Multi-Sensing Platform Based on 2D Monoelement Germanane

RESEARCH ARTICLE www.ad ma .de Mul i-Sensing Pla o m Based on 2D Monoelemen Ge manane Jay aj V. Vaghasiya, Ca men C. Mayo ga-Ma inez, Ke al K. Soniga a, Pe Laza , and Ma in Pume a* Co alen ly unc ionalized ge manane is a no el ype o fluo escen p obe ha can be employed in ma e ial science and analy ical sensing. He e, a fluo ome ic sensing pla o m based on me hyl- unc ionalized ge manane (CH3Ge) is de eloped o gas (humidi y and ammonia) sensing, pH (1–9) sensing, and an i-coun e ei ing. Luminescence ( ed–o ange) is seen when a gas molecule in e cala es in o he in e laye space o CH3Ge and he luminescence disappea s upon dein e cala ion. This allows o di ec de ec ion o gas abso p ion ia fluo ome ic measu emen s o he CH3Ge. S uc u al and op ical p ope ies o CH3Ge wi h in e cala ed gas molecules a e in es iga ed by densi y unc ional heo y (DFT). To demons a e eal- ime and on- he-spo es ing, abso bed gas molecules a e fi s p ecisely quan ified by CH3Ge using a sma phone came a wi h an ins alled colo in ensi y p ocessing applica ion (APP). Fu he , CH3Ge-pape -based senso is in eg a ed in o eal ood packe s (e.g., fish and milk) o moni o he shel li e o pe ishable oods. Finally, CH3Ge-based ew i able pape is applied in wa e je p in ing o illus a e he po en ial o sec e communica ion wi h quick colo a ion and good e e sibili y by wa e e apo a ion. 1. In oduc ion In ecen yea s, 2D-based g aphene analogs ha e opened up ascina ing oppo uni ies o basic and applied esea ch in di- e se field applica ions such as biomedical, en i onmen al, and elec onic de ices.[1–7] Ge manane has a ac ed a lo o in e - es as a unique elec onic ma e ial because i can une he J. V. Vaghasiya, K. K. Soniga a, M. Pume a Fu u e Ene gy and Inno a ion Labo a o y Cen al Eu opean Ins i u e o Technology B no Uni e si y o Technology Pu kyˇ no a 123, B no 61200, Czech Republic E-mail: [email p o ec ed].cz J.V.Vaghasiya,C.C.Mayo ga-Ma inez,M.Pume a Cen e o Ad ancedFunc ionalNano obo s Depa men o Ino ganicChemis y Facul y o ChemicalTechnology Uni e si yo Chemis yandTechnologyP ague Technická5,P ague16628,CzechRepublic The ORCID iden ifica ion numbe (s) o he au ho (s) o his a icle can be ound unde h ps://doi.o g/10.1002/adma.202304694 © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH. This is an open access a icle unde he e ms o he C ea i e Commons A ibu ion License, which pe mi s use, dis ibu ion and ep oduc ion in any medium, p o ided he o iginal wo k is p ope ly ci ed. DOI: 10.1002/adma.202304694 mo phological and physical p ope ies by changing he na u e o he co alen ly e - mina ed ligand.[8–12] Typically, his ma e- ial can be p oduced by ex olia ion o CaGe2(also known as he Zin l phase) in an acidic media. A e wa d, opochemical dein e cala ion o CaGe2wi h alkyl halide yields alkyl ge manane, ha is, hyd ogen o me hyl ge manane.[13,14] Ge manane has ecen ly been p esen ed as a no el ac i e ma e ial wi h ailo ed p ope ies o en- e gy s o age,[15,16] sensing (chemical and biological),[17,18] op oelec onic,[19,20] hyd o- gen s o age,[21,22] ene gy con e sion, and pho o-elec oca alysis.[23,24] The fine- uning o ge manane p ope ies (i.e., bandgap and physical p ope ies) can be achie ed by he co alen su ace e mina ion o ge manane. Recen ly, ou esea ch g oup uned he pho- oca aly ic p ope ies o ge manane by al- e ing a ious o ganic unc ional g oups.[14] When he me hyl unc ional g oup eplaced hyd ogen on he su ace o ge manane, i enhanced i s he mal s abili y and widened he bandgap.[25] Mo eo e , CH3Ge has been employed as a biosenso o iden- i y li e ci hosis bioma ke s and glucose.[17,18] Howe e , ge manane-based biosenso s a e s ill in hei in ancy and equi e mo e esea ch. CH3Ge also demons a es ou s anding band-edge fluo es- cence and pho oluminescence (PL) p ope ies.