While cathodic voltammetric measurements based on the reduction of nitro-containing explosive compounds have been well documented, little attention has been given for exploiting their anodic response, associated with the oxidation of their reaction products, for qualitative and quantitative security and forensic information. We demonstrate here that cyclic square-wave volammetry, combining the cathodic and anodic signals, offers distinct electrochemical profiles for trace nitroaromatic, nitramine and nitrate ester explosives compared to analogous cyclic-voltammetric and cathodic square-wave-voltammetric measurements. Unique electrochemical signatures are also obtained for commonly used explosive mixtures. Such distinct explosive signatures at disposable strip electrodes should facilitate rapid decentralized security screening applications.

This study examines the influence of textile substrates upon the behavior of wearable screen-printed electrodes and demonstrates the attractive sensing properties of these sensors towards the detection of nitroaromatic explosives. Compared to electrodes printed on common cotton or polyester substrates, GORE-TEX-based electrochemical sensors display reproducible background cyclic voltammograms, reflecting the excellent water-repellant properties of the GORE-TEX fabric. The wetting properties of different printed textile electrodes are elucidated using contact angle measurements. The influence of laundry washing and mechanical stress is explored. The GORE-TEX-based printed electrodes exhibit favorable detection of 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) explosives, including rapid detection of DNT vapor.

The simultaneous electrochemical measurement of heavy-metal and organic propellants relevant to gunshot residues (GSRs) is demonstrated. Cyclic voltammetry (CV) and cyclic square-wave stripping voltammetry (C-SWV) are shown to detect, in a single run, common propellants, such as nitroglycerin (NG) and dinitrotoluene (DNT), along with the heavy metal constituents of GSR, antimony (Sb), lead (Pb), zinc (Zn) and barium (Ba). The voltammetric detection of the stabilizer diphenylamine (DPA) along with inorganic constituents has also been examined. The resulting electrochemical signatures combine -in a single voltammogram- the response for the various metals and organic species, based on the reduction and oxidation peaks of the constituents. Cyclic square-wave voltammetry at the glassy carbon electrode (GCE), involving an intermittent accumulation at the reversal potentials of -0.95 V (for Sb, Pb, DNT and NG) and -1.3 V (for Sb, Pb, Zn and DPA) is particularly useful to offer distinct electrochemical signatures for these constituents of GSR mixtures, compared to analogous cyclic voltammetric measurements. Simultaneous voltammetric measurements of barium (at thin-film Hg GCE) and DNT (at bare GCE) are also demonstrated in connection to intermittent accumulation at the reversal potential of -2.4 V. Such generation of unique, single-run, information-rich inorganic/organic electrochemical fingerprints holds considerable promise for 'on-the-spot' field identification of individuals firing a weapon, as desired for diverse forensic investigations.

Here we report on a highly sensitive potentiometric detection of DNA hybridization. The new assay uses a low-volume solid-contact silver ion-selective electrode (Ag + -ISE) to monitor the depletion of silver ions induced by the biocatalytic reaction of the alkaline-phosphatase enzyme tag. The resultant potential change of the Ag + -ISE thus serves as the hybridization signal. Factors affecting the potentiometric hybridization response have been optimized to offer a detection limit of 50 fM (0.2 amol) DNA target. The new potentiometric assay was applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria to achieve a low detection limit of 10 CFU in the 4 μL sample. Such potentiometric transduction of biocatalytically-induced metallization processess holds great promise for monitoring various bioaffinity assays involving common enzyme tags.

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Amplified potentiometric transduction of DNA hybridization based on using liposome 'nanocarriers' loaded with the signaling ions is reported. The liposome-amplified potentiometric bioassay involved the duplex formation, followed by the capture of calcium-loaded liposomes, a surfactant-induced release and highly-sensitive measurements of the calcium signaling ions using a Ca(2+) ion-selective electrode (ISE). The high loading yield of nearly one million signaling ions per liposome leads to sub-fmol DNA detection limits. Factors affecting the ion encapsulation efficiency and signal amplification are evaluated and discussed. The influence of the surfactant lysing agent is also examined. Such use of 'green' calcium signaling ions addresses the inherent toxicity of Ag and CdS nanoparticle tags used in previous potentiometric bioassays. The new strategy was applied for the detection of low levels of E. coli bacteria. It could be readily extended to trace measurements of other important biomolecules in connection to different biorecognition events. The attractive analytical performance makes liposomes a useful addition to the armory of potentiometric bioassays.

The concept of locally heated polymeric membrane potentiometric sensors is introduced here for the first time. This is accomplished in an all solid state sensor configuration, utilizing poly(3-octylthiophene) as intermediate layer between the ion-selective membrane and underlying substrate that integrates the heating circuitry. Temperature pulse potentiometry (TPP) gives convenient peak-shaped analytical signals and affords an additional dimension with these sensors. Numerous advances are envisioned that will benefit the field. The heating step is shown to give an increase in the slope of the copper-selective electrode from 31 mV to 43 mV per 10-fold activity change, with a reproducibility of the heated potential pulses of 1% at 10 µM copper levels and a potential drift of 0.2 mV/h. Importantly, the magnitude of the potential pulse upon heating the electrode changes as a function of the copper activity, suggesting an attractive way for differential measurement of these devices. The heat pulse is also shown to decrease the detection limit by half an order of magnitude.