends he da a, one by e a a ime and o each by e mus wai o an acknowledged
signal ha he by e was well- ecei ed be o e sending he nex by e o da a. This ope a ion
66
con inues in his o m un il he mas e sends a s op condi ion o in e up he communica ion.
In igu e 31, i can be seen he schema ic o he communica ion.
In igu e 32, i can be seen all he s a es ha he LCD can show.
Figu e 31 - I2C communica ion p o ocol schema ic.
Figu e 32 - LCD showing he ou s a es o he sys em.
67
5. TESTS AND RESULTS
In his chap e , he expe imen al es s and consequen esul s o he p ojec a e
p esen ed and discussed. The de elopmen o he elec onic ci cui s in ol ed se e al es
s eps namely in 1) b eadboa d, 2) p o oboa d and 3) PCB es ing. Imp o emen s in he
elec onics ci cui s a e also p esen ed in his chap e .
5.1.1 B eadboa d es ing
Fi s ly, he ci cui was implemen ed in he b eadboa d (Figu e 33), wi hou il e and
wi h a gain o a ound 11 (as men ioned in sec ion 4.1.4).
This es ing was made o alida e he senso esponse using a ho pla e wi h a esolu ion
o 0.1°C o change he empe a u e. I was clea , as i can be seen in igu e 34, ha he senso
was esponding as expec ed, i s ou pu ol age inc eased wi h a sensi i i y o 0.73 mV/°C.
Howe e , he sys em s ill had some pe u ba ion de i a ed om noise and p esen a poo
esolu ion.
Figu e 34 - Mic osenso esponse wi h implemen ed elec onics o empe a u e a ia ion om 35 o 45 °C wi hou il e ing.
Figu e 33 - Ci cui implemen ed in he b eadboa d.
68
A e his, a il e wi h a cu ing equency o 106 kHz was implemen ed o pe mi he
eading o low- equency signals and a enua es equencies highe han he cu ing
equency. As can be seen in igu e 35, he noise was subs an ially educed, bu he
ampli ica ion ci cui s ill has poo esolu ion since om 35°C o 45°C he ou pu ol age only
changes a ound 10mV. Since i is in ended o ead he senso 's esponse wi h he STM, he
ou pu ange mus change signi ican ly. Fu he mo e, he ou pu ol age s ill has a signi ican
le el o noise, especially when is in ended o ead wi h a esolu ion o 0.1°C.
5.1.2 P o oboa d es ing
The nex s ep was he implemen a ion o he ci cui in a P o oboa d which can be seen
in igu e 36. This ci cui helped educe he noise om he b eadboa d acks and o alida e
hese changes be o e implemen ing he PCB. This ci cui didn’ ha e ye he AD620 and he
TMUX1104 because as a his s age he only objec i e was o alida e he esponse o he
senso . This ci cui was used an ins umen a ion ampli ie INA126 o alida e he ampli ica ion
sys em.
Figu e 36 - Ci cui implemen ed in P o oboa d.
Figu e 35 - Ou pu ol age o he senso wi h il e ing when he empe a u e is inc eased om 35 °C o 45 °C.

69
Also, he eading equency o he ADC was inc eased o 1kHz, which is equi alen o
eading alues each 1 ms. In igu e 37, i can be seen he ou pu ol age o he ci cui in he
p o oboa d when he empe a u e was inc eased om 35°C o 45°C.
High le els o luc ua ions and noise a e e i ied in he ou pu ol age when his
assemble was used. The P o oBoa d s ill p oduces noise om he connec ions be ween he
componen s and, heo e ically, he INA126 is no he ideal componen compa ed o he
AD620, as i p oduces mo e noise compa ing bo h cha ac e is ics [59,60]. Also, a digi al
echnique o summing up he alues o 250 eadings and aking he a e age numbe o ha
sum was implemen ed o emo e ou pu ol age picks o he senso esponse ( igu e 38). In
his g aph, he e a e wo cycles: 1) he blue line ep esen s an inc ease o empe a u e om
35 o 45°C and 2) he o ange line dec ease empe a u e om 45 o 35°C. I can be no ed ha
he ol age picks we e so ened as expec ed bu he e is s ill some noise and ins abili y ha
comes om he P o oBoa d ci cui . A sensi i i y o 3.37mV/°C was ob ained wi h his
app oach.
Figu e 37 - Resul s wi h P o oBoa d ci cui . Hea ing om 35°C o 45°C.
Figu e 38 - Resul s o a ull cycle o hea ing and cooling o he sys em om 35°C o 45°C in P o oboa d.
70
5.1.3 PCB es ing
A e alida ion o he en i e ci cui wi h b eadboa d and p o oboa d, he PCB was
designed and manu ac u ed wi h all he necessa y ci cui s. A e manu ac u e, he
expe imen al se up shown in igu e 39 was used o cha ac e ize he esponse o he senso s
using he PCB ci cui .
