Kseniya Girel

Progress in the Development of SERS-Active Substrates Based on Metal-Coated Porous Silicon

The present work gives an overview of the developments in surface-enhanced Raman scattering (SERS) with metal-coated porous silicon used as an active substrate. We focused this review on the research referenced to SERS-active materials based on porous silicon, beginning from the patent application in 2002 and enclosing the studies of this year. Porous silicon and metal deposition technologies are discussed. Since the earliest studies, a number of fundamentally different plasmonic nanostructures including metallic dendrites, quasi-ordered arrays of metallic nanoparticles (NPs), and metallic nanovoids have been grown on porous silicon, defined by the morphology of this host material. SERS-active substrates based on porous silicon have been found to combine a high and well-reproducible signal level, storage stability, cost-effective technology and handy use. They make it possible to identify and study many compounds including biomolecules with a detection limit varying from milli- to femtomolar concentrations. The progress reviewed here demonstrates the great prospects for the extensive use of the metal-coated porous silicon for bioanalysis by SERS-spectroscopy.

The alpha helix 1 from the first conserved region of HIV1 gp120 is reconstructed in the short NQ21 peptide

Investigations of short peptides that can be used in the next phase of synthetic HIV1 vaccine development are an urgent goal, as well as investigations of peptides that can be used in immunological tests with the aim to check the titer of antibodies against the alpha helix 1 from the first conserved region of HIV1 gp120 that are known to cause antibody-dependent cellular cytotoxicity (ADCC). The aim of this work was to study the structure of the NQ21 peptide corresponding to the less mutable part of the first conserved region of HIV1 gp120 (residues 94-114). The NQ21 peptide and its conjugate with biotin (biotin-NQ21) are absolutely alpha-helical in phosphate buffer solutions at pH = 6.8, 7.4 and 8.0, as well as in the dried form, according to the results of surface-enhanced Raman scattering (SERS) spectroscopy. Results of the native gel electrophoresis and thermal analysis under the control of spectrofluorometer and near UV circular dichroism (CD) showed that the peptide exists in form of octamers and tetramers at pH = 7.4, that is important information for further vaccine development. Strong signal of interacting Trp residues in oligomers in the far UV CD obscures the signal from secondary structure, but becomes less intensive during the heating.

Experimental study of the sensitivity of a porous silicon ring resonator sensor using continuous in-flow measurements

A highly sensitive photonic sensor based on a porous silicon ring resonator was developed and experimentally characterized. The photonic sensing structure was fabricated by exploiting a porous silicon double layer, where the top layer of a low porosity was used to form photonic elements by e-beam lithography and the bottom layer of a high porosity was used to confine light in the vertical direction. The sensing performance of the ring resonator sensor based on porous silicon was compared for the different resonances within the analyzed wavelength range both for transverse-electric and transverse-magnetic polarizations. We determined that a sensitivity up to 439 nm/RIU for low refractive index changes can be achieved depending on the optical field distribution given by each resonance/polarization.

Plasmonic silvered nanostructures on macroporous silicon decorated with graphene oxide for SERS-spectroscopy

A method for fabricating surface-enhanced Raman scattering (SERS)-active substrates by immersion deposition of silver on a macroporous silicon (macro-PS) template with pore diameters and depth ranging from 500-1000 nm is developed. The procedure for the formation of nanostructured silver films in the layers of macro-PS was optimized. Silver particles of dimensions in the nano- and submicron-scale were formed on the external surface of the macro-PS immersed in the water-ethanol solution of AgNO3, while the inner pore walls were covered by smaller, 10-30 nm diameter, silver nanoparticles. Upon introducing the hydrofluoric acid to the reaction mixture, the size of nanoparticles grown on the pore walls increased up to 100-150 nm. Such nanostructures were found to yield SERS-signal intensities from CuTMpyP4 analyte molecules of the same order to those obtained from silvered mesoporous silicon reported previously. The tested storage stability for the silvered macro-PS-based samples reached up to 8 months. However, degradation of the SERS intensity under illumination by the laser beam during spectral measurements was observed. To improve the stability of the SERS-signal a hybrid structure involving graphene oxide deposited on the top of analyte molecules adsorbed on the Ag/macro-PS was formed. A systematic observation of the time evolution of the characteristic peak at 1365 cm-1 showed that the addition of the oxidized graphene layer over the analyte results in ∼2 times slower decay of the Raman intensity, indicating that the graphene coating can be used to enhance the stability of the SERS-signal from the CuTMpyP4 molecules.

Particles of porous silicon formed from silica powders of plant origin and their structural properties

In this paper, we present the results on study of formation regularities, morphology, composition and photoluminescence of porous silicon particles fabricated by the magnesiothermal reduction of different samples of biogenic silicon dioxide based on rice husk, bamboo husk and bamboo joints at 650 °C at argon atmosphere.

Nanostructured Metal Films Formed onto Porous Silicon Template

The review reports on the results of our research work on nanostructured metal films onto porous silicon. Principal steps of the techniques allowing fabrication of metal films completely inheriting morphological pattern of different types of porous silicon are presented. It is shown, that giving of the nanostructured pattern to metal films by means of porous silicon template opens their new structural, optical, mechanical and electrical properties, which can be successfully applied in nanoelectronics and biomedicine, particularly including devices based on superconductivity effect, SERS analysis with picomolar sensitivity and transdermal drug delivery by electroporation.

Optical properties of silver/porous silicon nanostructures

The present paper concerns the study of nanostructures formed by immersion deposition of silver on porous silicon at different modes for their application in surface enhanced Raman spectroscopy. Porous silicon has been fabricated by anodization of monocrystalline silicon in water solution of isopropanol and hydrofluoric acid. Reflectance spectra of the obtained structures of silver/porous silicon have been studied. It has been revealed that the highest level of Raman signal requires using laser with wavelength of 400 - 450 nm.