Design and Characterization of ITO-Covered Resonant Nanopillars for Dual Optical and Electrochemical Sensing

Abstract

In this work we present a dual optical and electrochemical sensor based on SiO2/Si3N4 resonant nanopillars covered with an indium tin oxide (ITO) thin film. A 25–30 nm thick ITO layer deposited by magnetron sputtering acts as an electrode when incorporated onto the nanostructured array, without compromising the optical sensing capability of the nanopillars. Bulk sensing performances before and after ITO deposition have been measured and compared in accordance with theoretical calculations. The electrochemical activity has been determined by the ferri/ferrocyanide redox reaction, showing a remarkably higher activity than that of flat thin films of similar ITO nominal thickness, and proving that the nanopillar system covered by ITO presents electrical continuity. A label-free optical biological detection has been performed, where the presence of amyloid-β has been detected through an immunoassay enhanced with gold nanoparticles. Again, the experimental results have been corroborated by theoretical simulations. We have demonstrated that ITO can be a beneficial component for resonant nanopillars sensors by adding potential electrochemical sensing capabilities, without significantly altering their optical properties. We foresee that resonant nanopillars coated with a continuous ITO film could be used for simultaneous optical and electrochemical biosensing, improving the robustness of biomolecular identification.

Compact and efficient lossy mode resonant refractive index sensor for aqueous environment

“…Transparent conducting oxide thin films and particularly indium-tin-oxide (ITO) films find their applications in integrated touch sensors for flexible OLED displays, photovoltaic cells, LCDs, optical fiber sensor, gas sensing, analysis of ionized media and opto-electrochemical label free biosensors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. ITO films are transparent, conducting and chemically stable and can be used for integrated-optic sensing applications.…”

Perspective Coatings Based on Structured Conducting ITO Thin Films for General Optoelectronic Applications

“…Indium tin oxide (ITO) thin structures are n-type degenerated semiconductors with high optical transmittance in the visible and near-infrared ranges. Due to their relatively small sheet resistance (10 −4 -10 −3 Ω × cm) [1][2][3] and high transparency [4][5][6], thin films based on the ITO layer are widely used in optical electronics [7][8][9], biosensors [10][11][12] and electrochemistry [13][14][15]. The nanotechnology approach indeed provokes better basic Coatings 2024, 14, 178 2 of 16 features in the ITO.…”

Optical Properties in Mid-Infrared Range of Silicon Oxide Thin Films with Different Stoichiometries

“…Thin-film SiO 2 is a material that has been extensively studied and is widely used in numerous applications, such as materials with a low refractive index, a barrier for thermal diffusion, and for improving adhesion or enhancing mechanical strength, among many others [16][17][18][19][20][21][22][23][24]. The properties of SiO 2 and SiO x thin films have also been studied in the mid-infrared range [25][26][27], a spectral region that is of great interest in topics related to blackbody radiation at room temperature [28] or in astronomy, as well as in current research topics such as "epsilon near zero" metamaterials or the fabrication of perfect anti-reflective coatings at specific wavelengths [29][30][31][32][33][34].…”