Se e al hea ing and cooling cycles be ween 35 and 45°C we e applied o alida e he
PCB ci cui . Figu e 40 shows one o hese es s wi h s abiliza ion a 40°C. The esponse was
simila o p e ious es s, howe e , i is e i ied g ea e s abili y o he esponse wi h lowe
luc ua ions and noise. A sensi i i y o 7.61 mV/°C was ob ained wi h his app oach.
F om he cha ac e iza ion o he senso esponse, i was necessa y o implemen a
s ep o con e sion o he ou pu ol age o he sys em in o empe a u e alues. Fo ha was
used he equa ions men ioned in chap e 3, in subsec ion 3.1.1 This cha ac e iza ion was
made using he compa ison me hod, compa ing he alues o he RTD agains he senso o
he ho pla e.
Figu e 39 - Expe imen al se up used o he empe a u e mic osenso cha ac e iza ion using he implemen ed PCB.
Figu e 40 - Resul s om hea ing he sys em om 35°C o 45°C in PCB e sion.
71
In he de eloped so wa e i is possible o de ine speci ic a iables o each o he
senso s o be measu ed, i.e., gain, R0 and α. The R0 and α alues we e ob ained om he
measu emen o he elec ical esis ance alue o he RTD using a digi al mul ime e (Agilen
34410A 61/2). The measu ed esis ance alues a e shown in he g aph in igu e 41. F om hese
alues, i was possible o de ine he calib a ion line and calcula e he R0 and R100, and
consequen ly he α.
So, he s aigh equa ion is he ollowing:
𝑅 = 3,5765 ∗ 𝑇 + 1511,3
and his ga e a alue o 𝑅0 o 1511,3 Ω and also a alue o 𝑅100 o 1869,09 Ω. Wi h hese
wo alues, i was possible also calcula e he p ac ical alue o he empe a u e coe icien o
esis i i y (α) using he ollowing equa ion:
𝛼 = 𝑅100 − 𝑅0
𝑅0 ∗ ∆𝑇
whe e R100 and R0 a e he alues o esis ance and ∆𝑇 is he di e ence o empe a u e, in
his case, 100℃. The p ac ical alue o he coe icien o his senso was 0.002367432 Ω /
Ω /℃. This di e ence in he alue can be explained by he ac ha hese senso s a e
ab ica ed in hin ilm and he heo e ical alue o he pla inum was de ined o he bulk
ma e ial.
Figu e 41 – Cha ac e iza ion o he elec ical esis ance o he pla inum RTD.
(18)
ZZ)
(19)
72
In o de o assess i he senso s a e able o measu e empe a u e changes o 0.1°C,
was used a ho pla e o apply a hea ing cycle be ween 37.5 ℃ o 38.9 ℃ wi h an inc emen o
0.1°C. In igu e 42 a e showed he con e ed empe a u e alues o hese es s.
Wi h hese esul s, i can be seen ha he senso is esponding p ope ly o he
empe a u e inc emen s, despi e some di icul y o keep a cons an empe a u e in each s ep
due o he ins abili y o he ho pla e (lack o isola ion and hea ing losses). Howe e , e en i is
possible o see he a ia ions o 0.1°C, he ou pu ol age is s ill low o he esolu ion wan ed.
5.1.4 Imp o emen s o he ci cui
Wi h he objec i e o inc easing he esolu ion o he sys em, was implemen ed a new
app oach wi h wo s ages o ampli ica ion using he AD620. On his app oach, was gi en
special a en ion o he e e ence ol age o bo h AD620 o op imize he ou pu o ange
be ween 0 and 3.3V ( ol age alues measu ed by ADC) The i s s age o ampli ica ion has an
RG = 1kΩ, which gi es a gain o a ound 50.4 and on he second s age, he RG is 7.8kΩ which
gi es a gain o a ound 7.33. The combina ion o hese wo gains p o ides a o al gain o a ound
369.6.
To assu e ha he ou pu anges be ween 0 and 3.3 o he desi ed empe a u e
ange (35°C o 45°C) he e e ence o he i s s age was connec ed o -10V o allow he sys em
o ha e a mo e ampli ica ion ange. Wi h he ou pu o he i s s age connec ed o he
posi i e en ance o he second s age, he nega i e en ance can ma ch he ou pu alue o
he empe a u e ha is wan ed o be he i s alue o he empe a u e eading.
In his case, 23°C was chosen o be he ini ial alue. The ol age alue co esponding
o his empe a u e is connec ed o he nega i e en ance and he ampli ie will sub ac bo h
Figu e 42 - Resul s om he hea ing es wi h inc emen s o 0.1°C om 37.5°C o 38.9°C.
79
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2015, [Online]. A ailable: h ps:// inyu l.com/y228 xyw.