Gold/mercury amalgam (Au/Hg) microelectrodes with a diameter of 25 microm were developed for the detection of environmentally relevant analytes such as manganese and iron by scanning electrochemical microscopy (SECM), and applied to investigate the controlled dissolution of manganese carbonate (MnCO(3); rhodochrosite) in acidic conditions. Characterization of the amalgam electrode geometry via approach curves recorded during SECM experiments revealed Au/Hg microelectrodes with sphere cap geometry. Quantitative determination of Mn(2+) has been achieved by calibration of the Au/Hg microelectrode in bulk solution experiments. Subsequent SECM imaging experiments confirm the applicability of amalgam microelectrodes for imaging of Mn(2+) production during dissolution of MnCO(3) at pH 3.9. This study confirms feasibility and provides the fundamental basis of SECM imaging with amalgam microelectrodes to address biogeochemically relevant questions.

A detailed surface analytical study on the corrosion behavior of unprotected and diamond-like carbon (DLC)-coated mid-infrared (MIR) waveguides used in remote sensing applications at strongly oxidizing conditions is presented. High-quality DLC films, with a thickness of 100 nm serving as MIR-transparent corrosion barrier, have been produced at the surface of zinc selenide (ZnSe) attenuated total reflection waveguides via pulsed laser deposition techniques. IR microscopy and atomic force microscopy are applied to investigate the chemical inertness of DLC-based membranes against aqueous solutions of hydrogen peroxide. These stability studies show that uncoated ZnSe waveguides are subject to severe chemical surface modifications, while DLC-protected waveguides maintain their optical properties and chemical integrity. In situ studies on the corrosion behavior by a recently developed approach combining scanning electrochemical microscopy (SECM) with Au/Hg amalgam ultramicroelectrodes in a scanning stripping voltammetry experiment provides additional insight into the mechanisms of the corrosion process. It is demonstrated that the combination of surface analytical techniques and, in particular, the innovative application of SECM with amalgam electrodes provides superior information on corrosion processes at the surface of optical waveguides. This detailed study confirms the efficiency of protective DLC coatings deposited onto IR-transparent optical waveguides, rendering this novel concept ideal for sensing applications in harsh environments.

1IntroductionMicrobial metalr espiration is centralt oawide variety of environmentally relevant processes including biogeochemical cycling of metals,t race elements and phosphate, degradation of natural and contaminanto rganic matter, weathering of clays,a nd biomineralization, e.g.,o fm agnetite [1][2][3].I na ddition, microbial metal respiration has recently receiveda ttention as an attractive alternative strategyf or the production of electricity in microbial fuel cells [4-10],a nd for in-situ remediation of subsurface environments contaminated with toxic metals (e.g.,c hromium and mercury), and radionuclides (e.g.,u ranium and technetium) [11][12][13][14][15].Compared to respiratory processesc arried out by other bacteria (i.e., aerobic respiration, denitrification,s ulfate reduction, methanogenesis) [16][17][18][19],m etal-respiring bacteria are required to respire anaerobically on electron acceptorsf ound largelyi nc rystalline form or as amorphous (oxy)hydroxide particles,w hich are presumably unable to contact inner membrane (IM)-localized electron transport systems. To overcomet his problem, Fe(III)-and Mn(IV)respiring bacteria take advantage of novel respiratory strategies not foundi no ther gram-negative bacteria that respire on soluble electrona cceptors such as O 2 ,N O 3 À , and SO 4 2À .[19] These strategies include (i)d irect enzymatic reduction of solid Fe(III)-and Mn(IV)-oxides via outer membrane-localized metalr eductases [20,21],( ii)atwostep electron shuttling pathway where exogenous electron shuttling compounds (e.g.,h umic acids,m elanin,p henazines,a ntibiotics, AQDS) are first microbiallyr educed and subsequently chemically oxidized by solid Fe(III)and Mn(IV)-oxides in as econd (abiotic) electron transfer reaction [22][23][24][25][26],( iii)a na nalogous two-step reduction pathway involving endogenous electrons huttling compounds [25,[27][28][29],( iv) at wo-step Fe(III) solubilizationreduction pathway where solid Fe(III)-oxides are first non-reductively dissolved by bacterially-produced organic ligands followed by uptake and reduction of the soluble organic Fe(III) complexes via periplasmic Fe(III) reductases [23,30],o r( v) the synthesis of conductive pili (i.e., nanowires) that extend from the cell to transfere lectrons [31,32].Thed etection of reduced metal ions is ac ritical step for identifying the metal-reducing proteins of such metalrespiring bacteria.C onventional measurements of metal reductase activity generally include ex-situ colorimetric assays (e.g.,f errozine for Fe 2 + ,e ucoberbelin blue for Mn 4 + ,e tc.) that are relatively insensitive or require specific conditions for activity.E lectrochemical methods such as voltammetric techniques have been widely used Abstract:T he in-situ detection of dissolved redox-active metals and metalloids such as iron and manganese is attracting increasing interest for understanding the complex network of enzymatic and geochemicalr eactions occurring at the microbe-mineral interface.Aversatile and promising tool for the investigation of re...

This paper presents a novel batch fabrication process for manufacturing bifunctional Scanning Electrochemical-Atomic Force Microscopy (AFM-SECM) probes with a recessed integrated ring electrode. The presented tip fabrication procedure enables the integration of a micro ring electrode at a precisely defined distance above the apex of the AFM tip. The electroactive area integrated into a scanning probe tip allows obtaining electrochemical data independently and separated from the topographical image. The tip fabrication is based upon batch processing, which provides bifunctional scanning probe tips on a wafer scale at low cost with high processing reproducibility and uniformity. Electrochemical characterization of an AFM tip-integrated ring electrode and combined electrochemical and topographical imaging using the bifunctional probe are demonstrated in this study.