Abstract: A biosensor is an analytical device that responds in a direct. reversible. continuous. rapid. and accurate (precise) manner to changes in the concentration of chemical or biochemical species in an untreated sample. It may consist of a sensing microzone where a chemical or biochemical reaction (and. occasionally. a separation process) takes place. which is connected or integrated with an optical. electric. thermal. or mass transducer. Biosensor technology has emerged as a dynamic field of biotechnology with new methods of detecting specific chemicals at analytically useful levels [1, 2]. Its impact has been largely due to the advances made in bioelectrochemistry. microelectronics. and micro-optic technology. Biosensor research attracts scientists from far-ranging fields such as pharmacology. biochemistry. protein chemistry. material science. environmental science. electronics. and physics [3]. This coherent multidisciplinary approach is vital for the successful introduction of biosensors in new and existing fields. Biosensors have found applications in various analytical fields [4-18] including bioprocess control, biomedical analysis, environmental monitoring and control, food pharmaceutical or petrochemical analysis, and even defense. For instance, glucose biosensors are used to determine glucose in analytical [19] and clinical laboratories [20], monitor glucose levels in fermentation reactors [21, 22], estimate glucose in the food industry [23], and in pharmaceutical processes [24]. The performance and usefulness of these types of biosensors are often dictated by the immobilization methods and the immobilization matrixes employed for the deposition of the enzyme layer. For example, the sensor lifetime, its dynamic range, sensitivity, selectivity, response time, stability, and susceptibility to interferents are some of the operational parameters affected by the enzyme immobilization procedure and the type of support materials used for the biosensor fabrication. In this paper, we concisely review the theoretical aspects of the biosensor, the methods of enzyme immobilization, and the polymers as enzyme immobilization matrixes in the enzyme biosensors in recent publications.

Abstract: An immunosensor employing conducting polymer entrapment (CPE) method to immobilize immuno-protein on the quartz crystal microbalance (QCM) for clinical flow-injection-analysis (FIA) purpose was exploited. By comparing the CPE approach and the conventional physical immobilization (PI) method, a frequency shift of the former was 47% higher than that of the latter when measuring at 0.5 mg/ml human serum albumin antibody concentration. This implied that CPE was a feasible approach for developing QCM-FIA process. An immunoassay of anti-pseudorabies virus antibody in mouse sera further exemplified its practical potential in diagnostic implication.

Abstract: In this study, a quartz crystal microbalance (QCM) system operated repetitively in flow injection analysis (FIA) mode, is reported. Four immobilization approaches of seven different methods include: (i) physical adsorption; (ii) two thioamine thiolation methods, using cysteamine and cystamine for gold chemisorption and further coupling; (iii) two oxidized dextran spacer methods, coupling of cysteamine and cystamine thiolated QCM surface with periodate-oxidized dextran for further Schiff acid-base reaction; and (iv) two thiol-gold chemisorption-based self-assembled monolayer (SAM), applying short-chain, C-3, and longchain, C-11 mercapto fatty acids to insolubilize human serum albumin (HSA) on QCM surface. Effects of these protein immobilization methods on FIA immunoassay of anti-HSA were compared. At the 0.01 mg/ml anti-HSA level, the lowest analyte concentration tested, the SAM using 11-mercaptoundecanoic acid as QCM surface activating agent generated a larger frequency shift than the other immobilization methods. This implied that the use of thiolated long-chain fatty acid constructed as self-assembled monolayer may thereby potentially be a useful protein immobilization method in QCM-FIA application.