Hemant Kumar Daima

Active Control of Silver Nanoparticles Spacing Using Dielectrophoresis for Surface-Enhanced Raman Scattering

We demonstrate an active microfluidic platform that integrates dielectrophoresis for the control of silver nanoparticles spacing, as they flow in a liquid channel. By careful control of the nanoparticles spacing, we can effectively increase the surface-enhanced Raman scattering (SERS) signal intensity based on augmenting the number of SERS-active hot-spots, while avoiding irreversible aggregation of the particles. The system is benchmarked using dipicolinate (2,6-pyridinedicarboxylic acid) (DPA), which is a biomarker of Bacillus anthracis. The validity of the results is discussed using several complementing characterization scenarios.

Fine-Tuning the Antimicrobial Profile of Biocompatible Gold Nanoparticles by Sequential Surface Functionalization Using Polyoxometalates and Lysine

Antimicrobial action of nanomaterials is typically assigned to the nanomaterial composition, size and/or shape, whereas influence of complex corona stabilizing the nanoparticle surface is often neglected. We demonstrate sequential surface functionalization of tyrosine-reduced gold nanoparticles (AuNPsTyr) with polyoxometalates (POMs) and lysine to explore controlled chemical functionality-driven antimicrobial activity. Our investigations reveal that highly biocompatible gold nanoparticles can be tuned to be a strong antibacterial agent by fine-tuning their surface properties in a controllable manner. The observation from the antimicrobial studies on a gram negative bacterium Escherichia coli were further validated by investigating the anticancer properties of these step-wise surface-controlled materials against A549 human lung carcinoma cells, which showed a similar toxicity pattern. These studies highlight that the nanomaterial toxicity and biological applicability are strongly governed by their surface corona.

Tyrosine- and tryptophan-coated gold nanoparticles inhibit amyloid aggregation of insulin.

Here, we have strategically synthesized stable gold (AuNPsTyr, AuNPsTrp) and silver (AgNPsTyr) nanoparticles which are surface functionalized with either tyrosine or tryptophan residues and have examined their potential to inhibit amyloid aggregation of insulin. Inhibition of both spontaneous and seed-induced aggregation of insulin was observed in the presence of AuNPsTyr, AgNPsTyr, and AuNPsTrp nanoparticles. These nanoparticles also triggered the disassembly of insulin amyloid fibrils. Surface functionalization of amino acids appears to be important for the inhibition effect since isolated tryptophan and tyrosine molecules did not prevent insulin aggregation. Bioinformatics analysis predicts involvement of tyrosine in H-bonding interactions mediated by its C=O, –NH2, and aromatic moiety. These results offer significant opportunities for developing nanoparticle-based therapeutics against diseases related to protein aggregation.

Influence of Physicochemical Properties of Nanomaterials on Their Antibacterial Applications

The ongoing concern of antibiotic resistance in pathogenic bacteria has raised the need for development of new antibacterial agents to control infectious diseases. The recent developments in nanotechnology have led to a range of nanomaterials that provide new opportunities to target pathogenic bacteria. Time will reveal whether bacteria develop resistance against nano-based antimicrobial agents; however, at least at this stage, it appears unlikely because most nano-based antimicrobial agents cause physical disintegration of bacteria, which is typically not the case with antibiotics. To effectively use nanomaterials for antibacterial applications, it is critical to control their physicochemical properties, because these properties dictate their mode of action. This chapter provides a snapshot of how various physicochemical properties of engineered nanomaterials such as shape, size, composition, hydrophilicity/hydrophobicity, and surface corona influence their antibacterial action.

Tyrosine Mediated Gold, Silver and Their Alloy Nanoparticles Synthesis: Antibacterial Activity Toward Gram Positive and Gram Negative Bacterial Strains

Shape and size-controlled synthesis of metal and metal alloy nanoparticles have gained significant attention due to their unique physico-chemical properties. Most of these synthesis routes have thus far explored use of toxic chemicals for metal nanoparticles synthesis, which limit their biological applications. With the increasing focus on eco-friendly routes towards nanomaterials synthesis and their biological applications, we show that metal (gold and silver) and their alloy nanoparticles with controlled composition can be synthesized using tyrosine amino acid. Antimicrobial activities of these nanoparticles were tested against model Gram positive bacteria Staphylococcus albus and Gram negative bacteria Escherichia coli. Irrespective of metal composition, tyrosine synthesized nanoparticles including AuNPs were found to be highly toxic towards S. albus, while antibacterial activity against E. coli was exhibited only by AgNPs and Ag containing alloys. The toxicity of tyrosine synthesized nanoparticles towards S. albus arises due to its ability to hydrolyze the peptidoglycan cell wall. In the case of E. coli, these nanoparticles showed toxicity due to the partial oxidation of Ag0 into Ag+ ions. The alloy nanoparticles toxicity depends on the silver fraction towards E. coli while all nanoparticles irrespective of composition have a similar effect on S. albus. UV-vis, TEM, AAS and zeta potential measurements were used to characterize these nanoparticles and their influence on the observed antimicrobial properties. SEM was used to study morphological changes and bactericidal action of these nanoparticles. The SEM results confirmed that treated E. coli and S. albus cells were damaged, showing formation of big holes and cell wall lysis.