Virus-poly(3,4-ethylenedioxythiophene) composite films for impedance-based biosensing

Abstract

Composite films composed of poly(3,4-ethylenedioxythiophene), PEDOT, and the filamentous virus M13-K07 were prepared by electrooxidation of 3,4-ethylenedioxythiophene (EDOT) in aqueous solutions containing 8 nM of the virus at planar gold electrodes. These films were characterized using atomic force microscopy and scanning electron microscopy. The electrochemical impedance of virus-PEDOT films increases upon exposure to an antibody (p-Ab) that selectively binds to the M13 coat peptide. Exposure to p-Ab causes a shift in both real (Z(RE)) and imaginary (Z(IM)) impedance components across a broad range of frequencies from 50 Hz to 10 kHz. Within a narrower frequency range from 250 Hz to 5 kHz, the increase of the total impedance (Z(total)) with p-Ab concentration conforms to a Langmuir adsorption isotherm over the concentration range from from 6 to 66 nM, yielding a value for K(d) = 16.9 nM at 1000 Hz.

Figure 1

Electrodeposition of a virus-PEDOT composite film on gold. (a) Cyclic voltammograms at 50 mV/s in aqueous 12.5 mM LiClO₄, 2.0 mM EDOT and 8 nM M13 bacteriophage. The films studied in Figure 2 were prepared using ten deposition cycles on a 3 mm diameter gold electrode. (b) Plot of virus-PEDOT film thickness, measured on photolithographically patterned films using AFM, as a function of the number of deposition cycles. (c,d) SEM images showing the topography of a PEDOT film (c) and a virus-PEDOT-film (d). Both films were prepared using ten deposition cycles. (e,f) AFM images of a PEDOT film (e) and a virus-PEDOT composite film (f), both prepared using ten deposition cycles. (f). A representative line scan from each of these AFM images is shown at bottom. The rms roughness of the two films was ≈10 nm and ≈400 nm, respectively.

Figure 2

(a) Nyquist plots for a phage-PEDOT film (thickness ≈1.2 μm) immersed in PBF buffer (black) and PBF buffer + [p-Ab] = 66 nM (green) and PBF buffer + [n-Ab] = 66 nM (red). Five impedance measurements in each solution were averaged to obtain each curve; error bars, obscured by the data points in some cases, indicate ±1σ. (b) Plot of the signal-to-noise ratio, defined as ΔZ_tot/σ, versus frequency. [p-Ab] = [n-Ab] = 66 nM. (c,d) Log-log plots of ΔZ_tot versus frequency for a series of p-Ab (c) and n-Ab (d) concentrations ranging from 4 nM to 66 nM. In (d), the yellow interval indicates frequencies where ΔZ_tot increases monotonically with [p-Ab]. (e). χ² versus frequency for the fit of a Langmuir isotherm to the ΔZ_tot versus [p-Ab] data shown in (d). The minimum of this plot, corresponding to the best fit, is observed at 2-3 kHz. (f) Plot of ΔZ_total versus concentration for a PEDOT film containing M13, labeled (+) virus, and a second film containing no virus, labeled (−) virus. These two films were exposed to both n-Ab and p-Ab at the indicated concentrations. Impedance data for p-Ab exposures at the virus-PEDOT composite film are fitted with a Langmuir isotherm.

Scheme 1

Polymerization of (a) EDOT and (b) EDOT with M13 virus incorporation.