Detection and counting of micro-scale particles and pollen using a multi-aperture Coulter counter

We demonstrate a high throughput, all-electronic Coulter-type sensor with four sensing microapertures to detect and count micro-scale particles. Four particle samples are utilized for this study: polymethacrylate particles 40 mu m and 20 mu m in diameter, Juniper Scopulorum (Rocky Mountain Juniper) pollen and Cottonwood pollen particles. The two types of pollen particles are roughly 20 mu m in diameter. The particles are mixed with deionized water and forced to pass through the microapertures. Voltage pulses across all four apertures are recorded and analysed. Results demonstrate that the sensor can detect and count particles through its four sensing apertures simultaneously. Thus, the counting efficiency of the four-aperture sensor is approximately 300% higher than that of a single-channel Coulter counter, while maintaining the same accuracy, sensitivity and reliability. The counting efficiency can be improved further by integrating more sensing channels on a single micromachined chip. Results also demonstrate that the device can be used to differentiate between pollen and polymethacrylate particles; differentiation is based on a difference in surface charge for the two types of particles.