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Present study deals with synthesis and assessment of antimicrobial and antioxidant activity of silver nanoparticles using aqueous extract of mulberry leaves. The optical study showed the appearance of SPR peak in the range of 423-450 nm affirming nanosilver formation. FTIR analysis indicates the possible involvement of proteins, carbohydrate and secondary metabolites as reducing and capping agents. SEM, TEM and HR-TEM analysis reveals that the synthesized nanoparticles were spherical in shape with particle size ranges between 12 and 39 nm. EDX spectra showed maximum intensity at 3 keV, affirming silver crystal. XRD analysis showed silver nanoparticles were preferentially oriented along (111) revealing crystalline structure. DLS analysis confirms the stability of silver nanoparticles with zeta potential of + 37.4 mV. Silver nanoparticles showed effective antimicrobial activity against both gram positive and gram negative bacteria with highest activity against Salmonella typhimurium with MIC 40 µg/ml. Further silver nanoparticles also showed dose dependent antioxidant activity against free radicals like DPPH, ABTS + , superoxide and nitric oxide; besides this nanosilver also performed significant metal chelating activity.

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Morus alba is one of the most important cultivated crop in indian sub-continent contributing towards production of silk fibre that carries economic importance worldwide. Post harvest preservation of M. alba leaves is a challenging factor as decrease in concentration of essential metabolites that needed for silk gland development takes place. Decrease in chlorophyll, protein, sugar concentration and increase in accumulation of free radicals and RoS takes place at post harvest stage of preservation, putting negative impact on larval development indicated by high mortality rate. Silver nitrate and nanosilver solution acts as an effective preservative, enhances the activity of enzymatic and nonenzymatic antioxidants thereby reducing the harmful effect of accumulated free radicals and ROS. The effectiveness of nanosilver solution was found to be on the upper site without any significant difference than silver nitrate, as higher retention of primary metabolites like pigments, proteins, and sugar takes place. the impact of feeding nanosilver preserved leaves on silkworm was found on the positive trend as larval growth rate, cocoon weight, shell weight, effective rate of rearing was observed almost same to the larvae fed with fresh leaves.

In recent decades, studies have focused on inorganic nanozymes to overcome the intrinsic drawbacks of bioenzymes due to the demands of improving the reaction conditions and lack of robustness to harsh environmental factors. Many biochemical reactions catalyzed by enzymes require light activation. Light-activated nanozymes have distinct advantages, including being regulated by light stimuli, activating the molecular oxygen to produce reactive oxygen species (ROS) without interfering supplementary oxidants, and often showing a synergistic effect to catalyze some challenging reactions. Only a few studies have been done on this connection. Therefore, it is still a big challenge to develop a nanozyme regulated by light activation. Herein, we uncovered the light-activated oxidase mimicking activity of a conducting polymer polyaniline nanofibers (PANI-NFs). PANI-NFs exhibit intrinsic lightactivated brilliant oxidase-like activity, can catalyze the colorless tetramethyl benzidine (TMB) to produce a blue product TMBox, and have a distinct K m = 0.087 mM and a high V max = 2.32 μM min −1 value, measured by using Hanes−Woolf kinetics. We also report the light-activated oxidase activity of some other renowned carbocatalysts graphene oxide and graphitic carbon nitride and compare them with PANI-NFs. This type of property shown by the conductive polymer is amazing. The density functional theory is used to verify the stability and the mode of adsorption of the PANI NFs-TMB composite, which corroborates the experimental results. Furthermore, the current nanozyme demonstrated a significant ability to kill both Gram-negative and Gram-positive bacteria as well as effectively destroy biofilms under physiological conditions. We believe that this work provides the motivation to create a link between optoelectronics and biological activity in the near future.

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