Assessment on the antibacterial activity of nanosized silica derived from hypercoordinated silicon(IV) precursors

Silica nanoparticles were synthesized through a versatile sol-gel combustion method from hydrazide based hypercoordinated silicon complexes derived from the reaction of silicon tetrachloride with O-silylated hydrazide derivatives. The complexes were characterized by H-1, C-13, Si-29 NMR and ESI-mass spectrometric techniques. A refined morphology was observed in the product after sintering i.e. from spherical to rod shaped nanoparticles. The powder X-ray diffraction patterns and the TEM images of silica show the formation of silica nanoparticles. The IR spectra show Si-O linkages and DLS studies indicate the particle size distribution to be between 20 and 100 nm for the material before sintering and 70-120 nm after sintering at 1000 degrees C. A TEM image of the decomposed gel indicates the formation of crystalline silica rods. This work also demonstrates the influence of nano-sized silica particles on antibacterial activity (DIZ, MIC and MBC) i.e. better activity was shown for nano-rods derived from the hypercoordinated silicon complexes than the conventional TEOS (sol-gel) method. Experiments on the generation of reactive oxygen species (ROS) through oxidative stress demonstrate the toxicity of nanosilica particles.