Development of biocompatible plasmonic thin films composed of noble metal nanoparticles embedded in a dielectric matrix to enhance Raman signals

Abstract

This work focused on the production of nanocomposite thin films, composed of noble nanoparticles embedded in a dielectric matrix, to be tested as biocompatible plasmonic platforms for detection of molecules using Surface Enhance Raman Spectroscopy (SERS). Three different thin films systems were deposited by reactive DC magnetron sputtering, namely Au-Al2O3, Au-TiO2 and Ag-TiO2. The depositions were followed by a thermal treatment at different temperatures to promote the growth of the nanoparticles. Localized Surface Plasmon Resonance (LSPR) bands appeared already at 300 ºC, related to the presence of Au nanoparticles, and at 500 ºC in the case of Ag nanoparticles. Furthermore, at 700º C, the Ag-TiO2 films showed a broadband optical response due to the formation of Ag clusters at the film's surface. The biological experiments showed that the presence of the thin films didn't affect the growth of C. albicans, which is very convenient if one needs to detect low concentrations of this microorganism using SERS platforms. As for the SERS 2 measurements, an enhancement of R6G Raman spectra intensity was clearly perceivable, but only for the TiO2 matrix. Furthermore, the application of a plasma treatment allowed to better expose the nanoparticles, providing a further enhancement of Raman signals.

Tuning the Refractive Index Sensitivity of LSPR Transducers Based on Nanocomposite Thin Films Composed of Noble Metal Nanoparticles Dispersed in TiO2

“…The thin film prepared with 2.0 A contained 9 at.% of Ag, with Au content of 4 at.%, while at 75 A/m 2 , the film had an Au content of 10 at.%, and Ag content of 19 at.%. Considering the higher sputtering yield obtained for Ag, in comparison with Au, the chemical characterization results fall within expectations [64,65]. Previous studies with Au-Ag/TiO 2 thin films, with a 1:2 ratio of Au to Ag [49], showed the formation of Au-Ag NPs with smaller Ag NPs dispersed in the TiO 2 matrix.…”

“…Concerning the Ag/TiO 2 thin films (Figure 1b), the samples present a higher noble metal content, from 22 to 30 at.%. This is due to the higher sputtering yield of Ag in comparison to Au [64,65]. Starting at one Ag disk in the Ti target (16 mm 2 ) and 100 A/m 2 of current density, the films have 22 at.% of Ag in their composition.…”

Transmission electron microscopy reveals clusters of Au–Ag nanoparticles formed in TiO2 thin film, with enhanced plasmonic response

“…Physical Vapor Deposition techniques, such as magnetron sputtering, allow the production of thin films with randomly dispersed noble metal atoms in a dielectric matrix. By adjusting the deposition parameters, such as current, deposition rate [26], target material [27], and noble metal content, it is possible to optimize the thin films to produce reliable LSPR-based optical transducers. However, just using magnetron sputtering does not ensure the formation of NPs with LSPR behavior in the thin film.…”

Tunable optical and plasmonic response of Au nanoparticles embedded in Ta-doped TiO2 transparent conducting films

“…Other combined systems, such as Au-ZnO, take advantage of the antimicrobial properties of ZnO and plasmonic excitations typical of Au NPs for the development of optical sensing devices for fast molecule detection [25]. Regarding bioscience, the broadband LSPR absorption driven by coalesced nanoparticles is exploited in Au-Al2O3 and Au/Ag-TiO2 substrates for surface enhanced Raman spectroscopy (SERS) [25][26][27]. Most of the previous studies have examined the influence of the quantity of metal and annealing temperature on NP morphology and structure.…”