Facile Green Synthesis of Silver Bionanocomposite with Size Dependent Antibacterial and Synergistic Effects: A Combined Experimental and Theoretical Studies

The application of nanoparticles is largely rely on the size of the nanoparticle. This investigation reports a one pot size specific green synthesis with a study of comparative antibacterial activity of silver bionanocomposite (AgBNC). The variations of concentration of silver nitrate (AgNO3) with eco-friendly reducing agent (citric acid) and stabilizer (gelatin), leads to the synthesis of different size AgBNCs (~ 37, 46 and 58 nm) with extended stability up to 4 months and the size of the AgBNC increases with increasing the concentration of AgNO3. UV–Vis spectrophotometry, dynamic light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), studies were conducted to explain particle size, shape and stability of AgBNC. Furthermore, as capping of silver nanoparticle (AgNP) is major issue regarding the stability of AgBNC, electronic structure of gelatin-AgNP complex is presented using density functional theory (DFT) for better understanding of interaction energies of AgNPs and gelatin. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were investigated against five different pathogenic bacteria which showed that lowest sized AgBNC is more effective than other samples with an increased 3–30-fold activity when it combined with different antibiotics. Highest antibacterial activity was observed for ciprofloxacin with lowest size AgBNC against S. mutans. These observations have immense importance in the context of providing guidelines for efficient biomedical drug delivery protocol.