(S)TEM structural and compositional nanoanalyses of chemically synthesized glutathione-shelled nanoparticles

UNCORRECTED PROOF Journal : Large 13204 Article No : 1418 Pages : 7MS Code : 1418 Dispatch : 24-4-2020 Vol.:(0123456789) 1 3 Applied Nanoscience https://doi.org/10.1007/s13204-020-01418-7 ORIGINAL ARTICLE (S)TEM structural andcompositional nanoanalyses ofchemically synthesized glutathione-shelled nanoparticles A.M.Beltrán1 · J.M.Mánuel2,3 · R.Litrán2,3 · E.Félix2,3· A.J.Santos2,4 · F.M.Morales2,4 · O.Bomatí-Miguel2,3 Received: 11 March 2020 / Accepted: 15 April 2020 © King Abdulaziz City for Science and Technology 2020 Abstract This work is focused on the characterization by transmission and scanning–transmission electron microscopy-related techniques of core–shell nanoparticles synthesized via chemical methods. Diferent semiconducting, pure metallic or oxide materials have been utilized as the core (cadmium telluride, gold, magnetite, or magnetite covered with gold) of the nanoparticle, while they have been, in all cases, functionalized by a thin amorphous glutathione layer, with the goal of using the nanoparticles in biomedical applications such as biomarkers, and computerized tomography and image magnetic resonance contrast agents. The results show that it is possible to visualize the glutathione layer using spectroscopic and imaging techniques, associated with electron microscopy (such as energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy images), that this layer is present at the surfaces of all observed nanoparticles, and that it is no thicker than a few nanometers. Electron microscopy also revealed that the nanoparticles core is crystalline and, in average, around 5-nm size. Keywords Nanoparticle· Glutathione· Gold· Magnetite· QD· Electron microscopy Introduction Nanoparticles (NPs) are deined as solid aggregates of atoms which, having diferent shapes, present dimensions between 1 and 100nm (Hochella 2002), therefore, they can be considered a subgroup among the colloidal particles. Although irst described during the Royal Society Bakerian Lecture of 1857, by Michael Faraday, on the interactions between light an metals, NPs have been always present in nature and the human being have been using them, without a clear conscience of their existence, for centuries (Griin etal. 2018). Nevertheless, their artiicial synthetization, with the purpose of targeting speciic applications, only started in the second half of the twentieth century (Birrenbach and Speiser 1976; Kreuter 2009). The use of NPs is extensive and they are employed to develop novel environment-friendly techniques, such as chemical mechanical polishing slurries with diferent metals (Zhang etal. 2019, 2020), machining methods (Zhang etal. 2015), and diamond wheels (Zhang etal. 2012). Thanks to these technologies, ultra-smooth surfaces and high-performance devices are achieved for several applications, i.e., semiconductor, microelectronics, and aerospace industries, which is extremely diicult to be fabricated by traditional machining and manufacturing (Zhang etal. 2017). The small size of these materials causes efects such as quantum coninement, which, in combination with their high reactivity due to a high speciic surface area, makes NP engineering an ideal platform for custom-made functions, providing solutions for a large amount of disciplines, from electronics (Matsui 2005) to biomedicine (Karley etal. 2011; Ventola 2017; Gheibi Hayat and Darroudi 2019). Among a large variety of compositions, three types of NPs present interesting features for biomedical applications: * J. M. Mánuel [email protected] 1 Department ofIngeniería y Ciencia de los Materiales y del Transporte. Escuela Politécnica Superior, Universidad de Sevilla, 41011Sevilla, Sevilla, Spain 2 IMEYMAT: Institute ofResearch onElectron Microscopy andMaterials, University ofCádiz, 11510PuertoReal, Cádiz, Spain 3 Department ofCondensed Matter Physics, Faculty ofSciences, University ofCádiz, 11510PuertoReal, Cádiz, Spain 4 Department ofMaterials Science andMetallurgic Engineering, andInorganic Chemistry, Faculty ofSciences, University ofCádiz, 11510PuertoReal, Cádiz, Spain AQ1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A 11 A12 A13 A14 Author Proof UNCORRECTED PROOF Journal : Large 13204 Article No : 1418 Pages : 7MS Code : 1418 Dispatch : 24-4-2020 Applied Nanoscience 1 3 gold (Au) NPs, quantum dots (QDs), and magnetic NPs. Au NPs have been widely utilized during the last decade in medical