464410 A Tunable Ionic Transistor/Diode Molecular Sensor with Adjustable Sensitivity and Dynamic Range

Tuesday, November 15, 2016: 2:00 PM
Embarcadero (Parc 55 San Francisco)
Gongchen Sun, Satyajyoti Senapati and Hsueh-Chia Chang, Chemical & Biomolecular Engineering, University of Notre Dame, Notre Dame, IN

We report a new control ionic circuit for a membrane biosensor developed in our lab [Slouka et al, Annu Rev Anal Chem, 7, 317 (2014)]. The ionic circuit is designed such that the sensitivity and dynamic range of the membrane sensor can be tuned by a gating voltage, both over several orders of magnitude.

The principle behind the membrane sensor is based on ion depletion and charge polarization phenomena that occur at one ion-selective membrane surface when an electric field is applied across it, thus producing the well-known limiting and overlimiting currents. These two latter regimes of the I-V curve occur at much higher voltages (1-10 V) than the traditional electrochemical sensors that function at the redox potentials, thus offering much better signal-to-noise ratio. The biomolecular targets, captured by probes functionalized onto the membrane surface, are counterions. Their immobility after hybridization with the probes impedes the depletion action and produces an effective bipolar membrane, thus significantly delay the development of electroconvection vortices or enhance water splitting, the two key phenomena responsible for the overlimiting current [Slouka et al, Langmuir, 29, 8275-8283 (2013)].

The sensitivity of the membrane sensor is determined by the lowest fraction of hybridized probes that can be detected by the voltage shift in the overlimiting current regime. Scaling down the membrane area can significantly lower the detection limit but may also limit the dynamic range. We hence design an ionic circuit that can amplify this voltage drop with proper impedance matching. A key feature of the signal amplifying ionic circuit component is an ionic transistor, which allows a small normal gating voltage signal to control a large draining ionic cross current [Sun et al, LabChip,16, 1171-1177 (2016)]. The amplification in the voltage has been shown to exceed 10-fold. We use a bipolar diode membrane design with different external ionic circuits such that the amplification factor can be tuned by the gating voltage, thus effectively shifting both the sensitivity and dynamic range of the sensor. We are testing this ionic circuit design on nucleic acid sensing and expect to achieve a dynamic range of fM to mM with the same membrane chip.

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