Jeremy D. Glennon

Biosensor technology: Technology push versus market pull

Biosensor technology is based on a specific biological recognition element in combination with a transducer for signal processing. Since its inception, biosensors have been expected to play a significant analytical role in medicine, agriculture, food safety, homeland security, environmental and industrial monitoring. However, the commercialization of biosensor technology has significantly lagged behind the research output as reflected by a plethora of publications and patenting activities. The rationale behind the slow and limited technology transfer could be attributed to cost considerations and some key technical barriers. Analytical chemistry has changed considerably, driven by automation, miniaturization, and system integration with high throughput for multiple tasks. Such requirements pose a great challenge in biosensor technology which is often designed to detect one single or a few target analytes. Successful biosensors must be versatile to support interchangeable biorecognition elements, and in addition miniaturization must be feasible to allow automation for parallel sensing with ease of operation at a competitive cost. A significant upfront investment in research and development is a prerequisite in the commercialization of biosensors. The progress in such endeavors is incremental with limited success, thus, the market entry for a new venture is very difficult unless a niche product can be developed with a considerable market volume.

Direct electrochemistry of horseradish peroxidase immobilized on a monolayer modified nanowire array electrode

Vertically aligned nanowire array electrodes (NAEs) were prepared by electrodeposition of gold into an anodic aluminium oxide membrane (AAM), providing an ordered three-dimensional (3D) matrix for immobilization of redox proteins. Third-generation H(2)O(2) biosensors were prepared by covalent immobilization of horseradish peroxidase (HRP) on the self-assembled monolayer modified NAEs. Direct electron transfer and electrocatalytic performances of the HRP/NAEs with different nanowire lengths (deposition time of 2, 4 and 5h) were investigated. Results showed that with longer nanowires, better performances were achieved. The HRP/NAE(5h) (5h deposition time) exhibited remarkable sensitivity (45.86 microA mM(-1) cm(-2)) towards H(2)O(2) with a detection limit of 0.42 microM (S/N=3), linearity up to 15 mM and a response time of 4s. The ordered 3D gold nanowire array with high conductivity, excellent electron transfer capability and good biocompatibility proved promising for fabricating sensitive, selective, stable and mediator-free enzymatic biosensors.

Nanoparticles in Separation Science—Recent Developments

Abstract Nanotechnology has significantly impacted on many fields of science, including chemistry, materials, bioanalysis, electronics, optics, medicine and separation science. In separation science, significant advances have been made in electrophoresis and microchip separations employing nanoparticles. Some of the latest advances using nanoparticles include their use as stationary phases for liquid chromatography, gas chromatography, and capillary electrochromatography (CEC), as well as roles as run buffer additives to enhance electrophoresis, and for separation and selectivity control in microchip separations. This review aims to highlight these recent advances.

Silica-bonded calixarenes in chromatography: II. Chromatographic retention of metal ions and amino acid ester hydrochlorides

Abstract The chromatographic behaviour of alkali and alkaline earth metal ions on a silica-bonded macrocyclic calix[4]arene tetradiethylamide phase is reported. Selective retention of Na+ over other alkali metal ions and of Ca2+ over Mg2+ ions is found using water as the mobile phase and conductivity detection. A series of amino acid ester hydrochlorides are shown to be retained in order of their hydrophobicity on a silica bonded calix[4]arene tetraester phase with aqueous mobile phases containing lithium perchlorate and acetonitrile. Retention of metal ions and organic solutes on these new silica-bonded functionalised calixarene phases is dependent on the organic modifier concentration.

Rapid fabrication of microfluidic devices in poly(dimethylsiloxane) by photocopying

A very simple and fast method for the fabrication of poly(dimethylsiloxane) (PDMS) microfluidic devices is introduced. By using a photocopying machine to make a master on transparency instead of using lithographic equipment and photoresist, the fabrication process is greatly simplified and speeded up, requiring less than 1.5 h from design to device. Through SEM characterization, any micro-channel network with a width greater than 50 microm and a depth in the range of 8-14 microm can be made by this method. After sealing to a Pyrex glass plate with micromachined platinum electrodes, a microfluidic device was made and the device was tested in FIA mode with on-chip conductometric detection without using either high voltage or other pumping methods.

