Transducers screen printing

Sulphite Amperometric Sulfite oxidase with cytochrome c, as electron acceptor, and a screen-printed transducer Abass et al. (2000)... 

An SPCE modified with CoPC was employed as an H202 transducer in a cholesterol biosensor fabricated by the drop-coating of ChOx, followed by a cellulose acetate membrane [50]. The resulting cholesterol biosensors were operated in stirred solutions using an applied potential of +400 mV vs. screen-printed Ag/AgCl, and displayed a linear range of 0.06-5 mM. 

A.K. Abass, J.P. Hart and D. Cowell, Development of an amperometric sulphite biosensor based on sulphite oxidase with cytochrome c, as electron acceptor, and a screen-printed transducer, Sens. Actuators B Chem., 62 (2000) 148-153. 

Most electrochemical immunosensors use screen-printed electrodes produced by thick-film technology as transducers the importance of screen-printed electrodes in analytical chemistry is related to the interest for development of disposable and inexpensive immunosensors. A thick-film is based on the layers deposition of inks or pastes sequentially onto an insulating support or substrate the ink is forced through a screen onto a substrate and the open mesh pattern in the screen defines the pattern of the deposited ink. 

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. 

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. 

In literature, a direct competitive assay performed using magnetic beads protein G coated as solid phase and carbon screen-printed electrodes as transducers is reported [4], The main steps of the assay are shown in Fig. 25.4. 

In the traditional format, screen-printed electrodes are used as solid phase to carry out the immunoassay and as signal transducers. In recent years, different kinds of beads (glass, graphite particles or magnetic particles) have been used as solid phase to perform the immunoassay. For this reason, it is possible to use a new approach in the immunosensor construction coupling beads to screen-printed electrodes. 

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 traditional format. 

Our work deals with only a few examples (i) the immunosensor for the forest-spring encephalitis diagnosis (a metal label is used for signal generation), (ii) the enzyme-free urea sensor and (iii) the platinum sensor for antioxidant activity determination. What they all have in common is a screen-printed transducer consisting of graphite or Pt nanoparticles. Transducer configuration is shown in Fig. 27.1. 

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... 

Sodium phosphate monobasic [S 9638], sodium phosphate dibasic [S 0876], sodium chloride [S 7653], acetylcholinesterase from Elect-rophorus electricus (Type V-S) [C 2888], potassium chloride [P 3911], 1,2-diaminobenzenedihydrochloride [P 1526], paraoxon (o,o-diethyl o-4-nitrophenyl phosphate) [D 9286], ferrocene carboxylic acid [106887], aniline [A 9880] and acetylthiocholine chloride [A 5751] were purchased from the Sigma Chemical Company (Dorset, UK). Screen-printed transducers were purchased from Gwent Electronic Materials Ltd. (Gwent, Wales, UK). These electrode assemblies comprised a working electrode based on carbon ink doped with cobalt phthalocya-nine, an on board reference electrode (Ag/AgCl) and counter electrode (platinum) (see Fig. 24.1). 

ELECTROCHEMICAL IMMUNOSENSOR USING MAGNETIC BEADS AS SOLID PHASE AND CARBON SCREEN-PRINTED ELECTRODES (SPCES) AS TRANSDUCERS... 

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. 

Abstract The data reported in literature demonstrate that screen-printed carbon electrodes are very suitable for supporting nucleic-acid layers and to transduce effectively the DNA recognition event and many works have been devoted to developing self contained screen-printed DNA chips. 

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. 

Thus, this review will focus on an electrochemical genosensor developed using carbon screen-printed electrodes as the transducers the methods to immobilize DNA probes... 

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-... 

Lucarelli et al. describe a disposable indicator-free screen-printed genosensor applied to the detection of apoE sequences in PCR samples [26]. The biosensor format involved the immobilization of an inosine-modified (guanine-free) probe onto a SPE transducer and the detection of the duplex formation in connection with the square-wave voltammetric measurement of the guanine oxidation peak of the target sequence. 

Nanosensors for electrochemical detection have been made for years using more traditional fabrication methods, e.g., pulled platinum strings and carbon fibers. Carbon fibers can be purchased with diameters in the low /am range. These can subsequently be etched in an Ar beam until conically shaped tips are produced with tip diameters between 100 and 500 nm [61]. Similarly, a platinum wire can be heated and pulled in order to create tips of similar diameters. Thick film electrodes made by screen printing [62] have also been shown to find application as transducer in microchaimel systems [63]. 

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