Microbes have been shown to naturally form veritable electric grids in which different species acting as electron donors and others acting as electron acceptors cooperate. The uptake of electrons from cells adjacent to them is a mechanism used by microorganisms to gain energy for cell growth and maintenance. The external discharge of electrons in lieu of a terminal electron acceptor, and the reduction of external substrates to uphold certain metabolic processes, also plays a significant role in a variety of microbial environments. These vital microbial respiration events, viz. extracellular electron transfer to and from microorganisms, have attracted widespread attention in recent decades and have led to the development of fascinating research concerning microbial electrochemical sensors and bioelectrochemical systems for environmental and bioproduction applications involving different fuels and chemicals. In such systems, microorganisms use mainly either (1) indirect routes involving use of small redox-active organic molecules referred to as redox mediators, secreted by cells or added exogenously, (2) primary metabolites or other intermediates, or (3) direct modes involving physical contact in which naturally occurring outer-membrane c-type cytochromes shuttle electrons for the reduction or oxidation of electrodes. Electron transfer mechanisms play a role in maximizing the performance of microbe–electrode interaction-based systems and help very much in providing an understanding of how such systems operate. This review summarizes the mechanisms of electron transfer between bacteria and electrodes, at both the anode and the cathode, in bioelectrochemical systems. The use over the years of various electrochemical approaches and techniques, cyclic voltammetry in particular, for obtaining a better understanding of the microbial electrocatalysis and the electron transfer mechanisms involved is also described and exemplified.

Continuous monitoring of oxygen concentration is of great importance in many different areas of research which range from medical applications to food packaging. In the last three decades, significant progress has been made in the field of optical sensing technology and this review will highlight the one inherent to the development of oxygen indicators. The first section outlines the bioanalytical fields in which optical oxygen sensors have been applied. The second section gives the reader a comprehensive summary of the existing oxygen indicators with a critical highlight on their photophysical and sensing properties. Altogether, this review is meant to give the potential user a guide to select the most suitable oxygen indicator for the particular application of interest.

Fields of medicine and life sciences are constantly evolving and striving for improved understanding of how cells function at an individual level, small ensemble level, and tissue level. Such improved understanding will translate into developing therapeutic strategies as well as approaches for disease diagnosis. Behavior of cells at all levels is shaped in significant part by secreted molecules that serve as cues for proliferation, migration, death, and other cell life-altering events. Improved understanding of what signals released when by which cells requires novel tools for local detection of cell-secreted molecules. This paper reviews recent efforts by bioengineering and bioanalytical chemistry communities to develop biosensors for detecting molecules in extracellular space. Multiple topics including antibody-, enzyme- and aptamer-based biosensors for cell analysis as well as sensor miniaturization approaches are discussed.

The conformation of charged molecules tethered to conducting substrates can be controlled efficiently through the application of external voltages. Biomolecules like DNA or oligopeptides can be forced to stretch away from—or fold onto—surfaces biased at moderate potentials of merely hundreds of millivolts. These externally controlled conformation changes can be used to switch the biological function of molecular monolayers on and off, by revealing or concealing molecular recognition sites at will. Moreover, the electrical actuation of biomolecular surface probes bears great potential as a novel, label-free, yet highly sensitive measurement modality for the analysis of molecular interactions. The binding of target molecules to an oscillating probe layer significantly alters the layer’s switching behavior in terms of the conformation switching amplitude and, most remarkably, with respect to the molecular switching dynamics. Analyzing the switching response of target–probe complexes from the low- to the high-frequency regime reveals a wealth of previously inaccessible information. Besides “classical” interaction parameters like binding affinities and kinetic rate constants, information on the size, shape, bending flexibility, and elasticity of the target molecule may be obtained in a single assay. This review describes the advent of electrically switchable biosurfaces, focusing on DNA monolayers. The preparation of self-assembled switchable oligonucleotide monolayers and their electrical interactions with charged substrates are highlighted. Special attention is paid to the merits of evaluating the dynamic response of charged biolayers which are operated at high driving frequencies. Several applications of biosensors based on electrically manipulated molecules are exemplified. It is emphasized that the electrical actuation of biomolecules bears many advantages over passive sensor surfaces.

