Growth of silica layers on Ag2S nanoparticles and their effect on the physicochemical properties, cytotoxicity, and antibacterial activity of these nanoparticles

This work investigates the effect of a thin silica shell deposited on Ag 2 S nanoparticles capped with thioglycolic acid (TGA) on their physicochemical, optical, cytotoxic, and antibacterial properties. FTIR spectroscopy confirmed that TGA molecules were adsorbed on the Ag 2 S surface in their ionic form, with free carboxylic terminal groups, while TEOS molecules were chemisorbed to form Ag 2 S-TGA-SiO 2 core-shell nanostructures. The XRD analysis revealed the monoclinic crystalline structure of Ag 2 S and confirmed the successful formation of the SiO 2 shell. TEM images showed nearly spherical particles with an average diameter of 5.1 nm, while EDX spectra indicated a higher silver content in silica-coated nanoparticles. DLS results exhibited bimodal size distributions of 4.2- 67.5 nm for Ag 2 S-TGA and 13.3- 90.8 nm for Ag 2 S-TGA-SiO 2 nanostructures, indicating the presence of small clusters and some degree of aggregation. Photoluminescence (PL) spectra, recorded under 488 nm excitation from 15 to 65 °C, showed temperature-dependent NIR emissions below 1000 nm, suitable for optical nanothermometry. Ag 2 S-TGA displayed a broad emission around 915 nm, whereas Ag 2 S-TGA-SiO 2 exhibited an additional yellow/green band (∼600 nm) and a redshift of the main NIR band from 894 to 914 nm with temperature. The average PL lifetimes were 2.56 ns and 3.20 ns for Ag 2 S-TGA and Ag 2 S-TGA-Si 2 O, respectively. The MTT assays on U-87 MG cells revealed over 80% viability after 24h, confirming biocompatibility. Antibacterial tests showed that Ag 2 S-TGA exhibited stronger activity ( 𝑀 ⁢ 𝐼 ⁢ 𝐶 = 2 0 𝛭 ⁢ 𝑔 ⁡ / 𝑚 ⁢ 𝑙 against E. coli and Salmonella ) compared with Ag 2 S-TGA-SiO 2 ( 𝑀 ⁢ 𝐼 ⁢ 𝐶 = 1 6 6 6 and 61 μg/ml, respectively). Fluorescence microscopy confirmed nanoparticle internalization and homogeneous intracellular distribution, highlighting their potential for bioimaging and antibacterial applications.