Microorganisms have tremendous capability in using small molecules (e.g., CO2, CH4, N2, glucose, etc.) to construct complex and high-value chemicals (e.g., biofuels, biopolymers, fertilizers, and drugs) or transforming pollutants (e.g., heavy metals, synthetic polymers). What underlies this capability are the enzymes that catalyze specific chemical transformations and whose catalytic powers are orchestrated within a cell. Most of these transformations require significant energy input. Many microorganisms have evolved to use sunlight through light-harvesting complexes and biological photosynthesis to drive such transformations. However, the overall photosynthetic efficiency of natural systems is low.
By contrast, inorganic materials, in particular semiconducting QDs are highly efficient, tunable, and stable light harvesters. However, QD surfaces are unable to catalyze complex chemical reactions. Taken together, these considerations set the stage for compelling potential synergies between microbes and QDs. Hybrid inorganic-microbial systems present a potentially transformative approach to combine the light-harvesting capability of inorganic semiconductors and the ability of microbes to orchestrate complex chemical transformations. While pioneering studies have successfully demonstrated the viability of this approach, they have also highlighted the underlying complexities related to understanding and controlling the nature of charge transport between the QD and the microbe. Future progress to bringing the prospects photosynthetic semiconductor biohybrids to fruition risk stagnation without a firm foundational understanding of the thermodynamic and kinetic parameters governing the QD-microbe charge transfer. We embrace this challenge as an opportunity to develop novel bioelectronic platforms to interface QDs with microbial cell membranes to systematically investigate fundamental charge transport pathways.