applications such as drug delivery and diagnosis (Kumari etal. 2019; Ramalingam 2019), used as computerized tomography (CT) contrast agents, and even as therapeutic agents in optical hyperthermia. The physical, chemical and optical properties of Au NPs, like their surface plasmon band (Amendola etal. 2017) and their capability to enhance the X-ray attenuation and their low cytotoxicity, make them highly attractive to biomedical uses. Magnetite (Fe3O4) is a highly interesting material to utilize as NP since it is superparamagnetic at room temperature, and, when certain coating is used, its toxicity is reduced, even eliminated. Therefore, these types of NPs are ideal contrast agents for medical diagnosis via magnetic resonance (MRI). On the other hand, semiconductor QDs, such as cadmium telluride (CdTe) NPs, ofer an interesting tool for biomarkers due to their unique size-tunable optical properties and, consequently, their sizedependent luorescence (Le Trequesser etal. 2013). In this case, since the toxicity might also be a concern for these NPs, they are mostly utilized in exvivo biomedical diagnosis (Kairdolf etal. 2013). These systems ofer another advantage: NPs can be functionalized and coated with a polymer layer in the sense of achieving biomedical applications, such as targeted drug deliver, or marker for imaging certain types of cells, thanks to a high, speciic ainity of such polymer. Glutathione (C10H17N3O6S, or GSH) is a tripeptide containing a thiol group to be linked to the NP surface, as well as both, amino and carboxylic groups that remain free to be subsequently crosslinked with other biomolecules, as we have previously shown (Hong etal. 2006; Kumar etal. 2014). In this work, we have used GSH as capping agent for the functionalization of four types of NPs: CdTe QDs with potential applications as biomarkers, gold NPs with potential applications as CT contrast agent, magnetite NPs with potential applications as MRI contrast agent, and, inally, gold-magnetite NPs than can be used as dual contrast agents for bimodal MRI and CT bimodal imaging. In all cases, NPs are “in situ” functionalized during the synthesis step, using GSH. Achieving a correct functionalization process is one of the most important goals for potential medical applications that require subsequent crosslinking with speciic biomolecules. It has to be taken into account, nevertheless, that, if the GSH layer is not properly linked to the NP, undesired results (such as the formation of a non-homogenous or a too-thick GSH layer) could produce defective NP systems. Therefore, to ensure that a proper synthetization has been achieved, a complete set of analyses have to be carried out. Such analyses should not only include chemical techniques, but also methods that provide reliable information on the distribution of GSH around the NP. Direct visualization of hydrophilic molecules in colloidal NP coating layers is possible through the use of high-cost equipment and complex analyses, such as last-generation electron microscopes or cryogenic-trans- mission electron microscopes. For this reason, researchers on the colloidal NP ield commonly chose techniques that yield information on the electric charge of the NPs (such as measurements of zeta potential and isoelectric pH) or on the composition of the coating layers (such as Raman and X-ray photoelectron spectroscopies). However, those methods do not reveal the thickness or the homogeneity of these layers around the NP. Thus, in this work, transmission and scanning–transmission electron microscopy, or (S)TEM, has been chosen as the main tool for the NP–GSH system since it comprehends techniques that join the structural and compositional characterization, with high spatial resolution. Precisely, this is the emphasis of the study: to demonstrate the usefulness of the combination of (S)TEM techniques to properly characterize the GSH layer on NPs. In this sense, in this work, three diferent GSH-covered NP systems are fully characterized by the use of this microscopy. Since the goal of this work is the characterization of GSH-covered NPs, these systems do not have by themselves a speciic bio-func- tionalization; the carboxylic and amino terminal groups in GSH will allow subsequent crosslinking with biomolecules. Materials andmethods The nanoparticles of this work, which are schematically illustrated in Fig.1, were synthesized through diferent chemical methods and consist of four types of core materials, which are, in all cases, covered by a