One Spot—Two Sensors: Porous Silicon Interferometers in Combination With Gold Nanostructures Showing Localized Surface Plasmon Resonance

Abstract

Sensors composed of a porous silicon monolayer covered with a film of nanostructured gold layer, which provide two optical signal transduction methods, are fabricated and thoroughly characterized concerning their sensing performance. For this purpose, silicon substrates were electrochemically etched in order to obtain porous silicon monolayers, which were subsequently immersed in gold salt solution facilitating the formation of a porous gold nanoparticle layer on top of the porous silicon. The deposition process was monitored by reflectance spectroscopy, and the appearance of a dip in the interference pattern of the porous silicon layer was observed. This dip can be assigned to the absorption of light by the deposited gold nanostructures leading to localized surface plasmon resonance. The bulk sensitivity of these sensors was determined by recording reflectance spectra in media having different refractive indices and compared to sensors exclusively based on porous silicon or gold nanostructures. A thorough analysis of resulting shifts of the different optical signals in the reflectance spectra on the wavelength scale indicated that the optical response of the porous silicon sensor is not influenced by the presence of a gold nanostructure on top. Moreover, the adsorption of thiol-terminated polystyrene to the sensor surface was solely detected by changes in the position of the dip in the reflectance spectrum, which is assigned to localized surface plasmon resonance in the gold nanostructures. The interference pattern resulting from the porous silicon layer is not shifted to longer wavelengths by the adsorption indicating the independence of the optical response of the two nanostructures, namely porous silicon and nanostructured gold layer, to refractive index changes and pointing to the successful realization of two sensors in one spot.

Porous Silicon Biosensor for the Detection of Bacteria through Their Lysate

“…Solutions, such as the electrokinetic transport for the preconcentration of analyte, have been proposed but remain to be tested on bacteria [29]. Recently, porous silicon interferometers have also been combined with gold nanoparticles for localized surface plasmon spectroscopy (LSPS), enhancing the fringe pattern contrast and increasing the sensitivity of the porous layer [30,31].…”

Hybrid Porous Silicon Biosensors Using Plasmonic and Fluorescent Nanomaterials: A Mini Review

“…PSi nanostructures have been used as a host matrix for preparing hybrid platforms using different nanomaterials such as QDs, MNPs, graphene oxide, carbon nanotubes, fluorescent molecules, and polymers (Arshavsky-Graham et al, 2018;Tieu et al, 2019). PSi-based hybrid platforms improve the sensitivity and stability of the sensor and allow for dual-mode detection (Gaur et al, 2013;Pacholski et al, 2019). PSi biosensors designed with single-mode optical sensing suffer from poor sensitivity limited to the micromolar range and lack of simultaneous selective detection of more than one target analyte (Massad-Ivanir et al, 2018b).…”

“…In contrast, optical biosensors designed for dual-mode detection are characterized by their ability to combine the quantification and identification of molecules in a single substrate (Jiao et al, 2010;Yeom et al, 2011). The molecular quantification can be achieved via reflectance measurements of PSi matrix, whereas the molecular identification and conformation can be attained through Surface Enhanced Raman Spectroscopy (SERS) (Jiao et al, 2010;Pacholski et al, 2019) or LSPR (Pacholski et al, 2019) in case of using MNPs, or through fluorescence spectroscopy when fluorescent QDs are confined inside the PSi matrix (Massad-Ivanir et al, 2018a,b). The dual-mode biosensors with fluorescence or SERS characteristic enable the detection of multiple molecules with enhanced sensitivity and specificity (McNay et al, 2011).…”

“…A recent review by Bandarenka et al discussed the fabrication of PSi/metal nanoparticles hybrids and their application as SERS-active substrates, emphasizing two major advantages: (1) the long storage stability; and (2) the significant Raman enhancement factor (Bandarenka et al, 2018). PSi/Plasmonic nanoparticle hybrids allow for fabricating biosensors with SERS and refractive index sensing capability (Pacholski et al, 2019). Škrabi'c et al reported the application of silver-coated PSi photonic crystals as SERS substrates for nearinfrared (1064 nm) excitation, which has significant importance for the Raman detection of fragile biomolecules (Škrabić et al, 2019).…”

Metal Filled Nanostructured Silicon With Respect to Magnetic and Optical Properties

“…The wavelength of the plasmon resonance depends not only on the Au nanostructures but also on the refractive index of the surrounding medium. Plasmon resonance is sensitive to changes in the refractive index only close to the dielectric/metal interface [89]. Metal decorated porous silicon structures are feasible as sensors, especially to detect molecules.…”