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Fluorescent nanoparticles (NPs) have been increasingly studied as contrast agents for better understanding of biological processes at the cellular and molecular level. However, their use as bioimaging tools is strongly dependent on their optical emission as well as their biocompatibility. This work reports the fabrication and characterization of silk fibroin (SF) coated magnesium oxide (MgO) nanospheres, containing oxygen, Cr3+ and V2+ related optical defects, as a nontoxic and biodegradable hybrid platform for bioimaging applications. The MgO-SF spheres demonstrated enhanced emission efficiency compared to noncoated MgO NPs. Furthermore, SF sphere coating was found to overcome agglomeration limitations of the MgO NPs. The hybrid nanospheres were investigated as an in vitro bioimaging tool by recording their cellular uptake, trajectories, and mobility in human skin keratinocytes cells (HaCaT), human glioma cells (U87MG) and breast cancer cells (MCF7). Enhanced cellular uptake and improved intracellular mobilities of MgO-SF spheres compared to MgO NPs was demonstrated in three different cell lines. Validated infrared and bright emission of MgO-SF NP indicate their prospects for in vivo imaging. The results identify the potential of the hybrid MgO-SF nanospheres for bioimaging. This study may also open new avenues to optimize drug delivery through biodegradable silk and provide noninvasive functional imaging feedback on the therapeutic processes through fluorescent MgO.

Green approaches for the synthesis of nanoparticles provide advantages due to the fact that green protocols are benign and environmentally friendly. Among various green recipes, biogenic synthesis of nanoparticles have recently emerged as an active area of research due to simplicity of this method, with cost effective protocols, higher potential of reduction and low toxic effect on human health and the environment. Moreover, the biogenic reduction occurs at physiological conditions of temperature and pressure. The raw materials are easily available and therefore, the reaction can easily be scaled up. This paper presents a review to give an idea about the most reliable, cost-effective and environment friendly synthetic protocols for metal nanoparticles to control size, shape and dispersity.In this contribution, we have emphasized especially on various plants responsible for, and investigated so far, for the synthesis of palladium nanoparticles. Based on the isolated compounds/metabolites such as polyols, polyphenols, flavonoids and proteins from the respective plant extracts, a correlation is established where such metabolites are linked with the biogenic syntheses of Pd nanoparticles. Present investigation and works reviewed lead us to recommend few potential plants for the reduction of Pd 2+ ions into Pd 0 nanoparticles. This review not only summarizes the present literature but also highlights the potential of this field to open up new avenues for researchers.

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