Research ArticleAPPLIED SCIENCES AND ENGINEERING

Biosensing near the neutrality point of graphene

See allHide authors and affiliations

Science Advances  25 Oct 2017:
Vol. 3, no. 10, e1701247
DOI: 10.1126/sciadv.1701247
  • Fig. 1 Near–neutrality point operation and conventional GFET.

    (A) Schematic presentation of near–neutrality point operation of an electrolyte-gated GFET device. (B) The transfer curve I(Vref) of the GFET-II (black circles, after electrochemical cleaning) and the corresponding parabolic fitting (blue line) around the neutrality point and the linear fit (gray lines) away from the neutrality point. The working principle of the electrolyte-gated GFET operated near the neutrality point is also illustrated in the inset diagram: The output current contains both the second harmonic component 0.5a0Aac2 cos 4πft (IOUT at frequency 2f) and the fundamental component (IOUT at frequency f) 2a0AacΔVref sin 2πft. All recorded in 1 mM PBS buffer solution. (C) Schematic presentation of a conventional electrolyte-gated GFET device. (D) Upper panel: Sheet conductance mapping of the GFET-I during electrochemical cleaning cycles with an operational window of Vref = (−0.4 V, 0.6 V). Lower panel: G(Vref) curves of the GFET-I before cleaning (gray line), during the first (green line and arrow) and the fifth (blue line and arrow) cleaning cycle, and after 10 times continuous cleaning cycles (red line), which start to show a rather symmetric ambipolar behavior with field-effect mobilities of ~1100 cm2/Vs for both hole and electron carriers.

  • Fig. 2 1/f noise performance of electrolyte-gated GFET devices.

    (A) PSD SV(f) of GFET-I at different liquid-gate voltages Vref = −0.3, −0.1, 0.1, 0.3, and 0.6 V tested immediately after an initial cleaning. (B) G(Vref) curves (to the left axis) and the corresponding “V”-shaped normalized PSD SV/VDS2 (at f = 10 Hz with a bandwidth of 1 Hz, to the right axis) for the GFET-I after moderate electrochemical cleaning. (C) G(Vref) curves (to the left axis) and the corresponding “M”-shaped normalized PSD SV/VSD2 (at f = 10 Hz with a bandwidth of 1 Hz, to the right axis) for another GFET-III (also fabricated on a SiO2/Si substrate) after moderate electrochemical cleaning.

  • Fig. 3 Low-noise graphene transistors operated near the neutrality point.

    (A) Measured sensing response (red bars), root mean square (RMS) current noise level (gray bars), and the corresponding SNR (black circles) close to the neutrality point as a function of the amplitude Aac of the gate voltage swing. The sensing current was monitored in response to a 200-μV gate voltage change after surface refreshment with a moderate electrolysis window (−0.4 V, 0.8 V). A maximum SNR of 33 was achieved at Ain = 70.7 mV. Its corresponding responses to a 200-μV step gate voltage change versus time is shown in (B). (C and D) Comparison of the GFET-II in response to the 200-μV step gate voltage change when operated in conventional mode and near the neutrality point, respectively.

  • Fig. 4 DNA sensing near the neutrality point of graphene.

    (A) Upper panel: Optical micrographs of GFET-II. The left image shows the openings defined by a 1-μm-thick SU-8 photoresist. Scale bar, 200 μm. The right image is a zoom of the SU-8 liquid channel across a graphene flake (white dashed lines in between the two Pd electrodes). Scale bar, 20 μm. Lower panel: A 5 × 10 GFET device array fabricated on a SiO2/Si substrate. (B) Schematic illustration of negatively charged complementary ssDNA molecules bind to pPNA molecules that are noncovalently anchored on the graphene surface. Nonspecific binding of biomolecules directly on the GFET was prevented by self-assembling Tween 20 on the graphene surface. (C) Changes in ΔI of the graphene sensor in a conventional GFET measurement scheme upon the self-assembly processes of pPNA and Tween 20 with concentrations of 1 μM and 0.05 wt %, respectively. Current noise, 0.22 nA. (D) Changes in If of the graphene sensor operated near its neutrality point versus time upon the introduction of 1 nM and 10 pM (inset) fully complementary ssDNA. Current noise, 0.1 nA. All were tested in 1 mM PBS buffer solution.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/10/e1701247/DC1

    section S1. Single-crystal monolayer CVD graphene

    section S2. Electrochemical cleaning of graphene: Basic principle

    section S3. Noise characterizations

    section S4. SNR in conventional operated GFETs

    section S5. pPNA-DNA hybridization: 1-base mismatched

    fig. S1. High-quality single-crystal CVD graphene.

    fig. S2. Schematic presentation of in situ electrochemical cleaning of an electrolyte-gated GFET device.

    fig. S3. Electronic noise characterization for graphene on SiO2/Si substrate.

    fig. S4. Electronic noise characterization for graphene on Si3N4/Si and sapphire substrates.

    fig. S5. SNR in conventional operated GFET devices.

    fig. S6. No obvious changes in If of the graphene biosensor versus time upon the introduction of 10 pM 1-base–mismatched ssDNA in 1 mM PBS solution.

    References (3436)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Single-crystal monolayer CVD graphene
    • section S2. Electrochemical cleaning of graphene: Basic principle
    • section S3. Noise characterizations
    • section S4. SNR in conventional operated GFETs
    • section S5. pPNA-DNA hybridization: 1-base mismatched
    • fig. S1. High-quality single-crystal CVD graphene.
    • fig. S2. Schematic presentation of in situ electrochemical cleaning of an electrolyte-gated GFET device.
    • fig. S3. Electronic noise characterization for graphene on SiO2/Si substrate.
    • fig. S4. Electronic noise characterization for graphene on Si3N4/Si and sapphire substrates.
    • fig. S5. SNR in conventional operated GFET devices.
    • fig. S6. No obvious changes in If of the graphene biosensor versus time upon the introduction of 10 pM 1-base–mismatched ssDNA in 1 mM PBS solution.
    • References (34–36)

    Download PDF

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article