thin GSH layer. Later on, sets of nanoparticles were prepared and labeled, Fig. 1 NP concept, consisting of a core made from one out of four possible materials, and glutathione molecules covering it 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 Author Proof UNCORRECTED PROOF Journal : Large 13204 Article No : 1418 Pages : 7MS Code : 1418 Dispatch : 24-4-2020 Applied Nanoscience 1 3 according to these core materials, as samples S1–S4, which were afterwards characterized by means of electron microscopy. In this sense, the label S1 indicates a sample of GSH- capped CdTe NPs. The material under the GSH layer in sample S2 particles is magnetite. The label S3 is used for the sample in which the core is solely formed by gold. Finally, sample S4 consists in threefold-material particles: an inner Fe3O4 core underneath a thin Au interlayer and a glutathione shell at the surface of the NP. Synthesis ofsamples A brief description of the chemical methods to obtain each sample is described hereafter. These methods are presented in more detail in a diferent work by the authors focused in the application of these materials as biomarkers for medical purposes (Beato-López etal. 2012, 2017; Fernández-Ponce etal. 2018). Commercial GSH was utilized to obtain the coated NP. In all cases, NPs were synthesized at the facilities of the Department of Condensed Matter Physics, associated with the Institute of Research on Electron Microscopy and Materials (IMEYMAT), of the University of Cádiz. Synthesis ofGSH-capped CdTe NPs (sample S1) The synthesis of GSH–CdTe QDs was carried out in two steps, by introducing substantial changes on the methods shown in previous reports (Beato-López etal. 2012, 2017). First, tellurium (Te) powder was reduced in the presence of NaBH4, to obtain the Te precursor for QD preparation. The GSH–CdTe QDs were prepared by a co-precipitation reaction. For this purpose, 0.19g GSH, used as a stabilizing agent, and 0.046g CdCl2, used as the cadmium (Cd) precursor, were dissolved in 100ml MQ water. The Cd2+:NaHTe:GSH molar ratio was 4:1:10. To promote the formation of Cd2+–GSH complexes at the QD surface, pH was adjusted to 8 by dropwise addition of a 1M NaOH solution, under vigorous stirring. The obtained solution was placed in a 500-ml three-necked lask, where 2ml of fresh NaHTe (previously prepared in the irst step) was added. The solution was heated under relux in a nitrogen atmosphere. The inal QD sizes can be controlled increasing temperature and reaction time. Synthesis ofGSH-capped magnetite (sample S2) The synthesis of GSH–Fe3O4 NPs was also performed in two steps. The irst step consists of the preparation of a NaOH solution that was used as oxidizing agent for the coprecipitation of Fe and formation of Fe3O4. This solution was prepared by heating 20g of NaOH and 20ml of diethylene glycol at 120ºC for 1h. After this time, the resulting solution is stored at 70ºC for its posterior utilization. The second step was the main thermal decomposition and coprecipitation reaction. For that, 0.55g of FeCl3, used as iron (Fe) precursor, has been dissolved in 15ml of diethylene glycol solvent. The obtained solution has been placed in a 500-ml three-necked lask, where the GSH used as capping agent has been added. The solution was heated to 200ºC under relux in a nitrogen atmosphere to promote the thermal decomposition of Fe salt. After heating for 30min, the NaOH solution previously prepared had been added to provoke the co-precipitation of Fe and the formation of iron oxide. Synthesis ofGSH-capped Au NPs (sample S3) Au NPs were prepared by the reduction of 10ml of 0.01 MHAuCl4 mixed with 10ml 0.026M GSH. The mixture was vigorously stirred for 30min under a nitrogen atmosphere. Then NaBH4 was added dropwise at 1:5 HAuCl4/NaBH4 molar ratio. After 30 additional minutes, the red wine color solution was stored at 8ºC protected from light. All of them were aqueous solutions. Synthesis ofGSH–Au magnetite (sample S4) In this case, GSH–magnetite was added to a solution containing HAuCl4 and GSH in excess to form the Au core over the NPs previously prepared. Characterization techniques Structural and compositional characterizations of all samples have been performed using diferent (S)TEM-related techniques. Imaging methods such as conventional bright ield (BF-TEM), high-resolution (HRTEM) and high-angle annular dark ield STEM (HAADF-STEM) allowed to visualize structural features, such as size or atomic structure. On the other hand, energy-dispersive X-ray