Disposable Strip Biosensor for Visual Detection of Hg²⁺ Based on Hg²⁺-Triggered Toehold Binding and Exonuclease III-Assisted Signal Amplification

A disposable strip biosensor for the visual detection of Hg²⁺ in aqueous solution has been constructed on the basis of Hg²⁺-triggered toehold binding and exonuclease III (Exo III)-assisted signal amplification. Thymine-thymine (T-T) mismatches in the toehold domains can serve as specific recognition elements for Hg²⁺ binding with the help of T-Hg²⁺-T base pairs to initiate toehold-mediated strand displacement reaction. Exo III-catalyzed target recycling strategy is introduced to improve the sensitivity. Using gold nanoparticles as a tracer, the output signals can be directly observed by the naked eye. The assay is ultrasensitive, enabling the visual detection of trace amounts of Hg²⁺ as low as 1 pM without instrumentation. This sensing system also displays remarkable specificity to Hg²⁺ against other possible competing ions. This sensor is robust and can be applied to the reliable monitoring of spiked Hg²⁺ in environmental water samples with good recovery and accuracy. With the advantages of cost-effectiveness, simplicity, portability, and convenience, the disposable strip biosensor will be a promising candidate for point-of-use monitoring of Hg²⁺ in environmental and biological samples

Rapid Measurement of Microbial Extracellular Respiration Ability Using a High-Throughput Colorimetric Assay

Microbial extracellular respiration (MER) involves the transfer of electrons to extracellular substrates and has significant environmental implications. Conventional methods for MER ability determination are reagent- and time-consuming, have a low throughput, or require noncommercial instruments. In this study, a plate-based colorimetric assay is proposed to measure MER ability. This method utilizes the peroxidase activity of the key components (multi-heme <i>c</i>-type cytochromes) of the extracellular electron-transfer network. The bacterial intrinsic peroxidase-catalyzed oxidation of chromogen (e.g., tetramethylbenzidine) resulted in a measurable color change correlated with the MER ability of the tested microorganisms. The results of the proposed colorimetric assay correspond well with those of traditional methods, such as the dissimilatory Fe­(III) reduction method (Spearman’s ρ of 0.946; <i>P</i> < 0.01) and the electricity generation method (Spearman’s ρ of 0.893; <i>P</i> < 0.01). The proposed method allows researchers to identify extracellular respiring bacteria within several minutes and to measure their MER ability quantitatively by a plate-based assay

Table_1_Transcriptomic, Proteomic, and Bioelectrochemical Characterization of an Exoelectrogen Geobacter soli Grown With Different Electron Acceptors.xlsx

<p>The ability of Geobacter species to transfer electrons outside cells enables them to play an important role in biogeochemical and bioenergy processes. Our knowledge of the extracellular electron transfer (EET) process in the genus Geobacter is mainly from the study of G. sulfurreducens, and in order to fully investigate the EET mechanisms in the genus Geobacter, other Geobacter species should also be considered. This study focused on the EET of Geobacter soli GSS01, which exhibited a capability of reducing insoluble Fe(III) oxides and generating electrical current comparable with G. sulfurreducens PCA. Electrochemical characterization, including cyclic voltammetry, differential pulse voltammetry, and electrochemical in situ FTIR spectra, revealed that different redox proteins contributed to the electrochemical behaviors of G. soli and G. sulfurreducens. Based on comparative transcriptomic and proteomic analyses, OmcS was the most upregulated protein in both G. soli and G. sulfurreducens cells grown with insoluble Fe(III) oxides vs. soluble electron acceptor. However, the proteins including OmcE and PilA that were previously reported as being important for EET in G. sulfurreducens were downregulated or unchanged in G. soli cells grown with insoluble electron acceptors vs. soluble electron acceptor, and many proteins that were upregulated in G. soli cells grown with insoluble electron acceptors vs. soluble electron acceptor, such as OmcN, are not important for EET in G. sulfurreducens. We also identified 30 differentially expressed small RNAs (sRNAs) in G. soli cells grown with different acceptors. Taken together, these findings help to understand the versatile EET mechanisms that exist in the genus Geobacter and point to the possibility of sRNA in modulating EET gene expression.</p

Table_3_Transcriptomic, Proteomic, and Bioelectrochemical Characterization of an Exoelectrogen Geobacter soli Grown With Different Electron Acceptors.pdf

<p>The ability of Geobacter species to transfer electrons outside cells enables them to play an important role in biogeochemical and bioenergy processes. Our knowledge of the extracellular electron transfer (EET) process in the genus Geobacter is mainly from the study of G. sulfurreducens, and in order to fully investigate the EET mechanisms in the genus Geobacter, other Geobacter species should also be considered. This study focused on the EET of Geobacter soli GSS01, which exhibited a capability of reducing insoluble Fe(III) oxides and generating electrical current comparable with G. sulfurreducens PCA. Electrochemical characterization, including cyclic voltammetry, differential pulse voltammetry, and electrochemical in situ FTIR spectra, revealed that different redox proteins contributed to the electrochemical behaviors of G. soli and G. sulfurreducens. Based on comparative transcriptomic and proteomic analyses, OmcS was the most upregulated protein in both G. soli and G. sulfurreducens cells grown with insoluble Fe(III) oxides vs. soluble electron acceptor. However, the proteins including OmcE and PilA that were previously reported as being important for EET in G. sulfurreducens were downregulated or unchanged in G. soli cells grown with insoluble electron acceptors vs. soluble electron acceptor, and many proteins that were upregulated in G. soli cells grown with insoluble electron acceptors vs. soluble electron acceptor, such as OmcN, are not important for EET in G. sulfurreducens. We also identified 30 differentially expressed small RNAs (sRNAs) in G. soli cells grown with different acceptors. Taken together, these findings help to understand the versatile EET mechanisms that exist in the genus Geobacter and point to the possibility of sRNA in modulating EET gene expression.</p

Table_4_Transcriptomic, Proteomic, and Bioelectrochemical Characterization of an Exoelectrogen Geobacter soli Grown With Different Electron Acceptors.xlsx

<p>The ability of Geobacter species to transfer electrons outside cells enables them to play an important role in biogeochemical and bioenergy processes. Our knowledge of the extracellular electron transfer (EET) process in the genus Geobacter is mainly from the study of G. sulfurreducens, and in order to fully investigate the EET mechanisms in the genus Geobacter, other Geobacter species should also be considered. This study focused on the EET of Geobacter soli GSS01, which exhibited a capability of reducing insoluble Fe(III) oxides and generating electrical current comparable with G. sulfurreducens PCA. Electrochemical characterization, including cyclic voltammetry, differential pulse voltammetry, and electrochemical in situ FTIR spectra, revealed that different redox proteins contributed to the electrochemical behaviors of G. soli and G. sulfurreducens. Based on comparative transcriptomic and proteomic analyses, OmcS was the most upregulated protein in both G. soli and G. sulfurreducens cells grown with insoluble Fe(III) oxides vs. soluble electron acceptor. However, the proteins including OmcE and PilA that were previously reported as being important for EET in G. sulfurreducens were downregulated or unchanged in G. soli cells grown with insoluble electron acceptors vs. soluble electron acceptor, and many proteins that were upregulated in G. soli cells grown with insoluble electron acceptors vs. soluble electron acceptor, such as OmcN, are not important for EET in G. sulfurreducens. We also identified 30 differentially expressed small RNAs (sRNAs) in G. soli cells grown with different acceptors. Taken together, these findings help to understand the versatile EET mechanisms that exist in the genus Geobacter and point to the possibility of sRNA in modulating EET gene expression.</p