posted on 2021-09-29, 17:37authored byVahid Farmehini, Sadie Kiendzior, James P. Landers, Nathan S. Swami
The
utilization of bulk acoustic waves from a piezoelectric transducer
for selective particle trapping under flow in a microchannel is limited
by the high sensitivity of the resonance frequency to tolerances in
device geometry, drift during trapping, and variations in the local
flow or sample conditions in each channel. This is addressed by detecting
the resonance condition based on the impedance minimum obtained by
monitoring the amplitude of the stimulation voltage across the piezo
transducer and utilizing real-time feedback to control the stimulation
frequency. However, this requires an overlap in the frequency bandwidth
of the detection and the stimulation system and is also limited by
the decline in the acoustic trapping power when the stimulation and
resonance frequency measurement are conducted simultaneously. Instead,
we present a novel circuit implementation for on-chip real-time resonance
frequency measurement and feedback control based on monitoring the
current drawn from the amplifier used to stimulate the piezo transducer,
since the need for high measurement sensitivity in this mode does
not lower the power available for stimulation of the transducer. The
enhanced level of control of acoustic trapping utilizing this current
mode is validated for various localized channel perturbations, including
drift, wash steps, and buffer swaps, as well as for selective sperm
cell trapping from a heterogeneous sample that includes lysed epithelial
cells.