Simulations to Aid in the Design of Microbes for Synthesis of Metallic Nanomaterials

Synthesis of Palladium Nanoparticles by Electrode-Respiring Geobacter sulfurreducens Biofilms

Electroactive microorganisms such as Geobacter sulfurreducens can couple organic electron donor oxidation to the respiration of electrode surfaces, colonizing them in the process. These microbes can also reduce soluble metal ions, such as soluble Pd, resulting in metallic nanoparticle (NP) synthesis. Such NPs are valuable catalysts for industrially relevant chemical production; however, their chemical and solid-state syntheses are often energy-intensive and result in hazardous byproducts. Utilizing electroactive microbes for precious metal NP synthesis has the advantage of operating under more sustainable conditions. By combining G. sulfurreducens's ability to colonize electrodes and synthesize NPs, we performed electrode cultivation ahead of biogenic Pd NP synthesis for the self-assembled fabrication of a cell-Pd biomaterial. G. sulfurreducens biofilms were grown in electrochemical reactors with added soluble Pd, and electrochemistry, spectroscopy, and electron microscopy were used to confirm (1) metabolic current production before and after Pd addition, (2) simultaneous electrode respiration and soluble Pd reduction over time, and (3) biofilm-localized Pd NP synthesis. Utilizing electroactive microbes for the controlled synthesis of NPs can enable the self-assembly of novel cell-nanoparticle biomaterials with unique electron transport and catalytic properties.

Utilizing a divalent metal ion transporter to control biogenic nanoparticle synthesis

Biogenic synthesis of inorganic nanomaterials has been demonstrated for both wild and engineered bacterial strains. In many systems the nucleation and growth of nanomaterials is poorly controlled and requires concentrations of heavy metals toxic to living cells. Here, we utilized the tools of synthetic biology to engineer a strain of Escherichia coli capable of synthesizing cadmium sulfide nanoparticles from low concentrations of reactants with control over the location of synthesis. Informed by simulations of bacterially-assisted nanoparticle synthesis, we created a strain of E. coli expressing a broad-spectrum divalent metal transporter, ZupT, and a synthetic CdS nucleating peptide. Expression of ZupT in the outer membrane and placement of the nucleating peptide in the periplasm focused synthesis within the periplasmic space and enabled sufficient nucleation and growth of nanoparticles at sub-toxic levels of the reactants. This strain synthesized internal CdS quantum dot nanoparticles with spherical morphology and an average diameter of approximately 3.3 nm.

ONE-SENTENCE SUMMARY

Expression of a metal ion transporter regulates synthesis of cadmium sulfide nanoparticles in bacteria.

Eye-Visible Oxygen Sensing via In-Situ Synthesizing Blue-Emitting Cu(I) Cluster in Red-Emitting COF: Characterization and Performance

Covalent organic frameworks (COFs) have shown virtues of well-defined and uniform pores with structural diversity, including the shape, size and even chemical nature of pores. These features are excellent for the application of O₂ gas optical sensors. In this paper, two oxygen probes based on halogen-bridged Cu cluster were in-situ synthesized in the micropores of COFs, to allow a uniform distribution. The resulting composite samples were characterized in detail to confirm the successful probe loading. The doping level was determined as ~22%. The halogen-bridged Cu clusters showed blue emission peaking at ~440 nm, while COF host showed red emission peaking at 630 nm. These halogen-bridged Cu clusters had long emissive lifetime of ~6.7 μs and high emission quantum yield of 0.30 in pure N₂ atmosphere. Given pure O₂ atmosphere, lifetime and quantum yield were quenched to 2.5 μs and 0.11, showing oxygen-sensing possibility. A linear oxygen-sensing calibration curve was observed, with sensitivity of 12.25, response time of 13 s and recovery time of 38 s. Sample emission color was changed from blue to red when testing atmosphere was changed from pure N₂ to pure O₂, which was detectable by eyes.