The sensor is a Resistor loaded with either the enzyme glucose oxidase or lactate oxidase (GOD or LOD in diagram right).
This is made part of a passive LCR resonant tank circuit, which is coupled, through skin if necessary, to a second similar LCR tank, this time actively oscillated.
Physically, the coil is a single loop of fine wire <20mm in diameter and the sensor is tiny in comparison. Proposals include burying such a sensor under the skin, or building one into a contact lens.
“We modelled the characteristics of the wireless sensing system by using an eigenvalue solution and input impedance, and experimentally demonstrated the sensitivity enhancement at or near the exceptional point by using parallel LCR resonators,” said Waseda’s Professor Takeo Miyake, describing the telemetry as “robust and tunable”.
“The developed amplitude modulation-based bioresonator,” he continued, “can detect small biological signals that have been difficult to measure wirelessly until now. Moreover, our system provides two types of readout modes: threshold-based switching and linear detection. Different readout modes can be used for different sensing ranges.”
The glucose enzyme version was tested on human tear fluids, and could detect glucose concentrations from 0.1 to 0.6mM.
The lactate enzyme version could measure lactate levels from 0.0 to 4.0mM, with negligible loss of sensitivity if skin was placed between the inductively-linked coils.
“Compared to a conventional chip-less resonant antenna-based system, the [demonstrated] system achieved a 2,000-fold higher sensitivity in linear and a 78% relative change in threshold-based detection,” according to the university.
Waseda University worked with Beijing Institute of Technology and Japan Aerospace Exploration Agency.
The work is published in Advanced Materials Technologies as ‘Wearable, implantable, parity-time symmetric bioresonators for extremely small biological signal monitoring‘ (payment required for full access).
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