For the first time, hydrogels based on silica- and titanium-poly(ethylene glycol) have been used for immobilization of Gram-negative bacteria (Escherichia coli MG1655) and Gram-positive bacteria (Rhodococcus qingshengii X5) in a one-step sol–gel synthesis. Vibrational spectroscopy and thermogravimetric analysis have confirmed the formation of amorphous hybrid structures with a predominance of organic components and metal-oxide grids. Encapsulation efficiencies were 72–77% for Si-PEG-based hydrogel and 50–54% for Ti-PEG. Antimicrobial activity tests revealed that Si-PEG was non-toxic, while Ti-PEG reduced cell viability by 50%. For the first time, an analysis of the morphological properties of immobilized bacterial cells revealed the formation of a thin Si-PEG-based hydrogel shell around each cell and a thick polymer layer on the bacterial surface when encapsulated within Ti-PEG-based hydrogels. The catalytic activity of the biocatalysts, as measured by the ATP content, remained at 84–93% for Si-PEG-based hydrogel, and decreased to 5% for Ti-PEG-based hydrogel. Biocatalysts based on encapsulated bacteria in a Si-PEG-based hydrogel demonstrate high sensitivity and stability. Si-PEG-based hydrogel exhibits high biocompatibility, making it suitable for the effective encapsulation of various bacterial types with a “cell-in-shell” structure.

A one-step sol-gel synthesis of organosilica matrices based on silicon tetrapolyethylene glycolate (STP_EG) and silicon glycerolates (SiGl) at about pH 7.0 was performed to immobilize cells of the green algae Chlamydomonas reinhardtii. Infrared (IR) and Raman spectroscopy confirmed the formation of Si–O–Si and Si–O–C bonds, and the type of polymer in these matrices was determined. For the first time, scanning electron microscopy showed the formation of biohybrid “cell-in-shell” structures for the wild-type strain C. reinhardtii 137c. At the same time, when using mutant C. reinhardtii CC-503 deprived of their cell wall, effective cells immobilization has not been observed, indicating the key role of the cell wall in the immobilization process. Comparative analysis of matrices based on traditional precursors—tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES), revealed their toxicity to algal cells, although systems containing polyols ensured the preservation of cell morphology, but required optimization to increase cell viability. PAM fluorometry revealed a significant decrease in the photosynthetic activity of the algae cells of both strains studied (F_v/F_m < 0.07), which is associated with the degradation of photosystem II. However, immobilization in agarose gel confirms the fundamental possibility of forming biohybrid systems with high viability of C. reinhardtii cells.