Abstract
The emerging field of wearable devices for monitoring bioanalytes calls for the miniaturization of biochemical sensors. The only commercially available electrochemical wearable monitoring medical devices for bioanalytes are the amperometric continuous glucose monitoring (CGM) systems. The use of such amperometric methods to monitor glucose levels requires a relatively large electrode surface area for sufficient redox species collection, allowing accurate measurements to be made. Consequently, miniaturization of such sensors bearing large electrodes is challenging. Furthermore, it is difficult to introduce and deploy more than one electrode–based sensor per device, thereby limiting the number of analytes that can be monitored in parallel. To address these limitations, we have employed a non-referenced, single polarizable electrode coupled to a fin-shaped field-effect transistor (Fin-FET). We have discovered that by passivating the FET area by a relatively thick oxide and/or polytetrafluoroethylene (PTFE) polymer, leaving only the polarizable working electrode (WE) exposed, we can monitor redox analytes at the micromolar to millimolar concentration range. We attribute this effect to the WE polarization by the solution redox species. We have exploited the superior sensitivity of the adjacent silicon-based Fin-FET to detect changes in sensor electrode potentials induced by the redox species. Furthermore, we demonstrated the correlation between a specific analyte and the biasing WE potential on the accumulation/depletion of the coupled Fin-FET channel as manifested by the transistor source-drain current. Moreover, we utilized the analyte-electrode potential interaction, which is analyte-specific, to tune the specificity of the sensor towards an analyte of choice. In addition, we demonstrated the use of a single-electrode potentiometric sweep to assist in identifying the accumulation/depletion as a result of analyte-WE state. Collectively, the tiny potentio-tunable electrochemical sensor (PTEchem sensor) area is ~50 × 50 µm, and dedicated wireless transducer facilitates the use of this sensor for wearable continuous, multi-metabolite monitoring.Graphical abstract
Highlights
The majority of commercial wearable, continuous bioanalytes monitoring devices rely mostly on amperometric techniques [1]
Small changes in the working electrode (WE) polarization are amplified by the adjacent finshaped field-effect transistor (Fin-Field-effect transistor (FET)), generating charge carrier depletion/accumulation at the FET’s channel, which results in a change of the source-drain current
This paper presents a new paradigm of potentiometric electrochemical sensing, which is based on the electric potential difference between the solution analyte and a polarizable electrode
Summary
The majority of commercial wearable, continuous bioanalytes monitoring devices rely mostly on amperometric techniques [1]. Sensitive, sophisticated setup as well as noise shielding systems to reach an acceptable signal-to-noise ratio (SNR) Such sensors are generally less applicable for use as wearable devices, relying on a simple battery-operated wireless setup. Field-effect transistor (FET)–based biosensors, employing a potentiometric approach for electrochemical signal capture, have been extensively researched for label-free biomolecular sensing for different analytes and sensing applications [8] These potentiometric sensors benefit from well-established solid-state technologies, such as high sensitivity, miniaturization, low power consumption, and simplicity [9]. Most ISFETs and ChemFETs employ a reference electrode [17], limiting their miniaturization potential Such devices have been shown to detect redox activity via their reactive gate oxide surface [18]. The use of noble metal as gate electrode building material, on the other hand, should allow for a relatively fast and reversible electrochemical response
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