[26–28] The e o e, P. Laza Regional Cen e o Ad anced Technologies and Ma e ials Czech Ad anced Technology and Resea ch Ins i u e (CATRIN) Palacký Uni e si y Olomouc Šlech i el˚ u 27, Olomouc 779 00, Czechia M. Pume a Facul y o Elec ical Enginee ing and Compu e Science VSB – Technical Uni e si y o Os a a 17. lis opadu 2172/15, Os a a 70800, Czech Republic M. Pume a Depa men o Medical Resea ch China Medical Uni e si y Hospi al China Medical Uni e si y No. 91 Hsueh-Shih Road, Taichung 40402, Taiwan M. Pume a Depa men o Chemical and Biomolecula Enginee ing Yonsei Uni e si y 50 Yonsei- o, Seodaemun-gu, Seoul 03722, Sou h Ko ea Ad . Ma e . 2023,35, 2304694 2304694 (1 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH www.ad ancedsciencenews.com www.ad ma .de CH3Ge has been documen ed as a fluo escen ma ke on a mi- c o obo sys em o d ug deli e y.[29] On he o he hand, he PL o CH3Ge is highly associa ed wi h he abso p ion o wa e molecules in i s in e laye space. The s udy e eals ha when CH3Ge is hyd a ed, i exhibi s eddish–o ange luminescence bu when i is d y he luminescence is in isible. Bu owing o a lack o ge manane-based senso enginee ing knowledge in he esea ch communi y, i is ye o be in es iga ed as a eal-scale applica ion. The mul i-s acked compac s uc u e o CH3Ge makes i chal- lenging o in eg a e in sensing de ices wi h p ecise in e aces. Hence, he e we demons a ed ma e ial enginee ing o de elop a mul i unc ional pape -based senso om CH3Ge. CH3Ge’s buckled honeycomb s uc u e wi h sp3hyb idiza ion could help inc ease i s abso p ion o gas molecules (humidi y) and chemi- cal eac i i y. Due o i s unique s uc u al and PL p ope ies, i is concei able o exploi CH3Ge o de ec o he ola ile gases in he a mosphe e such as wa e apo , and acidic and basic gases. This would be a new di ec ion o he de elopmen o CH3Ge-based gas senso s. G aphene-analogous 2D ma e ials, such as ansi ion me al dichalcogenides (e.g., MoS2,MoSe 2,andWS 2),[30–32] ansi ion me al ca bides (e.g., MXene Ti3C2Tx),[33,34] hexagonal bo on ni ide,[35] and black phospho ous[36] ha e become popula e- cen yea s o gas sensing. Func ionalized ge manane also has ou s anding capabili ies o sense a b oad ange o ha m ul gases such as NH3,SO 2,andNO 2.[37] Un o una ely, epo ed s a e-o - a de ices o gas sensing applica ions ely on elec ochemical wo ks a ions ha a e ully dependen on powe sou ces and no sui able o on-si e and eal- ime applica ions.[29–35,37] The e o e, i is c i ically impo an o de elop quick, ins umen - ee, and apidly sensi i e senso s o he effec i e de ec ion o a a ie y o gases. Addi ionally, ma e ials ha change colo in esponse o chem- ical inpu s (gas, pH, and sol en ) ac as he p ima y compo- nen s in biome ic secu i y and sec e communica ion applica- ions. Recen ly de eloped ew i able imaging echnologies ha e been unc ionalized o wa e je ew i able pape s, sel -e asing images, and pho och omic pape .[38,39] The majo i y o ma e ials used in his echnology a e based on o ganic ma e ials (polyme s, dyes, and pigmen s) and ino ganic ma e ials (pe o ski e).[40–42] Ne e heless, he echnology is no eco- iendly enough due o he complex syn hesis p ocess o ma e ials and he e asing sol- en s a e ei he flammable o only a ailable om specific chem- ical endo s.[43,44] Thus, he de elopmen o ew i able pape us- ing new ma e ials in an en i onmen ally iendly manne is es- sen ial. He e, we p esen a fi s - ime simple and s aigh o wa d CH3Ge fluo ome ic sensing pla o m ha can be used o gas and pH de ec ion and sec e communica ion. The abso bed gases can be iden ified based on hei pa icula luminescence e- sponse ( ed- o blueshi ) h ough he in e cala ion o gases in o he CH3Ge an de Waals gap. The ex en o abso bed gases affec s PL in ensi y, making i possible o di ec ly moni o gas abso p ion by quan i ying he luminescence in ensi y o he CH3Ge. Sma phone-based fluo ome ic senso s ha e ecei ed a lo o in e es ecen ly due o easily quan ified colo changes in he sample by using a sma phone applica ion.