Micro coulter counters with platinum black electroplated electrodes for human blood cell sensing.

We demonstrated a novel micro Coulter counter featuring platinum-black electrodes for human blood cell counting application. Two designs of micro Coulter counter were fabricated using two distinct technologies: integrated parylene and soft lithography. Platinum-black enhanced detection in the intermediate frequency range ( approximately 100 Hz to 7 MHz), which is the operation frequency suitable for sensing the cells flowing by the electrodes. A detailed theoretical modeling of the sensing mechanism has been performed for the design of the electrodes, and electrical impedance spectra measurements confirmed the theoretical model. The surface morphology and roughness of the platinum black electroplated surface were characterized by SEM and AFM measurements. Polystyrene beads of various sizes were initially used to validate the operation of the devices, and using excitation frequency of 10 kHz, the signal magnitude was found to be correlated with the volume of the individual bead. Human blood cell sensing was successfully demonstrated with diluted whole blood and leukocyte rich plasma under the same excitation frequency. The histogram of impedance magnitude of the cells matched well with volume distributions of erythrocytes and leukocytes measured by conventional counting techniques. Micro Coulter counters have the advantages of small foot-print, low sample volume, and reduced cost of operation. Further development of the devices can lead to the development of a highly-sensitive and high-throughput handheld blood counting system for point-of-care applications.