This paper reviews the range of sensors used in electronic nose (e‐nose) systems to date. It outlines the operating principles and fabrication methods of each sensor type as well as the applications in which the different sensors have been utilised. It also outlines the advantages and disadvantages of each sensor for application in a cost‐effective low‐power handheld e‐nose system.

A review of gas sensors employed in electronic nose applications

The widespread exploitation of biosensors in the analysis of molecular recognition has its origins in the mid-1990s following the release of commercial systems based on surface plasmon resonance (SPR). More recently, platforms based on piezoelectric acoustic sensors (principally 'bulk acoustic wave' (BAW), 'thickness shear mode' (TSM) sensors or 'quartz crystal microbalances' (QCM)), have been released that are driving the publication of a large number of papers analysing binding specificities, affinities, kinetics and conformational changes associated with a molecular recognition event. This article highlights salient theoretical and practical aspects of the technologies that underpin acoustic analysis, then reviews exemplary papers in key application areas involving small molecular weight ligands, carbohydrates, proteins, nucleic acids, viruses, bacteria, cells and lipidic and polymeric interfaces. Key differentiators between optical and acoustic sensing modalities are also reviewed.

A survey of the 2001 to 2005 quartz crystal microbalance biosensor literature: applications of acoustic physics to the analysis of biomolecular interactions.

Polymer brush coatings for combating marine biofouling

Corrosion protection by multilayered conducting polymer coatings

The removal of toxic hexavalent chromium (Cr(VI)) from polluted water by magnetic polyaniline (PANI) polymer nanocomposites (PNCs) was investigated. The PNCs were synthesized using a facile surface initiated polymerization (SIP) method and demonstrated unique capability to remove Cr(VI) from polluted solutions with a wide pH range. Complete Cr(VI) removal from a 20.0 mL neutral solution with an initial Cr(VI) concentration of 1.0–3.0 mg L−1 was observed after a 5 min treatment period with a PNC load of 10 mg. The PNC dose of 0.6 g L−1 was found to be sufficient for complete Cr(VI) removal from 20.0 mL of 9.0 mg L−1 Cr(VI) solution. The saturation magnetization was observed to have no obvious decrease after treatment with Cr(VI) solution, and these PNCs could be easily recovered using a permanent magnet and recycled. The Cr(VI) removal kinetics were determined to follow pseudo-first-order behavior with calculated room temperature pseudo-first-order rate constants of 0.185, 0.095 and 0.156 min−1 for the solutions with pH values of 1.0, 7.0 and 11.0, respectively. The Cr(VI) removal mechanism was investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and energy-filter transmission electron microscopy (EFTEM). The results showed that PANI was partially oxidized after treatment with Cr(VI) solution, with Cr(VI) being reduced to Cr(III). The EFTEM observation indicated that the adsorbed Cr(III) had penetrated into the interior of the PNCs instead of simply adsorbing on the PNC surface. This synthesized material was found to be easily regenerated by 1.0 mol L−1p-toluene sulfonic acid (PTSA) or 1.0 mol L−1 hydrochloric acid (HCl) and efficiently reused for further Cr(VI) removal.

https://pubs.rsc.org/en/content/articlepdf/2012/ra/c2ra21991c

Magnetic polyaniline nanocomposites toward toxic hexavalent chromium removal

Anti-corrosive properties of polyaniline coating on iron

Polyvinylpyrrolidone (PVP) modified quartz crystal microbalance (QCM) has been used for determination of ammonia and a number of short chain primary aliphatic amines in atmospheric media. A solution casting method was used for modification of quartz crystal with a thin layer of PVP. Determination was based on frequency shifts due to adsorption of the compounds at the surface of the modified electrode. The frequency shifts were found to be linear against the concentration of analyte in the range between 0.5 and 30 mg l−1 with correlation coefficients of above 0.9903. The sensitivity factors in the range of 7.5–48.2 Hz/mg l−1 was obtained. A storage period of over 5 months proved no loss in sensitivity and performance. Among some possible interference tested, no major interference was involved in the performance of the sensor except for water vapor, which may be resolved by drying the samples prior to injection.

Construction of a sensor for determination of ammonia and aliphatic amines using polyvinylpyrrolidone coated quartz crystal microbalance

Conducting polymers such as polyaniline and polypyrrole exhibit novel sensoric properties and are able to interact chemically or electrochemically with the species of interest for detection. In the current investigation, construction of a sensor based on an electrochemical reaction between CrVI and a thin layer of polyaniline, coated at the surface of quartz crystal electrode, is reported. Polyaniline was synthesized, electrochemically, at the surface of quartz crystal electrode. It was then reduced at −0.1 V versus Ag/AgCl. The modified electrode was exposed to various concentrations of CrVI solutions ranging from 10−7 to 10−1M. Mass changes of the polymer-modified electrode due to the reaction between CrVI and polyaniline was found to be linear, corresponding to the concentration of CrVI. The experiments in both acidic and nonacidic conditions were performed. In both conditions, linear double-loga thmic calibration curves of mass change of the polymer film versus CrVI concentration were obtained. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2772–2780, 2002

Detection and determination of CrVI in solution using polyaniline modified quartz crystal electrode

Polymethylmetacrylate (PMMA) modified quartz crystal microbalance (QCM) has been tested for determination of phenol in solution. A solution casting method was used for modification of quartz crystal with a thin layer of PMMA. Determination was based on frequency shifts of PMMA modified quartz crystal electrode due to the adsorption of phenol at the surface of modified electrode. Measurements were carried out by exposure of PMMA modified electrode both directly to the phenol solutions and indirectly to the phenol vapors exist in the head space of phenol solutions (head space analysis). The frequency shifts were found to be linear against the concentration of phenol in the range between 0 and 10 ppm for direct exposure and 1–100 ppm for head space analysis. The sensitivity factors of 37.87 and 1.47 Hz ppm−1 were found for direct exposure and head space analysis, respectively. Treatment of phenol solutions by acidification with hydrochloric acid (pH∼3) and salt addition (saturation with sodium chloride) caused an increase of sensitivity of the sensor. Sensitivity factors of 49.7 and 6.5 Hz ppm−1 were found for direct and head space analysis, respectively, after solution treatment by acidification and salt addition.

Application of the quartz crystal microbalance for determination of phenol in solution

A quartz crystal microbalance (QCM) modified with a thin layer of standard gas chromatographic stationary phase of methyl phenyl silicon, 75% phenyl (OV25) was used to determine a number of chlorinated aliphatic hydrocarbons in atmospheric media. A solution casting method was used for modification of quartz crystal with a thin layer of OV25. Determination was based on the frequency shifts due to the adsorption of compounds at the surface of modified quartz crystal electrode. The frequency shifts were found to be linear against the concentration of analytes within the concentration range of 15–150 mg l−1 with the correlation coefficients of above 0.9910. The sensitivity factors in the range of 0.71–1.17 Hz per mg l−1 was obtained. Storage period of over 4 months proved no loss in sensitivity and performance of the sensor. Among some possible interferents tested (CO, CO2, NO2, O2 and H2O), no major interference was involved in the performance of the sensor.

Ali Oladegaragoze

Papers

Anti-corrosive properties of polyaniline coating on iron

Construction of a sensor for determination of ammonia and aliphatic amines using polyvinylpyrrolidone coated quartz crystal microbalance

Detection and determination of CrVI in solution using polyaniline modified quartz crystal electrode

Application of the quartz crystal microbalance for determination of phenol in solution

Determination of chlorinated aliphatic hydrocarbons in air using a polymer coated quartz crystal microbalance sensor