3.2 Characterization of BSA-CuNCsTo

3.2 Characterization of BSA-CuNCsTo characterize BSA-CuNCs, Transmission Electron Microscopic (TEM) andAttenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopictechniques were employed. To eliminate the unreacted particles, BSA-CuNCs was filtered ina dialysis membrane (12000 Da, 6 hours) prior to TEM analysis. The TEM image(Fig. 1 c&d) shows spherical morphology of BSA-CuNCs with average size of 3.3±0.8 nm.When higher resolution was attempted, the protein matrix charred and resolution beyond2 nm was not possible. The irradiation of stray electron beam caused the nanocluster to fuseinto crystalline form [29] and was confirmed by the Selected Area Electron Diffraction(SAED) pattern (Fig. 1c inset). The ATR-FTIR spectra of BSA and BSA-CuNCs were taken(Fig. S4). In BSA, the peak near 1540 cm-1 and 1240 cm-1 attributes to –NH bending or –CNstretching vibrations and peak near 1635 cm-1 corresponding to amine scissoring. In addition,the peak at 1385 cm-1 corresponds to the –OH bending vibrations in carboxylic acids.Presence of these functionalities favors the formation of BSA-CuNCs. The similar peak is observed in BSA-CuNCs illustrating CuNCs entrapped within BSA. Other characteristicpeaks observed in BSA-CuNCs were for –NH bending at 1598 cm-1 and –CN stretchingfrequency at 1300 cm-1. Absence of –NH scissoring can be correlated to the involvement of–NH moiety with copper during the linkage and subsequent formation of CuNCs.