[45,46] Specifi- cally, he amoun o gas abso bed by CH3Ge was measu ed us- ing a sma phone came a enabled wi h he Colo G ab colo in ensi y p ocessing applica ion o measu e changes o he R ( ed)/G (g een)/B (blue) colo componen s. This sma phone- assis ed fluo ome ic pla o m could p o ide quick and on-si e analysis wi hou he use o complica ed ins umen s. To demon- s a e he applica ion, he CH3Ge-pape -based senso was used o moni o he eshness o eal ood (i.e., fish and milk). Ano he impo an applica ion has been illus a ed by p in ing confiden- ial in o ma ion on CH3Ge-based pape using a wa e inkje - p in ing echnique, whe e wa e is used as a sec e ink sou ce o hide symbolic o ex ual in o ma ion on op-sec e documen s. Mos impo an ly, once such a documen is ead, he in o ma- ion can be easily emo ed by simple wa e e apo a ion. This is he fi s ime demons a ing he use o CH3Ge o eal-wo ld applica ions such as humidi y moni o ing, ood quali y analy- sis, and sec e communica ion. To he bes o ou knowledge, he mono-elemen 2D ma e ials-based wa e inkje ew i able pape has ne e been epo ed o sec e communica ion applica ions. 2. Resul and Discussion In he amily o laye ed an de Waals 2D ma e ials, CH3Ge is one o he ascina ing ma e ials wi h s ong PL p ope ies as- socia ed wi h wa e in e ac ion. He e, we de elop o he fi s imeaCH 3Ge-based fluo ome ic sensing pla o m ha can be used o he de ec ion o gas, pH, and sec e communica ion. The PL in ensi y o CH3Ge is highly dependen on he pH o sol en ha is in e cala ed in o he in e laye spacing o CH3Ge and emi s ligh acco dingly. The in ensi y o PL is igge ed by he in e cala ed molecules owing o local s uc u al dis o ion o he CH3Ge caused by he da i e in e ac ion o wa e molecules wi h he Ge─C. Taking benefi o his p ope y, we ocused on he de ec ion o diffe en gases (humidi y and ammonia) and pH o wa e (1–9). The abso bed gases can be iden ified based on he pa icula colo esponse, ha is, acidic gases emi ed ligh and basic gases emi ed–o ange ligh .[27] Besides, luminescence in ensi y is influenced by he abso bed gases. This colo change abili y can be used o e alua e bo h gases ( ela i e humidi y and ammonia) and he eshness o ood (Figu e 1a,b). Fo ins ance, ammonia gas p oduced by spoiling fish and lac ic acid gene a ed by spoiling milk[23] could be easily measu ed using a CH3Ge sen- so . A e ha , he amoun o gases abso bed by CH3Ge was e al- ua ed using a sma phone came a and colo in ensi y p ocess- ing so wa e o quan i y he colo change wi h RGB colo compo- nen s (Figu e 1d). Taking he benefi o hyd och omic p ope ies, CH3Ge has been used o sec e communica ion as well. He e, we show a apid and acile app oach o he p epa a ion o a com- munica ion medium by applying CH3Ge ma e ials o he su ace o o dina y p in ing pape ; a e ha , CH3Ge-coa ed pape could be p in ed mul iple imes using wa e as an ink (Figu e 1c). In- e es ingly, when he CH3Ge pape comes in con ac wi h wa- e , he p in ed in o ma ion appea s upon exposu e o UV ligh and hen disappea s when he wa e e apo a es. Conce ns abou an inc ease in leaks o confiden ial in o ma ion and coun e ei - ing indica e an oppo uni y o an i-coun e ei ing and enc yp ed communica ions as illus a ed he ein. Be o e e alua ing CH3Ge senso pe o mance in gases and pH de ec ion, i is c i ical o fi s in es iga e he mo phology and s uc u al p ope ies o CH3Ge. Ad . Ma e . 2023,35, 2304694 2304694 (2 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH 15214095, 2023, 44, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adma.202304694 by Technical Uni e si y In B no, Wiley Online Lib a y on [21/02/2024]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License www.ad ancedsciencenews.com www.ad ma .de Figu e 1. Sma phone-assis ed fluo ome ic pla o m using CH3Ge-based pape o sensing and sec e communica ion. a) CH3Ge-based gas senso s o humidi y moni o ing and ood quali y analysis (by ammonia sensing). b) CH3Ge-based pH- esponsi e senso o ood quali y analysis (by lac ic acid sensing). c) Schema ic illus a ion o CH3Ge-based ew i able pape wi h wa e je p in ing o an i-coun e ei ing and enc yp ed communica ions. d) Colo in ensi y was de e mined using a sma phone module. 