Disposable Electrode Materials

Nowadays, two important electrode materials are in widespread use for disposable sensor technology: carbon and gold (Au).[5] Especially, carbon is desired because of its rich surface chemistry, low background current, wide potential window, low-cost, and chemical inertness. Disposable carbon electrodes are suitable for various kinds of surface modifications, thus enabling a major number of applications in many fields. However, the electron-transfer rates obtained from carbon electrodes are reported to be slower than those obtained from metal electrodes.[6] Recently, this major drawback has been overcome by the modification of the carbon surface with carbon nanotubes (CNT). Carbon nanotubes enabled enhanced electron transfer on electrode surface owing to their small size providing a larger active surface for easy DNA attachment.1-7-1 Recently, CNT-based screen-printed electrodes (CNTSPE) have been fabricated by Wang and Musameh.[8] Carbon nanotube-based screen-printed electrodes with their well-defined electrochemical activity and mechanical stability are promising candidates for DNA-based testing.

Highly oriented pyrolytic graphite electrodes (HOPGE) have also been attractive for electrochemical DNA biosensor research.[9-12] The renewal of HOPGE surface is also simple and rapid. A freshly cleaved surface of HOPGE can easily be prepared by contacting a piece of adhesive tape to the graphite surface, and then removing a thin layer of graphite with the tape. Thus the same electrode can be used for several different measurements. DNA and DNA-drug interaction were examined on thin-film mercury-coated HOPGE by Hason et al.[9] Voltam-metric microanalysis of DNA adducts with osmium tetroxide,2,2'-bipyridine (Os,bipy) using a HOPGE provided the detection of 140 pg of DNA-Os,bipy after a 5-min accumulation period.[10] Anodic voltammetry and atomic force microscopy (AFM) imaging were performed for the detection of adriamycin and DNA interaction on HOPGE surfaces.[11] Atomic force microscopy surface characterization of the effect of pH and applied potential on the adsorption of DNA on HOPGE has recently been reported by Oliveira-Brett and Chiorcea.[12]

The use of a rigid carbon-polymer composite material as an electrochemical transducer in hybridization geno-sensors has recently been reported by Alegret and coworkers.[13-15] Graphite-epoxy composites (GEC) have an uneven surface suitable for strong DNA adsorption. Especially, ssDNA was reported to bind strongly to GEC in a way that prevents the strands from self-associating, while permitting hybridization with complementary DNA. Hybridization was detected by monitoring guanine oxidation signal[15] and also through biotin-streptavidin interaction using a streptavidin conjugated to horseradish peroxidase without nonspecific adsorption onto GEC, even when the surface was treated by blocking re-agents.[14] Thus screen-printed GEC-based electrodes are also promising candidates for highly specific DNA hybridization detection.

Au is the noble metal of choice for screen printing of disposable sensor strips. Au strips offer a very favorable electron-transfer kinetics and a wide anodic potential range. The main disadvantage would be the limitation of the cathodic potential window.

The disposable electrode designs can be classified into two groups. The most generally used one is the screen-printed (thick-film) electrode (SPE). The second one is the recently developed pencil graphite electrode (PGE). Screen-printed electrode technology has developed rapidly with the help of the recent advancements in microfabrication; however, the PGEs still need to be improved to eliminate the use of external reference and counter electrodes. Whereas SPE is sufficient to perform an electrochemical analysis, a PGE still requires a beaker-type system. The important advantage of using PGE would be that the preparation does not require sophisticated instruments, because commercially available carbon graphite leads constitute the main source of PGEs. A carbon graphite lead with 1-mm i.d. provides a more comfortable electrode system in a beaker as well as a significantly bigger electrode surface with its cylindrical shape in comparison with the planar surface of the traditional Teflon-encased electrodes. A simple mechanical extrusion enables the renewal of the surface of PGE-based biosensors, hence obviating the need for an additional regeneration step and erasing memory effects.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

Get My Free Ebook


Post a comment