Surface chemical sensors

Furlong D N, Gedded N J, Paschinger E, Okahata Y, Ebato H, Ebara Y and Tanaka K 1993 Surface chemical sensors for bitter/sweets, smells and antibodies in aqueous solution Chem. Australia October 552-5... 

There are three advantages to study molecular recognition on surfaces and interfaces (monolayers, films, membranes or soHds) (175) (/) rigid receptor sites can be designed (2) the synthetic chemistry may be simplified (J) the surface can be attached to transducers which makes analysis easier and may transform the molecular recognition interface to a chemical sensor. And, which is also a typical fact, this kind of molecular recognition involves outside directed interaction sites, ie, exo-receptor function (9) (see Fig. 5b). 

A new chemical sensor based on surface transverse device has been developed (99) (see Sensors). It resembles a surface acoustic wave sensor with the addition of a metal grating between the tranducer and a different crystal orientation. This sensor operates at 250 mH2 and is ideally suited to measurements of surface-attached mass under fluid immersion. By immohi1i2ing atra2ine to the surface of the sensor device, the detection of atra2ine in the range of 0.06 ppb to 10 ppm was demonstrated. 

Bulk and surface imprinting strategies are straightforward tools to generate artificial antibodies. Combined with transducers such as QCM (quartz crystal microbalance), SAW (surface acoustic wave resonator), IDC (interdigital capacitor) or SPR (surface plasmon resonator) they yield powerful chemical sensors for a very broad range of analytes. 

Self-organized materials with high surface area and pore size 3-25 nm was produced used templating and coassembly. The highly porous nature of the ordered combined with low adsorption and emission in the visible spectrum, facile diffusion makes them good candidate for optical and chemical sensor and provide new avenues for encapsulation/ immobilization processes and solve the problems mentioned above. 

We showed that these mesoporous silica materials, with variable pore sizes and susceptible surface areas for functionalization, can be utilized as good separation devices and immobilization for biomolecules, where the ones are sequestered and released depending on their size and charge, within the channels. Mesoporous silica with large-pore-size stmctures, are best suited for this purpose, since more molecules can be immobilized and the large porosity of the materials provide better access for the substrates to the immobilized molecules. The mechanism of bimolecular adsorption in the mesopore channels was suggested to be ionic interaction. On the first stage on the way of creation of chemical sensors on the basis of functionalized mesoporous silica materials for selective determination of herbicide in an environment was conducted research of sorption activity number of such materials in relation to 2,4-D. 

In nanotechnology, dimensions of interest are shrinking from the fiva to the nm range. For many microelectronic devices, such as laterally structured surfaces, particles, sensors, their physical as well as their chemical properties are decisively determined by their chemical composition. Its knowledge is mandatory for understanding their behavior, as well as for their successful and reliable technical application. This presents a challenge for TOF-SIMS, because of its demand for the unique combination of spatial resolution and sensitivity. 

Matsubara, K., Kawata, S. and Minami, S. (1988) Optical chemical sensor based on surface plasmon measurement Appl. Opt., 27, 1160-1163. 

A large number of possible applications of arrays of nanoparticles on solid surfaces is reviewed in Refs. [23,24]. They include, for example, development of new (elect-ro)catalytical systems for applications as chemical sensors, biosensors or (bio)fuel cells, preparation of optical biosensors exploiting localized plasmonic effect or surface enhanced Raman scattering, development of single electron devices and electroluminescent structures and many other applications. 

In Chapter 1 we consider the physical and diemical basis of the method of semiconductor chemical sensors. The items dealing with mechanisms of interaction of gaseous phase with the surface of solids are considered in substantial detail. We also consider in this part the various forms of adsorption and adsorption kinetics processes as well as adsorption equilibria existing in real gas-semiconductor oxide adsorbent systems. We analyze the role of electron theory of chemisorption on... 

Let us start with a definition. Semiconductor chemical sensor is an electronic device designed to monitor the content of particles of a certain gas in surrounding medium. The operational principle of this device is based on transformation of the value of adsorption directly into electrical signal. This signal corresponds to amount of particles adsorbed from surrounding medium or deposited on the surface of operational element of the sensor due to heterogeneous diemical reaction. 

