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Bioimaging has drastically transformed the field of medicine, and made the process of diagnosis easy and fast. Visualization of complete organ to complex biological processes has now become possible. Among the various imaging processes, fluorescence imaging using nontoxic fluorescent nanomaterials is advantageous for several beneficial features including high sensitivity, minimal invasiveness, and safe detection limit. In this study, we have synthesized and characterized a new class of nontoxic, self-activated fluorescent hydroxyapatite nanoparticles (fHAps) with different aspect ratios (thin-rods, short-rods, rods) by changing the stabilizing agents (triethyl amine and acetyl acetone) and solvents (water and dimethyl sulfoxide). fHAps showed excellent fluorescence with a broad emission spectrum ranging from 350 to 750 nm and maximum at 502 nm. The presence of fluorescence was attributed to the electronic transition in the asymmetric structure of fHAps as confirmed by ESR spectroscopy and the absence of fluorescence in symmetric HAp NPs. In addition to exceptional fluorescence behavior, these NPs were found to be nontoxic in nature and could be easily internalized in both prokaryotic and eukaryotic systems. We propose that the fHAps provide a safe and a potential alternative to the current fluorescent materials in use for biolabeling and bioimaging applications.

Silver doped hydroxyapatite (Ag x Ca 100-x (PO 4 ) 6 (OH) 2 ) nanorods were synthesized using a modified sol gel method at a low temperature of 100°C. Silver concentration was varied as x = 1, 3 and 5. X-ray diffraction studies showed that the synthesized silver doped hydroxyapatite (Ag-HAp) was fully crystalline with hexagonal structure and an average crystallite size of 25 nm. At all the doping concentrations, the nanoparticles were rod shaped with an average length of 110-180 nm and diameter of 20-25 nm as determined from transmission electron microscopy (TEM) studies. These compounds were tested for their antimicrobial activities against E. coli (MTCC 2345) and S. aureus (MTCC 737). Antimicrobial activity was observed for all the three silver doping concentrations with the highest activity for x = 3, in terms of the zone of inhibition and the percentage reduction in the number of colonies. Hemolysis ratios for x = 1 and 3 Ag-HAp samples were below 2 %, indicating that they are highly hemocompatible and can be a promising biomaterial for tissue engineering applications in orthopedics.