A portable battery powered microfluidic impedance cytometer with smartphone readout: towards personal health monitoring

Abstract

We present a portable system for personalized blood cell counting consisting of a microfluidic impedance cytometer and portable analog readout electronics, feeding into an analog-to-digital converter (ADC), and being transmitted via Bluetooth to a user-accessible mobile application. We fabricated a microfluidic impedance cytometer with a novel portable analog readout. The novel design of the analog readout, which consists of a lock-in-amplifier followed by a high-pass filter stage for subtraction of drift and DC offset, and a post-subtraction high gain stage, enables detection of particles and cells as small as 1 μm in diameter, despite using a low-end 8-bit ADC. The lock-in-amplifier and the ADC were set up to receive and transmit data from a Bluetooth module. In order to initiate the system, as well as to transmit all of the data, a user friendly mobile application was developed, and a proof-of-concept trial was run on a blood sample. Applications such as personalized health monitoring require robust device operation and resilience to clogging. It is desirable to avoid using channels comparable in size to the particles being detected thus requiring high levels of sensitivity. Despite using low-end off-the-shelf hardware, our sensing platform was capable of detecting changes in impedance as small as 0.032%, allowing detection of 3 μm diameter particles in a 300 μm wide channel. The sensitivity of our system is comparable to that of a high-end bench-top impedance spectrometer when tested using the same sensors. The novel analog design allowed for an instrument with a footprint of less than 80 cm. The aim of this work is to demonstrate the potential of using microfluidic impedance spectroscopy for low cost health monitoring. We demonstrated the utility of the platform technology towards cell counting, however, our platform is broadly applicable to assaying wide panels of biomarkers including proteins, nucleic acids, and various cell types.

Point‐of‐Care Smartphone‐based Electrochemical Biosensing

“…Recently more and more peripherals have begun using Bluetooth to wirelessly transmit data to and from the smartphone, as seen in the examples in Figure . The obvious benefit is that these types of peripherals are compatible with all types of smartphones regardless of the make or model.…”

“…Furthermore, in assays where there are redox reactions, setting the bias point accurately is crucial to the measurement. Custom EIS circuits have been created to obtain more accurate results that use on‐board ADCs, DACs, and microcontrollers relying on separate batteries to provide enough power . However, Jiang et al., as illustrated in Figure (B), shifts the generation of the stimulus signal and quantization to the smartphone through the headphone jack, negating the need for a microcontroller and mixed‐signal circuits allowing for a very low power (2.5 mW) EIS peripheral, which is mostly analog, albeit with a frequency range limited to the audio band .…”

Biosensors for Personal Mobile Health: A System Architecture Perspective

“…Further, the system was able to discriminate acetone from other VOCs, like formaldehyde, via impedance spectroscopy. Impedance readout was also adapted for blood cell counting in a work by Talukder et al They developed a portable cytometer capable of detecting the small change in impedance from cells flowing past the electrode. The minimum change in impedance that the sensor could detect using 3 µm beads was 0.032%.…”

Toward Wireless Health Monitoring via an Analog Signal Compression-Based Biosensing Platform

“…The bead size is 7.8 µm. A sequence of pulses is generated with beads flowing over the electrode pair and the signal is recovered using the lock-in amplifier analog circuit [13].…”

“…This class of sensors has been shown to be well suited for detecting biomarkers with high sensitivity [11], [12]. Impedance-based sensors can be made portable with miniaturized analog front-end circuitry such as lock-in-amplifiers [13], and wireless transmitters. Functionalization of microfluidic The authors are with the Department of Electrical and Computer Engineering, Rutgers University-New Brunswick, NJ, USA.…”