Photoactive and conductive biohybrid films by polymerization of pyrrole through voids in photosystem I multilayer films

The combination of conducting polymers with electro- and photoactive proteins into thin films holds promise for advanced energy conversion materials and devices. The emerging field of protein electronics requires conductive soft materials in a composite with electrically insulating proteins. The electropolymerization of pyrrole through voids in a drop-casted photosystem I (PSI) multilayer film enables the straightforward fabrication of photoactive and conductive biohybrid films. The rate of polypyrrole (PPy) growth is reduced by the presence of the PSI film but is insensitive to its thickness, suggesting that rapid diffusion of pyrrole through the voids within the PSI film enables initiation at vacant areas on the gold surface. The base thickness of the composite tends to increase with time, as PPy chains propagate through and beyond the PSI film, coalescing to exhibit a tubule-like morphology as observed by scanning electron microscopy. Increasing amounts of PPy greatly increase the capacitance of the composite films in a manner almost identical to that of pure PPy films grown from unmodified gold, consistent with a high polymer/aqueous interfacial area and a conductive composite film. While PPy is not photoactive here, all composite films, including those with large amounts of PPy, exhibit photocurrents when irradiated by white light in the presence of redox mediator species. Optimization of the Py electropolymerization time is necessary, as increasing amounts of PPy lead to decreased photocurrent density due to a combination of light absorbance by the polymer and reduced accessibility of redox species to active PSI sites.

1 Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN 37235-1604 2 Department of Chemistry, Vanderbilt University, Nashville, TN 37235-1822 * Author to whom correspondence should be addressed.For PPy grown on PSI/Au, the initial PSI film is very rough, and as PPy polymerization proceeds to higher levels of charge, the base thickness increases while the high level of roughness remains.At the highest charge, comparing profiles for PPy on Au versus that on PSI/Au, the roughness is apparently a combination of that due to PSI and PPy.

Cross-Sectional Scanning Electron Microscopy (SEM).
To provide additional information on the morphology of the films, Figure S2 shows cross-sectional SEM images of a pure PSI film and a PSI-PPy composite film where the polymer was deposited at 70 mC/cm 2 charge density.Both films are rough, but the composite film is significantly thicker due to the loading of the PPy.We were unable to distinguish PPy or PSI regions of the film through either these images or energydispersive spectroscopy.
Fitted Parameters from Electrochemical Impedance Spectroscopy (EIS).The electrochemical impedance spectra in Figures 6a and 6b of the main text were fit with the equivalent circuit in the inset of Figure 6c to determine electrochemical parameters.Table S1 shows double layer capacitance (Cdl), charge transfer resistance (Rct), and the Warburg coefficient (s) for the spectra in Figures 6a and 6b.Reflectance UV-Vis Spectroscopy.Figure S4 shows reflectance uv-vis spectra for gold substrates containing a PSI film and an electrodeposited PPy film at 270 mC/cm 2 of charge, as well as a PSI-coated gold substate with an electrodeposited PPy film at the same charge density.PSI shows absorbance peaks around 430 nm and 670 nm due to a-chlorophylls in the protein.PPy alone absorbs broadly across most of the visible region, thus suggesting that the polymer absorbs light that could be used by the protein when the two components are combined in the composite.
For the PSI-PPy composite, we observe elevated light absorbance from 480 -730 nm that could be attributed to component absorbances from both PPy and PSI.

Figure S1 .
Figure S1.Surface profiles for Ppy grown on Au and PSI/Au…

Figure S2 .
Figure S2.Cross-sectional SEM images of (a) a PSI film, and (b) a composite PSI-PPy film at 70 mC/cm 2 charge density.White arrows indicate the approximate floor of the film.

Figure S4 .
Figure S4.Reflectance UV-Vis spectra of PSI, PPy, and a composite PSI-PPy film on Au. 210 mC/cm 2 of polymer was deposited for both the PPy and composite films.

Table S1
. Electrochemical parameters of Ppy films grown to the charge densities indicated onto Au and PSI/Au… Figure S3.Sample PCA of a PSI film and composite PSI-PPy films… Figure S4.Reflectance UV-Vis spectra of PSI, PPy, and a composite PSI-PPy film on Au…

Table S1 .
Electrochemical parameters of Ppy films grown to the charge densities indicated onto Au and PSI/Au.Parameters were determined by fitting the impedance spectra in Figure6to the equivalent circuit in Figure6c.† Warburg coefficient