2.1. Mo phological, S uc u al, and Op ical P ope ies Figu e 2a shows a schema ic ep esen a ion o he syn hesis o CH3Ge and he ab ica ion o he CH3Ge-based senso . In a nu - shell, CH3Ge was p epa ed by he opo ac ic dein e cala ion o CaGe2wi h me hyl iodide in an o ganic sol en .[14,18] The ob- ained mul ilaye CH3Ge was ex olia ed by he liquid phase ex o- lia ion me hod[11] and CH3Ge flakes we e hen sp ay-coa ed on o cellulose pape o u he use. A mo e de ailed desc ip ion o he syn hesis and sp ay coa ing p ocedu e is gi en in he Expe - imen al Sec ion. The mo phology o p epa ed samples was in- es iga ed by scanning elec on mic oscopy (SEM) and ene gy- dispe si e X- ay spec oscopy (EDS). The mul ilaye s uc u e o CH3Ge is clea ly isible in he SEM image (Figu e 2b). The magnified SEM image (Figu e 2c) e eals an enla ged lamella s uc u e, indica ing ha calcium was success ully emo ed. A - e ul asonic ea men , CH3Ge has a nanoflake-like mo phol- ogy wi h la e al sizes in he mic ome e ange (Figu e 2d). The scanning ansmission elec on mic oscopy (STEM) image also depic s a anspa en flake-like s uc u e o CH3Ge, no ing good delamina ion. A omic o ce mic oscopy opog aphy image shows ha he delamina ed CH3Ge flakes hickness o 4.2 ±0.5 nm (Figu e S2, Suppo ing In o ma ion), which is compa able wi h p e iously published epo s.[47] EDS analysis (Figu e 2e, ) Ad . Ma e . 2023,35, 2304694 2304694 (3 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH 15214095, 2023, 44, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adma.202304694 by Technical Uni e si y In B no, Wiley Online Lib a y on [21/02/2024]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License www.ad ancedsciencenews.com www.ad ma .de Figu e 2. P epa a ion and mo phology s udy o CH3Ge. a) Syn hesis p ocedu e o CH3Ge and sp ay-coa ed CH3Ge-based pape . b,c) Low- and high- esolu ion SEM images o bulk CH3Ge. d) STEM image o CH3Ge flakes. e, ) EDS images o CH3Ge flakes. g) SEM images o CH3Ge-coa ed pape . e eals ha Ge and C a e dis ibu ed uni o mly h oughou he flakes, confi ming he success o me hyl unc ionaliza ion on ge - manane. Figu e 2g shows SEM images o CH3Ge-deco a ed cel- lulose pape . The pape ab ic has a andomly o ien ed fib ous s uc u e and a clean su ace as shown in Figu e S1a, Suppo - ing In o ma ion. In con as , CH3Ge-deco a ed pape (Figu e 2g) shows a ough su ace and CH3Ge flakes can be seen on he su - ace o pape fibe and gaps. High- esolu ion SEM image (in- se o Figu e 2g) and EDS mapping (Figu e S1b–e, Suppo ing In o ma ion) indica e ha fibe s we e uni o mly co e ed by he CH3Ge flakes. Fu he CH3Ge op ical and s uc u al s udies in d ied and hyd a ed condi ions we e conduc ed o in es iga e he PL colo change mechanism. In humid condi ions, CH3Ge-deco a ed pa- pe quickly changes PL colo om whi e o ed upon 365 nm ligh i adia ion (Figu e 3a). Figu e 3b depic s PL spec a in bo h d ied and hyd a ed s a es, demons a ing ha PL in ensi y in- c eases when wa e molecules a e abso bed. P e ious esea ch ound ha he in e cala ion o wa e molecules in o he in e - laye space o CH3Ge causes abo e-bandgap luminescence.[27] The in ensi y o he PL will also change depending on he el- a i e humidi y (RH) le els. Fu he , he luminescence in ensi y was con e ed o he ch oma ici y alues xand y.Figu e3cde- pic s he colo change a e exposu e o humidi y. The Commis- sion in e na ionale de l’éclai age (CIE) coo dina es change om x=0.586, y=0.412 in d ied CH3Ge o x=0.626, y=0.372 in hy- d a ed CH3Ge. The X- ay diff ac ion (XRD) pa e n (Figu e 3d) in d ied-s a e CH3Ge exhibi s a highly c ys alline phase ha Ad . Ma e . 