Nanoscale colloidal particles display fascinating electronic, optical and reinforcement properties as a consequence of their dimensions. Stable dispersions of nanoscale colloids find applications in drug delivery, biodiagnostics, photonic and electronic devices, and polymer nanocomposites. Most nanoparticles are unstable in dispersions and polymeric surfactants are added generally to improve dispersability and control self-assembly. However, the effect of polymeric modifiers on nanocolloid properties is poorly understood and design of modifiers is guided usually by empirical approaches. Monte Carlo simulations are used to gain a fundamental molecular-level understanding of the effect of modifiers properties on the thermodynamics and interaction forces of nanoscale colloidal particles. A novel method based on the expanded ensemble Monte Carlo technique has been developed for calculation of the chemical potential of colloidal particles in colloid-polymer mixtures (CPM). Using this method, the effect of molecular parameters like colloid diameter, polymer chain length, colloid-polymer interaction strength, and colloid and polymer concentrations, on the colloid chemical potential is investigated for both hard-sphere and attractive Lennard-Jones CPM. The presence of short-chain polymeric modifiers reduces the colloid chemical potential in attractive as well as athermal systems. In attractive CPM, there is a strong correlation between polymer adsorption and colloid chemical potential, as both show a similar dependence on the polymer molecular weight. Based on the simulation results, simple scaling relationships are proposed that capture the functional dependence of the thermodynamic properties on the molecular parameters. The polymer-induced interaction forces between the nanoparticles have been calculated as a function of the above parameters for freely-adsorbing and end-grafted homopolymer modifiers. The polymer-induced force profiles are used to identify design criteria for effective modifiers. Adsorbing modifiers give rise to attractive interactions between the nanoparticles over the whole parameter range explored in this study. Grafted surface modifiers lead to attraction or repulsion based on the polymer chain length and grafting density. The polymer-induced attraction in both adsorbing and grafted modifiers is attributed primarily to polymer intersegmental interactions and bridging. The location of the thermodynamic minimum corresponding to the equilibrium particle spacing in nanoparticle-polymer mixtures can be controlled by tuning the modifier properties.

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Due to their therapeutic applications such as radical scavenging, MRI contrast imaging, Photoluminescence imaging, drug delivery, etc., nanoparticles (NPs) have a significant importance in bio-nanotechnology. The reason that prevents the utilizing NPs for drug delivery in medical field is mostly due to their biocompatibility issues (incompatibility can lead to toxicity and cell death). Changes in the surface conditions of NPs often lead to NP cytotoxicity. Investigating the role of NP surface properties (surface charges and surface chemistry) on their interactions with biomolecules (Cells, protein and DNA) could enhance the current understanding of NP cytotoxicity. Hence, it is highly beneficial to the nanotechnology community to bring more attention towards the enhancement of surface properties of NPs to make them more biocompatible and less toxic to biological systems. Surface functionalization of NPs using specific ligand biomolecules have shown to enhance the protein adsorption and cellular uptake through more favorable interaction pathways. Cerium oxide NPs (CNPs also known as nanoceria) are potential antioxidants in cell culture models and understanding the nature of interaction between cerium oxide NPs and biological proteins and cells are important due to their therapeutic application (especially in site specific drug delivery systems). The surface charges and surface chemistry of CNPs play a major role in protein adsorption and cellular uptake. Hence, by tuning the surface charges and by selecting proper functional molecules on the surface, CNPs exhibiting strong adhesion to biological materials can be prepared. By probing the nanoscale interaction forces acting between CNPs and protein molecules using Atomic Force Microscopy (AFM) based force-distance (F-D) spectroscopy, the mechanism of CNP-protein adsorption and CNP cellular uptake can be understood more quantitatively. The work presented in this dissertation is based on the application of AFM in studying the interaction forces as well as the mechanical properties of nanobiomaterials. The research protocol employed in the earlier part of the dissertation is specifically aimed to understand the operation of F-D spectroscopy technique. The elastic properties of thin films of silicon dioxide NPs were investigated using F-D spectroscopy in the high force regime of few 100 nN to 1 µN. Here, sol-gel derived porous nanosilica thin films of varying surface morphology, particle size and porosity were prepared through acid and base catalyzed process. AFM nanoindentation experiments were conducted on these films using the F-D spectroscopy mode and the nanoscale elastic properties of these films were evaluated. The major contribution of this dissertation is a study exploring the interaction forces acting between CNPs and transferrin proteins in picoNewton scale regime using the force-distance spectroscopy technique. This study projects the importance of obtaining appropriate surface charges and surface chemistry so that the NP can exhibit enhanced protein adsorption and NP cellular uptake.