Thus, sensor effect deals with the change of various electrophysical characteristics of semiconductor adsorbent when detected particles occur on its surface irrespective of the mechanism of their creation. This happens because the surface chemical compounds obtained as a result of chemisorption are substantially stable and capable on numerous occasions of exchanging charge with the volume bands of adsorbent or directly interact with electrically active defects of a semiconductor, which leads to direct change in concentration of free carriers and, in several cases, the charge state of the surface. 

Even listing all above problems and requirements leading to their solution indicates that development of the method of semiconductor chemical sensors opens a wide research domain. In order to resolve this problems and implement all capabilities of the method of semiconductor sensors there are two ways now the old trial and error approach and approach related to further studies of physical and chemical properties of surface phenomena, reactions and processes underlying this method. It is quite clear that the second approach is more promising in order to obtain semiconductor sensors designed for the use in accurate scientific studies and for practical gas analysis. 

Therefore, the interaction of the EEPs with the surface of sensors is a complex process that, being dependent on the nature of the surface and the nature of the active particle, results either in chemical transformation (chemisorption, for instance), or in transfer of excitation energy to a solid body, the processes that proceed at different velocities. 

The monograph is devoted to scientific basis of semiconductor chemical sensors technique. Its attention is focused at the usage of semiconductor sensors in the precision physico-chemical studies. The monograph expounds physical and chemical basis underlying the semiconductor sensor method, discusses the mechanism of processes occurring under interaction of gas with semiconductor adsorbent surface, leading to changed electrophysical parameters of the latter. 

In these sensors, the intrinsic absorption of the analyte is measured directly. No indicator chemistry is involved. Thus, it is more a kind of remote spectroscopy, except that the instrument comes to the sample (rather than the sample to the instrument or cuvette). Numerous geometries have been designed for plain fiber chemical sensors, all kinds of spectroscopies (from IR to mid-IR and visible to the UV from Raman to light scatter, and from fluorescence and phosphorescence intensity to the respective decay times) have been exploited, and more sophisticated methods including evanescent wave spectroscopy and surface plasmon resonance have been applied. 

In practice, surface modifications are restricted to sensors of the ATR- or FEWS-type. For other transducer layouts, the sample - radiation interaction is less localised, making a modification difficult to impossible. Depending on the analytes and the environment of the sensor, two basic surface modification strategies can be used to enhance the function of vibrational spectroscopic optical chemical sensors. The functional layers can either be... 

Han L., Niemczyk T.M., Lu Y., Lopez G.P., Chemical Sensors Based on Surface-Modified Sol-Gel-Coated Infrared Waveguides, Appl. Spectrosc., 1998 52(1) 119-122. 

Jorgenson R.C., Yee S.S., A fiber-optic chemical sensor based on surface plasmon resonance, Sensors and Actuators B 1993 12 213-220. 

Figure 3 Schematic diagram of a solid-phase N02 sensor. The sensor consists of a small cell supporting the polymer-coated, glass substrate behind a glass window in full view of a PMT. The CL reagent is immobilized on the hydrogel substrate. The gel is sandwiched between the glass window and a Teflon PTFE membrane. The purpose of the Teflon membrane is to permit the diffusion of N02 from the airstream into the gel while preventing the loss of water from the hydrogel. Inlet and outlet tubes (PTFE) allow a vacuum pump to sample air (2 L/min) directly across the surface of the chemical sensor. (Adapted with permission from Ref. 12.)...

Introduction of chemical sensors for water quality monitoring. This includes parameters like turbidity, color, surface tension, detergent concentrations, pH-value etc. Optoelectronic systems are used to monitor the turbidity of washing water, which then determines the number of rinsing cycles (aqua-sensor system). 

Chemical sensors for water quality determination. The parameters measured include turbidity, color, surface tension, detergent concentration, pH-value etc. 

Fig. 7.14 Zeolite thin film FPI chemical sensor, (a) As synthesized outer surface and interference signal, (b) polished outer surface and improved interference signal, and (c) sensor schematic. Reprinted from Ref. 22 with permission. 2008 Molecular Diversity Preservation International...

---