Circular shaped microelectrodes for single cell electrical measurements for lab-on-a-chip applications.

The impedimetric sensing techniques for single cell characterization have witnessed growing interest due to their high sensitivity and widespread applications. However, adapting the method to different biological measurements in microfluidic environments under various input conditions can result in feeble signal detection leading to a drastic decrease in the sensor sensitivity. The reduced signal-to-noise ratio (SNR) hinders the signal differentiation, sensor accuracy and prohibits fully integrated point-of-care applications. Here, we address the sensitivity enhancement for microfluidic impedimetric sensing of micron and submicron-sized microparticles by exploring novel circular shape electrodes in a simulation study. The influence of radial electrode parameters on differential electrical signal is systematically analyzed in COMSOL Multiphysics using spherical particles ranging from 0.75 µm to 5 µm in diameter. Detailed analysis revealed the strong impact of the circular shape microelectrode geometry and the electrode gap on the signal strength, resulting SNR, and device sensitivity for multiple bioparticles detection. Specifically, ˃ 50 dB improvement in SNR was enabled by optimizing the circular electrode geometrical parameters. Our proposed sensing modality can be adapted for nanoparticles detection by further optimizing the microfluidic device parameters.

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 (~ max. SNR = 38.78 dB). For the proposed design, the SNR was adequate to enable good detection and differentiation of 10 µm diameter polystyrene beads and leukemia cells (~ 6-21 µm). 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.