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.