Electrochemical and optical bioassays of nerve agents based on the organophosphorus-hydrolase mediated growth of cupric ferrocyanide nanoparticles

A new biometallization route for detecting low levels of organophosphorus nerve agents based on organophosphorus-hydrolase (OPH)-stimulated formation of cupric-ferrocyanide (CuFeCN) nanoparticles is described. The growth and accumulation of these nanoparticles onto the surface of carbon paste electrodes, coupled with their favorable redox activity, allow the amplified electrochemical detection of nerve agents. The results clearly demonstrate the applicability of the biocatalytic formation and surface preconcentration of CuFeCN nanoparticles as a new and attractive bioamplification route and its potential for monitoring of a wide range of biocatalytic transformations.     

Magnetic movement of biological fluid droplets

Magnetic fields can be used to control the movement of aqueous drops on non-patterned, silicon nanowire superhydrophobic surfaces. Drops of aqueous and biological fluids are controlled by introducing magnetizable carbonyl iron microparticles into the liquid. Key elements of operations such as movement, coalescence, and splitting of water and biological fluid drops, as well as electrochemical measurement of an analyte are demonstrated. Superhydrophobic surfaces were prepared using vapor–liquid–solid (VLS) growth systems followed by coating with a perfluorinated hydrocarbon molecule. Drops were made from aqueous and biological fluid suspensions with magnetizable microparticle concentrations ranging from 0.1 to 10 wt%.     

Electrocatalytic activity of ordered intermetallic phases for fuel cell applications

The electrocatalytic activities of a wide range of ordered intermetallic phases toward a variety of potential fuels have been studied, and results have been compared to those of a pure polycrystalline platinum (Pt(pc)) electrode. A significant number of the ordered intermetallic phases exhibited enhanced electrocatalytic activity when compared to that of Pt, in terms of both oxidation onset potential and current density. The PtBi, PtIn, and PtPb ordered intermetallic phases appeared to be the most promising electrocatalysts tested thus far for fuel cell applications. PtPb, in particular, showed an onset potential that was 100 mV less positive and a peak current density approximately 40 times higher than those observed for Pt in the case of methanol oxidation. The ability to control the geometric and electronic structures of the electrocatalytic material by using ordered intermetallic phases has been shown to be a promising direction of inquiry in the search for superior electrocatalysts for fuel cell applications.     

Electrocatalytic detection of insulin at RuOx/carbon nanotube-modified carbon electrodes

A bilayer surface coating, prepared by electrodepositing ruthenium oxide (RuOx) onto a carbon nanotube (CNT) layer, offers dramatic improvements in the stability and sensitivity of voltammetric and amperometric measurements of insulin compared to the individual (CNT or RuOx) coated electrodes. The enhanced electrocatalytic activity towards insulin is indicated from lowering the potential of the oxidation process (starting around 0.35 versus Ag/AgCl) and the substantially higher sensitivity over the entire potential range. A wide linear dynamic range (10-800 nM) was achieved with a detection limit of 1 nM. The marked electrocatalytic activity of the RuOx/CNT coating towards insulin is coupled with a greatly enhanced stability. For example, the insulin amperometric response of the RuOx/CNT-coated electrodes is highly stable, with 97% of the initial activity remaining after 60 min stirring of 2 × 10⁻⁶ M solution (compared to significantly faster current diminutions at the RuOx- or CNT-coated surfaces). The results suggest great promise for miniaturized sensors and detectors for monitoring insulin.     

Discrete microfluidics with electrochemical detection

A droplet-based electrochemical digital magnetofluidics system has been developed. The system relies on the magnetic movement, in air, of different aqueous microdroplets containing magnetic microparticles--serving as the 'sample', 'blank', 'wash' and 'reagent' solutions--into and out of a three-electrode assembly. The movement of all droplets was controlled using the magnetic fields generated by three separate external magnets positioned below the superhydrophobic surface. Square-wave voltammetry was used for rapid measurements of dopamine in multiple successive microdrops with minimal cross talk. The ability of the droplet-based electrochemical microfluidic system to manipulate microliter solutions was also illustrated in bioassays of glucose, involving the merging of enzyme (GOx) and substrate droplets, followed by chronoamperometric measurements of the hydrogen peroxide product in the merged droplet. Variables of the new electrochemical digital magnetomicrofluidic technique were examined and optimized. The new droplet-based electrochemical microfluidic system offers a promising platform for automated clinical diagnostics and drug discovery.     

Thermally induced electrode protection against biofouling

This paper demonstrates that a combined thermal and electrochemical conditioning step can greatly minimize electrode blocking. We detected 50 ppm dopamine after a blocking step in 1000 ppm gelatine solution. Only a treatment of the electrode at −1.5 V and 61.5 °C can reveal the voltammetric dopamine signals to 82%. The increase of the peak separation of the cyclic voltammograms obtained in 50 ppm dopamine is limited to 14%, whereas negative polarization (−1.5 V) alone leads to a 31% increase compared to 109% upon thermal and 105% without any conditioning. The positive effects can be addressed to an enforced reductive degradation and accelerated removal of the blocking agents. Also the formation of hydrogen bubbles might play a significant role. Thermo-electrochemical treatment holds great promise for electrochemical sensors and detectors which are applied for long-term monitoring of samples that contain blocking matrices.