Screen-printed electrodes SPEs

The 2 x SSC buffer solution contained 300 mM of NaCl and 30 mM C3H5Na307 (pH 7.4). The acetate buffer solution (ABS) was prepared at the final concentration of 0.25 M, with 10 mM of NaCl (pH 4.7). All oligonucleotides, probes and complementary strands were purchased from Sigma Genosys (UK). All measurements were performed using screen-printed electrodes (SPEs). SPEs were used as disposable. The three-electrode system used was formed by a graphite working electrode, a counter electrode and a silver-based reference electrode. 

In this section, we discuss about the screen printed electrode (SPE) based AChE sensors for the selective determination of OP and CA pesticides. In the past decades, several attempts were made by the researchers to develop SPE based pesticide sensors, where the enzyme AChE was immobilized either directly onto the electrode or above other matrices incorporated SPE surfaces. Both approaches resulted in the good, rapid detection of OP and CA pesticides. Earlier, Hart et al. employed AChE/SPE to detect OP and CA pesticides [21], They measured the enzyme activity from the rate of hydrolysis of acetylthiocholine iodide. Three polymers such as hydroxyethyl cellulose, dimethylaminoethyl methacrylate, and polyethyleneimine were used as enzyme immobilization matrices. Initially, electrodes were exposed to drops of water or pesticide solution, dried and their activity was screened after 24 h. They found that, when the enzyme matrix was hydroxyethyl cellulose, electrode activity inhibited both by water as well as by pesticides. While with co-polymer matrix, a significant response towards pesticides alone was observed. Further, the long-term storage stability of electrodes was highest when the enzyme matrix consisted of the co-polymer. The electrodes retained their activity for nearly one year. In contrast, the electrodes made of hydroxyethyl cellulose or polyethyleneimine possess less stability. 

Potential Functions of the Screen Printed Electrodes (SPEs)/PalmSens Device in the Frame of the WFD with Regard to the Performance Criteria... 

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). 

The aim of this work is to demonstrate how the screen printed electrodes (SPEs) can be used for on site heavy metals monitoring in surface waters in the frame of the WFD. The sensors used consist of mercury-coated screen-printed electrodes coupled with square wave anodic stripping voltammetry (SWASV) (Palchetti et al., 1999). Three metals Cu, Cd, and Pb which are classically analysed in water matrices have been considered. Moreover, Cd and Pb belong to the priority substances list of the WFD. Performance criteria of the device are first established to evaluate the level of confidence of the method. The potential use of the device and its main advantages are then highlighted through two illustrative field applications. 

The sensor developed by the University of Florence (I) (Palchetti etal., 2005) consists of three screen-printed electrodes (SPEs) (Figure 4.2.1) ... 

Figure 4.2.1 (a) (b) Screen-Printed Electrodes (SPEs) (c) (SPEs) in combination with SWASV... 

POTENTIAL FUNCTIONS OF THE SCREEN PRINTED ELECTRODES (SPEs)/PALMSENS DEVICE IN THE FRAME OF THE WFD WITH REGARD TO THE PERFORMANCE CRITERIA... 

Screen-Printed Planar screen-printed electrodes (SPEs) were obtained from Biode-... 

Fig. 4. (A) Photograph of screen-printed gold and carbon electrode with the three-electrode system including a carbon-based counter electrode and Ag/AgCI-based inner reference electrode. (B) Photograph of a typical electrochemical setup with a computer-controlled potentiostat connected to a screen-printed electrode (SPE).

Most biosensors based on AChE have the enzymes immobilized on the surface of the sensor. The inhibition reaction being irreversible, the membrane with immobilized enzyme has to be replaced after several measurements or the biosensor can be use for only one determination. Due to this fact, the researchers tried to realize pesticide biosensors with a renewable surface or disposable biosensors based on screen-printed electrodes (SPE). The screen-printing technology provides a simple, fast and inexpensive method for mass production of disposable biosensors for different biomolecules starting with glucose, lactate and finishing with environmental contaminants as pesticides (Kulys et al., 1991) and herbicides (Skladal, 1992). 

Figure 9.8. Steps of the sandwich-type assay (1] The redox polymer and the oligonucleotide probe are electrodeposited on the screen-printed electrode (SPE) [2] the capture probe and the target are hybridized (3] the electrode-bound target and the HRP-labeled oligonucleotide are hybridized, the HRP labels are in electrical contact with the redox polymer and (4] the electrocatal5dic reduction current of H2O2 to water is measured. Reprinted with permission from ACS [38].

Fig. 8.19 Key step of the magnetic electrochemical assay using an organo-metalllc complex S as substrate for an enzyme (Alkaline Phosphatase) linked to the analyte and a screen-printed electrode (SPE) coated with Nation for the electrochemical detection of the cationic product P. (Adapted from [89]).

This immunosensor-type assay uses ferrocene methanol as co-substrate (redox mediator) of glucose oxidase (GOD). The various steps of the assay, shown in Fig. 8.20, are as follows (1) Covalent immobilization of protein A on graphite-polystyrene screen-printed electrodes (SPEs) (2) Addition of the rabbit IgG to be quantified which is captured specifically by protein A (3) Addition of a biotinylated goat anti-rabbit antibody (4) Addition of avidin-GOD conjugate (5) Addition of glucose and ferrocene methanol (6) Measurement of catalytic current by flow injection immunoassay. The voltammetric current corresponds to the one-electron oxidation of the ferrocenyl group to ferricinium. The electrode can subsequently be regenerated up to 30 times. The feasibility of the assay has been demonstrated for the case of monoclonal mouse anti-human prolactin (PL) with a detection limit of 0.02 pg mL [90]. 

Fig, 12 SEM micrographs of the various screen printed electrodes SPEs edge-like plane ESPE (A) basal-like plane BSPE (B) and graphene SPE from different commercially graphene inks GSPEl (C) and GSPE2 (D). Reproduced from Randviir etal. with permission of publisher. 

Fig. 16 (A) Screen printed electrode SPE platform, (B) TEM micrographs of the mesoporous carbons on SPE and (C) structures of poly (2-hydroxyethyl methacrylate) (PEIEMA), poly (hydroxybutyl methacrylate) (PEIBMA), poly (tert-butyl methacrylate) (PTBMA) and poly (n-propyl methacrylate) (PPMA) polymer binders. Reproduced from Dai et a/. with permission of publisher.

An example of the selective detection of E. coli involved an impedimetric immunosensor developed using SAM-modified gold screen-printed electrodes (SPEs) [27]. In this... 

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