Enzyme-Based Biosensors With Optical Detection

Enzyme-Based Biosensors with Optical Detection 

A decrease in PO2 arising from the enzyme-catalyzed oxidation of glucose results in an increase in luminescence intensity of the ruthenium tris(phenanthrene). 

Similar optical biosensors have been prepared for many other analytes. For example, a cholesterol optical biosensor has been devised based on fluorescence quenching of an oxygen-sensitive dye that is coupled to consumption of oxygen resulting from the enzyme-catalyzed oxidation of cholesterol by the enzyme cholesterol oxidase. Serum bilirubin has been detected using bilirubin oxidase, coimmobilized with a ruthenium dye, on an optical fiber.The bilirubin sensor was reported to exhibit a lower detection limit of iO Xmol/L, a linear range up to 30mmol/L, and a typical reproducibihty of 3% (CV), certainly adequate for clinical application. 

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Enzyme-Based Biosensors with Optical Detection... 

A review of chemical sensors and arrays [6] focuses on conducting polymers as inherent receptors, the modification of conducting polymers with receptors, the use of conducting polymers as transducers as well as some applications in combinatorial and high-throughput assays. Fundamental aspects of redox-related conductivity and pH-sensitive conductivity are included, and applications to chemical- and enzyme-based biosensors are summarized based on analyte. A variety of detection methods (electrical, electrochemical, and optical) are surveyed. 

Enzyme-based biosensors have been used also for the detection of phenolic estrogens. The detection principle was based on the ability of tyrosinase to catalyze the oxidation of phenolic estrogens to o-diphenol and o-quinone. Using this principle tyrosinase-carbon paste electrodes have been used for the detection of phenol, catechol, bisphenol A, genistein, quercetin, nonylphenol, and diethylstilbestrol with detection levels in the micromolar range.Optical and amperometric biosensors based on estrogen receptors have also been developed. 

Enzyme sensors can measure analytes that are the substrates of enzymatic reactions. Thermometric sensors can measure the heat produced by the enzyme reaction [31], while optical or electrochemical transducers measure a product produced or cofactor consumed in the reaction. For example, several urea sensors are based on the hydrolysis of urea by urease producing ammonia, which can be detected by an ammonium ion-selective ISE or ISFET [48] or a conductometric device [49]. Amperometric enzyme sensors are based on the measurement of an electroactive product or cofactor [50] an example is the glucose oxidase-based sensor for glucose, the most commercially successful biosensor. Enzymes are incorporated in amperometric sensors in functionalised monolayers [51], entrapped in polymers [52], carbon pastes [53] or zeolites [54]. Other catalytic biological systems such as micro-organisms, abzymes, organelles and tissue slices have also been combined with electrochemical transducers. 

A DNA optical sensor system was proposed by Cass and co-workers [35] based on the combination of sandwich solution hybridization, magnetic bead capture, flow injection and chemiluminescence for the rapid detection of DNA hybridization. Sandwich solution hybridization uses two sets of DNA probes, one labelled with biotin, the other with an enzyme marker and hybridization is performed in solution where the mobility is greater and the hybridization process is faster, rather than on a surface. The hybrids were bound to the streptavidin-coated magnetic beads through biotin-streptavidin binding reaction. A chemiluminescence fibre-optic biosensor for the detection of hybridization of horseradish peroxidase-labelled complementary DNA to covalent immobilized DNA probes was developed by Zhou and co-workers [36]. 

Enzyme biosensors have been described using a range of transduction elements (amper-ometry, potentiometry, optical and photo-thermal). The first biosensor was described in the literature by Clarck and Lyons (1962a) and was based on the use of glucose oxidase combined with electrochemical detection. Since then, this principle has been widely applied in biosensor development, and the enzyme systems used have been mainly oxido-reductases (e.g. tyrosinase, peroxidase and lactase) (Cass etal., 1984 Kulis and Vidziunaite, 2003), and hydrolases (choline esterases) (Andreescu etal., 2002 Nunes etal., 1998). 

Dancil KPS, Greiner DP, Sailor MJ (1999) A porous silicon optical biosensor detection of reversible binding of IgG to a protein A-modified surface. J Am Chem Soc 121 7925 De Stefano L, Arcari P, Lambert A, Sanges C, Rotiroti L, Rea I, Rendina I (2007) DNA optical detection based on porous silicon technology from biosensors to biochips. Sensors 7 214 DeLouise LA, Kou PM, Miller BL (2005) Cross-correlation of optical microcavity biosensor response with immobilized enzyme activity. Insights into biosensor sensitivity. Anal Chem 77 3222... 

The creation of an optical sensor that detects the cofactors on which many enzymes dqiend is a much massociated with many enzymes, particularly dehydrogenases. This cofactor has a maximal absorption at 340 nm and a maximal fluorescence emission at 400 nm, which is easily detectable with a photomultiplier. NADH also has the advantage that it can be immobilized on the same support as the enzyme (see 3.3.1.e). nber-optic biosensors based on the fluorimetric detection of NADH have been constructed for the determination of lactate and pyruvate [208]. These sensors use inunobilized lactate dehydrogenase AD) to catalyse the following equilibrium reaction ... 

Absorbance- and reflectance-based measurements are widespread, as there are many enzymatic reaction products or intermediates that are colored or if not, can react with the appropriate indicator. Sensors using acetylcholinesterase for carbamate pesticides detection are an example of indirect optical fiber biosensors. This enzyme catalyses the hydrolysis of acetylcholine with concomitant decrease in pH41 ... 

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