Electrochemistry, biosensors and microfluidics are popular research topics that have attracted widespread attention from chemists, biologists, physicists, and engineers. Here, we introduce the basic concepts and recent histories of electrochemistry, biosensors, and microfluidics, and describe how they are combining to form new application-areas, including so-called "point-of-care" systems in which measurements traditionally performed in a laboratory are moved into the field. We propose that this review can serve both as a useful starting-point for researchers who are new to these topics, as well as being a compendium of the current state-of-the art for experts in these evolving areas.

Digital microfluidics (DMF) has emerged as a popular format for implementing quantitative immunoassays for diagnostic biomarkers. All previous reports of such assays have relied on optical detection; here, we introduce the first digital microfluidic immunoassay relying on electrochemical detection. In this system, an indium tin oxide (ITO) based DMF top plate was modified to include gold sensing electrodes and silver counter/pseudoreference electrodes suitable for in-line amperometric measurements. A thyroid stimulating hormone (TSH) immunoassay procedure was developed relying on magnetic microparticles conjugated with primary antibody (Ab1). Antigen molecules are captured followed by capture of a secondary antibody (Ab2) conjugated with horseradish peroxidase enzyme (HRP). HRP catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) which can be detected amperometrically. The limit of detection of the technique (2.4 μIU mL(-1)) is compatible with clinical applications; moreover, the simplicity and the small size of the detector suggest utility in the future for portable analysis.

DNA-wrapped halloysite nanotubes were obtained by a mechanochemical reaction in the solid state. The characterization by scanning electron microscopy showed that the nanotubes were cut into shorter lengths and were completely covered with DNA. This resulted in a high aqueous solubility of the product with stability of the solution for about 6 weeks. The nanotubes were cut to different fractions with lengths of 200-400 nm (30-40%), 400-600 nm (10-20%) and 600-800 nm (5-10%) after ball milling. FTIR spectroscopic analysis shows that the DNA in the product remained intact. This straightforward technique for obtaining water-soluble halloysite nanotubes by a solid-state reaction has great potential for biomedical applications of nanotubes.

This review will examine the integration of two fields that are currently at the forefront of science, i.e. biosensors and microfluidics. As a lab-on-a-chip (LOC) technology, microfluidics has been enriched by the integration of various detection tools for analyte detection and quantitation. The application of such microfluidic platforms is greatly increased in the area of biosensors geared towards point-of-care diagnostics. Together, the merger of microfluidics and biosensors has generated miniaturized devices for sample processing and sensitive detection with quantitation. We believe that microfluidic biosensors (biosensors-on-chip) are essential for developing robust and cost effective point-of-care diagnostics. This review is relevant to a variety of disciplines, such as medical science, clinical diagnostics, LOC technologies including MEMs/NEMs, and analytical science. Specifically, this review will appeal to scientists working in the two overlapping fields of biosensors and microfluidics, and will also help new scientists to find their directions in developing point-of-care devices.

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Digital microfluidics (DMF) is an emerging technique for manipulating small volumes of liquids. DMF is particularly well suited for analytical applications as it allows automated handling of discrete samples, and it has been integrated with several inline analysis techniques. However, examples of the integration of DMF with electroanalytical methods are notably scarce, and those that have been reported rely on external electrodes that impose limitations on complexity. To combine the full capabilities of DMF with voltammetry, we designed a platform featuring a three-electrode electrochemical cell integrated in a microfabricated DMF device, removing the need for external electrodes and allowing for complete droplet control. The performance of the DMF/voltammetry system is comparable to that of a commercial screen printed electrode, and the new platform was applied to generating a calibration series for acetaminophen with a limit of detection of 76 μM and good precision (4% average RSD), all with minimal human intervention. We propose that this platform and variations thereof may be a useful new tool for microscale electroanalysis and will be a complementary system to existing inline analysis techniques for DMF.

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The first sequence-dependent study of DNA films containing metal-mediated base pairs was performed to investigate the charge transfer resistance (R ) of metal-modified DNA. The imidazole (Im) deoxyribonucleoside was chosen as a highly Ag -specific ligandoside for the formation of Im-Ag -Im complexes within the duplexes. This new class of site-specifically metal-modified DNA films was characterized by UV, circular dichroism (CD), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of these systems were investigated by means of electron impedance spectroscopy and scanning electrochemical microscopy. Taken together, these experiments indicated that the incorporation of Ag ions into the DNA films leads to reduced electron transfer through the DNA films. A simple device was proposed that can be switched reversibly between two distinct states with different charge transfer resistance.