Magnetic Bead-Based Biosensing on an Automated & Integrated Lab-on-a-Disc Platform

The PhD thesis presents the development and utilization of magnetic bead-based agglutination assays for the detection of biomarkers in biofluids as well as discovery of a biomarker relevant to the mechanism of action of a type-2 diabetes (T2D) drug while integrating the assays on an automated centrifugal microfluidic platform with incorporated readout units.

The assays were developed through surface functionalization of micro or nano-sized magnetic beads with specific antibodies or aptamers to specifically bind with the biomarker of interest resulting in the formation of the biomarker-bridged magnetic bead clusters and hence called ‘agglutination’ assay.

The concentration of the analyte or biomarker was quantified based on the size of the clusters. The model biomarkers studied in this project were thrombin – a blood coagulation protein; C-reactive protein – an acute phase protein-biomarker for inflammatory diseases; and mononuclear white blood cell count – a biomarker for the prognosis of different medical conditions.

Furthermore, the concept of the agglutination assay was utilized for a biomarker discovery application by investigating the mechanism of action of a T2D drug - metformin through the analysis and quantification of the aggregation and disaggregation phenomena of the magnetic beads in response to the presence of the drug.

The assays were either partially or fully integrated on disc-shaped polymeric microfluidic substrates i.e. microfluidic discs for incorporating the advantages of centrifugal microfluidics e.g. eliminating the need for external fluidic connectors or pumps, and facilitating simple, compact and low-cost instrumentation along with effective multiplexing of microfluidic units.

All the discs were fabricated in-house using multiple layers of polymeric substrates. Two specific valving mechanisms namely centrifugo-pneumatic and event-triggered valving were incorporated into the microfluidic platform in order to facilitate the integration of the assay from sample-to-answer. The readouts were performed by two different optical methods: Blu-ray based optomagnetic readout and optical imaging method.

The readout instruments were customized and incorporated with the automated centrifugation microfluidic platform to produce an integrated and automated biosensing platform with a potential for operating in an out-of-lab setting which can pave the way for future development of a point-of-care diagnostic tool.