Cytometry and Velocimetry on a Microfluidic Chip Using Polyelectrolytic Salt Bridges

Abstract

This paper reports a polyelectrolytic salt bridge-based electrode (PSBE), which is a key embedded unit in a microchip device that can size-selectively count microparticles and measure their velocities. The construction of salt bridges at specific locations within a microfluidic chip enables dc-driven electrical detection to be performed successfully. This is expected to be a competitive alternative to the optical methods currently used in conventional cell sorters. The PSBEs were fabricated by irradiating ultraviolet light over a patterned mask on the parts of interest, which were filled with an aqueous monomer solution containing diallyldimethylammonium chloride. A pair of such PSBEs was easily formed at the two lateral branches perpendicular to the main microchannel and was found to be very useful for dc impedometry. The human blood cells as well as the fluorescent microbeads passing between the two PSBEs produced impedance signals in proportional to their size. The information about the velocity of a microparticle was extracted from a doublet of the dc impedance signals, which were generated when cells or microbeads sequentially passed through two PSBE pairs separated from each other by a fixed distance. The plot of peak amplitude versus velocity of the moving microbeads and cells indicated only a slight correlation between the size and the velocity, which means that the peak amplitude of the dc impedance signals alone can provide information about the size of the cells in a mixture. The experimental results showed a screening rate of over 1000 cells s(-1) and a velocity of the cells of over 100 mm s(-1). Compared with the previously suggested electrical detection system based on metal electrodes, the sensitivity and selectivity in cell detection were remarkably improved. In addition, the detection unit including the operating circuit became innovatively simple and the whole device could be miniaturized.

Microparticle photometry in a CMOS microsystem combining magnetic actuation and in situ optical detection

“…We demonstrated that a decrease in the distance between the sensor and the particle can increase the particle size resolution, but limits the range of detection. The simultaneous and automated detection of velocity and size of single particles enables a wide range of particle characterizations and offers many applications in bio-analytical systems [20]. Since the principles of actuation and detection are not coupled, we can envisage using the particles as mobile substrates to transport biomaterials of interest, e.g.…”

Recent advances in microfluidic techniques for single-cell biophysical characterization

“…100,101 Although other metal electrodes can be more readily integrated into microfluidic channels, the electrical double layers formed between the interface of electrodes and the liquid, which are mainly capacitive, pose difficulties in applying DC signals. Methods for minimizing the electrical double layer effect include the modification of the electrode surface roughness in order to increase the surface area 102 and the utilization of polyelectrolytic salt bridges (PSBEs) 103 or polyelectrolyte gel electrodes (PGEs). 104 Most recently, a DC impedance-based microcytometer device integrating PGEs was reported for CTC cell detection.…”

Microfluidic impedance‐based flow cytometry

“…Low-frequency or DC input can also cause Faradaic reactions at metal electrodes, causing them to erode. Chun et al have developed salt-bridge based electrodes (72) to improve the sensitivity of particle sizing. The salt bridges fabricated by Chun et al consisted of microfluidic channels filled with NaCl solution, into which Ag/AgCl electrodes were immersed.…”