Malachite Nanoparticle: A New Basic Hydrophilic Surface for pH-Controlled Adsorption of Bovine Serum Albumin with a High Loading Capacity

Interaction of proteins at different solid interfaces is a major concern in various emerging fields like bionanotechnology and material sciences. In this article, malachite nanoparticles with an average size of 100-150 nm have been synthesized via a new and simple sodium dodecyl sulfate (SDS)-mediated reaction in aqueous solution. In this study, malachite nanoparticles have been used for the first time as a new basic-hydrophilic surface for pH-controlled adsorption of bovine serum albumin (BSA). We report an atypical surface coverage of BSA on malachite nanoparticle at pH beyond the isoelectric point (TEP) of BSA. Unlike other hydrophilic acidic surfaces like silica, an almost invariant surface coverage of BSA has been achieved beyond its TEP up to pH similar to 7.0. Adsorption is reduced beyond pH similar to 7.0, and desorption is complete at pH > 10.0. In-depth conformational analysis of proteins in adsorption-desorption cycles has been done by circular dichroism (CD), fluorescence, and Fourier transform infrared (FT-IR) spectroscopic methods. Steady-state and time-resolved fluorescence study reveals partial unfolding and smaller lifetime of BSA upon adsorption to malachite surface. Secondary structural content of adsorbed BSA reduces as confirmed from CD and FTIR analysis. The BSA molecule gains its secondary conformation partially after desorption from the malachite surface. Efforts were also made to understand the influence Of Surface modification of malachite nanoparticles (NPs) by stearic acid oil protein interaction. Adsorbed stearic acid layers on malachite NPs have shown a reduced BSA adsorption compared to bare malachite nanoparticle surface. Moreover, detailed conformational analysis revealed that BSA undergoes a minor tertiary and secondary structural change upon interaction with stearic acid coated malachite NPs,