spectrometry (EDX) has been used for subtracting compositions in punctual areas, as well as to draw compositional maps of areas ranging from few nm2 up to µm2. Those techniques were applied in three STEM microscopes, supplied by Thermo Fisher Scientiic: a double-aberration corrected TITAN3 Themis and a Talos F200X, both managed by the Central Services of Research, Science and Technology (SC-ICYT, by its initials in Spanish) of the University of Cádiz, and a Talos F200S microscope equipped with Super-X system which includes two silicon drift detectors, which belong to the Research, Technology and Innovation Center of the University of Seville (CITIUS). All three of these microscopes were operated at a 200kV accelerating voltage. To observe the samples under the electron beam, the chemically obtained NPs were deposited in holey and/or lacey carbon ilms on copper TEM grids. For that purpose, 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 2 11 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 Author Proof UNCORRECTED PROOF Journal : Large 13204 Article No : 1418 Pages : 7MS Code : 1418 Dispatch : 24-4-2020 Applied Nanoscience 1 3 NP powders were irst dissolved in water at diferent concentrations or even directly deposited on the grid, with the idea of obtaining the optimal particle concentration for TEM observation. To avoid an excessive amount of magnetic NPs in the grid later entered in the TEM microscope (which uses magnetic ield-based lenses), a magnet was moved close to the NP-containing grid before its insertion in the microscope sample holder. Results anddiscussion Structural characterization Depending on the dissolution degree with which the NP powders have been deposited on the TEM grids, it is possible to observe conglomerates of NP of diferent sizes, as it is presented in Fig.2, besides isolated NPs. In the case of NPs with magnetic cores (Fig.2b, d), conglomerates are more frequently detected than in the other cases, due to the magnetic forces among those NPs. Nevertheless, in all cases, it was possible to resolve a statistically signiicant number of particles to carry out size and compositional quantiications. In this sense, as presented in Table1, it was possible to determine that the fabrication methods lead to average NP sizes lower than 10nm. The lower size corresponds to GSH-capped CdTe NP, S1, which explains the diiculty for distinguishing among those NPs in low-magniication images, such as the one presented in Fig.2a. Note that the carbon supporting structure (“C-support”, in the image), due to its amorphous atomic arrangement, should not appear in HAADF images since it does not produce electron beam diffraction. Nevertheless, it is not uncommon if brightness level is high enough, for these supporting structures to appear in STEM images. In all cases, rounded and spherical-shaped NPs seemed to be predominant, even more in those samples using gold (samples S3 and S4, Fig.2c, d), although observations using HRTEM, as it will be commented next in the text, reveal cubic-shaped NP crystalline cores, as it was expected. The phase-contrast TEM mode, also known as high-res- olution TEM or HRTEM, reveals areas with a crystalline structure, such as the NPs cores, by presenting atomic columns or fringes, depending on how the crystalline planes diffract the electronic beam emitted by the microscope source. If the material under observation is amorphous, as it is the case of the GSH shell and the carbon matrix supporting the NPs, these images would show a continuous region where the intensity is distributed without any particular order. This allowed (1) to observe the crystalline nature of the NP core and its size [which is an important property of the particle (Kumari etal. 2019)] and (2) to determinate the maximum thickness of the GSH forming the cap layer in these systems. This is also possible thanks to the use of lacey carbon-type grids, in which particles are frequently found at the border of the carbon-web, and thus the carbon signal does not screen the one from the amorphous NP cover along all the particle surface. With this in mind, it was possible to complete Table1, indicating also the average size of the core in the nanoparticles and the maximum amorphous glutathione cover thickness, for each studied sample. As a complement to this table, Fig.3 shows the histograms for the measurements of the NP size. Although the standard deviation in the measurements of these sizes is similar, as it can be observed in Table1, the diiculty