The search for DNA biomarkers of oxidative stress has been hampered for several decades by the lack of relevant information on base oxidation products and the challenging issue of measuring low amounts of lesions, typically a few modifications within the range 106–108 normal bases. In addition and this was ignored for a long time, there is a risk of artifactual oxidation of overwhelming nucleobases during DNA extraction and subsequent workup that has led to overestimation of some base damage up to 2–3 orders of magnitude. The main aim of the survey is to critically review the available methods that have been developed for measuring oxidatively generated base damage in nuclear and mitochondrial DNA. Among the chromatographic methods, high-performance liquid chromatography associated with tandem mass spectrometry (HPLC–MS/MS) is the most accurate and versatile approach whereas HPLC–electrochemical detection (ECD) is restricted to electrochemically active modifications. These methods allow measuring several single oxidized pyrimidine and purine bases, tandem base lesions and interstrand DNA cross-links in nuclear DNA. As complementary analytical tools, enzymatic methods that associate DNA repair enzymes with either the alkaline comet assay or the alkaline elution technique are suitable for assessing low variations in the level of different classes of oxidatively generated DNA lesions. Most of the immunoassays suffer from a lack of specificity due to the occurrence of cross-reactivity with overwhelming normal bases. One major exception concerns the immunodetection of 5-hydroxymethylcytosine, produced in a relatively high yield as an epigenetic DNA modification. HPLC–MS/MS is now recognized as the gold standard for measuring oxidized bases and nucleosides in human fluids such as urine, saliva, and plasma.

The analysis of autoantibodies in human serum plays a crucial role in the diagnosis and follow-up of autoimmune diseases. The analytical tools available for the determination of these analytes, however, are still far from mature, lack standardization, and give low negative predictive values. Approaches using biosensor technology for analysis are an attractive alternative to classical techniques. In special applications, biosensors already have been proven to be effective for clinical diagnostics. This is due to the fact that real-time monitoring of the antigen/antibody interaction gives valuable information on autoantibody affinity to the respective antigenic structure. The potentials of biosensors for the serological analysis of autoantibodies are evident from the increasing number of publications on the subject. Thus, this review focuses on underlying biosensor techniques and published clinical trials. The advantages of multiplexed analyses of autoantibodies by use of microarrays are also emphasized. This promising bioanalytical technique is also particularly important for the structural identification of novel antigens.

Recent developments in the bioelectroanalysis of pharmaceutical compounds are reviewed, concentrating particularly on the development of electrode materials and measurement strategies and on their application. The advantages of electroanalytical techniques as alternatives to other analytical procedures such as rapid response, sensitivity and low detection limits are highlighted and illustrated. Particular emphasis is given to carbon-based materials for voltammetric electroanalysis; new potentiometric sensors and electrochemical biosensors are also reviewed.

Aptamers are single-stranded DNA or RNA oligonucleotides, which are able to bind with high affinity and specificity to their target. This property is used for a multitude of applications, for instance as molecular recognition elements in biosensors and other assays. Biosensor application of aptamers offers the possibility for fast and easy detection of environmental relevant substances. Pharmaceutical residues, deriving from human or animal medical treatment, are found in surface, ground, and drinking water. At least the whole range of frequently administered drugs can be detected in noticeable concentrations. Biosensors and assays based on aptamers as specific recognition elements are very convenient for this application because aptamer development is possible for toxic targets. Commonly used biological receptors for biosensors like enzymes or antibodies are mostly unavailable for the detection of pharmaceuticals. This review describes the research activities of aptamer and sensor developments for pharmaceutical detection, with focus on environmental applications.

Fluorescence lifetime (FLT) measurements in the long-wavelength red and near-infrared (NIR) range are expected to improve the reliability and robustness of fluorescence-based detection. This review provides a summary of suitable classes of red and NIR luminescent reporters for use in FLT-based applications.

Capillary electromigration techniques are often considered ideal methods for enantioseparations due to their high separation selectivity and flexibility. Thus, numerous methods employing a chiral selector as pseudostationary phase in a background electrolyte have been developed and applied for the chiral analysis of drugs in bulk ware, pharmaceutical formulations and biological matrices. Furthermore, electromigration techniques have been combined with spectroscopic methods such as nuclear magnetic resonance in order to understand the complexation of analytes by chiral selectors. The present review focuses on recent developments and applications of chiral electromigration techniques in pharmaceutical and biomedical analysis including examples illustrating analyte–selector complex formation or mechanistic studies which have been published between January 2009 and July 2011. Selector-mediated chiral separations clearly dominate while no applications of capillary electrochromatography to pharmaceutical or biomedical analysis have been reported during this period of time.