Sensitivity screen-printed electrodes

Biosensors ai e widely used to the detection of hazardous contaminants in foodstuffs, soil and fresh waters. Due to high sensitivity, simple design, low cost and real-time measurement mode biosensors ai e considered as an alternative to conventional analytical techniques, e.g. GC or HPLC. Although the sensitivity and selectivity of contaminant detection is mainly determined by a biological component, i.e. enzyme or antibodies, the biosensor performance can be efficiently controlled by the optimization of its assembly and working conditions. In this report, the prospects to the improvement of pesticide detection with cholinesterase sensors based on modified screen-printed electrodes are summarized. The following opportunities for the controlled improvement of analytical characteristics of anticholinesterase pesticides ai e discussed ... 

MWNTs favored the detection of insecticide from 1.5 to 80 nM with a detection limit of InM at an inhibition of 10% (Fig. 2.7). Bucur et al. [58] employed two kinds of AChE, wild type Drosophila melanogaster and a mutant E69W, for the pesticide detection using flow injection analysis. Mutant AChE showed lower detection limit (1 X 10-7 M) than the wild type (1 X 10 6 M) for omethoate. An amperometric FIA biosensor was reported by immobilizing OPH on aminopropyl control pore glass beads [27], The amperometric response of the biosensor was linear up to 120 and 140 pM for paraoxon and methyl-parathion, respectively, with a detection limit of 20 nM (for both the pesticides). Neufeld et al. [59] reported a sensitive, rapid, small, and inexpensive amperometric microflow injection electrochemical biosensor for the identification and quantification of dimethyl 2,2 -dichlorovinyl phosphate (DDVP) on the spot. The electrochemical cell was made up of a screen-printed electrode covered with an enzymatic membrane and combined with a flow cell and computer-controlled potentiostat. Potassium hexacyanoferrate (III) was used as mediator to generate very sharp, rapid, and reproducible electric signals. Other reports on pesticide biosensors could be found in review [17],... 

L. Authier, B. Schollhorn and B. Limoges, Detection of cationic phenolic derivatives at a surfactant-doped screen-printed electrode for the sensitive indirect determination of alkaline phosphatase, Electroanalysis, 10... 

Prussian blue modified screen-printed electrodes as sensitive and stable probes for H202 and thiol measurements... 

PB-modified screen-printed electrodes were first tested in batch amperometry for H202 detection. The sensors showed a good linearity in the range between 0.1 and lOOpmoll-1 with a detection limit of 0.1 pmol 1 The regression equation of the linear part of the curve was y = 22.90a —0.013, where y represents the current in pA and x the H202 concentration in mmoll the R2 value was 0.9980. The sensitivity was 324 pA mmoll 1cm 2 with an RSD% of 5% (for all the concentrations tested by six different electrodes) (see Table 24.1). 

Coupling of screen-printed electrodes and magnetic beads for rapid and sensitive immunodetection polychlorinated biphenyls analysis in environmental samples... 

The use of the electrode surface as solid phase in immunoassay can present some problems a shielding of the surface by antibody or antigen molecules can cause hindrance in the electron transfer, resulting in a reduced signal and so a loss of sensitivity. There are different ways that can be used to improve the sensitivity of the system an interesting approach could involve the screen-printed electrodes are used only for the transduction step, whereas the affinity reaction could be performed using another physical support [24]. 

This configuration based on the use of two surfaces, magnetic beads for immunoassay and screen-printed electrodes for electrochemical detection, allows to obtain a faster and a more sensitive detection of the immunoreaction than using a unique surface (screen-printed electrode) in this case it is possible to perform the electrochemical measurement in faster times (less then 30 min) and improve the sensitivity (around two magnitude orders). For this reason, this approach is advised in the development of an electrochemical immunosensor specific to any analyte. 

Electrochemical immunosensors are valid tools for the measurement of environmental pollutants such as PCBs. These devices are based on the principles of solid-phase immunoassays and couple the specificity of the immunoassay test to the sensitivity of electrochemical techniques. Screen-printed electrodes are used in the immunosensor development, because they can have a field use and their technology allows mass production at low cost. 

Applications of electrochemical transducers have relied on conventional and bulky disk (C, Au) or mercury drop electrodes, as well as on mass-producible, single-use, thick-film carbon screen-printed electrodes. The sensitivity of such devices, coupled to their compatibility with modern microfabrication technologies, portability, low cost (disposability), minimal power requirements, and independence of sample turbidity or optical pathway, make them excellent candidates for DNA diagnostics. In addition, electrochem-... 

