In this work we concentrate on enhancing the antibacterial activity of ZnO nanoparticles by Cr doping, synthesized using a microwave assisted method. The obtained nanoparticles were systematically characterized by X-ray diffraction, Fourier transformation infrared spectroscopy, UV-Vis spectroscopy and field emission scanning microscopy, and the results were correlated. Powder diffraction patterns reveal that Cr is incorporated into the ZnO crystal lattice without disturbing the original wurtzite crystal structure. The vibrational spectra show significant shifts in the peaks with Cr addition, indicating the successful incorporation of Cr ions into ZnO. Optical absorption measurements reveal that the band gap of ZnO decreased from 3.19 to 3.09 eV, which confirmed the existence of a ZnO–Cr catalyst influence interaction. The surface morphology of ZnO changed from hexagonal rod to spherical-hexagonal nanorod structures after Cr doping. Energy dispersive spectral analysis confirms the phase-purity of the synthesized powders. Here, we show that in addition to altering the structure, composition, morphology and optical absorption characteristics of ZnO, the introduction of Cr dopant can also lead to dramatic changes in the antibacterial activity of Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. The investigated Cr doped ZnO nanocomposite material showed excellent antimicrobial activity compared to ZnO. The bacterial activity was found to be higher for Gram positive bacteria possessing thicker cell walls than that for Gram negative bacteria.

The present study reports the fabrication of silver substituted hydroxyapatite/functionalized multiwall carbon nanotube (Ag-HA/f-MWCNT) on 316L stainless steel (SS) implant by spray pyrolysis technique. XRD results show an enhanced crystallinity and crystallite sizes with increasing concentration of silver in HA/f-MWCNT. The vibrational spectral analysis revealed the presence of P-O stretching vibration of phosphate group (PO43-) in all the samples. The morphology of Ag substituted HA/f-MWCNT coatings revealed regular rod-like particles arranged in the form of sheet exhibiting slight variation in the size of the particle with increasing the Ag concentration. All the samples indicate the presence of calcium, phosphor, carbon, silver and oxygen constituents in the coating surface. The minimum inhibitory concentration of the nanocomposite decreased from 0.25 mg to 0.125 mg with the increase of Ag concentration, and AO/EB results confirmed the mode of cell distraction. The 1 and 3 wt% Ag-HA/f-MWCNT nanocomposite revealed less toxic effect to the normal human osteoblast cells. The corrosion efficiencies of the fabricated films in the stimulated body fluid reveal the increase in polarization resistance with a decrease in current density (icorr) from 3.9 to 3.5 μA due to the increase of Ag concentration. The estimated hemolysis rate for 1 and 3 wt% Ag substituted HA/f-MWCNT was less than 10%. Therefore, it can be concluded that 3 wt% Ag substituted HA/f-MWCNT coating on passivated 316L SS is nonhemolytic and most suited as a novel alternative to dental and orthopaedic implants.

In this work, we investigated the antibacterial activity of TiO₂ and Ba doped TiO₂ nanoparticles synthesised by a microwave assisted method. The obtained nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, ultra-violet visible spectroscopy, energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy. XRD patterns revealed preferentially oriented (101) TiO₂ anatase phase, which changed to anatase–rutile mixed phase after Ba²⁺ doping. The vibrational spectra show significant shifts in the peaks with Ba addition, indicating the successful incorporation of Ba²⁺ ions into TiO₂. The optical spectra revealed increase in band gap with Ba doping, thereby allowing the delay in recombination rate, favouring antibacterial activity. The surface morphology of TiO₂ show spherical shaped grains with increased porosity after Ba doping. EDS analysis confirmed the phase-purity of the synthesized powders. The potential toxicity of nanosized TiO₂ and Ba doped TiO₂ were investigated using both Gram positive and Gram negative bacteria as test organisms. The antibacterial activity was found to be higher for Ba doped TiO₂ nanoparticles compared to pure TiO₂ nanoparticles, due to reduced particle size and high specific surface area leading to enhanced particle surface reactivity to light and H₂O adsorption.