Interaction and Binding of Protein with Cu₂ZnSnS₄ and Cu₂ZnSnSe₄ Chalcogenide NIR Semiconducting Nanoparticles

In this research, we focused the detailed study of the interaction and bio-conjugate formation of grown NIR responsive nanostructured Cu₂ZnSnS₄ (CZTS) and Cu₂ZnSnSe₄ (CZTSe) with model bovine serum albumin (BSA) protein. The dynamics of binding showed that corona formation time for CZTS NPs-BSA (~ 806 min) was larger than CZTSe NPs-BSA (~ 15 min). Time for reorganization of BSA due to binding with CZTS NPs (~ 24 min) was much less than that of CZTSe NPs (~ 311 min). BSA binding was more significant than unfolding at the interface of CZTS whereas for CZTSe NPs-BSA unfolding was more significant than binding. The protein secondary structural denaturation through quenching and denaturation has been observed. In case of CZTSe NPs-BSA, the strong positive cooperative reaction (n ~ 1.95) was more prominent than CZTS NPs-BSA (n ~ 1.44). Both Trp and Tyr residues responded at the surface of CZTS whereas only Trp responded at the surface of CZTSe during quenching of protein. CZTS NPs-BSA showed formation of both soft and hard corona, whereas very small sizes CZTSe NPs (~ 5 nm) were selectively formed hard corona on their surface. The average ultrafast life time (τ) of CZTS NPs-BSA varied from 3.76 ns to 3 ns, whereas CZTSe NPs-BSA showed life time (τ) variation from 3.75 ns to 3.53 ns.