Enzyme DNA hybridization assays with electrochemical detection can offer enhanced sensitivity and reduced instrumentation costs in comparison with their optical counterparts. Efforts to prevent non-specific binding of the codissolved enzyme and to avoid fouling problems by selecting conditions suitable to amplify the electrode response have been reported by Heller and co-workers [107]. A disposable electrochemical sensor based on an ion-exchange film-coated screen-printed electrode was described by Limoges and co-workers for an enzyme nucleic acid hybridization assay using alkaline phosphatase [108] or horseradish peroxidase [109]. In another methodology to improve sensitivity, a carbon paste electrode with an immobilized nucleotide on the electrode surface and methylene blue as hybridization indicator was coupled, by Mascini and co-workers [110], with PGR amplification of DNA extracted from human blood for the electrochemical detection of virus. 

Applications. A biotinylated GOX-based biosensor was developed based on a new electropolymerized material consisting of a pol3rp3uidyl complex of ruthenium(II) functionalized with a pyrrole group [90]. Because histidine, lysine and arginine functions also coordinate Os /Os , biosensors based on co-electrodeposited GOX, HRP, soybean peroxidase (SBP) and laccase with redox Os /Os polymer have been developed [89]. A metal chelate formed by nickel and nitrilotriacetic acid was used to modify a screen-printed electrode surface. The functionalized support allowed stable attachment of acetylcholinesterase and the resulting biosensor was used for sensitive detection of organophosphorus insecticides [91]. This method is attractive because it ensures a controlled and oriented enzyme immobilization, considerably improving the sensitivity and the detection limit. 

Sometimes it is necessary to use different substrates, cofactors and mediators in order to increase the sensitivity. Due to the irreversible nature of many analyte-enzyme interactions, sensing elements must either be reactivated or should be disposable elements. An example is the determination of diazinon and dichlorvos that uses tyrosinase immobilized on screen printed electrodes, and a redox mediator (l,2-naphtaquinone-4-sulfonate) (Everett and Rechnitz, 1998). For other systems a further drawback is the lack of selectivity of some of the enzymes involved. 

For chemical monitoring, a list of priority substances has been established that includes metals such as cadmium, lead, and nickel. As far as metals are concerned, voltammetric techniques and more precisely electrochemical stripping analysis has long been recognized as a powerful technique in environmental samples. In particular, anodic stripping voltammetry (ASV) coupled with screen-printed electrodes (SPEs) is a great simplification in the design and operation of on site heavy metal determination in water, for reasons of cost, simplicity, speed, sensitivity, portability and simultaneous multi-analyte capabilities. The wide applications in the field for heavy metal detection were extensively reviewed (Honeychurch and Hart, 2003 Palchetti et al., 2005). 

Koblizek M, Maly J, Masojidek J et al. A Sensitive photosystem Il-based biosensor for detection of a class of herbicides. Screen printed electrodes as transduction devices. Biotechnol Bioeng 2002 78 110-116. 

An aptamer-based sandwich assay with electrochemical detection for thrombin analysis in complex matrixes using a target-capturing step by aptamer-functionalized magnetic beads was recently reported (Centi et al., 2007). The aptamer-sensing layers were fabricated on a surface of screen-printed electrodes. The high sensitivity of this sensor was demonstrated in the analysis of thrombin in buffer, spiked serum, and plasma. The concentrations detected by the electrochemical assay were in agreement with simulation software that mimics the kinetics of thrombin formation. 

HPLC with UV-based diode array detection (DAD-UV) or electrochemical detection is normally used to determine ascorbic acid. Many types of electrochemical determinations of ascorbic acid have been proposed. Although the electrochemical determinations using enzyme-based biosensors exhibited high specificity and sensitivity, these methods suffer in the fabrication of the electrodes and in automatic analysis. Recently, chemically modified screen-printed electrodes have been constructed for the determination of ascorbic acid. This is one of the most promising routes for mass production of inexpensive, reproducible, and reliable electrochemical sensors. 

Carrara, S., Shumyantseva, V.V., Archakov, A.I., and Samori, B. (2008) Screen-printed electrodes based on carbon nanotubes and cytochrome P450SCC for highly sensitive cholesterol biosensors. Biosens. Bioelectron., 24, 148-150. 

---