Research ArticleMATERIALS SCIENCE

Direct metabolite detection with an n-type accumulation mode organic electrochemical transistor

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Science Advances  22 Jun 2018:
Vol. 4, no. 6, eaat0911
DOI: 10.1126/sciadv.aat0911
  • Fig. 1 Mediator and reference electrode–free sensing of lactate with an accumulation mode OECT based on an n-type OMC.

    (A) Chemical structure of the n-type copolymer P-90. (B) Schematic of the OECT [gate dimensions, 500 μm2; channel dimensions, 10 μm (length) × 100 μm (width) × ~100 nm (thickness)]. (C) Schematic of the OECT biosensor showing the presumed interactions between the enzyme, LOx, and the n-type channel (note also that the gate electrode is exposed to LOx and lactate). (D) Real-time response of the OECT (source-drain current, ID, as a function of time) as successive amounts of lactate are added to the PBS solution containing the enzyme, LOx, and the corresponding calibration curve in semilogarithmic scale. Arrows indicate the addition of lactate. After 10 mM lactate, the device is washed with PBS, and the output signal decreases back to its initial value. The insets represent the magnified response of the transistor to low amounts of the analyte (10 to 500 μM).

  • Fig. 2 Investigating the interactions between the n-type polymer and the enzyme, which lead to efficient electrical communication.

    (A) QCM-D measurements showing the interactions between the enzyme and the polymer film in three stages: when the film is exposed to the electrolyte (PBS), when the enzyme is injected into the PBS solution (+LOx), and when the enzyme-exposed film is rinsed with PBS (Rinse). The mass of the film was calculated using a viscoelastic model. Three-dimensional AFM images (2 × 2 μm2) show the changes on the surface of the film during the three stages. (B) CV curve of the P-90 film cast on gold (Au)–coated glass substrate recorded in PBS (dashed black lines) and with LOx (black solid lines). The spectrum changes further upon addition of increasing concentrations of lactate into the solution because of the reaction with LOx. The scan rate is 50 mV s−1. (C) The changes in the UV-VIS-NIR spectrum of the P-90 film, cast on an indium tin oxide (ITO) substrate, in PBS solution containing the enzyme (black curve) and upon addition of 10 mM lactate (red curve). The curves are normalized to the absorbance value at 1000 nm where no changes occur during electrochemical switching (fig. S8). a.u., arbitrary units. (D) The number of charges generated by this film while a reduction potential (−0.5 V) was applied using an Ag/AgCl electrode immersed in the same solution as in (C). The red curve represents the current generated in the co-presence of lactate and LOx in the solution. The inset shows the same plot, this time in semilogarithmic scale, magnifying the current generated at low voltages.

  • Fig. 3 Elucidating the sensing mechanism and control over the sensor performance.

    (A) NR of the OECT to H2O2 (red triangles) and to lactate in the presence of LOx (black circles). The inset shows the sensitivity of the device to pH. The pH was adjusted using HCl and measured with an external pH electrode. The plot shows that the sensor cannot catalyze H2O2 oxidation and exhibits negligible response to changes in pH. Error bars represent the SD from four measurements on two devices. (B) The proposed mechanism of lactate sensing based on the direct ET from the enzyme to the n-type OMC. (C) Normalized calibration curves of the device operated under different biasing conditions at the gate electrode for a VD fixed at 0.7 V. The inset shows the response of the device to lactate, this time represented in linear scale, with the slope indicating the sensitivity of the device. (D) The distribution of electrolyte potential at the critical interfaces (gate/electrolyte and channel/electrolyte) in the presence of the enzymatic reaction under different relative biasing conditions.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaat0911/DC1

    fig. S1. The output and transfer characteristics of a typical all n-type polymer (P-90)–based OECT.

    fig. S2. Transfer curves of the OECT in the absence and presence of the enzymatic reaction.

    fig. S3. Calibration curve relating the NR of the device to a range of lactate concentrations.

    fig. S4. QCM-D response of the P-90–coated sensor immersed in PBS.

    fig. S5. AFM topography images of the P-90 film coated on Au substrate.

    fig. S6. The CV curve of the P-90 film before and after addition of the enzyme into the PBS solution and a scheme of bioelectrocatalytic reactions.

    fig. S7. The effect of pH on the CV curve of the P-90 film.

    fig. S8. The changes in the absorbance spectrum of the P-90 film during the electrochemical switch.

    fig. S9. The effect of air on the reaction of lactate with LOx-functionalized P-90.

    fig. S10. Sensitivity of the device to lactate and when operated under different biasing conditions at the channel and the gate.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. The output and transfer characteristics of a typical all n-type polymer (P-90)–based OECT.
    • fig. S2. Transfer curves of the OECT in the absence and presence of the enzymatic reaction.
    • fig. S3. Calibration curve relating the NR of the device to a range of lactate concentrations.
    • fig. S4. QCM-D response of the P-90–coated sensor immersed in PBS.
    • fig. S5. AFM topography images of the P-90 film coated on Au substrate.
    • fig. S6. The CV curve of the P-90 film before and after addition of the enzyme into the PBS solution and a scheme of bioelectrocatalytic reactions.
    • fig. S7. The effect of pH on the CV curve of the P-90 film.
    • fig. S8. The changes in the absorbance spectrum of the P-90 film during the electrochemical switch.
    • fig. S9. The effect of air on the reaction of lactate with LOx-functionalized P-90.
    • fig. S10. Sensitivity of the device to lactate and when operated under different biasing conditions at the channel and the gate.

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