Electronically transduced films

ELECTRONICALLY TRANSDUCED PHOTOCHEMICAL SWITCHING OF ORGANIC MONOLAYERS AND THIN FILMS... 

Electronically Transduced Photochemical Switching of Organic Monolayers and Thin Films 221... 

Nickel, A.M.L. Seker, F. Ziemer, B.P. Ellis, A.B. Imprinted poly (acrylic acid) films on cadmium selenide. A composite sensor structure that couples selective amine binding with semiconductor substrate photoluminescence. Chem. Mater. 2001, 13, 1391-1397. Sallacan, N. Zayats, M. Bourenko, T. Kharitonov, A.B. Willner, I. Imprinting of nucleotide and monosaccharide recognition sites in acrylamidephenylboronic acid-acrylamide copolymer membranes associated with electronic transducers. Anal. Chem. 2002, 74, 702 712. 

Mousavi et al. have used PEDOT-CNT composite as ion-to-electron transducer in the fabrication of potassium ISEs [19]. In this work, PEDOT was electrochemically S5mthesized using negatively charged multi-walled CNTs (MWCNTs) as counterions. Results from cyclic voltammetric (CV) and electrochemical impedance spectroscopic (EIS) measurements shown in Fig. 11.1, reveal that the PEDOT-MWCNT film exhibits higher redox capacitance than a film based on PEDOT doped with chloride [Cr) ions, i.e., PEDOT-Cl. This sufficiently high redox capacitance is one of the conditions necessary for stable potential in all-solid-state ISEs having an ECP as the solid contact [23]. 

Biosensors based on biorecognition events occurring in monolayer or thin-fihn assemblies on electronic transducers represent an important recent advance in bioelectronics [15]. The nano-architecture of the sensing interface in a mono-layer, multilayer, or thin-fihn structures precludes diffusion barriers, and hence the rapid response-times of the sensing devices are achieved. Enzyme-electrodes [16,17], immunosensors [18,19], or DNA sensors [13] were developed by tailoring nanoscale sensing interfaces on the transducer. We will specifically address the development of DNA sensors in monolayer and thin-film confignrations. 

Therefore, investigators have shown considerable interest in the adoption of the Langmuir-Blodgett technique, or its modifications, to make molecular electronic devices using, in particular, as an active component, a light-transducing protein, such as BR. In fact, the ability of BR to form thin films with excellent optical properties and the intrinsic properties themselves make it an outstanding candidate for use in optically coupled devices. 

The pH optical fiber sensor without any pH-sensitive dye was also described70. Porous silica layer made by the sol-gel method was cladded onto optical fibre core and was exploited as the optical transducer. Acid-base properties of silica surface caused that the surface charge of silica changed with pH of the solution. For example saturation of the sol-gel layer with cations leads to an increase of the electron density of the film, hence, the refractive index of the film. Since the surface charge of silica depends on pH, the refractive index of silica film varies also with pH. Thus, changes of... 

Mainly, three approaches have been used to immobilize the enzyme on transducer or electrode surface, single layer, bilayer, and sandwich configurations [69, 98], In some studies enzymes are covalently linked with sol-gel thin films [99], Sol-gel thin films are highly convenient for fast, large, and homogeneous electron transfer [17]. With an increase in gel thickness the signal decays and diffusion of analytes to biomolecule active site becomes difficult eventually these factors lead to poor response. By employing thin films various biosensors such as optical and electrochemical biosensors have been reported. 

Figure 1. Stylised chemical sensor comprising a conducting cable or track to convey the electronic signal to the outside world, a transducer to sense the chemical signal and convert it into an electronic form, and a chemically sensitive film or membrane at which the molecular binding event occurs.

They produced high performance electrets from thin polymer films metallized so as to yield high capacitance. Both electrical and mechanical properties of these transducers have been remarkable examples of how applications of science of solids, including knowledge of electron traps, conduction processes in insulators and the viscoelastic phenomena of semicrystalline polymers, can be combined.(6) Incidentally, similar ideas have been applied to optimization of the properties of particle microphones, through assemblies of perfectly microspherical polymer carbon systems. These have shown what limits of performance... 

Figure 1. Implantation of electrons in polytetrafluoroethylene films to form electric transducer of high stability and sensitivity.

Most microhotplate-based chemical sensors have been realized as multi-chip solutions with separate transducer and electronics chips. One example includes a gas sensor based on a thin metal film [16]. Another example is a hybrid sensor system comprising a tin-oxide-coated microhotplate, an alcohol sensor, a humidity sensor and a corresponding ASIC chip (Application Specific Integrated Circuit) [17]. More recent developments include an interface-circuit chip for metal oxide gas sensors and the conccept for an on-chip driving circuitry architecture of a gas sensor array [18,19]. 

Magnetic properties are important in the function of electronic devices. An example is the use of yttrium iron garnet (YIG) in microwave devices. On applying an external magnetic field to a YIG disk, the input, say energy of one particular frequency selectively passes to the output. Thin films based of YIG within which magnetic waves can pass have proven to be useful. The use of lanthanides in magnetic devices as transducers is listed in Table 12.18. 

ZnO is a wide band gap semiconductor, which is used for various applications. Based on textured ZnO films one can build highly effective piezo field emitters. On the other hand ZnO is a very effective electron-excited phosphor. ZnO films easily withstand electron fluence more than 1 W/cm. ZnO films doped with Al, Ga, or In have a low resistivity of about 10 " Qcm and a high transparency of about 90%. This is sufficient for applications as a front contact in solar cells, liquid crystal displays etc. Dielectric ZnO films have a high electromechanical coupling factor that allow using ZnO in various surface acoustic wave (SAW) devices such as delay lines, delay-line filters, resonators, transducers and SAW convolvers. 

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