2023,35, 2304694 2304694 (4 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH 15214095, 2023, 44, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adma.202304694 by Technical Uni e si y In B no, Wiley Online Lib a y on [21/02/2024]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License www.ad ancedsciencenews.com www.ad ma .de Figu e 3. S uc u al and pho ophysical p ope ies o CH3Ge. a) Pho og aph o CH3Ge-deco a ed pape o change colo in humid condi ions upon 𝜆ex =365 nm. b) PL spec a (𝜆ex =365 nm) o CH3Ge in d ied and hyd a ed s a es. c) CH3Ge colo s in CIE 1931 colo space. d) XRD pa e n o d ied and hyd a ed CH3Ge. e) ATR-FTIR spec a o CH3Ge eco ded a a diffe en ime in 30% humidi y. ) DFT calcula ions o CH3Ge in e ac ing wi h wa e molecules (ge manane: ligh g ay; ca bon; da k g ay; hyd ogen: whi e; oxygen: ed). is consis en wi h p e iously published epo s.[25] In con as , he high-in ensi y diff ac ion peak (002) changes om 9.661 o 9.850 Å upon exposed humidi y due o he ac ha wa e molecules could en e he in e laye space and b oaden he lay- e s. Fu he , FTIR spec oscopy was used o in es iga e CH3Ge wa e abso p ion (30% humidi y) p ope ies as a unc ion o ime. As shown in Figu e 3e, he CH3Ge abso p ion band a 3299 cm−1 inc eases as a unc ion o ime. This is due o he s e ching i- b a ion peak c ea ed by ─OH when wa e is abso bed by CH3Ge. Ul ima ely, long- ime humidi y exposu e aises he numbe o ─OH g oups by inc easing bound wa e molecules on CH3Ge. The e o e, all humidi y expe imen s we e ca ied ou in cons an ime in e als. The ypical abso p ion peaks a 2898 and 580 cm−1 a e esponsible o ─CH3and Ge─C s e ching ib a ions, e- spec i ely. Peaks a 1403 and 1226 cm−1a e a ibu ed o ─CH3 bending ib a ion while peaks a 758 cm−1a e asc ibed o ─CH3 ocking ib a ion.[14,25] A sligh diffe ence obse ed a ≈700 cm−1, indica ing enhanced hyd ogen bonding be ween wa e molecules and CH3Ge. We pe o med densi y unc ional heo y (DFT) calcula ions o CH3Ge in e ac ing wi h wa e molecules o gain u he insigh in o he cha ac e is ics o he s uc u al and op ical esponse. We Ad . Ma e . 2023,35, 2304694 2304694 (5 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH 15214095, 2023, 44, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adma.202304694 by Technical Uni e si y In B no, Wiley Online Lib a y on [21/02/2024]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License www.ad ancedsciencenews.com www.ad ma .de conside ully unc ionalized bulk CH3Ge in he 1T p imi i e cell as he compu a ional model (Figu e 3 ). The calcula ed la ice pa ame e s o he ully elaxed p imi i e cell a e a=3.98 and c=8.01 Ǻ. We no e ha he calcula ed alue o he cla ice pa- ame e is smalle han ha ob ained om powde XRD due o he in e laye u bos a ic diso de and cu a u e, which a e o - en p esen in he syn hesized CH3Ge flakes. Nex , we add a wa e molecule in e cala ed in be ween he laye s. No ice ha we in e - cala e wa e in he laye s o he bulk p imi i e cell so he model co esponds o he ully in e cala ed wa e laye because he wa- e molecule is pe iodically epea ed in he xy (in-plane) di ec- ion. The oxygen a om o a wa e molecule c ea es he hyd ogen bond o he hyd ogen o he CH3g oup ( he O─H bond leng h o 2.57 Ǻ), making he in e cala ion p ocess he modynamically exo he mic, ha is, he o ma ion ene gy o in e cala ion is neg- a i e (−0.03 eV). In e cala ion o wa e inc eases he cla ice con- s an o 10.3 Ǻ. This alue should be conside ed as he uppe bounda y o he la ice expansion because i is calcula ed o he ully in e cala ed wa e laye . The s uc u e o CH3Ge does no unde go any no able de o ma ion upon wa e in e cala ion (apa om he inc ease o he in e laye spacing); he bond leng hs o he C─Ge and C─H bonds a e unchanged and he me hyl g oup nex o he wa e molecule is no de o med o il ed. We calcu- la ed he ue op ical bandgap using he ime-dependen DFT (TD-DFT) me hod wi h hyb id- unc ional HSE06 as he ke nel. The op ical gap is he lowes ene gy dipole-allowed ansi ion ob- se ed in he abso p ion spec a and is due o exci onic effec s gene ally lowe han he elec onic gap, which is commonly cal- cula ed as he ene gy diffe ence be ween he DFT ene gy le els. The calcula ed op ical band gap o pu e bulk CH3Ge is 1.76 eV while wa e in e cala ion inc eases he bandgap o 2.01 eV. No mid-gap s a e eme ges upon wa e in e cala ion and he bandgap emains as he di ec gap, loca ed a he Γpoin o he fi s B il- louin zone. Thus, he in e cala ion blueshi s he op ical esponse in o he ed pa o isible ligh in ag eemen wi h expe imen al spec a. Asel e al. s udied he mechanism o wa e in e cala ion in o CH3Ge and demons a ed ha he in ense abo e-gap pho o- luminescence was caused by a local s uc u al dis o ion o he Ge amewo k due o he da i e bonding o in e cala ed wa e molecules.