CC BY
21LD-I-17
SERS-active substrates based on Au/Ag-decorated silicon nanostructures for the rapid detection of chemical and biomolecules
L.A. Osminkina12
1- Lomonosov Moscow State University, Physics Department, Leninskie Gory 1, 119991 Moscow, Russian
Federation
2- Institute for Biological Instrumentation of Russian Academy of Sciences, 142290 Pushchino, Moscow Region,
Russian Federation
osminkina@physics. msu. ru
Surface-enhanced Raman scattering (SERS) has proven itself to successfully detect different biomarkers of diseases, viruses, and bacteria, etc. Due to the SERS effect, the intensity of Raman scattering of light by molecules adsorbed on nanostructured surfaces of noble metals usually increases by 6-8 orders of magnitude. The observed increase in Raman intensity can be explained by two mechanisms: electromagnetic, which is associated with localized surface plasmon resonance in nanostructures of noble metals, and chemical, caused by charge transfer between adsorbed molecules and the nanostructures. The main characteristics of a proper SERS-substrate are its homogeneity, batch-to-batch reproducibility, the stability of SERS signal intensity, and easy and cost-effective fabrication.
Silicon nanostructures such as arrays of silicon nanowires (SiNWs) and porous silicon films (PSi) are attractive objects for creating sensitive sensors due to the simplicity of their preparation methods and silicon surface tailorability. Since arrays of nanowires and porous films have a huge surface area, a high number of metallic nanoparticles (NPs) could be packed on them, which would yield a high enhancement factor when using such nanostructures as SERS-active substrates. SiNWs can be obtained by several different methods, but among the others, metal-assisted chemical etching is the simplest method that does not require expensive equipment and is attracting more and more attention in the large-scale production of SiNWs. PSi films are usually produced by electrochemical etching of crystalline silicon wafers. In our study, the fabrication process of a SiNW matrix differently modified with Ag and Au NPs was demonstrated [1]. The process combines SiNW synthesis by the metal-assisted chemical etching with or without native Ag/Au NPs and subsequent Ag or/and Au NPs chemical deposition. This fabrication method has a short processing time, is cost-effective, and provides structural variability with high potential for SERS applications. We evaluated the SERS activity of PSi with pores ranging in size from meso to macro, the surface of which was coated with Au NPs [2]. We found that different pore diameters in the PSi layers provide different morphology of the gold coating, from an almost monolayer to 50 nm distance between nanoparticles. Methylene blue (MB) and 4-mercaptopyridine (4-MPy) were used to describe the SERS activity of obtained Au/PSi surfaces. The best Raman signal enhancement was shown when the internal diameter of torus-shaped Au NPs is around 35 nm [2]. It has been shown that molecules of pyocyanin (PYO), a specific metabolite of the bacteria Pseudomonas aeruginosa, can be successfully detected in artificial sputum up to 6.25 ^M, which is the lower limit of the clinically significant range [1]. Moreover, the label-free rapid detection of unconjugated bilirubin up to a concentration in the clinically relevant range has been demonstrated with high reproducibility. To understand the role of plasmonic resonances in the observed SERS spectrum, we performed electromagnetic simulations of Raman scattering intensity as a function of the internal diameter. The results of these simulations are consistent with the obtained experimental data [1, 2]. These results open up the possibility of using the developed SERS-active substrates as platforms for point-of-care clinical diagnostics.
The research was funded by the Russian Science Foundation (grant number 20-12-00297).
[1] O. Zukovskaja, S. Agafilushkina, V. Sivakov, K. Weber, D. Cialla-May, L. Osminkina, J. Popp, Rapid detection of the bacterial biomarker pyocyanin in artificial sputum using a SERS-active silicon nanowire matrix covered by bimetallic noble metal nanoparticles. Talanta, 202, 171177, (2019).
[2] S. N. Agafilushkina, O. Zukovskaja, S. A. Dyakov, K. Weber, V. Sivakov, J. Popp, D. Cialla-May, L.A. Osminkina Raman Signal Enhancement Tunable by Gold-Covered Porous Silicon Films with Different Morphology. Sensors, 20(19), 5634, (2020).
