Abstract
Point-of-care testing (POCT) has revolutionized traditional diagnosis by enabling decentralized testing outside of laboratories. It has played an important role in early disease detection for several decades and has gained widespread acceptance since the COVID-19 pandemic. POCT platforms now support varied clinical applications in the market, including blood glucose monitoring and infectious disease screening (e.g., SARS-CoV-2 rapid test). These systems are designed to deliver rapid detection results without requiring complicated procedures or specialized technical experts.The integration of self-powered microfluidics with multimodal detection technologies has significantly advanced POCT, enabling rapid, low-cost, and equipment-free biomarker quantification using small volumes of complex specimens (e.g., water, blood plasma, nasal secretions, urine). This approach overcomes limitations of traditional laboratory testing - prolonged processing time, high costs, and technical complexity. However, most commercial POCT rapid tests remain qualitative, while other quantitative POCT devices predominantly rely on fluorescent or electrochemical signaling, which can be expensive and sophisticated. The technological gap highlights an urgent need to develop quantitative, instrument-free POCT platforms to meet clinical diagnostic standards while preserving operational simplicity, affordability. and accessibility.
This study introduces a novel distance-based microfluidic platform for quantitative analysis via a visible microparticle accumulation bar. The system demonstrates exceptional sample versatility, addressing a critical challenge in environmental monitoring and medical diagnostics where biomarkers exhibit distinct distribution profiles across different matrices (e.g., water, blood, nasal secretion, etc). We developed multiple chip architectures to accommodate varying specimen properties while maintaining detection accuracy, thus enabling broad environmental and clinical applicability.
First, we developed a ready-to-use sensor integrating automated sampling, on-chip reaction, gravitational-magnetic separation, and distance-based detection for heavy metal analysis. The system employs a novel microparticle-based detection mechanism where target metal ions selectively cleave specific DNAzyme linkages between functionalized MMPs and PMPs. The amount of free PMPs is directly proportional to the metal ion concentration. Pre-loaded reagents and microparticles in the chip enable simple operation for users. Upon sample introduction and resuspension, tilt-controlled fluidics enables on-chip reactions, followed by gravity-assisted magnetic separation. The free PMPs migrate into capture channels, forming visible bands for quantitative analysis. Through parallel integration of three identical detection channels, simultaneous quantification of Cu²⁺, Pb²⁺, and Ag⁺ was achieved with detection limits of 103.1 nM, 69.5 nM, and 793.6 nM, respectively.
Second, during the COVID-19 pandemic, we developed a rapid, non-invasive microfluidic platform to assess mucosal immunity by quantifying anti-spike RBD IgG in nasal secretions. Recognizing the upper respiratory tract as the primary infection site and first line of defense, we targeted these antibodies due to their crucial role in blocking viral attachment to ACE2 receptors. Our system employs functionalized magnetic microparticles (MMPs) and polystyrene microparticles (PMPs) that form immunocomplexes “MMP-anti-spike RBD IgG-PMP” proportional to antibody levels. Following magnetic separation, unbound PMPs are quantified via capillary-driven accumulation in a microfluidic chip, forming a distance bar visible to the naked eye. The platform offers two operational modes, a sensitive mode [limit of detection (LOD): 14.0 ng/mL; sample-to-answer time: 70 min] and an equipment-free rapid mode (LOD: 37.4 ng/mL; sample-to-answer time: 20 min). Clinical test results from 87 volunteer samples show good correlations of 0.9301 (for sensitive mode) and 0.9318 (for rapid mode) when comparing our assay to the gold standard ELISA test, indicating the accuracy and reliability of our system.
Third, we move on to quantify serum prostate-specific antigen (PSA) for prostate cancer screening. Prostate cancer, ranking the sixth most prevalent cancer worldwide and the third leading malignancy in men, is often diagnosed at advanced stages due to its asymptomatic early progression. Current PSA testing faces critical limitations, including prolonged turnaround times (typically 24-72 hours) and limited accessibility in low-resource settings. To address these challenges, we developed a capillary-driven microfluidic chip for rapid, equipment-free PSA quantification directly from whole blood. The platform integrates three key innovations: (1) a two-layer membrane for plasma extraction (50% yield), (2) geometrically optimized capillary valves for autonomous fluid control, and (3) a visual particle accumulation readout inversely proportional to PSA concentration. The assay utilizes antibody-conjugated MMPs and PMPs to form specific complexes that are separated magnetically, while unbound PMPs accumulate in the detection channel for visual quantification. The limit of detection reaches 3.69 ng/mL, covering the clinically critical 4–10 ng/mL diagnostic gray zone. We also demonstrate >2000-fold selectivity against interfering proteins. Tens of clinical samples were tested with the integrated microfluidic chip and the results showed a high correlation with ELISA and results obtained in < 1h, which is significantly faster than conventional laboratory experiments. This technology combines laboratory-grade accuracy with the convenience of instant testing and can achieve timely monitoring of PSA in various medical settings, especially in resource-poor areas. Early detection and post-treatment monitoring of prostate cancer is expected in various settings.
By decentralizing diagnostic testing, this technology empowers individuals to monitor their health and environmental pollution at home while expanding the reach of healthcare access to underserved regions. The platform's modular architecture permits adaptation for various markers, demonstrating potential for broad applications in environmental monitoring and early disease screening. This work combines rigorous analytical capabilities with practicality to advance the development of microfluidic point-of-care diagnostic (POCT) solutions and contribute to improving global health through convenient, affordable, and accurate diagnostic methods.
| Date of Award | 3 Nov 2025 |
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| Original language | English |
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| Supervisor | Ting Hsuan CHEN (Supervisor) |