[27] 2.2. CH3Ge-Pape -Based Gas-Responsi e Senso Based on he unique in e ac ion o CH3Ge wi h wa e molecules and colo -changing p ope ies, CH3Ge-deco a ed pape can be u ilized as a humidi y senso . Al hough he emission colo in p esence o humidi y could be ecognized isually, i could no achie e a o able accu acy by human eyes due o incapabili y o dis inguish monoch oma ic in ensi y change. In gene al, such de ec ion s ill depends on sophis ica ed and bulky labo a o y in- s umen s ha a e ime-consuming, necessi a e qualified man- powe o ope a e, and a e no app op ia e o on-si e o eal- ime de ec ion. The e o e, he in ensi y o he CH3Ge-deco a ed pape as a unc ion o RH was measu ed using a sma phone and an- alyzed using he Colo G ab applica ion (Figu e 4a). The sma - phone and CH3Ge pape we e placed ≈15 cm apa and pe pen- dicula o one ano he , wi h he inciden 365 nm ligh p o iding homogeneous illumina ion a 60°. To achie e a be e humid- i y esponse o he CH3Ge-deco a ed pape , he amoun o ac- i e ma e ials loaded on he subs a e mus be op imized. He e, we sp ay-coa ed h ee diffe en amoun s o CH3Ge flakes on o a pape subs a e: 0.3 mg cm−2(sample 1), 0.65 mg cm−2(sam- ple 2), and 1 mg cm−2(sample 3) (Figu e 4b). The colo in en- si y change o he CH3Ge-deco a ed pape du ing he 30% hu- midi y exposu e can be seen isually in he inse o Figu e 4b. We can also say he pape becomes edde as he loading o he ac i e ma e ial inc eases. A sma phone can be u ilized o iew he exac alue o colo in ensi y change. Especially in compa - ison wi h spec ofluo ome e s, he use o a mobile de ice as a colo in ensi y de ec o has been defined as one o he as es and simples ools. In g ayscale pe cen ages, he mean in ensi y o diffe en loading samples 1, 2, and 3 a e 37.66% (±1.45), 46% (±2.3), and 55.3% (±1.45), espec i ely. When an excess amoun o CH3Ge (>1mgcm −2) is coa ed on pape causes c acking, in- c eased su ace non-in o ma i i y, and nanoshee agg ega ion, all o which educe sensing pe o mance. Thus, we decided o un- de ake all subsequen humidi y and pH sensing s udies wi h op- imum sample 3. In o de o demons a e he CH3Ge-deco a ed pape ’s abil- i y o change colo in ensi y upon a ious RH le els, he R/G/B alues o CH3Ge pape s we e measu ed be ween RH 0% and RH 100% using a sma phone module. Figu e 4d (g een colo squa e) depic s o iginal pho og aphs o CH3Ge pape a a i- ous humidi y le els. I can be challenging o dis inguish colo changes wi h ou naked eyes. The ob ained diffe en colo in en- si y shades p ocessed by he Colo G ab sma phone applica ion we e eplica ed o c ea e a solid colo as depic ed in Figu e 4e (black-colo ed squa e). Figu e 4c shows ha he R- alue ises om 148 in RH 10% o 216 in RH 100% while a sub le diffe ence is ound in G and B alues. A simila end was also obse ed in he g ayscale pe cen age (Figu e 4 ). This in es iga ion success- ully e ealed he hues and hei ela ed in ensi ies isually in he o m o g ayscale pe cen age and RGB alue. The acqui ed end as a unc ion o RH was u he alida ed by a spec opho ome e (Figu e 4g). I clea ly depic s he inc ease in PL in ensi y a a - ious RH le els. Simila ends o fluo escence de ec ion we e also seen on he sma phone sensing pla o m wi hou he use o addi ional ins umen s. Fu he , we demons a ed a p o o ype mono colo change CH3Ge-based humidi y indica o ca d ha can de ec he en i e ange (Figu e 4h). This ca d can be u ilized in ood/medicine packaging applica ions o p o ide a isual cue when he ela i e humidi y is inc easing. The e a e many diffe - en kinds o comme cial humidi y indica o ca ds a ailable and some p o ide benefi s such as low cos , ease o use, and long li es- pan. Howe e , hei low sensi i i y and de ec ion ange emain