Recent developments miniaturization

What is the electrode selectivity in relation to other species in solution Remember that this is given by (k faZi,Zi) and not only by the selectivity coefficient kff. 

All these factors have to be considered. The effect of the variation of potential with temperature and alteration of the slope of the potential vs. activity profile can be minimized by periodic calibration. This period depends on the type of analysis being carried out, but calibration cannot be dispensed with. 

A diagram of a typical ISFET is shown in Fig. 13.11. Instead of using a metallic gate as in a normal FET, a thin film of a material sensitive to an ion is used (ISM). The difference in potential between the ISM and the solution is a function of ion activity. The potential developed alters the concentration of carriers in the region marked channel which in turn alters the I-V characteristics between source and drain. The current is a low-impedance signal that can be related directly to the activity of the ions in solution. 

This sensor is extremely small. The construction of many ISFETs on the same chip is possible, either identical or sensitive to different ions. A chip of 1 x 2 mm can have five or six ISFETs. 

One of the important applications possible with these sensors is for in vivo studies17. 

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One of the most fascinating recent developments in biology has been the discovery of numerous highly complex biopolymer assemblies (see also section C2.14.2.3) such as the ribosome or the bacterial flagellum [93, 94 and 95], the envy of nanoteclmologists seeking to miniaturize man-made mechanical devices (note that the word machinery is also sometimes used to refer to multienzyme complexes such as the proteasome [96]), and an entire... 

The FPI principle can also be used to develop thin-film-coating-based chemical sensors. For example, a thin layer of zeolite film has been coated to a cleaved endface of a single-mode fiber to form a low-finesse FPI sensor for chemical detection. Zeolite presents a group of crystalline aluminosilicate materials with uniform subnanometer or nanometer scale pores. Traditionally, porous zeolite materials have been used as adsorbents, catalysts, and molecular sieves for molecular or ionic separation, electrode modification, and selectivity enhancement for chemical sensors. Recently, it has been revealed that zeolites possess a unique combination of chemical and optical properties. When properly integrated with a photonic device, these unique properties may be fully utilized to develop miniaturized optical chemical sensors with high sensitivity and potentially high selectivity for various in situ monitoring applications. 

The need for improved sensor performance has led to the emergence of micro and nanofluidics. These fields seek to develop miniaturized analysis systems that combine the desired attributes in a compact and cost-effective setting. These platforms are commonly labeled as labs-on-chip or micro total analysis systems (pTAS)2, often using optical methods to realize a desired functionality. The preeminent role that optics play has recently led to the notion of optofluidics as an independent field that deals with devices and methods in which optics and fluidics enable each other3. Most of the initial lab-on-chip advances, however, occurred in the area of fluidics, while the optical components continued to consist largely of bulk components such as polarizers, filters, lenses, and objectives. 

Recently, a miniaturized thermal apparatus, [t-ThFFF, was developed and applied to characterize the molar mass distribution of synthetic polymers in organic solvent as well to determine the particle size distribution of nanoparticles (PSs latex) in aqueous carrier. This 4-ThFFF proved to performed well in both macromolecule and particle analysis [48]. 

Another relatively recent development is electron generators that are essentially sealed vacuum tubes with a 2.5 pm-thick silica ceramic window or a 5-10 pm titanium window as the beam exit. Such electron beam tubes or bulbs are capable of operating at 50 to 150 kV,64-67 71 and can be stacked into modules to cure wide webs. It is conceivable that a miniature electron beam could provide an efficient low-cost means to cure thin coatings, adhesives (clear and filled) and inks. Examples of such miniature electron beam equipment are shown in Figures 3.21 and 3.22. 

Several new methods and instruments based on infrared spectroscopy are being developed for food applications. Advances in spectroscopic instruments and data analysis have enabled the rapid and nondestructive analysis of cheese parameters in just a few seconds (e.g., Nicolet Antaris FT-NIR by Thermo Electron Corp.). Another recent development is the miniaturization of FTIR instrumentation, which would enable onsite analysis, while the cheese is being produced. The TruDefender FT handheld FTIR by Ahura Scientific, Inc. (Fig. 5.7) is a portable handheld spectrometer that could be applied to food analysis. With numerous developments in FTIR spectroscopy and several potential food analysis applications still unexplored, there is great research potential in this technique that could benefit the industry and research institutions. 

Recent developments in sensor technology allow to create different integrated and miniaturized sensor arrays. Using microsystemtechnology fluidics can be added creating whole micro-analytical devices on chip. However, there are drawbacks involving inappropriate sensor function in media and production. Using sophisticated sensor construction and microfluidics such drawbacks can be overcome. In this chapter different sensor systems and whole micro-analytical devices are presented with emphasis on their applications. 

In the third part of the book areas in which there are important applications of electrochemistry are described. Chapters 13 and 14 look at potentiometric and amperometric/voltammetric sensors respectively, focusing particularly on recent developments such as new electrode materials and miniaturization. Electrochemistry in industry, which produces many materials used directly or indirectly in everyday life, as well as batteries, is described in Chapter 15. The electrochemical phenomenon... 

Recent development in multilayer sensor architecture using sequential electrochemical polymerization of pyrrole and pyrrole derivatives to entrap enzymes was tested on a tyrosinase-based phenol sensor [127]. A phenothia-zine dye, thionine served as redox mediator and was covalently attached to the thin, functionalized first polypyrrole layer on Platinum disk electrodes. Then, a second layer of polypyrrole with entrapped tyrosinase was electrochemically deposited. The phenol sensor constructed in this manner effectively transferred electron from enz3Tne to the electrode surface. As all steps in preparation, including deposition of the enzyme-containing layer are carried out electrochemically, this technique may prove to be applicable for mass production of miniature sensors. 

Finally, it should be noted that the recent development of so-called third generation biosensors to achieve direct electron transfer from redox enzyme, oxidoreductase to the electrode without mediators, but through a series of enzyme cofactors or conductive polymers to transfer electrons from the enzyme redox center to the electrode surface [161-164]. This concept with the current technology for preparing miniature sensors with nanotechnology is of great interest to many researchers trying to develop practical sensors in clinical, environmental and industrial analysis. Whether with mediators or without, research for optimum sensor development for various purposes will be intensive in the future. 

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