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I NSTITUTE OF PHYSICS PUBLISHING M EASUREMENT SCIENCE AND TECHNOLOGY Meas. Sci. Technol. 17 (2006) 1706–1714 doi:10.1088/0957-0233/17/7/008 Detection and counting of micro-scale particles and pollen using a multi-aperture Coulter counter Ashish V Jagtiani 1 , Jiang Zhe 1 ,JunHu 2 and Joan Carletta 3 1 Department of Mechanical Engineering, University of Akron, Akron, OH 44325, USA 2 Department of Chemistry, University of Akron, Akron, OH 44325, USA 3 Department of Electrical and Computer Engineering, University of Akron, Akron, OH 44325, USA E-mail: [email protected] Received 6 January 2006, in ±nal form 25 April 2006 Published 7 June 2006 Online at stacks.iop.org/MST/17/1706 Abstract 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 µ m and 20 µ m in diameter, Juniper Scopulorum (Rocky Mountain Juniper) pollen and Cottonwood pollen particles. The two types of pollen particles are roughly 20 µ 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 ef±ciency 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 ef±ciency 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. Keywords: high throughput particle counter, pollen analysis, Coulter counter, biosensor, micro particle 1. Introduction Coulter counting, invented in 1953 [ 1 ], is a well-developed technology used to measure the size and concentration of biological cells and colloidal particles in electrolyte solution. A typical Coulter counter device consists of a single microaperture or pore that separates two chambers. When a particle ²ows through the microaperture, it causes a change in the electrical resistance of the microaperture. The change in resistance can be measured in terms of current or voltage pulses, which can be correlated to size, shape, mobility, surface charge and concentration of the particles. Because of their simplicity, high sensitivity and reliability, Coulter- type devices have been used for an extensive number of applications, from the analysis of blood cells to the detection and counting of colloidal beads [ 2 , 3 ], pollen [ 4 ], metal ions [ 5 ] and viruses [ 6 ]. More recently, the use of Coulter-type devices has been extended to the detection of nano-scale particles, including single molecules [ 7 ], DNA [ 8 ] and antibody–antigen binding [ 9 ].
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