majo issues. Figu e 4h clea ly shows he colo change a ia ion wi h diffe en RH. Un o una ely, his ca d only p o ided a ange o humidi y le els. Fo hese easons, we used a sma phone pla - o m o measu e accu a ely and p ecisely he humidi y in eal ime. To examine he sol en selec i i y o he de eloped CH3Ge- pape -based senso , RGB alues we e eco ded a e he addi ion o me hanol, ace one, e hanol, chlo o o m, dichlo ome hane, iso- p opyl alcohol, and wa e . Figu e 5a depic s RGB alues o he CH3Ge senso in diffe en sol en apo . The RGB alue o CH3Ge senso s in wa e apo is he g ea es , e ealing high specifici y in compa ison o all o he sol en s. Howe e , he Ad . Ma e . 2023,35, 2304694 2304694 (6 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH 15214095, 2023, 44, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adma.202304694 by Technical Uni e si y In B no, Wiley Online Lib a y on [21/02/2024]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License www.ad ancedsciencenews.com www.ad ma .de Figu e 4. CH3Ge-based humidi y- esponsi e senso . a) Schema ic ep esen a ion o colo in ensi y quan ifica ion using a sma phone pla o m equipped wi h he Colo G ab APP. b) Mean in ensi y o diffe en amoun s o CH3Ge loading on a pape subs a e. c) Mean RGB alue as a unc ion o humidi y. d) Real images in diffe en humidi y le els cap u ed by a sma phone came a. e) Colo G ab APP-gene a ed duplica ed images. ) A e age g ayscale pe cen age in diffe en humidi y le els. g) PL spec a as a unc ion o humidi y. h) Mono-colo -change o CH3Ge-based humidi y indica o . sligh ly highe alue obse ed in e hanol compa ed o o he o - ganicsol en sisdue oi s>1.0% wa e con en . The de ec ion o wa e o ace le els o humidi y om comme cial o ganic sol- en s will be made easie by his senso . Fu he mo e, he limi o de ec ion (LOD) o he CH3Ge senso was calcula ed using he inc easing luminescence in ensi y a diffe en RH. As shown in Figu e 5b, he LOD o he CH3Ge-pape -based humidi y senso was as low as 9.32% RH. Fu he mo e, we use CH3Ge pape o de ec ammonia gas. Figu e 5c inse depic s a no iceable a ia ion ollowing ammo- nia gas exposu e on CH3Ge, which esul s in an emission ha appea s mo e o ange. The ed colo alue ound a ound 189 us- ing he colo in ensi y p ocessing so wa e Colo G ab. To un- de s and his colo shi , we calcula ed he op ical bandgap o CH3Ge in e cala ed by ammonia. The TD-DFT alue o he op- ical bandgap is 2.11 eV, highe han he alue o in e cala ed Ad . Ma e . 2023,35, 2304694 2304694 (7 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH 15214095, 2023, 44, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adma.202304694 by Technical Uni e si y In B no, Wiley Online Lib a y on [21/02/2024]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License www.ad ancedsciencenews.com www.ad ma .de Figu e 5. CH3Ge-based ammonia esponsi e senso . a) Sol en apo selec i i y wi h CH3Ge-deco a ed pape . b) Low limi o de ec ion (LOD) plo o CH3Ge senso . c) R- alue as a unc ion o ammonia exposu e. d) RGB alues o CH3Ge in esh and spoiled fish. Inse : digi al images o CH3Ge pape s in esh fish (g een squa e) and spoiled fish (black squa e). e) Schema ic ep esen a ion o colo change o CH3Ge pape in ela ion o fish spoilage and quan ifica ion using a sma phone wi h colo in ensi y p ocessing so wa e, Colo G ab. wa e calcula ed wi h he same compu a ional pa ame e s. Thus, his inc ease explains he shi o mo e o ange colo . In e ca- la ion o ammonia is also exo he mic: he o ma ion ene gy is −0.038 eV, simila o ha o wa e . We also in es iga ed exposu e o ammonia gas a a ious ime in e als on CH3Ge and he esul s a e shown in Figu e 5d. Fol- lowing ha , fish mea eshness and spoilage we e examined in ela ion o he package en i onmen shi ing o an alkaline con- di ion. A e 5 days o s o age a oom empe a u e, he colo o CH3Ge pape changes om ed o ligh o ange (Figu e 5e). Us- ing Colo G ab so wa e o p ocess colo in ensi y, he ed colo alue inc eased om 161 o 186, indica ing a mo e alkaline pack- age en i onmen (Figu e 5i). The ola ile basic gases gene a ed om spoiled fish may ha e been a majo ac o in changing he colo o CH3Ge pape . Ammonia compounds (e.g., di- and i- me hylamine) a e a common by-p oduc o spoiled fish due o p o ein decomposi ion by enzymes and bac e ia.