Enhanced chromatographic selectivity for Na+ ions on a calixarene-bonded silica phase

Abstract Functional esters of calixarenes, which are phenolic metacyclophanes annulated by a single methylene bridge, are immobilised onto silica particles for use in the separation of alkali metal ions by high performance liquid chromatography with conductivity detection. The immobilisation of tetrameric and hexameric calixarene ethyl esters was carried out using the triethoxy silane derivatives of p-allylcalix[n]arene ethyl esters. At an injected concentration of 10−2M, optimum selectivity for Na ions was achieved using a mobile phase of 30% MeOH/H2O with the calix[4]arene ester stationary phase. A mixture of four alkali metal chlorides is shown on injection to give a clear separation of Na+ from the other unresolved ions, the retention order being Na+ » K+ > Cs+ > Li+ = to.

Silica-bonded calixarenes in chromatography: I. Synthesis and characterization by solid-state NMR spectroscopy

Abstract Two different reaction schemes have been used to synthesize silica-bonded calixarene phases. Specifically, a triethoxysilyl calix[4]arene is reacted with silica to produce a bonded calix[4]arene tetraamide phase, and a hydridederivatized silica undergoes a hydrosilylation reaction with p-allylcalix[6]arene hexaester to give a calix[6]arene hexaester phase. The resulting products were characterized by 13C and 29Si cross polarization/magic angle spinning NMR spectroscopy. The spectra clearly show calixarene bonding to the silica surface and are invaluable in determining the nature and extent of chemical modification of the surface with these macrocyclic compounds.

Solid phase extraction of metal ions using immobilised chelating calixarene tetrahydroxamates

Abstract The synthetic macrocycles, known as calixarenes, have been shown to possess high ionophoric selectivity and form inclusion complexes with many ions. A tetrameric calixarene bearing hydroxamic acid functional groups was synthesised and supported on octadecylsilica and XAD-4 resin. When loaded with Fe(III), V(V) and Cu(II), the materials display the characteristic visible absorption spectra associated with hydroxamate coordination. The chemical bonding of the calixarene tetrahydroxamic acid to silica particles was also carried out using the triethoxysilane derivative of the p -allylcalix[4]arene hydroxamic acid. When packed into small cartridges, these materials are used for the solid phase extraction of transition metal ions from aqueous solution. Metal uptake profiles as a function of pH are presented for Fe(III), Co(II), Pb(II), Cd(II), Mn(II), Ni(II), Zn(II) and Cu(II). The quantitative trace enrichment of Cu(II), Zn(II) and Mn(II) from water samples prior to ion chromatographic analysis is demonstrated

An environmental monitoring system for trace metals using stripping voltammetry

Abstract There is increasing pressure on industry and regulatory bodies to monitor the discharge of trace metals into the aquatic environment. The determination of trace metals can be achieved to parts per billion (ppb) levels using anodic stripping voltammetry (ASV) at screen printed electrodes, controlled using an NMRC potentiostat coupled with software control. The disposable testheads consist of inexpensive materials and allow for low-cost production in batch processes. Voltammetric (the measurement of current as a function of potential) methods of analysis are attractive for the determination of copper, cadmium, lead and zinc. A three electrode set-up is used both in the preparation of the mercury film on a carbon electrode and in the subsequent anodic stripping voltammetric detection step. The performances of the reference electrodes, the screen-printed carbon and the FPGA based unit have been investigated in this paper.

Selective Nanomolar Detection of Dopamine Using a Boron-Doped Diamond Electrode Modified with an Electropolymerized Sulfobutylether-β-cyclodextrin-Doped Poly(N-acetyltyramine) and Polypyrrole Composite Film

N-acetyltyramine was synthesized and electropolymerized together with a negatively charged sulfobutylether-beta-cyclodextrin on a boron-doped diamond (BDD) electrode followed by the electropolymerization of pyrrole to form a stable and permselective film for selective dopamine detection. The selectivity and sensitivity of the formed layer-by-layer film was governed by the sequence of deposition and the applied potential. Raman results showed a decrease in the peak intensity at 1329 cm(-1) (sp(3)), the main feature of BDD, upon each electrodeposition step. Such a decrease was correlated well with the change of the charge-transfer resistance derived from impedance data, i.e., reflecting the formation of the layer-by-layer film. The polycrystalline BDD surface became more even with lower surface roughness as revealed by scanning electron and atomic force microscopy. The modified BDD electrode exhibited rapid response to dopamine within 1.5-2 s and a low detection limit of 4-5 nM with excellent reproducibility. Electroactive interferences caused by 4-dihydroxyphenylalanine, 3,4-dihydroxyphenylacetic acid, ascorbic acid, and uric acid were completely eliminated, whereas the signal response of epinephrine and norepinephrine was significantly suppressed by the permselective film.