Nanoscale membranes that chemically isolate and electronically wire up the abiotic/biotic interface

By electrochemically coupling microbial and abiotic catalysts, bioelectrochemical systems such as microbial electrolysis cells and microbial electrosynthesis systems synthesize energy-rich chemicals from energy-poor precursors with unmatched efficiency. However, to circumvent chemical incompatibilities between the microbial cells and inorganic materials that result in toxicity, corrosion, fouling, and efficiency-degrading cross-reactions between oxidation and reduction environments, bioelectrochemical systems physically separate the microbial and inorganic catalysts by macroscopic distances, thus introducing ohmic losses, rendering these systems impractical at scale. Here we electrochemically couple an inorganic catalyst, a SnO2 anode, with a microbial catalyst, Shewanella oneidensis, via a 2-nm-thick silica membrane containing -CN and -NO2 functionalized p-oligo(phenylene vinylene) molecular wires. This membrane enables electron flow at 0.51 μA cm−2 from microbial catalysts to the inorganic anode, while blocking small molecule transport. Thus the modular architecture avoids chemical incompatibilities without ohmic losses and introduces an immense design space for scale up of bioelectrochemical systems.

After stirring for 1h, the mixture was acidified by 2N hydrochloric acid to generate a yellow precipitate, which was centrifuged and washed with ethyl acetate. A yellow solid was obtained after drying overnight. To completely transform carboxylate residue to acid, the yellow solid was dispersed in 10 mL dimethylformamide and 2N hydrochloric acid was added until the dark green suspension completely changed to yellow. 50 mL water was subsequently added for further precipitation. The precipitate was filtered, washed with water and dried, and identified as the S4 target product. Yield: 320 mg (31%). 1

S6
As shown by the comparison of the FT-IR traces (1) and (2) of Figure 3a, the only modes associated with the TMSA amine group that underwent significant red shifts upon anchoring are the NH 2 scissoring mode at 1643 cm -1 by 15 cm -1 and the CN stretch at 1303 cm -1 by 27 cm -1 , which is consistent with the change of environment of this group upon surface attachment 2,3 .
With all other modes unchanged, this indicates that the silyl aniline remained intact upon anchoring. To confirm attachment of PV3 to the TMSA anchor, we examined both solid PV3 with aniline end groups and PV3 attached to TMSA on Pt/SnO 2 by infrared spectroscopy and XPS as presented in Figure 3a traces (3) and (4) Figure 6A) indicates that the wire molecules possess predominantly S7 perpendicular orientation relative to the SnO 2 surface 4 .

Assignments of XPS spectra of embedded molecular wires
In addition to the 406.2 eV N 1s band of the nitro group observed upon attachment of the PV3 wire to TMSA anchored on Pt/SnO 2 (Figure 3b, trace (3)), two overlapping components at 399.69 eV (blue) and 399.44 eV (red) which arise from nitrile and amine groups 5 are seen, and a shoulder at 402.59 eV assigned to shake-up involving intramolecular charge transfer between the molecule π system (donor) and functional nitro groups (acceptor), or the PV3 π  π* transition 6 .
Ellipsometry shows that on top of the 4.7 nm SnO 2 layer is an organic layer that is 0.6 ± 0.25 nm thick, which corresponds to the TMSA height of 0.6 nm, consistent with perpendicular orientation relative to the surface. Taken together, these infrared and XPS analyses confirm that the two-step anchoring method results in the attachment of the intact wire molecules on the inorganic oxide material.

Supplementary Figures
Supplementary Figure 1