Investigating the Biomolecular Dynamics of Human Serum Components upon Their Interaction with Different Nanoparticles

The use of nanoscale materials in the field of nanomedicine continues to garner considerable attention from the scientific community. To date, nanoparticles have been incorporated in applications such as sensing, imaging, delivery, and therapy etc. However, a key challenge impeding the translation of such nanotechnologies is the complex interplay between nanoparticles (NPs) and biomolecules. For instance, NPs of different sizes, shapes, compositions, and surface characteristics interact differently with biomolecules as soon as they are exposed to biological fluids, altering their properties and function. This interaction typically results in the formation of a biological corona, which changes what the biological system ‘sees’ when it encounters the nanoparticle. This altered corona-formed NP surface can result in a different ‘see and process’ than what the NP was originally intended for. This interaction can influence both the in vivo and the in vitro applications of nanoparticles. Despite the potential applicability of NPs in nanomedicine, the key challenge is to understand the interaction between NPs and biomolecules and to understand the mechanisms of biomolecular corona formation. Of the different biofluids used in nanomedicine, blood, serum and plasma are the most common. Human serum albumin (HSA), one of the most abundant proteins found in these biofluids, makes it an excellent surrogate for understanding the interaction between biomolecules and NPs. A thorough review of the literature highlights the vital factors that influence the protein corona formation, which includes the properties of both the NP as well as the protein. However, a detailed analysis of the literature reveals conflicting perspectives on NP-protein interactions. This suggests that multiple NP/protein systems need to be investigated in a concerted manner to obtain a comprehensive understanding of the NP-protein interactions and identify the molecular basis of such interactions. The current work is an attempt to understand the intricate molecular mechanism of how NPs with different compositions would interact with HSA and L-cysteine as a model protein and an amino acid, respectively. The first aspect (Chapter 2) is focused on understanding how metal NPs of different compositions (Au, Ag, Pt and Pd), but with the same surface chemistry, interact with HSA. The outcomes showed that PtNPs exhibit the strongest binding to HSA, while AgNPs and AuNPs show weaker binding affinities. The outcomes also reveal that in addition to the NP composition, the interaction temperature is critical in modulating the interaction. Furthermore, thermodynamic parameters showed that PdNPs and AgNPs have the highest tunability with temperature. The second aspect (Chapter 3) is focused on understanding the important role of pH in the interaction between HSA and AuNPs. The findings revealed unique binding mechanisms at different pH, where static binding occurred at pH 2, 7, and 9, dynamic interactions at pH 3.5, and a combination of static and dynamic at pH 11, depending on the temperature. The difference in the binding was correlated to the pH-induced changes in HSA’s secondary structure. Chapters 2 and 3 provide evidence that pH, NP composition and temperature are critical to control HSA-NP interactions, offering possibilities to minimise the formation of protein corona. The third aspect (Chapter 4) focuses on creating nanoparticles of specific compositions to facilitate interactions with biomolecules. The work revealed that cobalt sulfide nanosheets (NS) specifically interact with L-cysteine, a clinically important amino acid found in serum. In-depth interaction studies showed that the sulfur atoms in cobalt sulfide interact with the sulfur atom in L-cysteine due to high affinity. This resulted in surface passivation of the NS and a loss of its inherent catalytic activity. This allowed development of a highly sensitive sensor for detecting L-cysteine. Overall, the work presented in this thesis provides a comprehensive understanding of the biomolecular interaction dynamics of human serum components with NPs, with the hope that the learnings from these studies will contribute to the translation of NPs to mainstream therapeutics and diagnostics applications.