Fabrications screen-printed electrodes

Electrochemical sensors and biosensors offer the achievable opportunity of simplifying the analyses of complex matrices, outside of the laboratory, by suitable modification of appropriate electrode materials [1-5]. One of the most attractive methods for the fabrication of such devices involves the use of screen-printing technology. This allows the (bio)sensors to be manufactured in a wide range of geometries at low cost, particularly when carbon is used therefore, this allows the devices to become disposable [1,2]. A typical screen-printed electrode design commonly used in our laboratories for prototype investigations is shown in Fig. 23.1. 

For convenient fabrication of batches of screen-printed electrodes, the SPCEs are usually printed as groups of eight, which can be cut up into individual electrodes. We have used relatively small rectangular distal pads with a geometric area of 2.5 x 4 mm. The size and shape of the electrodes is up to the individual researcher who should decide for themselves the appropriate quantities of inks to generate. 

FIGURE 9.1 Scheme of screen-printing electrodes. Fabrication process of the sensor consisted of three steps including consecutive printing of the silver layer (b), carbon layer (c), and insulating layer (d) on the polyester substrate. The sensors were produced in sheets of 20 electrodes. 

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. 

The screen printing process uses a porous mesh stretched tightly over a frame made of wood or metal. Fig. 9.1 The mesh is made of porous fabric or stainless steel. A stencil is produced on the screen either manually or photochemically defining the image to be printed. Thus, the design of the stencil allows to obtain a wide range of screen-printed electrodes in which the electrodic configuration, as well as the size and form of these electrodes can be controlled. 

The most employed inks for the fabrication of screen-printed electrodes are made of carbon, gold, platinum, or silver. Nevertheless, other materials can be easily used. 

As it has been shown in previous sections, the use of screen-printed electrodes as support for genosensor devices offers enormous opportunities for their application in molecular diagnosis. The technologies used in the fabrication of these electrodes allow the mass production of reproducible, inexpensive and mechanically robust strip solid electrodes. Other important advantages of these electrodes are the possibility of miniaturization as well as their easy manipulation in a disposable manner and therefore the use of small volumes, diminishing the cost of the analysis. This is an important issue that makes this methodology for the detection of DNA more attractive. 

Other attachment integrations on a paper microfluidic sensor are required in terms of various detecting appUcatimis. Screen-printed electrodes are fabricated on a filter paper for electrochenucal signal detection. In another study, gold nanoparticles are deposited on paper detecting region as the colorimetric indicator for molecular marker and DNA detection [3]. 

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. 

A performant reagentless ECL system for H2O2 detection based on electrop-olymerized luminol on pre-treated screen-printed electrodes was developed [64]. An ECL biosensor based on carboxylic acid-functionaUzed multi-walled carbon nanotubes (CCX)H-F-MWNT) and Au nanoparticles [65] and immobilization in sol-gel hybrid material was fabricated for sensing the efficiency of ethanol. The intensity of ECL increased linearly with ethanol concentration from 2.5 x 10 5.0 X 10 M and detection limit was 1.0 x 10 M [66]. 

Figure 8.11 Fabrication of a boronic acid based immune-assay sensor on a screen printed electrode platform. (Reproduced from ref. 83 with the permission of Elsevier.)...

The effect of mechanical stress on screen-printed sensors fabricated upon differing electrode substrates has been studied by Wang et al. [80]. The different substrates utilised within the study included Mylar, polyethylene naphthalate (PEN) and Kapton. In this instance, the bending of the electrodes to extremely small radii of curvature was determined to have minimal effect upon the electrochemical behaviour, resulting in only a small increase in the electrical resistance of the sensors. Additionally, the study determined that the electrochemical signal was not adversely impacted from cyclic bending this illustrates the robust nature of screen-printed electrodes upon flexible substrates [80],... 

Other work by Kadara et al. [91] reported the fabrication of disposable and flexible screen-printed microelectrodes characterised by microscopy and cyclic voltammetry. The advantages presented by the fabricated electrodes included reduced expenditure and cleaning processes, as each of the microelecttodes is designed to be disposable the removal of the requirement of cleaning stages, but also pre-treatment between analyses, allows for a much more efficient and rapid analysis of samples the work also boasted exceptional detection limits with the screen-printed electrodes providing comparable detection limits to that obtained in the literature at insonated boron-doped diamond electrodes [91]. 

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