Microwave Contactless Current-Sensing for Live/Dead Differentiation of Single Bioparticles on a Microfluidic Platform

The combination of microwave and microfluidic technologies enables the creation of efficient platforms to rapidly quantify live/dead bioparticles in industrial processes, biomedical research, and environmental monitoring applications. In this regard, this work demonstrates the differentiation of single live/dead bioparticles with a microwave-microfluidic platform. The system is composed of a contactless current-sensing superheterodyne architecture with broadband frequency-operation bowtie electrodes. Furthermore, the
$20\times20$
mm bowtie electrode has been designed and manufactured with a −10 dB frequency range, from 4 to 8 GHz, and is capable of confining the electric field in a micrometric volume. The gap of the bowtie geometry of the electrodes is adjusted to the dimensions of the 50
$\times $
50
$\mu \text{m}$
cross section and 40 mm long microfluidic channel. In particular, a 10 mL sample with 109 bacteria/mL flows through the microchannel at 19.8
$\mu \text{L}$
/min, focused with elasto-inertial effect enhanced with 500 ppm of polyethylene oxide (PEO). Accordingly, from the signal captured by the electrodes, the energy variation of the applied electric field produced by the bioparticles is sensed by a current-based transimpedance amplifier (TIA). Here, the incorporation of the TIA in the measurement system improves the signal-to-noise ratio (SNR) by 4 dB. In addition, the superheterodyne transceiver has been optimized in terms of local oscillator power and bandwidth. Furthermore, the microfluidic system has been adjusted so that the balance of hydrodynamic forces confines bioparticles at the centerline of the microchannel within less than 5
$\mu \text{m}$
. As a result, the system measures the cytoplasmic content of live and dead-flowing bacteria with a difference of 6 dB and a relative deviation of 3.2%.