Solar-driven carbon dioxide fixation using photosynthetic semiconductor bio-hybrids.

Solar-driven conversion of carbon dioxide to value-added carbon products is an ambitious objective of ongoing research efforts. However, high overpotential, low selectivity and poor CO2 mass transfer plague purely inorganic electrocatalysts. In this instance, we can consider a class of biological organisms that have evolved to achieve CO2 fixation. We can harness and combine the streamlined CO2 fixation pathways of these whole organisms with the exceptional ability of semiconducting nanomaterials to harvest solar energy. A novel nanomaterial-biological interface has been pioneered in which light-capturing cadmium sulfide nanoparticles reside within individual organisms essentially powering biological CO2 fixation by solar energy. In order to further develop the photosensitized organism platform, more biocompatible photosensitizers and cytoprotective strategies are required as well as elucidation of charge transfer mechanisms. Here, we discuss the ability of gold nanoclusters to photosensitize a model acetogen effectively and biocompatibly. Additionally, we present innovative materials including two-dimensional metal organic framework sheets and alginate hydrogels to shield photosensitized cells. Finally, we delve into original work using transient absorption spectroscopy to inform on charge transfer mechanisms

Physical Biology of the Materials-Microorganism Interface.

Future solar-to-chemical production will rely upon a deep understanding of the material-microorganism interface. Hybrid technologies, which combine inorganic semiconductor light harvesters with biological catalysis to transform light, air, and water into chemicals, already demonstrate a wide product scope and energy efficiencies surpassing that of natural photosynthesis. But optimization to economic competitiveness and fundamental curiosity beg for answers to two basic questions: (1) how do materials transfer energy and charge to microorganisms, and (2) how do we design for bio- and chemocompatibility between these seemingly unnatural partners? This Perspective highlights the state-of-the-art and outlines future research paths to inform the cadre of spectroscopists, electrochemists, bioinorganic chemists, material scientists, and biologists who will ultimately solve these mysteries

Bacteria photosensitized by intracellular gold nanoclusters for solar fuel production.

The demand for renewable and sustainable fuel has prompted the rapid development of advanced nanotechnologies to effectively harness solar power. The construction of photosynthetic biohybrid systems (PBSs) aims to link preassembled biosynthetic pathways with inorganic light absorbers. This strategy inherits both the high light-harvesting efficiency of solid-state semiconductors and the superior catalytic performance of whole-cell microorganisms. Here, we introduce an intracellular, biocompatible light absorber, in the form of gold nanoclusters (AuNCs), to circumvent the sluggish kinetics of electron transfer for existing PBSs. Translocation of these AuNCs into non-photosynthetic bacteria enables photosynthesis of acetic acid from CO2. The AuNCs also serve as inhibitors of reactive oxygen species (ROS) to maintain high bacterium viability. With the dual advantages of light absorption and biocompatibility, this new generation of PBS can efficiently harvest sunlight and transfer photogenerated electrons to cellular metabolism, realizing CO2 fixation continuously over several days

Roadmap on semiconductor-cell biointerfaces.

This roadmap outlines the role semiconductor-based materials play in understanding the complex biophysical dynamics at multiple length scales, as well as the design and implementation of next-generation electronic, optoelectronic, and mechanical devices for biointerfaces. The roadmap emphasizes the advantages of semiconductor building blocks in interfacing, monitoring, and manipulating the activity of biological components, and discusses the possibility of using active semiconductor-cell interfaces for discovering new signaling processes in the biological world

Abiotic sugar synthesis from CO2 electrolysis

CO2 valorization is aimed at converting waste CO2 to value-added products. While steady progress has been achieved through diverse catalytic strategies, including CO2 electrosynthesis, CO2 thermocatalysis, and biological CO2 fixation, each of these approaches have distinct limitations. Inorganic catalysts only enable synthesis beyond C2 and C3 products with poor selectivity and with a high energy requirement. Meanwhile, although biological organisms can selectively produce complex products from CO2, their slow autotrophic metabolism limits their industrial feasibility. Here, we present an abiotic approach leveraging electrochemical and thermochemical catalysis to complete the conversion of CO2 to life-sustaining carbohydrate sugars akin to photosynthesis. CO2 was electrochemically converted to glycolaldehyde and formaldehyde using copper nanoparticles and boron-doped diamond cathodes, respectively. CO2-derived glycolaldehyde then served as the key autocatalyst for the formose reaction, where glycolaldehyde and formaldehyde combined in the presence of an alkaline earth metal catalyst to form a variety of C4 - C8 sugars, including glucose. In turn, these sugars were used as a feedstock for fast-growing and genetically modifiable Escherichia coli. Altogether, we have assembled a platform that pushes the boundaries of product complexity achievable from CO2 conversion while demonstrating CO2 integration into life-sustaining sugars

Miniaturized Antimicrobial Susceptibility Test by Combining Concentration Gradient Generation and Rapid Cell Culturing

Effective treatment of bacterial infection relies on timely diagnosis and proper prescription of antibiotic drugs. The antimicrobial susceptibility test (AST) is one of the most crucial experimental procedures, providing the baseline information for choosing effective antibiotic agents and their dosages. Conventional methods, however, require long incubation times or significant instrumentation costs to obtain test results. We propose a lab-on-a-chip approach to perform AST in a simple, economic, and rapid manner. Our assay platform miniaturizes the standard broth microdilution method on a microfluidic device (20 × 20 mm) that generates an antibiotic concentration gradient and delivers antibiotic-containing culture media to eight 30-nL chambers for cell culture. When tested with 20 μL samples of a model bacterial strain (E. coli ATCC 25922) treated with ampicillin or streptomycin, our method allows for the determination of minimum inhibitory concentrations consistent with the microdilution test in three hours, which is almost a factor of ten more rapid than the standard method

Enhancing Biohybrid CO2 to Multicarbon Reduction via Adapted Whole-Cell Catalysts.

Catalytic CO2 conversion to renewable fuel is of utmost importance to establish a carbon-neutral society. Bioelectrochemical CO2 reduction, in which a solid cathode interfaces with CO2-reducing bacteria, represents a promising approach for renewable and sustainable fuel production. The rational design of biocatalysts in the biohybrid system is imperative to effectively reduce CO2 into valuable chemicals. Here, we introduce methanol adapted Sporomusa ovata (S. ovata) to enhance the slow metabolic activity of wild-type microorganisms to our semiconductive silicon nanowires (Si NWs) array for efficient CO2 reduction. The adapted whole-cell catalysts enable an enhancement of CO2 fixation with a superior faradaic efficiency on the poised Si NWs cathode. The synergy of the high-surface-area cathode and the adapted strain achieves a CO2-reducing current density of 0.88 ± 0.11 mA/cm2, which is 2.4-fold higher than the wild-type strain. This new generation of biohybrids using adapted S. ovata also decreases the charge transfer resistance at the cathodic interface and facilitates the faster charge transfer from the solid electrode to bacteria