in distinguishing the CdTe QDs (due to the fact that these particles were found in sample S1 forming clusters or accumulations and not so much isolated) is relected in the histogram in Fig.3a, from which it is clear that a lower number of NPs were measured in sample S1. As expected, the histogram closer to a normal distribution corresponds to the Au NPs (sample S3) since their synthesis is better controlled and it does not present Fig. 2 Accumulations of NPs in samples S1(a), S2(b), S3(c) and S4(d). Images for S1 and S3 correspond to STEM-HAADF mode, and images for S2 and S4 are taken in BF-TEM mode Table 1 NPs and their core average sizes and GSH maximum thicknesses n.m. not measured Sample NP core NP size (nm) Core size (nm) GSH max. thickness (nm) S1 CdTe 3.9 ± 1.1 n.m. n.m. S2 Fe3O47.4 ± 1.0 5.0 ± 0.3 0.4 ± 0.1 S3 Au 5.1 ± 0.7 5.1 ± 0.9 2.4 ± 0.3 S4 Fe3O4@Au 6.5 ± 1.1 4.4 ± 1.0 1.1 ± 0.3 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 Author Proof UNCORRECTED PROOF Journal : Large 13204 Article No : 1418 Pages : 7MS Code : 1418 Dispatch : 24-4-2020 Applied Nanoscience 1 3 magnetic behavior that leads to the cluster formations that would make diicult the measurement of the particle size. Data in Table1 together with the results from TEM images such as the ones presented in Fig.2 indicate the NPs in this work could be a good choice as nanoparticle in medicine since the most attractive NPs for biomedical applications are those spherical and with sizes ranging from 2 to 10nm (Khan etal. 2018). Many body barriers fall in the sub-10-nm regime, but, on the other hand, NPs smaller than 2nm could considerably increase their toxicity. In this sense, it can be mentioned that an appropriate method, easier than those based on hydrophobic routs, to prepare small soluble and functionalized NPs is to carry out a reduction in aqueous media using a strong reducing agent, like sodium borohydride, in the presence of strong capping ligands to control particle growth. Some advantages of this route reside in the possibility to choose a capping ligand that directly biofunctionalizes the NP or that facilitates its subsequent biofunctionalization (Fratoddi 2018). This route also allows for the use of thiols as capping agents, due to the high ainity of this group for the NP surface(Dehn etal. 2018). In this work, we have used this NaBH4 reduction reaction, adding both, the capping and the reduction agent in excess to promote the fast nucleation and successive growth to homogenize NP size. Increasing the nucleation step rate, a high proportion of nuclei will be formed before starting the growth step. This enhances the formation of small homogeneous and spherical cores. Figure4 illustrates these ideas through HRTEM images for three types of NPs of this work. This igure does not show particles from sample S1 since it was not possible to achieve high-resolution conditions for NPs with CdTe cores. On the other hand, for the rest of samples, it was possible to observe NPs both inside the conglomerates (Fig.4a) and isolated ones (Fig.4b, c). Some NP core and coating layers, according with the ideas commented before, are also pointed out in this igure. It is possible to obtain valuable information from the regions corresponding to the NP core using these HRTEM images. In this sense, the comparison of measurements for atomic planes distances with the ones theoretically expected for the diferent materials agrees with the airmation that the NPs cores are formed, indeed, by magnetite and/or gold. In this sense, measurements in images such as the one in Fig.4a revealed experimental distances of 2.9Å, which agree with the expected distances between {220} atomic planes in magnetite particles (Haavik etal. 2000). Figure4b shows an example of a HRTEM image from a NP in sample S4. From this image and other analogous ones, it was possible to measure distances between atomic planes of 3.0 and 4.9Å. This is in agreement with theoretical distances between the {220} and {111} families of planes of magnetite (2.97 and 4.85Å, respectively) (Haavik etal. 2000), and also 2.4Å, which can be associated with the ones for the {111} planes in the case of Au (Righter etal. 2011). The HRTEM images of nanoparticles in Fig.4d shows atomic distances of 2.1 and 2.4Å, which, respectively, agree well with the spacing between {002} and {111} families of atomic planes for cubic Au (2.04 and 2.35Å, respectively) (Righter etal. 2011). Fig. 3 Histograms for NP sizes in samples S1(a), S2(b), S3(c), and