Fig. 6: Wireless trapping with real-time sensing.
a Before particle trapping, the impedance spectrum (black) was measured as a function of frequency with a coil separation of 2.5 cm. The regions where pDEP occurs is shaded blue (i.e. frequencies in which the real part of the CMF is greater than 0). The voltage amplitude coupled wirelessly over the microhole DEP device was recorded and peaked at 1.1 MHz (orange curve). These two curves were fit using nonlinear least squares with our measured circuit components. (Inset) The impedance spectrum over a focused region measured in which ZIN was reduced from 94 to 89 Ω at the target frequency of 1.3 MHz after two minutes of particle trapping. b The change in absolute impedance was recorded on the transmitting circuit as a function of time for DI water and a solution containing 1 µm PS beads. A larger change in impedance is observed as more particles are collected. After 5 min, particles are released as the network analyzer is disconnected. Trapping resumes after 1 min. c Microhole array device and microscope images. Fluorescent images were taken at the array edge for clearly demonstrating trap and release events under the fluorescent microscope. Initially, no particles are observed along the indicated edge region of the array. After 5 min, particles have collected and were trapped on the array. They were then allowed to diffuse for 1 min before trapping once again. d The particle count taken from a 180 × 135 µm microscope field of view is plotted as a function of time. The particle count coincides with the observed change in impedance recorded in Fig. 6b.
