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Rapid Finger-Pump Microfluidic Paper-Based Assay Platform for Monitoring Calcium Ions in Human Biofluids
Kuan-Hsun Huang1, Chin-Chung Tseng2,3, Chia-Chun Lee2,3
1Department of Engineering Science, National Cheng Kung University, Tainan 701, Taiwan.
Insights
This study introduces a novel microfluidic platform for rapid, point-of-care calcium monitoring in chronic kidney disease (CKD) patients. The device accurately quantifies calcium levels in small biofluid samples, aiding in CKD-mineral and bone disorder management.
Area of Science:
- Biomedical Engineering
- Analytical Chemistry
- Clinical Diagnostics
Background:
- Chronic kidney disease (CKD) management requires serial calcium monitoring due to its impact on mineral homeostasis and cardiovascular health.
- Current calcium measurement methods using centralized analyzers are accurate but not suitable for rapid point-of-care testing with limited biofluid volumes.
- CKD-mineral and bone disorder (CKD-MBD) is a common complication, necessitating accessible diagnostic tools.
Purpose of the Study:
- To develop and validate a finger-actuated microfluidic colorimetric platform for rapid calcium ion determination in human biofluids.
- To enable point-of-care calcium measurement using microliter-scale samples relevant to CKD patient monitoring.
- To assess the platform's performance against established assays for clinical CKD specimens.
Main Methods:
- A microfluidic platform was engineered using a 3D PMMA/paper microchip with integrated filtration and a compact reader for optical detection.
- A finger-actuated mechanism was employed to process small biofluid volumes (6 μL) and facilitate reaction with a pre-deposited murexide reagent.
- Optimized reaction conditions (1.6% reagent, 50 °C, 3 min) were established to achieve a logarithmic relationship between signal intensity and calcium concentration.
Main Results:
- The developed platform demonstrated a strong logarithmic correlation (R² = 0.9905) for calcium quantification in the 1-40 mg/dL range, with a detection limit of 0.2 mg/dL.
- The system accurately measured calcium concentrations in various biofluids, including whole blood, serum, and urine.
- Results from 80 clinical CKD specimens showed high agreement (R² > 0.97) with the NM-BAPTA reference assay.
Conclusions:
- The finger-actuated microfluidic colorimetric platform offers a viable solution for rapid, point-of-care calcium measurement in CKD management.
- This technology facilitates efficient monitoring of calcium levels using minimal sample volumes, addressing limitations of conventional laboratory assays.
- The platform's accuracy and close correlation with reference methods support its potential clinical utility in diagnosing and managing CKD-MBD.
Abstract:
Chronic kidney disease (CKD) is a progressively worsening condition that erodes renal function over time, reduces quality of life, and can ultimately culminate in kidney failure with far-reaching systemic complications. In addition to reduced filtration, worsening kidney function disrupts mineral homeostasis and leads to CKD-mineral and bone disorder (CKD-MBD). Dysregulated calcium handling and maladaptive endocrine responses contribute to bone pathology and increase cardiovascular calcification risk; therefore, serial calcium monitoring remains clinically relevant for longitudinal CKD management. Conventional calcium measurements are typically obtained with centralized analyzers or laboratory assays (e.g., colorimetry and electrode/optical readouts). Despite high accuracy, the required instrumentation, controlled operating conditions, and pretreatment steps complicate rapid point-of-care deployment, especially when only microliter-scale biofluids are available. Accordingly, this study develops a finger-actuated microfluidic colorimetric platform capable of determining calcium ion concentrations in human biofluids, such as whole blood, serum, and urine. The platform integrates a three-dimensional PMMA/paper microchip with a compact reader that maintains stable temperature control while enabling CMOS-based optical detection. With just 6 μL of sample, a brief finger press propels the biofluid across an internal filtration layer, generating serum or cleaned urine that subsequently reacts with a pre-deposited murexide reagent. Under optimized conditions (1.6% reagent, 50 °C, 3 min), the signal follows a strong logarithmic relationship with calcium concentration (Y = 47.273 ln X + 28.890; R2 = 0.9905), supporting quantification over 1-40 mg/dL and a detection limit of 0.2 mg/dL. Across 80 clinical CKD specimens spanning serum, whole blood, and urine, results aligned closely with the NM-BAPTA reference assay, with R2 values exceeding 0.97.
