A first as a metal-free disposable glucose sensor, the three electrode (reference, working and counter) device reported in the Flexible Electronics journal under the paper title “A fully inkjet-printed disposable glucose sensor on paper” does not rely on external Ag/AgCl electrodes and hence consist of 100% organic materials.
Instead, all the electronic components including the contact pads are composed of the same material, the printed conducting polymer poly(3,4 ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS). But in order to insulate or separate the active area from the contact pads area, the authors printed a layer of UV-curable dielectric ink on top of the electrode interconnects. The biorecognition element was printed as an aqueous solution containing glucose oxidase (GOx) and a ferrocene (Fc) complex on top of the working electrode. A thin layer of nafion printed over the sensing area completed the device, forming a barrier for any interfering species present in saliva or formed as a result of unspecific redox reactions during electrode operation.
In enzymatic glucose sensors, the biochemical reaction of glucose with the enzyme glucose oxidase generates a change in the electrical current of the electrode nearby that is correlated with glucose concentration. The devices were fabricated via four stages of automated deposition of vertical films, which the researchers say could easily be transferred to a roll-to-roll process for low cost high volume manufacture.
The device was able to operate at low concentrations down to 0.025mM and up to 0.9mM with good sensitivity for glucose concentrations in saliva sufficient for screening abnormal concentrations.
When stored at room temperature under vacuum, sensors were proven to maintain their function one month after fabrication with only minor performance loss (under 25%).
The authors conclude that although the platform was benchmarked for glucose as the target metabolite, the analyte repertoire could be expanded to a variety of biorecognition elements by simply changing the enzyme, potentially enabling the design of multifunctional sensors.
Once integrated with wearable biocompatible substrates, the design could also be adapted to continuously monitor glucose from saliva.
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