tailieunhanh - New Perspectives in Biosensors Technology and Applications Part 11

Tham khảo tài liệu 'new perspectives in biosensors technology and applications part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 292 New Perspectives in Biosensors Technology and Applications ELECTROCHEMICAL MEASUREMENT OPTICAL MEASUREMENT light beam bulk concentration bulk concentration Outer Helmholz plane Inner Helmholz plane a b Fig. 1. Difference between electrochemical a and optical b measurement. surface. The locus of electrical centres of ions adsorbed in the Helmholz layer more precisely centres of symmetry of ion electrical field is called the inner Helmholz plane. The outer Helmholz layer is formed by the space charge region which is created by interaction between electrode and charged ions in solutions. The outer Helmholz plane is the locus of centres of the nearest solvated ions with respect of to the electrode surface Bard Faulkner 1980 . The third layer is created by Nernst layer where the concentration differs from the bulk concentration due to the diffusion of electro active compounds to the electrode surface. The response of the sensor will depend on the structure of each of these layers and on the chemical reactions which run in each of these layers. There are also fluctuations of properties of each of this layer. It is obvious that these fluctuations will be averaged on the electrode surface but not in the distance x. The electrochemical biosensor is prepared from electrochemical sensor by immobilization of bioactive compound Macholán 1991 Turner et al. 1987 . The immobilized layer lies in the outer Helmholz layer and in the Nernst layer. It assures not only the run of reaction which is responsible for sensor selectivity but it influences the structure of inner Helmholz layer. The process of immobilization significantly changes the specific adsorption on the active electrode. The influence of bioactive layer on the structure of outer Helmholz layer and Nernst layer is dramatic. The bioactive membrane changes the space distribution of the charge solvation processes pH equilibration in outer Helmholz layer. The bioactive layer also changes the concentration distribution in