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We present Raman spectroscopy and quantum chemical computational study for model phospholipid membrane molecule dipalmitoylphosphatidylcholine (DPPC) mixed with cholesterol or melatonin at various concentrations. Utilizing a confocal Raman microspectroscopy setup, we capture a DPPC conformation state by evaluating the number of trans/gauche bonds using I1064/I1090 and I1128/I1090 vibrational modes intensity ratios. We show that the cholesterol increases the number of trans bonds in DPPC hydrocarbon chains, i.e. causes membrane ordering, while melatonin addition introduces gauche conformers, generating disorder. It is noticed that the I1128/I1090 intensity ratio is more suitable parameter for the characterization of DPPC hydrocarbon chains structural properties compared with I1064/I1090. We thus clarify our experimental observations by performing careful density functional theory (DFT) calculations of Raman spectra for DPPC tails, containing up to three gauche bonds at different chain positions. The obtained results demonstrate strong interconnection between 1064 and 1090 cm-1 vibrational modes originated from their complex splitting and shifting along with continuous Raman activity redistribution upon various gauche bonds introduction, while it is not the case for 1128 cm-1 and 1090 cm-1 modes pair.

Silicon nanowires (SiNWs) were comprehensively characterized in dependence on conditions of their formation via metal (Ag) -assisted chemical etching (MACE) of monocrystalline Si. The Ag structures remained on/between SiNWs based on both n- and p-Si were found to promote surface enhancement of Raman scattering (SERS) from organic molecules adsorbed on their surface. The Ag structures on/between the SiNWs/p-Si facilitated two times higher SERS-signal from 10-6 M rhodamine 6G than those in the SiNWs/n-Si. The activity of the SERS-substrates based on p-Si was improved by modification with small Au dendrites, which provided rich family of hot spots and prevented degradation of the SERS-activity observed for pure Ag dendrites due to formation of Ag2S during one week of storage in air. The SERS-substrates based on the Au/Ag dendrites on SiNWs/p-Si allowed to achieve nanomolar detection limit of rhodamine 6G and 5,5 -dithiobis (2-nitrobenzoic acid).

In this study, we developed a filtering material for facial masks, which is capable of trapping and subsequent inactivation of bacteria under white light emitting diodes (LED) or sunlight irradiation. Such a functionality is achieved via the modification of the composite membrane based on porous polymer with photocatalytic (TiO2) and plasmonic (Ag) nanoparticles. The porous polymer is produced by means of a computer numerical control machine, which rolls a photoresist/thermoplastic mixture into a ~20-µm-thick membrane followed by its thermal/ultraviolet (UV) hardening and porosification. TiO2 nanoparticles are prepared by hydrothermal and sol-gel techniques. Colloidal synthesis is utilized to fabricate Ag nanoparticles. The TiO2 photocatalytic activity under UV excitation as well as a photothermal effect generated by plasmonic Ag nanoparticles subjected to LED irradiation are studied by the assessment of methylene blue (MB) decomposition. We demonstrate that, in contrast to the filter of the standard facial medical mask, the polymer membrane modified with spray-coated TiO2 and Ag nanoparticles prevents the penetration of bacillus subtilis from its top to bottom side and significantly inhibits bacterial growth when exposed to LED or sunlight.

Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most prospective methods combining state-of-the-art nanomaterials and optical techniques for highly sensitive express-analysis and detection of organic and bioorganic objects in liquids and gases. Special programs have been recently started all over the world to bring the SERS-spectroscopy closer to wide implementation in medical diagnostics, forensics, security, monitoring sanitary conditions, etc. Despite outstanding features of SERS-spectroscopy, its effective practical use has been particularly slowed down by moderate reproducibility, non-versatility, and restrictions imposed by commercially available SERS-active substrates to measurement and storage regimes. The present review reports SERS-active substrates constituted by noble metals' nanoparticles (NPs) and porous silicon (PS), which potentially can be a tool to overcome the above-mentioned limitations. The PS template acts as a highly ordered host nanomaterial for the formation of a variety of metallic nanostructures, which morphological and optical properties can be easily tuned for the best performance to meet the customer requirements via managing PS synthesis regimes. An indubitable advantage of PS is the compatibility of its fabrication process with basic microelectronics operations and micro-electromechanical systems (MEMS) that make it possible to integrate SERS-active areas in a silicon chip. In contrast to the previously published reviews in the field, this one covers the most recent results on formation, characterization, and application of PS-based substrates demonstrating prominent SERS-activity that have been achieved for the last decade including modifications with graphene or Bragg structures, detection of molecules at amount down to attomolar concentration, bacteria recognition, etc.

