Magnetic forces for surface-based bioanalysis in microfluidic devices

Peyman, Sally A.

Abstract

Biochemical analysis is a critical part of clinical diagnostics, forensic science and environmental monitoring. Typically, this form of analysis involves the use of bioanalytical procedures which are extremely sensitive and highly specific. However, such assays often involve many different reaction and washing steps, which means that a single analysis could take hours or even days to perform. There is an urgent demand for high through-put analysis systems that are rapid, simple to use and can be utilised in the field or at the point-of-care. Microfluidic technology has gone some way to producing such systems, however many of the current devices still incorporate batch methods of analysis, which are still time consuming or do not integrate all steps of the analysis on one device.

Two aspects of particle handling utilising magnetic forces were investigated. 1) The use of single magnetic particles as mobile solid-supports in a continuous flow system for bioanalysis. 2) The use of diamagnetic repulsion forces for label-free on-chip particle handling.

For the continuous flow system, a magnetic particle type was selected from eight commercially available brands of particles and characterised using on and off-chip measurements. Dynabead M-270 particles were ultimately used as mobile solidsupports for performing entire bioanalytical processes in continuous flow, for the first time. This was achieved by generating multiple laminar flow streams along the length of a rectangular chamber and applying a magnetic field gradient perpendicular to flow. Each reagent stream contained reagents for a molecular binding assay and functionalised magnetic particles were deflected across the width of the chamber. As the particles were deflected through reagent streams, washing and reaction steps were performed on the surface of the particle in one operation in continuous flow. The system was used to perform a one-step streptavidin - biotin binding assay with an LOD of 20 µg mL-1 , a two-step mouse IgG immunoassay with an LOD of 0.1 µg mL-1 and a qualitative sandwich immunoassay for C-reactive protein (CRP). All three procedures were performed within one minute with no manual intervention.

For the diamagnetic repulsion forces for label-free particle handling, 10 µm polystyrene particles were trapped into plugs on a glass capillary by suspending them in a paramagnetic solution and creating an area of high magnetic field gradient between two magnets. Particles were repelled by the field and formed a plug upstream from the magnets. The system was used to simultaneously perform positive and negative controls on a sample of fluorescently labelled biotin using two plugs; one containing streptavidin functionalised polystyrene particles and one containing plain polystyrene particles. In addition, diamagnetic repulsion was used to deflect polystyrene particles from flow inside a square deflection chamber. A particle mixture of 5 µm and 10 µm particles were separated into different exits at a flow rate of 20 µLh-1 based on the difference in their volume, termed free-flow diamagnetophoresis. Potential applications include label-free cell manipulation.

Citation

Peyman, S. A. (2010). Magnetic forces for surface-based bioanalysis in microfluidic devices. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4213006

• Thesis Type: Thesis
• Deposit Date: Sep 12, 2012
• Publicly Available Date: Feb 22, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4213006
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Apr 1, 2010