Exploring the interfacial molecular level behavior of biomacromolecules and nanomaterials using non-linear vibrational spectroscopy

Abstract

Biomolecular adsorption is an important process which arises over the surface of several different biomedical devices and sensing surfaces. Nanotechnology involves a rich study of materials with modified physico-chemical, electrical, and optical properties. Amalgamating biomolecules with nanomaterials is ubiquitously involved in sensor chip designs or biomedical devices or in-vivo theragnostic. Hence, it is crucial to know the interfacial behavior and molecular conformation of biomolecules and nanoparticles distinctively in order to correlate the fundamental attributes of their complexation. We have worked with protein and DNA, both of which provide adaptability, structural flexibility, amphiphilicity, and site-specificity. DNA and protein molecules proffer a suitable opportunity to understand the bottom-up oriented approach of biomolecular interfaces and nano-bio interactions. The present thesis work encompasses the importance of interfaces in decoding the molecular-scale phenomena involving phase-separation, surface tensiometry perturbations, surface adsorption propensity, molecular kinetics, understanding binding interactions at interface, surface density, molecular orientation, and the role of the surrounding environment in modulating the molecular structure. Several research works done in analyzing the biomolecular fundamentals and nano-bio interactions have been performed using surface-specific spectroscopic techniques like surface plasmon resonance, mass spectrometry, X-ray diffraction, or surface-enhanced Raman spectroscopy. However, they involved vacuum-aided functioning, need of crystallite sample, sample labeling or modification, and sophisticated high-energy synchrotron sources which could change the morphology and molecular associations under analysis. Our main aim is to study these processes with minimal modification procedures and under pristine conditions without utilizing strong perturbates. These parameters are crucial in utilizing biomolecules or employing nano-bio complexes to develop fine-tuned functional surfaces/interfaces, which could be potentially characterized by an interface-sensitive label-free detection approach of sum frequency generation vibrational spectroscopy (SFG-VS). It is capable of providing information of only highly aligned molecular systems which are both IR- and Raman-active. Information regarding structural composition, molecular interaction, kinetics, orientation, and impact on neighboring environment can be explored simultaneously in one experimental configuration itself at the interface. Hence, this work could provide a fresh look to the existing knowledge related to biomolecular mechanism and nano-bio interactions, which has yet not been explored fully in the SFG community itself. We have also extended our studies on tensiometry, dynamic light scattering, zeta-potential, and ATR-FTIR spectroscopy to gather information related to the bulk-features. We have characterized the biomolecular adsorption and kinetics, molecularly-imprinted surfaces for BHb recognition, complex interaction between two protein molecules with quantum dots, and hydrophobically-modified organic nanoparticle behavior at interface and with dsDNA. From the research work performed, we conclude that the interfacial directionality of molecular groups is determined by the interplay of different intermolecular forces such as electrostatic, van der Waals, and hydrogen bonding. These events decide the fine-tuning of the interfacial properties and its dynamics. Our work could offer significant contribution towards the rapidly growing domains of bio-mimicking systems, soft functional materials, micro-fluidic device fabrications and biomolecular sensing applications. Thus, it provides an exploratory research domain in the area of interfacial science, which could be evaluated in a variety of experimental sets further.