Enhanced antibacterial activity of self-fluorescent Zn-coordinated tryptophan nanoparticles: a mechanistic approach to study bacterial disintegration

Proteins and Peptides originated nanoparticles have been used in various biomedical applications such as cell imaging, drug delivery and antibacterial activity. Due to the complexity of long chain amino acids present in peptides and proteins, there is a dire need for simple molecules-based strategies to synthesize functional nanoparticles. A single amino acid, tryptophan, has been used for synthesis of functional nanostructure which are tune able and efficient antimicrobial agents against variety of pathogens. The Zn (II) ion coordinated tryptophane nanoparticles (Trp-ZNPs) have been synthesized through chemical methods and were characterized with spectroscopic and microscopic techniques. The Trp-ZNPs nanoparticles have been investigated for enhanced antimicrobial properties due to the intrinsic characteristics of tryptophan molecule and its coordination with Zn (II) and make them biocompatible, biodegradable and fluorescence efficient materials. Fluorescence spectroscopy confirmed the fluorescent behavior of Trp-ZNPs in green and red regions with excitation wavelengths 488 nm and 543 respectively. The Scanning Electron Microscopy, Transmission Electron Microscopy and Zeta sizer confirmed the size of Trp-ZNPs which is approximately 73 nm. The monodispersed Trp-ZNPs were studied against two types of bacterial strains Escherichia coli and Pseudomonas aeruginosa for antimicrobial evaluation. Furthermore, two types of antibiotic drugs were encapsulated with Trp-ZNPs to impart them the efficient drug carriers, properly target the antibiotics. Moreover, Trp-ZNPs improved the antimicrobial potential of ciprofloxacin and cefixime antibiotics and increased their bioavailability. Cell toxicity of Trp-ZNPs was studied to ensure them as promising agents for clinical trials. MTT assay was employed in two types of experimental cell lines, HEK293T and Huh 7.0. Trp-ZNPs exhibited lower toxicity in Huh 7.0 cells compared to HEK293T cells. Mechanistic insights of bacterial disintegration were investigated using Scanning electron and transmission electron microscopy.