CapSense-Flex: A Self-Powered Capillary Lab-on-Chip for Universal Electrochemical Biosensing

Area of Science:

• Microfluidics
• Biosensing
• Point-of-Care Diagnostics

Background:

• Existing capillary microfluidic platforms for point-of-care (POC) diagnostics are limited by continuous flow, short residence times, and wash cycles.
• These limitations hinder integration with affinity-based assays, restricting their diagnostic capabilities.

Purpose of the Study:

• To introduce CapSense-Flex, a novel capillary chip for wash-free, diffusion-dominated molecular sensing.
• To demonstrate its capability for programmable incubation windows (6-30 min) suitable for molecularly imprinted polymer (MIP)-based electrochemical detection.
• To establish a universal architecture for scalable MIP-based biosensing in decentralized diagnostic formats.

Main Methods:

• Laser-cut, roll-to-roll manufacturable capillary chip enabling autonomous fluid transport (≤25 μL) of various biofluids without pumps or valves.
• Integration of a cortisol-selective MIP electrode for electrochemical detection.
• Fiber-assisted wicking to prevent bubble formation and ensure accurate fluid-front arrival times (<5% deviation from predictions).

Main Results:

• Log-linear quantification of cortisol in buffer and saliva (1-1000 ng mL⁻¹) with high linearity (R² = 0.9835) and a low limit of detection (0.1 ng mL⁻¹).
• Demonstrated sensor stability with ~90% signal retention after 60 days at 4 °C.
• Accurate quantification of cortisol in unprocessed saliva samples with minimal signal loss (<12%) compared to standards.

Conclusions:

• CapSense-Flex offers a scalable, cost-effective (<$0.40/chip) platform for wash-free biosensing, decoupling transport from binding kinetics.
• The plug-and-replace electrode design allows adaptation for various MIP targets.
• This technology enables advanced MIP-based electrochemical detection for handheld, wearable, and decentralized diagnostic applications.