Here we present results of our research work on an electroless corrosive deposition of coinage metals on nanostructured silicon. Principal steps of nanostructured silicon fabrication and further deposition of metals allowing growth of metallic films controlled by dopant type of a silicon substrate, morphology of silicon skeleton and electroless deposition regimes are presented. Imprinting of the nanostructured pattern to metallic films by means of the sculpted silicon template opens their new morphological, optical, mechanical and electrical properties, which can be successfully applied in micro- and nanosystems and biomedicine. In the context of the latter, we pay special attention to activity of the metal-coated silicon nanostructures in surface enhanced Raman scattering (SERS) spectroscopy and profits provided both by using silicon templating and electroless deposition of metals. The electroless corrosion is mostly associated with undesirable surface destruction of different materials. Indeed, corrosion can lead to the irreparable harm both in macro- and nanoscaled worlds. Oxidation/degradation of metallic components of massive constructions in aggressive environment are very dangerous as well as corrosion of conductive metallic wires in ICs and MEMS causing further failure of the whole device. Surprisingly, but it has opened an opportunity to turn corrosion effect into positive way in some applications. For instance, since the 90-th of the last century corrosion of monocrystalline silicon (c-Si) in solutions for chemical cleaning, containing trace amounts of Cu ions, has been actively studied [1]. Solutions for chemical cleaning usually contain deionized water and HF. However, the Cu ions can unpredictably appear in solutions from environment on different stages of ICs production. Corrosion of c-Si also takes a place in HF-based solutions containing ions of other coinage metals (Ag, Au, etc.). Understanding mechanism of corrosion has allowed to apply this process for fabrication of the Cu conductive interconnections, which possess improved adhesion to the Si wafers [2]. New wave of interest to this process has been raised due to an opportunity to fabricate metallic nanostructures of variable morphology by electroless corrosive deposition of metals on silicon nanostructures. During our work related to the electroless corrosive deposition of coinage metals on silicon nanostructures we found that this process occurs according to mechanism of island film growth. It was revealed that Si nanocrystallites corrode faster than c-Si because of a great number of the surface states. Metallic atoms were observed to prevalently deposit on an external surface of silicon skeleton based on n-Si because of excess of electrons from dopant atoms. On the other hand, the inner growth of metallic atoms has been found to dominate on the substrates based on p-Si due to absence of dopant atoms supplying electrons. In the last case the reduction of metallic ions to the atomic form is connected only with taking electronts from the silicon atoms. As a result of our systematic investigations we developed a technique of electroless corrosive deposition of Cu, Ag and Au on nanostructured Si, which provides precise control of metallic deposit morphology from quasi-continuous films consisted of metallic nanoparticles to dendrites or nanovoids. The obtained films were found to show activity in the SERS-spectroscopy that is known as an extremely sensitive method of qualitative and quantitative analysis in analytical chemistry, biomedicine, environment and food control, forensics, etc. It was shown that nanosculpted silicon acts not only as a source of electrons for reduction of metal ions and template defining shape, sizes and special location of metallic nanostructures, but also prevents their fast oxidation and coalescence, which usually lead to the inhibition of SERS-activity. SERS-activity of the substrates was observed even for the 2 years aged samples. Morphology of these substrates can be adjusted to detect certain analyte molecules in dependence on their molecular weight including to achieve attomolar detection limit. [1] H. Morinaga, M. Suyama, T. Ohmi, J. Electrochem. Soc. 1994, 141, 2834. [2] J.L. Gole, L.T. Seals, P.T. Lillehei, J. Electrochem. Soc. 2000, 147, 3785–3789.

Dielectrophoresis (DEP) is a versatile tool for the precise microscale manipulation of a broad range of substances. To unleash the full potential of DEP for the manipulation of complex molecular-sized particulates such as proteins requires the development of appropriate theoretical models and their comprehensive experimental verification. Here, we construct an original DEP platform and test the Holzel-Pethig empirical model for protein DEP. Three different proteins are studied: lysozyme, BSA, and lactoferrin. Their molecular Clausius-Mossotti function is obtained by detecting their trapping event via the measurement of the fluorescence intensity to identify the minimum electric field gradient required to overcome dispersive forces. We observe a significant discrepancy with published theoretical data and, after a very careful analysis to rule out experimental errors, conclude that more sophisticated theoretical models are required for the response of molecular entities in DEP fields. The developed experimental platform, which includes arrays of sawtooth metal electrode pairs with varying gaps and produces variations of the electric field gradient, provides a versatile tool that can broaden the utilization of DEP for molecular entities.