Screen-Printed Transducer Surface

Electrochemical immunosensors based on screen-printed electrodes have recently been applied to the detection of environmental pollutants such as PCBs, PAHs, pesticides [17-20] and of important molecules in clinical and food field [21-23]. In this case, the screen-printed electrodes are both the solid-phase for the immunoassay and the electrochemical transducers antibody or antigen molecules are directly immobilised at the sensor surface (transducer) and one of these species is enzyme-labelled in order to generate an electroactive product which can be detected at the screen-printed electrode surface. 

The objective is to describe a new non-enzymatic urea sensor based on catalytic chemical reaction. The sensor consists of screen-printed transducer (IVA, Ekaterinburg, Russia) and catalytic system which is immobilized on the transducer surface as a mixture with carbon ink. The sensor is used for measuring concentration of urea in blood serum, dialysis liquid. Detection limit is 0.007 mM, while the correlation coefficient is 0.99. Some analysis data of serum samples using the proposed sensor and urease-containing sensor (Vitros BUN/UREA Slide, Johnson Johnson Clinical Diagnostics, Inc.) are presented. 

In an effort to develop a rapid and efficient scheme for immobilizing nucleic acids onto carbon screen-printed transducers, many authors took advantage of the strong adsorptive accumulation of these biomolecules at the screen-printed carbon surfaces. In particular, many of them reported that electrochemical adsorption (adsorption controlled by a positive potential) enhances the stability of the probe and this technique was preferentially chosen. 

Electrochemical genosensors for the detection of bacteria were introduced about a decade ago. Miniaturization and advanced microfabrication technology have made it compatible with bacteria DNA diagnostic. This technology is cost effective, fast, and accurate. The bioaffinity and biocatalysis reactions generate either amper-ometric, voltametric, impedimetric, or conductimetric signals on screen-printed transducer chips (SPC), which is proportional to the number of immobilized DNA copies on the SPC surface. 

This approach separates the steps relative to the immunoreaction from the step of electrochemical detection and for this reason the working electrode surface is easily accessible by enzymatic product, which diffuse onto bare electrode surface [28,33] (Fig. 25.3). Using this strategy, finding the optimum conditions for the immunoassay on the magnetic beads and for electrochemical detection on the transducer (carbon screen-printed electrodes) is much easier than in the usual one (electrode) surface systems, because optimum conditions for immunoassay do not conform with those for electrochemical detection and vice versa. 

Screen-printed electrodes manufactured with the use of carbon-containing ink were used, (i) Catalytic system was inserted into carbon ink prior to ink immobilization on polymer substrate (ii) catalyst or polymer matrix (nation), containing catalyst, was immobilized on the working surface of the transducer. Table 27.1 displays the results of urea determination with the application of catalytic systems inserted into ink or immobilized on the transducer by different techniques. Optimum results (minimum mean square deviation and maximum correlation between the introduced and determined concentrations) are... 

Levels of lactate in buttermilk and yoghurt (and blood) were estimated using disposable sensors formed from screen-printed graphite laminated between two polymer sheets [18]. Platinum (deposited by sputter-coating) was the transducing surface. Layers of Nation were added to reduce interference and were surmounted by lactate oxidase in a mixture of polyethyleneimine and poly (carbamoyl) sulphonate hydrogel. The samples were measured in stirred buffer. A good correlation between biosensor results and those obtained with an enzyme kit was claimed but the data had a considerable amount of scatter—if the enzyme kit is taken as the reference method then a more severe analysis of the biosensor results [33] would not have shown them in a... 

Thus, this review will focus on electrochemical genosensor developed using carbon screen-printed electrodes as the transducer the methods to immobilize oligonucleotides onto carbon based surfaces will be reviewed and special emphasis will be given to describe the electrochemical adsorptive accumulation. 

In this approach double-stranded oligonucleotide PCR amplicons are labeled with a hapten on one end and another different hapten on the other end during PC R. The transducer surface (gold or carbon screen-printed chips) is treated with protein based anti-haptens that capture one of the hapten label on the PCR amplicons. The second hapten label on the PCR amplicons will bind to a specific anti-hapten-conjugated HRP or AP reporter enzyme to labeled PCR amplicons. Addition of the enzyme-specific redox substrate and application of a fixed potential between working and reference... 

Oflier applications Other applications of thin films include pyroelectric detectors and surface acoustic wave (SAW) substrates. The latter devices consist of a piezoelectric substrate onto which interdigital electrodes are deposited, for example by screen printing. An elastic wave generated at the input interdigital transducer (IDT) travels along the surface and is detected by the output interdigital transducer (OIT). These devices are mainly used as delay lines and filters in microwave and television communications (see also Chilla et al., 2003). 

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