G. C. Fiaccabrino

Mercury-plated iridium-based microelectrode arrays for trace metals detection by voltammetry: optimum conditions and reliability

An amperometric microsensor for the detection of trace metals in the low or sub nanomolar range is presented. It is obtained by successively evaporating iridium (2000 A) and Si3N4 (2000 A) on a silicon wafer, followed by a photolithographic pattering procedure. It consists of an array of 10 x 10 iridium microdisc electrodes with a recessed depth of 0.2 μm, separated by 50 or 150 μm. The electrical contacts are isolated by a layer of Agolit or Epoxy resin. Scanning electron microscopy and Atomic force microscopy have been used to control the regularity of the microelectrode array geometry and morphology. For the analysis of trace metals, mercury is deposited on the iridium-based microelectrode array. A given array is able to sustain the operations of Hg deposition/dissolution at least 10 times. The reliability of the mercury-plated iridium-based microelectrode arrays has been tested by a series of systematic Square Wave Anodic Striping Voltammetry (SWASV) analyses in synthetic solutions of lead and cadmium ions in the concentration range 1-10 nM. Repeated measurements over long periods of time on a given mercury layer showed good stability when the Epoxy resin was used and good reproducibility (± 4%) for at least 5 h. A good reproducibility was also found between different arrays. Finally, the mercury-plated iridium-based microelectrode arrays were applied to the lead and cadmium speciation in river water, by direct SWASV measurements, without any separation. A detection limit of 50 pM was established for a preconcentration time of 15 min. The results were compared with other techniques, in particular a similar procedure using a single Hg-plated Ir-based microelectrode.

Microreactor and electrochemical detectors fabricated using Si and EPON SU-8

Abstract An electrochemiluminescence (ECL) detector and a microenzymatic reactor (MER) combining Si and SU-8 technologies are described. Both devices were fabricated using standard processing techniques to produce on-wafer sensor elements, which were composed of a platinum or, alternatively, carbon interdigitated electrode array. The platinum array was resting on top of an Si pn photodiode. After these elements were completed, the entire wafer was modified with SU-8, which was structured to form a series of shaped spacers surrounding each device. For the ECL detector, a simple flow-channel was defined whereas for the microreactor a more complex layout defining two chambers separated by a series of SU-8 columns was employed. The upstream chamber of the microreactor was packed with porous glass beads modified with immobilised enzyme glucose oxidase whereas the downstream chamber contained the electrochemical detector. The performance of the ECL detector was assessed by the detection of codeine using ruthenium (II) tris(2,2′-bipyridyl). A detection limit of 100 μM was obtained and pharmaceutical preparations were successfully assayed. The MER was first evaluated by electrochemical determination of glucose and as a next step, a miniature ECL detector was placed on line downstream the MER to perform glucose measurements by ECL. Glucose was determined with detection limits of 2 and 50 μM by electrochemistry and ECL, respectively. This system was found to have a lifetime of at least 1 month when stored at 4°C.

Thin-film microfabrication of electrochemical transducers

Note: 186 Reference SAMLAB-ARTICLE-1998-009doi:10.1002/(SICI)1521-4109(199804)10:4 3.0.CO;2-W Record created on 2009-05-12, modified on 2016-08-08

Electrochemiluminescence of Tris(2,2'-bipyridine)ruthenium in Water at Carbon Microelectrodes.

Electrochemiluminescence (ECL) of Ru(bpy)(3)(2+) in water only, without any added electrolyte or reducing agents, has been obtained at carbon interdigitated microelectrode arrays (C-IDAs) of 2 μm width and spacing. In a generation/collection biasing mode, ECL can be clearly seen with the naked eye in normal room lighting at concentrations greater than 1 mM. Using a conventional photomultiplier tube (PMT), a detection limit of 10(-)(7) M Ru(bpy)(3)(2+) has been achieved for an electrode area of 0.25 mm(2). In comparison, the ECL intensity produced at Pt-IDA of the same geometry, under identical experimental conditions, was more than 300 times less. The ECL obtained at C-IDAs is attributed to the annihilation reaction of the reduced and oxidized forms of the Ru(bpy)(3)(2+) made possible due to the small electrode spacing.

Interdigitated Microelectrode Arrays Based on Sputtered Carbon Thin-Films

Note: 142 Reference SAMLAB-ARTICLE-1996-005 Record created on 2009-05-12, modified on 2016-08-08

Electrochemical characterization of thin-film carbon interdigitated electrode arrays

A carbon-based interdigitated electrode array (IDA) was fabricated by photolithographic patterning of RF sputtered thin-film carbon layers. The IDAs consisted of 125 pairs having the finger width of 2.5 μm and 1.5 μm gap. The electrochemical behavior of these electrodes was characterized using hexacyanoferrate(II), dopamine and acetaminophen.

Reagentless Sensor Integrating Electrodes, Photodetector, and Immobilized Co-Substrate for Electrochemiluminescence-Based Assays

Note: 205 Reference SAMLAB-ARTICLE-1999-016doi:10.1002/(SICI)1521-4109(199912)11:18 3.0.CO;2-C Record created on 2009-05-12, modified on 2016-08-08

Enzymatic microreactor using Si, glass and EPON SU-8

This article describes the design, fabrication and initial testing of an enzymatic microreactor using Si, glass, epoxy and Perspex components. The microreactor geometry was defined by a photostructured EPON SU-8 spacer. This gave two chambers, an upstream chamber (vol. ∼2.7 μl) which was packed with control pore glass (CPG) and a downstream chamber (vol. ∼1.5 μl) which contained the detectors. Eleven EPON SU-8 columns separated the chambers and prevented the CPG from passing. Glucose detection via glucose oxidase immobilized to the CPG was used as a model system. Conversion efficiencies between 15 and 60% at flow rates of 150 and 26 μ1 min−1 respectively were obtained. Overall the system was found to be robust and to have a lifetime of at least one month.

Fabrication and characterization of stop flow valves for fluid handling

Monolithic stop flow valves produced by Deep Reactive Ion Etching (DRIE) are proposed for the handling and the processing of small metered fluid volumes in capillary channels. A 2 /spl mu/l sampling unit has been successfully integrated as an element of a miniaturized chemical analysis system to improve analysis reproducibility. The net pressure needed to overcome the stop flow valve was determined experimentally for different valve diameters and compared to theoretical values. A 60 /spl mu/m diameter valve diameter can typically withstand a water pressure head of 20 cm, which is largely sufficient for most applications. Sampling of 2 /spl mu/l of selection of solvents was successfully demonstrated.

Microsystem for electrochemiluminescence-based analysis

A stand-alone microsystem, consisting of an electrochemical transducer, photodetector and a flow-through cell was realized and characterized for the electrochemiluminescence (ECL) measurements of a luminol/peroxide system and a ruthenium bipyridyl complex. The luminol/peroxide system was then associated with glucose oxidase for the detection of glucose.