Thin flexible lab-on-a-film for impedimetric sensing in biomedical applications

Microfluidic cytometers based on coulter principle have recently shown a great potential for point of care biosensors for medical diagnostics. Here, we explore the design of an impedimetric microfluidic cytometer on flexible substrate. Two coplanar microfluidic geometries are compared to highlight the sensitivity of the device to the microelectrode positions relative to the detection volume. We show that the microelectrodes surface area and the geometry of the sensing volume for the cells strongly influence the output response of the sensor. Reducing the sensing volume decreases the pulse width but increases the overall pulse amplitude with an enhanced signal-to-noise ratio (similar to max. SNR = 38.78 dB). For the proposed design, the SNR was adequate to enable good detection and differentiation of 10 mu m diameter polystyrene beads and leukemia cells (similar to 6-21 mu m). Also, a systematic approach for irreversible & strong bond strength between the thin flexible surfaces that make up the biochip is explored in this work. We observed the changes in surface wettability due to various methods of surface treatment can be a valuable metric for determining bond strength. We observed permanent bonding between microelectrode defined polypropylene surface and microchannel carved PDMS due to polar/silanol groups formed by plasma treatment and consequent covalent crosslinking by amine groups. These experimental insights provide valuable design guidelines for enhancing the sensitivity of coulter based flexible lab-on-a-chip devices which have a wide range of applications in point of care diagnostics.

Automated summary

This study explores the design of an impedimetric microfluidic cytometer on a flexible substrate and compares two microfluidic geometries for their sensitivity. The results show that the microelectrode surface area and the geometry of the sensing volume significantly affect the sensor's output response. Reducing the sensing volume improves pulse amplitude and signal-to-noise ratio. The proposed design demonstrates good detection and differentiation of polystyrene beads and leukemia cells. Additionally, the study presents a feasible approach to achieve irreversible and strong bond strength between thin flexible surfaces in a biochip.