Fluorescence emission and interaction nature of protein coated gold and copper nanoclusters at different ionic environments as ion sensor
Ashim Chandra Bhowal, Subhankar Pandit, Sarathi Kundu
Journal of Physics D: Applied Physics
Lysozyme protein induced luminescent gold and copper nanoclusters (AuNCs and CuNCs) are prepared and their sensing ability is studied in the presence of different valent ions, i.e., for Na+, Ca2+, Hg2+, Pb2+, Fe3+ and La3+ ions in aqueous solutions up to 100 µM of salt concentration. Both the nanoclusters show good stability in aqueous conditions and among all the chosen valent ions it is found that for AuNCs and CuNCs, maximum fluorescence quenching is observed in the presence of Hg2+ and Pb2+ ions respectively. From the steady state fluorescence study and by using Stern-volmer plots, the Stern-Volmer constant (Ksv) and the other important thermodynamical parameters, i.e., change in enthalphy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) are calculated. We proposed a two step interaction process between nanoclusters and dissolved ions, first the interaction occurs between the nanocluster surface covered proteins and ions followd by the interaction of metallic nanocluster core with the ions. Although, thermodynamic study implies that both types of the interactions are electrostatic in nature, however, selective fluorescence quenching of AuNCs and CuNCs in the presence of Hg2+ and Pb2+ ions occurs due the non covalent metallophilic interaction between the cluster core and the dissolved ions.
Fluorescence, Photoluminescence, Optical properties, Quenching, Chemical stability, Thermal stability, Thermodynamics, Nanostructures, Materials