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Porous silicon nanowires (pSi NWs) have attracted considerable interest due to their unique structural, optical properties and biocompatibility. The most common method for their top-down synthesis is metal-assisted chemical etching (MACE) of crystalline silicon (c-Si) wafers using silver nanoparticles as a catalyst. However, the replacement of silver with bioinert gold nanoparticles (Au NPs) markedly improves the efficiency of pSi NWs in biomedical applications. The present study demonstrates the fabrication of porous pSi NWs arrays using Au NPs as the catalyst in MACE of c-Si wafers with a resistivity of 1–5 mOhm·cm. Using scanning electron microscopy (SEM), the formation of arrays of porous nanowires with a diameter of 50 nm that consist of small silicon nanocrystals (nc-Si) and pores was observed. Raman spectroscopy analysis determined the size of nc-Si is about 4 nm. The pSi NWs exhibit effective photoluminescence (PL) with a peak in the red spectrum, which is attributed to the quantum confinement effect occurred in small 4 nm nc-Si. In addition, the pSi NWs exhibit low toxicity towards MCF-7 cancer cells, and their PL characteristics allow them to be used as contrast agents for bioimaging

The work is related to the study of a biohybrid material based on mammalian 3T3 NIH mouse fibroblast cells with immobilized porous silicon particles including nanocrystals about 10 nm in size by photoelectron spectroscopy. The influence of the surface material of the substrate on which the biohybrid material is grown on the possibility of conducting studies of the physico-chemical state of the developed surface is studied. Nickel as well as gold and titanium, known for their biocompatibility, were used as surface materials for cell growth and subsequent internalization of silicon particles. The method of optical microscopy in the reflected light mode was used to assess the distribution of cells on surfaces. It is shown that the nickel surface is not suitable for the synthesis and subsequent studies of biohybrid structures. At the same time, on the surface of gold and titanium, cellular material and structures based on it are available for measurements, including by photoelectron spectroscopy, a high-precision method for studying the atoms charge state and the physico-chemical state of the surface as a whole. The X-ray photoelectronic spectra show all the main components expected to be detected after drying and subsequent vacuuming of the studied objects: the surface material of the substrates and arrays of cell cultures grown on the substrates. No signal from silicon atoms was detected on the nickel surface. In the case of a gold surface, the proximity of the binding energies of the gold core levels (substrate) and silicon (internalized particles) leads to the fact that the signal of gold atoms, which is significant in its intensity, does not allow detecting a signal from silicon atoms, which is weaker in intensity. The signal of silicon atoms in biohybrid structures is reliably detected only when using titanium substrates, including for a control sample containing porous silicon nanoparticles without incubation in cells. Thus, it is shown that the surface of the titanium foil can be used for studies by photoelectron spectroscopy of a biohybrid material based on mammalian 3T3 NIH mouse fibroblast cells with immobilized porous silicon particles.The obtained result is important for high-precision diagnostics of the physico-chemical state of biohybrid materials and structures based on them with a low content of silicon atoms when solving problems of studying the compatibility and possibilities of using silicon nanomaterials for medical, including therapeutic and other applications.