S4(d). The horizontal axes indicate the NP size, in nm, while the vertical ones present the amount of NPs corresponding to each size range. The histogram bars correspond to increments in the size of 0.3nm Fig. 4 HRTEM images of individual NPs in samples S2(a), S4(b), and S3(c) 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 3 11 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 Author Proof UNCORRECTED PROOF Journal : Large 13204 Article No : 1418 Pages : 7MS Code : 1418 Dispatch : 24-4-2020 Applied Nanoscience 1 3 Compositional characterization Figure5 displays representative punctual EDX spectra for NPs in the four samples (Fig.5a), as well as EDX maps for NPs (Fig.5b–d) and accumulations of those (Fig.5e–g). It is possible to observe, in Fig.5a, that the NPs have, indeed, the expected chemical composition, revealing a sulfur Kα-peak, at 2.31keV, in all cases (the gold M-peak, at 2.12keV, which appears in samples S3 and S4, partly overlap the sulfur signal). This element is associated with the presence of the glutathione shell around the NP core. Figure5b presents a HAADF image of a single NP (sample S3) for which an EDX map has been recorded. Figure5c reveals that this NP has a gold core, while it is clear, according to Fig.5d, that the NP is totally covered with the S-containing compound (glutathione). In this sense, it is also possible to show that the glutathione coats the NPs even when they form conglomerates. Figure5e presents a HAADF image of a 30-nm-size NP agglomeration. EDX maps of iron (Fig.5f) and sulfur (Fig.5g) reveal that there is a homogeneous distribution of magnetite and GSH, respectively, indicating that the synthesis method leads to a majority of NPs in the sample with the desired core and the glutathione layer. This result is also observed in the other samples. Conclusions A series of samples of GSH-capped NPs have been successfully developed via chemical methods. The smallest and rounder NPs, with the most clearly monocrystalline structure of the core, have been obtained for gold-containing NPs. On the other hand, worse results have been obtained for the NPs with a CdTe core. (S)TEM-based techniques represent a good choice to completely characterize these systems. The spectroscopic techniques, combined with STEM images, are especially indicated to reveal the sulfur in the glutathione layer, which allows the visualization of this NP shell. Acknowledgements The authors would like to acknowledge the SCICYT and the CITIUS central services of the Universities of Cádiz and Seville, respectively, which made possible the sample preparation and TEM studies in this work. A. J. Santos would like to thank the IMEYMAT Institute and the Spanish Ministry of Education and Culture for the concessions of Grants ICARO-173873 and FPU16-04386. The authors would like to thank the Spanish Ministry of Economy and Competitiveness for the economic support to the research project MAT2015-67354-R (Program “Plan I + D + i”, subprogram “Retos”). Author contributions RL and OB-M contributed to the study conception and design. Nanoparticle systems were synthetized by RL and EF. (S)TEM microscopy techniques were carried out at three diferent microscopes by AMB, JMM, AJS and FMM. OB-M and JMM, as “investigadores principales” (main researchers) of Research Project MAT2015-67,354-R, managed the necessary economical funds that allowed this work. The irst draft of the manuscript was written by AMB and JMM and all authors commented on the previous versions of the manuscript. All authors read and approved the inal manuscript. Funding This work has been funded by the Spanish Ministry of Economy and Competitiveness, through the research project “Síntesis asistida por láser de nanopartículas ternarias: una ruta alternativa para la fabricación de nuevos agentes de contraste multimodales para el diagnóstico temprano del cáncer de mama”, reference: MAT2015- 67354-R, of the Program “Plan I + D + i”, subprogram “Retos”. Data availability Any of the data and material utilized to develop this manuscript can be available at request of any researcher, via the corresponding author. Code availability Not applicable. Compliance with ethical standards Conflict of interest The authors declare that there is no conlict of interest/competing interests associated with the work presented in this manuscript. References Amendola V, Pilot R, Frasconi M etal (2017) Surface plasmon resonance in gold nanoparticles: a review. 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