[48] These e- sul s indica e ha CH3Ge has a good esponse o ammonia gases and can imply he quali y o oods in he beginning phases o spoilage. 2.3. CH3Ge-Pape -Based pH-Responsi e Senso A e success ully demons a ing he changing colo in ensi y o CH3Ge in diffe en gas en i onmen s, we ound ha he emis- sion ene gy o CH3Ge a ies depending on he pH. pH is an im- po an pa ame e in many fields, including ood es ing, medical diagnosis, and soil moni o ing.[49,50] The de elopmen o unique isual and quan i a i e pH measu ing pla o ms emains c i i- cal o some pa icula on-si e applica ion fields (e.g., ood anal- ysis). The e o e, we ab ica ed a CH3Ge-pape -based pH senso . The p o ona ed lone pai s on wa e molecules emo ed he na- i e in e ac ion be ween he oxygen and ge manane, which could cause colo changes a a ious pH.[27] Hence, he pe o mance o a colo -changing CH3Ge-based pH senso was ho oughly Ad . Ma e . 2023,35, 2304694 2304694 (8 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH 15214095, 2023, 44, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adma.202304694 by Technical Uni e si y In B no, Wiley Online Lib a y on [21/02/2024]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License www.ad ancedsciencenews.com www.ad ma .de Figu e 6. CH3Ge-based pH- esponsi e senso . a) Images o he pH colo change CH3Ge pape cap u ed wi h a sma phone came a. b) RGB alues a diffe en pH. c) PL spec a as a unc ion o pH. d) DRS in pH 1, 7, and 11. e) RGB alues o CH3Ge in esh and spoiled milk. ) Schema ic ep esen a ion colo change o CH3Ge pape in ela ion o milk spoilage and quan ifica ion using a sma phone wi h Colo G ab colo in ensi y p ocessing so wa e. in es iga ed. As shown in Figu e 6a, he colo o CH3Ge g ad- ually changes as pH inc eases. When pH le els a e in acidic and basic anges, he CH3Ge changes om da k ed o o ange, e- spec i ely. These isible colo changes aid use s in de e mining he es ima ed pH o he sample using hei naked eyes and wi h- ou any help om ins umen s. Howe e , he pe cep ion o colo diffe ences a ies om pe son o pe son, and some iewe s may ha e a colo ision deficiency. These obs acles could be o e come by using a sma phone equipped wi h a colo in ensi y p ocess- ing applica ion as we ha e demons a ed he e. The pH ange was quan ified by measu ing he colo pa ame- e (RGB alue) om images cap u ed wi h a sma phone came a using he Colo G ab applica ion (Figu e 6b). The ed colo in- ensi y was a unc ion o inc easing pH while sub le diffe ences we e obse ed in he blue and g een colo alues. Figu e 6c de- pic s he PL spec a o CH3Ge a diffe en pH le els. The ed ligh emission in pH 1, 3, and 5 is ≈1.977 eV (627 nm) while 1.971 eV (629 nm) was obse ed in pH 7. A pH 9 and 11, he blueshi o he CH3Ge was ound a 1.990 (623 nm) and 1.996 eV (621 nm), espec i ely. The obse ed blueshi is p obably a ibu able o pa ial decomposi ion, which will gene a e Ge(OH)2.[27] Mul iple pH sensing cycles o CH3Ge pape we e pe o med a pH 9 and pH 11. The e is no significan change obse ed in sensing pe - o mance a pH 9, whe eas a d ama ic change was obse ed a pH 11 (Figu e S3, Suppo ing In o ma ion). This indica es ha a CH3Ge-based senso can unc ion below pH 11 o eal-wo ld ap- plica ions. Fu he mo e, he a ia ion in band edge as a unc ion o pH was eco ded using diffuse eflec ance spec oscopy (DRS). The bandgap was calcula ed om DRS using he Kubelka–Munk unc ion. Figu e 6d shows a clea diffe ence in band edge wi h Ad . Ma e . 2023,35, 2304694 2304694 (9 o 13) © 2023 The Au ho s. Ad anced Ma e ials published by Wiley-VCH GmbH 15214095, 2023, 44, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adma.202304694 by Technical Uni e si y In B no, Wiley Online Lib a y on [21/02/2024]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License