Thesis Examination Committee

Prof Hongtao ZHANG, ISOM/HKUST (Chairperson)
Prof Levent YOBAS, ECE/HKUST (Thesis Supervisor)
Prof Bo ZHENG, Department of Chemistry, The Chinese University of Hong Kong (External Examiner)
Prof Andrew Wing On POON, ECE/HKUST
Prof Man WONG, ECE/HKUST
Prof Hongkai WU, CHEM/HKUST

Abstract

The analysis of nucleic acids and proteins is of great significance in genomics, proteomics, and clinical diagnostics. The past decades have witnessed the booming development of nanofluidic devices, which have outperformed traditional diagnostic and analysis techniques in terms of accuracy, sensitivity, efficiency, and sample consumption. Nanofluidic channels (capillaries) featuring critical dimensions comparable to those of biomolecules provide alternative routes to the manipulation and detection of such species, in an attempt to develop the micro total analysis system (μ-TAS). 
 
This thesis describes the development of monolithically integrated, robust, and cost-effective glass nanocapillaries and nanopores that can be utilized for the separation and detection of biomolecules. First, the integrated glass nanocapillaries featuring distinct cross-sectional profiles are demonstrated for different chromatographic modes, including normal phase, ion-valance, reverse phase, and hydrodynamic liquid chromatograph. The minimum plate heights achieved are typically below 2 μm and the theoretical plate numbers are in the order of 105 plates/m for most chromatography modes investigated in the pressure range up to 100 psi. Second, an on-chip hydrodynamic chromatography of DNA fragments is demonstrated, based on centimeters-long glass nanocapillaries that are essential for resolving DNA in this chromatography mode. The microchip can rapidly separate a digest of Lambda-phage DNA in free solution (< 5 min under the elution pressure of 60 psi to 120 psi) and the number of theoretical plates exceeds 105 plates per meter for 3.5- and 21-kbp-long DNA fragments. Third, continuous-flow electrophoresis of macromolecules is presented using an integrated capillary-well sieve arranged into a two-dimensional anisotropic array on silicon. The periodic array features thousands of entropic barriers, each resulting from an abrupt interface between a 2-μm-deep well (channel) and a 70-nm capillary. The baseline separation is achieved in less than 1 min within a horizontal migration length of ~1.5 mm. Last, a monolithically integrated nanofluidic diode biosensor featuring a highly regular pore diameter of ~50 nm is demonstrated for multiplexed detection of low-abundance specific biomarkers presented in both electrolyte buffer and human serum. The nanopore diode exhibits a comparable rectification behavior to that of a nanoslit but it can achieve an order of magnitude lower detection limit for cardiac troponin T (~ 1 fg/mL). This nanopore biosensor can multiplex detect various biomarkers, including Alpha-fetoprotein, Carcinoembryonic Antigen, and Human Epidermal growth factor Receptor 2 within human serum and therefore provide accurate information for the early diagnosis of cancer. Further applications of such nanopore arrays are also proposed, including a fast and high-throughput DNA sequence, and novel power generators relying on the osmotic pressure gradient.