Light Mediated Generation of Silver Nanoparticles by Spinach Thylakoids/Chloroplasts

The unique potential of chloroplasts/thylakoids to harness light energy to transport electrons from H(2)O to various entities was exploited for reduction of Ag(+) to generate nanoparticles (NPs). Spinach thylakoids/chloroplasts turned AgNO(3) solutions brown in light, but not in dark. Besides showing Ag-NPs specific surface plasmon resonance band, these brown solutions showed presence of 5–30 nm crystalline NPs composed of Ag. Powder X-ray diffraction (PXRD) analysis revealed that Ag-NPs were biphasic composed of face-centered cubic Ag(0) and cubic Ag(2)O. X-ray photoelectron spectroscopy (XPS) data further corroborated the presence of Ag(2)O in Ag-NPs. Limited formation of Ag-NPs in dark and increased generation of Ag(0)/Ag(2)O–NPs with increase in light intensity (photon flux density) by thylakoids/chloroplasts, established the role of light-harvesting photosynthetic machinery in generation of Ag(0)/Ag(2)O-NPs. Potential of thylakoids/chloroplasts to generate Ag-NPs from Ag(+) on exposure to red and blue wavelength regions of visible light of electromagnetic spectrum, further confirmed the involvement of photosynthetic electron transport in reduction of Ag(+) and generation of Ag-NPs. While light energy mediated photosynthetic electron transport donates energized electrons extracted from H(2)O to Ag(+) to form Ag(0)-NPs, O(2) released as a by-product during photolysis of H(2)O oxidizes Ag(0) to form Ag(2)O-NPs. Our findings furnish a novel, simple, economic and green method that can be exploited for commercial production of Ag(0)/Ag(2)O-NPs.