Anchalee Samphao

Flow-injection amperometric determination of glucose using a biosensor based on immobilization of glucose oxidase onto Au seeds decorated on core Fe3O4 nanoparticles

An amperometric biosensor based on chemisorption of glucose oxidase (GOx) on Au seeds decorated on magnetic core Fe3O4 nanoparticles (Fe3O4@Au) and their immobilization on screen-printed carbon electrode bulk-modified with manganese oxide (SPCE{MnO2}) was designed for the determination of glucose. The Fe3O4@Au/GOx modified SPCE{MnO2} was used in a flow-injection analysis (FIA) arrangement. The experimental conditions were investigated in amperometric mode with the following optimized parameters: flow rate 1.7 mL min(-1), applied potential +0.38 V, phosphate buffer solution (PBS; 0.1 mol L(-1), pH 7.0) as carrier and 3.89 unit mm(-2) enzyme glucose oxidase loading on the active surface of the SPCE. The designed biosensor in FIA arrangement yielded a linear dynamic range for glucose from 0.2 to 9.0 mmol L(-1) with a sensitivity of 2.52 µA mM(-1) cm(-2), a detection limit of 0.1 mmol L(-1) and a quantification limit of 0.3 mmol L(-1). Moreover, a good repeatability of 2.8% (number of measurements n=10) and a sufficient reproducibility of 4.0% (number of sensors n=3) were achieved. It was found that the studied system Fe3O4@Au facilitated not only a simpler enzyme immobilization but also provided wider linear range. The practical application of the proposed biosensor for FIA quantification of glucose was tested in glucose sirup samples, honeys and energy drinks with the results in good accordance with those obtained by an optical glucose meter and with the contents declared by the producers.

Development of a cobalt(II) phthalocyanine- MWCNT modified carbon paste electrode for the detection of polyunsaturated fatty acids

In this work the development of an electrochemical sensor for the determination of polyunsaturated fatty acids (PUFAs), in particular linoleic acid, in commercially available safflower oil as complex matrix is described. The sensor consists of a carbon paste electrode with cobalt(II) phthalocyanine, Co(II)Pc, as mediator and multiwalled carbon-nanotubes (MWCNT) as nanomaterial. As carrier medium a sodium borate buffer (0.1 M, pH 9) was used. PUFAs were detected at a working voltage of 0.35-0.45 V (vs. Ag/AgCl). The sensor development was carried out in a batch system with differential pulse voltammetry (DPV) and cyclic voltammetry (CV). Sensor specification was tested by using various fatty acids (stearic acid, oleic acid, linoleic acid, linolenic acid and arachidonic acid) as well as esterified fatty acids, resulting in a specific applicability towards PUFAs, especially linoleic acid (LAH). The optimized sensor was applied in a flow injection analysis system (FIA) for the analysis of PUFAs in complex matrix. Linoleic acid was used as standard substrate to determine the analytical parameters. The linearity ranges between 7.5 and 200 μg mL-1 LAH, while the limit of detection was determined to be 2.5 μg mL-1 and the limit of quantification is approximately 7.5 μg mL-1 LAH. The LAH content was successfully detected in commercially available safflower oil via standard addition method and the results could be confirmed by a reference method. The PUFA content was calculated as LAH-equivalent.

Electrochemical Sensors: Practical Approaches

The design and manufacturing of sensors is an important issue for both fields, sensors research and application. For commercialization sensors need to be of constant, reproducible quality and characteristics which are of particular interest for mass-produced one-shot sensors. Apart from these requirements a sufficiently long shelf-lifetime is necessary in order to guarantee the logistic supply with the devices. Sensors research starts usually with laboratory-made or commercially available simple electrodes which are tailored and modified according to the needs and intentions. An important aspect is the miniaturization of sensing devices, which can be achieved by either a diminishing of the dimension of macrosensors or by new concepts of placing micro- and nanosized systems directly on semiconductors and integrating them in the electronic circuits on chips, such as SoC (system on a chip, lab on a chip) and μTAS (micro total analytical system) approaches. In such cases, combination with microsystems and micromachines, also known as MEMS or MOEMS (micro-electro-mechanical systems, micro-optoelectro-mechanical systems), allows the realization of mechanical tasks in more complex analytical approaches, such as pumping, and valve-splitting, in a single microsized chip. Thus, also theoretical considerations concerning micro- and ultramicro-electrodes gain increasing importance. In the chapter here a brief overview is given on the basic transducers and on preparation techniques to create electrochemical sensors. Due to the huge amount of literature in this field, only characteristic examples and review articles are cited.