Photosynthetic
semiconductor biohybrids (PSBs) convert light energy
to chemical energy through photo-driven charge transfer from nanocrystals
to microorganisms that perform bioreactions of interest. Initial proof-of-concept
PSB studies with an emphasis on enhanced CO2 conversion
have been encouraging; however, bringing the broad prospects of PSBs
to fruition is contingent on establishing a firm fundamental understanding
of underlying interfacial charge transfer processes. We introduce
a bioelectronic platform that reduces the complexity of PSBs by focusing
explicitly on interactions between colloidal quantum dots (QDs), microbial
outer membranes, and native, small-molecule redox mediators. Our model
platform employs a standard three-electrode electrochemical cell with
supported outer membranes of Pseudomonas aeruginosa, pyocyanin redox mediators, and semiconducting CdSe QDs dispersed
in an aqueous electrolyte. We present a comprehensive electrochemical
analysis of this platform via electrochemical impedance spectroscopy
(EIS), cyclic voltammetry (CV), and chronoamperometry (CA). EIS reveals
the formation and electronic properties of supported outer membrane
films. CV reveals the electrochemically active surface area of P. aeruginosa outer membranes and that pyocyanin
is the sole species that performs redox with these outer membranes
under sweeping applied potential. CA demonstrates that photoexcited
charge transfer in this system is driven by the reduction of pyocyanin
at the QD surface followed by diffusion of reduced pyocyanin through
the outer membrane. The broad applicability of this platform across
many bacterial species, QD architectures, and controlled environmental
conditions affords the possibility to define design principles for
future PSB systems to synergistically integrate concurrent advances
in genetically engineered organisms and inorganic nanomaterials.