Thesis Defence Moein Talebian Gevari: Design and optimization of a microchip biosensor utilizing streaming current

Abstract

Biosensors are devices used for detecting biomolecules. They have wide applications including clinical diagnosis, drug discovery, fundamental biological investigation, and personalized medicine.

This thesis introduces a novel biosensing platform leveraging streaming current for detecting small extracellular vesicles (sEVs) and single-stranded DNA (ss-DNA).

First, fundamental electrokinetic theories are outlined to establish the relationship between streaming current and key parameters influencing the sensing performance. A silicon-based microfluidic device and a robust experimental setup are designed to enable multiplexed detection. The microchip achieves an improved limit of detection (LoD) of 1 × 10⁴ sEVs/mL. Using this LoD, clinically relevant biomarkers for early-stage lung cancer are detected, demonstrating the platform’s diagnostic potential.

Additionally, two novel labeling techniques are introduced to address sEV heterogeneity and amplify streaming current for improved detection sensitivity and specificity. The former uses secondary antibodies tagged with charged molecules to engineer surface charges and profile sEV surface proteins. Results demonstrate the capability of the microchips in multimarker profiling of sEVs. The latter uses an innovative nanoparticle-mediated sandwich assay to introduce new charges on the interface and amplify streaming current signal, enabling ss-DNA detection at picomolar concentrations. This method, benefiting from analyte size and charge, improves the LoD by four orders of magnitude over prior reports.

Finally, the thesis advances toward a standalone EV analyzer by developing two modules. The first is a microfluidic system for sEV isolation and enrichment based on surface protein expression levels, pre-selecting and enriching sEVs before membrane protein profiling. The second is a picoammeter designed on a printed circuit board (PCB) to replace bulky and costly measurement units.

Together, these innovations contribute to the creation of a highly sensitive and versatile biosensing platform.