The separate fields of conducting polymer-based electrochemical sensors and virus-based molecular recognition offer numerous advantages for biosensing. Grafting M13 bacteriophage into an array of poly (3,4-ethylenedioxythiophene) (PEDOT) nanowires generated hybrids of conducting polymers and viruses. The virus incorporation into the polymeric backbone of PEDOT occurs during electropolymerization via lithographically patterned nanowire electrodeposition (LPNE). The resultant arrays of virus-PEDOT nanowires enable real-time, reagent-free electrochemical biosensing of analytes in physiologically relevant buffers.

The sensitive detection of cancer biomarkers in urine could revolutionize cancer diagnosis and treatment. Such detectors must be inexpensive, easy to interpret, and sensitive. This report describes a bioaffinity matrix of viruses integrated into PEDOT films for electrochemical sensing of prostate specific membrane antigen (PSMA), a prostate cancer biomarker. High sensitivity to PSMA resulted from synergistic action by two different ligands to PSMA on the same phage particle. One ligand was genetically encoded, and the secondary recognition ligand was chemically synthesized to wrap around the phage. The dual ligands result in a bidentate binder with high copy, dense ligand display for enhanced PSMA detection through a chelate-based, avidity effect. Biosensing with virus-PEDOT films provides a 100 pM limit of detection for PSMA in synthetic urine without requiring enzymatic or other amplification.

We demonstrate the de novo fabrication of a biosensor, based upon virus-containing PEDOT nanowires, that detects prostate-specific membrane antigen (PSMA). This development process occurs in three phases: 1) isolation of a M13 virus with a displayed polypeptide receptor, from a library of ≈1011 phage-displayed peptides, which binds PSMA with high affinity and selectivity, 2) microfabrication of poly(3,4-ethylene-dioxythiophene) (PEDOT) nanowires that entrain these virus particles using the lithographically-patterned nanowire electrodeposition (LPNE) method, and, 3) electrical detection of the PSMA in high ionic strength (150 mM salt) media, including synthetic urine, using an array of virus-PEDOT nanowires using the electrical resistance of these nanowires for transduction. The electrical resistance of an array of these nanowires increases linearly with the PSMA concentration from 20 nM to 120 nM in high ionic strength PBF buffer, yielding a LOD for PSMA of 56 nM.

Composite films composed of poly(3,4-ethylenedioxythiophene), PEDOT, and the filamentous virus M13K07 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 (ZRE) and imaginary (ZIM) 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 (Ztotal) with p-Ab concentration conforms to a Langmuir adsorption isotherm over the concentration range from from 6 to 66 nM, yielding a value for Kd = 16.9 nM at 1000 Hz.

Virus-poly(3,4-ethylenedioxythiophene) (virus-PEDOT) biocomposite films are prepared by electropolymerizing 3,4-ethylenedioxythiophene (EDOT) in aqueous electrolytes containing 12 mM LiClO4 and the bacteriophage M13. The concentration of virus in these solutions, [virus]soln, is varied from 3 nM to 15 nM. A quartz crystal microbalance is used to directly measure the total mass of the biocomposite film during its electrodeposition. In combination with a measurement of the electrodeposition charge, the mass of the virus incorporated into the film is calculated. These data show that concentration of the M13 within the electropolymerized film, [virus]film, increases linearly with [virus]soln. The incorporation of virus particles into the PEDOT film from solution is efficient, resulting in a concentration ratio: [virus]film:[virus]soln ≈450. Virus incorporation into the PEDOT causes roughening of the film topography that is observed using scanning electron microscopy and atomic force microscopy (AFM). The electrical conductivity of the virus-PEDOT film, measured perpendicular to the plane of the film using conductive tip AFM, decreases linearly with virus loading, from 270 μS/cm for pure PE-DOT films to 50 μS/cm for films containing 100 μM virus. The presence on the virus surface of displayed affinity peptides did not significantly influence the efficiency of incorporation into virus-PEDOT biocomposite films.