Multifunctional Nanopipette for Single Nanoparticles and Proteins Analysis

Complex biological processes occur in the nanoscale (1-100 nm) regime. ‘DNA’ which is just 2 nm in dimension is a fundamental building block of all life. ‘Hemoglobin’, a blood protein that transports oxygen throughout our body is only 5 nm in diameter. Importantly, the structure, composition, and dynamics of these nanoscale entities determine their biological function. A slight alteration in the structure and composition can lead to the malfunction of the protein which is key to various diseases including cancer. Therefore, the single-molecule measurement approach is essential to characterize both the average properties and the rare and dynamic changes of these nanoscale entities. This dissertation focused on the development of a novel single-entity method by fabricating nanopore and nanoelectrode integrated nanopipette for multi-mode electroanalytical detection of individual nanoparticles (NPs) and biomolecules. The multifunctional nanopipette was fabricated, characterized, and initially used to study model NPs. First, polystyrene (PS) NPs was studied as it mimics the dielectric nature of the biomolecules. Hybrid dielectrophoretic (DEP) method was developed to efficiently preconcentrate the PS NPs to form large assemblies outside the nanopipette tip, for high-throughput single-NP detection and analysis. Second, a highly effective and facile electroanalytical method was developed to differentiate metallic NPs and dielectric NPs in solution based on their polarizability by implementing single-NP collision events at the nanoelectrode (‘nanoimpact’). Third, the multifunctional nanopipette was used to probe magneto-electric NPs (MENPs) composed of a piezoelectric shell and a ferromagnetic core. For the first time, the nanopipette based electrochemical single-entity approach was used to probe AC B-field induced strain mediated surface potential enhancement on a MENP surface via “nanoimpact’. The results confirmed that the AC B-field stimulation caused localized surface potential enhancement of MENP. This observation is associated with the presence of a piezoelectric shell whereas magnetic NPs were found unaffected under the identical stimulation. Finally, the nanopipette was used to probe proteins at the single-molecule level. We demonstrated a facile yet highly sensitive ‘nanoimpact’ based potentiometric method of detecting electrochemically inactive bio-macromolecules, by sensing open circuit potential (OCP) change when they approach towards and/or collides with and/or scatter away from the nanoelectrode of the nanopipette. In summary, this dissertation presents the fabrication, development, and optimization of multifunctional nanopipette based electroanalytical biosensing platforms. First, it presents a systematic study using model NPs and later expands its use for biomolecule studies. With both experimental and simulation results, this dissertation announces a facile, cost-effective, versatile, sensitive, easy integration with scanning probe technique, robust and label-free electroanalytical sensing method to study individual NPs including biomolecules based on a charge sensing mechanism. The nanopipette based multi-mode biosensing platform developed in this project has great potential to be used as a smart sensor for various biomedical applications, health monitoring, quality control, and environmental sensing