Ions, electrodes and biosensors

Understanding Bioanalytical Chemistry Principles and applications Victor A. Gault and Neville H. McClenaghan 2009 John Wiley Sons, Ltd 

---

Role of Polymeric Materials in the Fabrication of Ion-Selective Electrodes and Biosensors... 

Kuan SS, Guilbault GG. Ion selective electrodes and biosensors based on ISEs. In Turner APF, Karube I, Wilson GS, editors. Bioserisors, fundamentals and apphcations. Oxford Oxford University Press, 1987. 

Of the achievements of scientific research only those find industrial applications for which there is a demand and which are likely to provide reliable results under industrial conditions. In our opinion good new sensors and sensor arrays, like ISFETs and CHEMFETs, biosensors have great future prospects. Accordingly, remarkable efforts are being expended in sensor research and development. The wide range of compounds that can be measured with biosensors has been summarized by Mullen and Evans. Compounds that can be measured by electrochemical methods are listed in Table 1. There is a large volume of litterature on the combination of ion-selective electrodes and biosensors. 

Different analytes are determined by using electrochemical techniques such as differential pulse voltammetry (e.g., metal ions and chlorhexidine in oral care products, glycolic acid in creams, dyes in lipsticks) or potentiometry (e.g., inorganic compounds and anionic and cationic surfactants in personal care products). Modified carbon electrodes and biosensors have been developed to determine some cosmetic ingredients by techniques such as voltammetry or potentiometry. 

Potcntiomctric Biosensors Potentiometric electrodes for the analysis of molecules of biochemical importance can be constructed in a fashion similar to that used for gas-sensing electrodes. The most common class of potentiometric biosensors are the so-called enzyme electrodes, in which an enzyme is trapped or immobilized at the surface of an ion-selective electrode. Reaction of the analyte with the enzyme produces a product whose concentration is monitored by the ion-selective electrode. Potentiometric biosensors have also been designed around other biologically active species, including antibodies, bacterial particles, tissue, and hormone receptors. 

Few potentiometric biosensors are commercially available. As shown in Figures 11.16 and 11.17, however, available ion-selective and gas-sensing electrodes may be easily converted into biosensors. Several representative examples are described in Table 11.5, and additional examples can be found in several reviews listed in the suggested readings at the end of the chapter. 

Composite potentiometric sensors involve systems based on ion-selective electrodes separated from the test solution by another membrane that either selectively separates a certain component of the analyte or modifies this component by a suitable reaction. This group includes gas probes, enzyme electrodes and other biosensors. Gas probes are discussed in this section and chapter 8 is devoted to potentiometric biosensors. 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

NADH can be readily monitored electrochemically, and can be used as a simple and effective method to monitor metal ion concentrations. Such an approach has been recently utilised by Rodriguez et al. [149] for an SPCE-based biosensor for the amperometric detection of Hg2+, Cu2+, Cd2+, Zn+ and Pb2+. Devices used in this study were printed onto 250 pm thick polyester sheet. The working electrode (planar area 0.16 cm2) was fabricated from a commercially available carbon powder containing 5% rhodium plus promoters, which was made into a screen-printable paste by mixing 1 4 in 2.5% (w/v) hydroxyethyl cellulose in water. The reference electrode ink contained 15% silver chloride in silver paste. The counter electrode and basal tracks were fabricated... 

---