Nanostructured boron-aluminum-silicon (BAlSi) thin films: Synthesis via sol-gel and evaluation of antimicrobial efficacy

In this study, boron oxide–aluminum oxide–silicon (BAlSi) nanoparticles (NPs) and thin films were synthesized via the sol–gel method and spin coating technique. The thin films (S1 and S2) were fabricated using two ap- proaches: coating with the sol form of boron oxide–aluminum oxide–silicon precursors (BAlSi-1 NPs) and applying a 1% (w/v) solution of BAlSi nano powder dispersed in 70% (v/v) ethanol (BAlSi-2 NPs). The physi- cochemical properties of the synthesized BAlSi NPs and thin films were characterized using various character- ization techniques. The antimicrobial activity of the NPs and thin films was assessed against Staphylococcus aureus ATCC6538P, Escherichia coli DSM1103, Pseudomonas sp. and Exiguobacterium sp. using 96-well microplate broth dilution method, direct contact test and modified Kirby–Bauer test. X-ray diffraction (XRD) analysis confirmed that the synthesized BAlSi NPs exhibited crystalline structures, corresponding to the (111), (012), (110), and (− 223) crystallographic planes, with respective crystallite sizes of 13.4 nm, 40.4 nm, and 39.0 nm. In contrast, both S1 and S2 thin films were found to be amorphous. Scanning electron microscopy (SEM) imaging revealed that the BAlSi NPs possessed a spherical morphology, while the thin films exhibited a uniform nanoscale structure. Water contact angle (WCA) measurements indicated that the S1 and S2 films exhibited hydrophilic properties, with values of 25.46◦ and 11.32◦, respectively. Antimicrobial efficacy testing demonstrated that the BAlSi-1 sol samples exhibited MIC and MBC values in the range of 0.78–3.13% (v/v), while BAlSi-2 nano powder suspensions showed MIC/MBC values between 12.5 and 50 mg/mL against the tested strains. The inhibition zones for the thin films ranged between 1.50 mm and 2.50 mm, while both films exhibited over 90% microbial inhibition in direct contact tests following a two-hour exposure period.