Combination of acoustic trapping and impedance spectroscopy for platelet analysis
Abstract: A combination of acoustic trapping and impedance spectroscopy for micrometer-sized objects is here presented for the first time. Acoustic trapping has proven to be a well-functioning method for non-contact immobilization and positioning of particles or cells in microfluidic channels. The combination with impedance spectroscopy allows for simultaneous electrical measurements on the trapped objects. Silica (8 μm) and polystyrene particles (3, 7, 10, and 12 μm) in saline solution, as well as human platelets in TAB buffer, have been trapped and measured. Both the saline and buffer solution had a base impedance magnitude of ̴ 500 Ω at the utilized frequency range (100 kHz–5 MHz). The impedance magnitude for the trapped particles was ̴ 30 Ω higher than the base impedance magnitude for the saline solution at 100 kHz–15 MHz. For the platelets, the impedance magnitude was ̴ 60 Ω higher compared to the buffer at 100 kHz. Furthermore, the setup can be used for studies on the reaction of a trapped cluster of objects, for example cells, when the environment is changed. One way of changing the environment would be to introduce drugs in different concentrations into the channel. However, the electrical characteristics of the fluid cannot be changed. An application is presented where the system is used for measurements on platelet activation. Platelets were activated by 20 μM TRAP while trapped, which yielded a reversible impedance magnitude decrease of ̴̴ 15 Ω at 100 kHz. 40 μM TRAP resulted in an initial decrease of ̴ 24 Ω and a sustained decrease of ̴ 15 Ω at 100 kHz. The setup presented shows great potential for being developed to an analysis system for micrometer-sized objects, for example for characterization of platelet activation.
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