Optofluidic nanostructures for transport, concentration and sensing

• Main Author: Escobedo, Carlos
• Other Authors: Sinton, David A.
• Language: en
• Published: 2011
• Subjects: Microfluidics; Optofluidics; Plasmonics; Nanohole Array
• Online Access: http://hdl.handle.net/1828/3492

This thesis presents optofluidic nanostructures for analyte transport, concentration and sensing. This work was part of a larger collaborative project between the BC Cancer Agency and the departments of Chemistry, Electrical and Mechanical Engineering at the University of Victoria. In this work, arrays of nanoholes are used as optofluidic platforms for sensing, combining the characteristics of these nanostructures for both fluidic transport and plasmonic (optical) sensing. Two different modes are considered: flow-over mode, where the sample solution containing the analyte flows on top of the nanohole arrays, and a novel flow-through mode, where the nanoholes are used as nanochannels, enabling solution transport and analyte sieving. Flow-through nanohole array operation and sensing is first demonstrated, offering a six-fold improvement in sensor response compared to established flow-over sensing formats. Through a subsequent theoretical scaling analysis and computational analyses, the benefits of the flow-through nanohole sensing format are further quantified. A first analysis is dedicated to study the enhancement offered by the flow-through operation mode using a mass transport approach. A second analysis offers an ample study of benefits and limitations of the flow-through nanostructure operation using the combination of mass transport and binding kinetic parameters for different analytes with characteristics of clinical relevance. The mass transport analysis indicates much higher analyte collection efficiency (~ 99%) offered by the flow-through mode, compared to the flow-over platform (~ 2%). The analysis including both mass transport and binding kinetics demonstrate up to 20-fold improvement in response time for typical biomarkers. This thesis also presents the use of the flow-through optofluidic platform as an active analyte concentrator. In combination with a pressure bias, an electric field is used to concentrate electrically charged analyte for subsequent sensing. Fluorescein enrichment of 180-fold in 60 s was achieved, and 100-fold enrichment and simultaneous surface plasmon resonance (SPR) sensing of a protein (bovine serum albumin, BSA) was demonstrated. These experiments represent the first active utilization of a nanohole metallic layer as an electrode, and the first demonstration of a photonic nanostructure achieving both concentration and sensing of analytes. Towards the integration of optofluidic nanostructures into microfluidic environments for portable lab-on-chip diagnostic systems, this dissertation also includes the development of two nanohole array based sensing systems with simple flow-over operation. The first system consisted of a hand-held device with a dual-wavelength light source to increase the spectral diversity. The second system consisted of nanohole arrays integrated with a microfluidic concentration gradient generator for the detection and quantification of ovarian cancer antibody and antigen. Additionally, this dissertation includes a novel technique to actuate liquids in microchannels through ground-directed electric discharges. Experiments demonstrate average fluid velocities on the order of 5cm/s and applicability of the technique in serpentine channels, for on-demand fluid routing, to initiate a mixing process, and through an on-chip integrated microelectrode. === Graduate