Photoluminescence dynamics of copper nanoclusters synthesized by cellulase: role of the random-coil structure

This study demonstrates the one-pot cellulase-directed synthesis of magic numbered copper nanoclusters (Cu NCs) with blue-, cyan-, and green-luminescence from Cu12, Cu20, and Cu34, respectively. The developed Cu NCs have an excellent luminescence quantum yield, photostability and better colloidal stability. The temperature-dependent response of the blue luminescent nanocluster gets flipped over by changing the aqueous medium to a methanolic one. Moreover, the preferential stabilization of large-sized Cu34 (green-luminescent) NCs–cellulase over a relatively small one, Cu20 NCs–cellulase is found to be dependent on both temperature as well as solvent. The luminescence of Cu20 NCs–cellulase can be greatly augmented by the addition of Zn(II) and Cd(II) ions, whereas the Fe(III) ions quench the luminescence. The random coil structure of the enzyme dictates the size and luminescent properties of the Cu NCs. This unique and beneficial aspect of the Cu NCs warrants them to find possible applications as a sensitive marker for cell imaging, and nanophotonic materials.