Biological system, sensors

Lubbers D.W., Opitz N., Optical fluorescence sensors for continuous measurement of chemical concentrations in biological systems, Sensors Actuat. 1983 3 641. 

Yotter RA, Wilson DM (2003) A review of photodetectors for sensing light-emitting reporters in biological systems. Sensors J, IEEE 3(3) 288-303... 

Many complex systems have been spread on liquid interfaces for a variety of reasons. We begin this chapter with a discussion of the behavior of synthetic polymers at the liquid-air interface. Most of these systems are linear macromolecules however, rigid-rod polymers and more complex structures are of interest for potential optoelectronic applications. Biological macromolecules are spread at the liquid-vapor interface to fabricate sensors and other biomedical devices. In addition, the study of proteins at the air-water interface yields important information on enzymatic recognition, and membrane protein behavior. We touch on other biological systems, namely, phospholipids and cholesterol monolayers. These systems are so widely and routinely studied these days that they were also mentioned in some detail in Chapter IV. The closely related matter of bilayers and vesicles is also briefly addressed. 

The bioeompatible potentiometric ion sensors have been successfully applied for ion assay in biological systems such as human blood. They might be used in in-vivo cation assay in biological systems such as intra-arterial assay in the near future. 

Probes based on macrocyclic amines include dansylamidoethylcyclen, which can detect zinc at sub-nanomolar concentrations and probes containing xanthene as the chromophore with an ideal wavelength range for intracellular studies.953,962 It is also important that the sensors can differentiate between the alkali metals, which are present at higher concentrations, and zinc. 2, 7-dichlorofluorescein-based sensors have been used in biological systems and reveal concentrations up to ca. 0.3 mM in hippocampal nerve synaptic vesicles.963... 

This is the first Cys fluorescent sensor derived from FONs, in which the fluorescence enhancing property is in conjunction with a remarkable red-shifted fluorescence emission. Despite the potential sources of error when considering complicated clinical samples, the authors believe that this probe can be applied to study the effects of Cys in a biological system. 

Brovkovych et al. [38] applied the electrochemical porphyrinic sensor technique for the direct measurement of NO concentrations in the single endothelial cell. It was found that NO concentration was the highest at the cell membrane (about 1 pmoll-1) and decreased exponentially with distance from the cell, becoming undetectable at the distance of 50 pm. Now we will consider the principal reactions of nitric oxide relevant to real biological systems. 

An example of the use of soft sensors is given by the automation of a penicillin production dependent on strict adherence to certain hmits in the fermentation process since such biological systems are sensitive to changes in operational conditions. An important issue in the use of soft sensors is what to do if one or more of the input variables are not available due, for example, to sensor failure or maintenance needs. Under such circumstances, one must rely on multivariate models to reconstruct or infer the missing sensor variable. ... 

Molecular recognition in biological systems (active sites on the surfaces of macromolecule, antibody-antigen) and biological sensors (enzyme activity, biosensors). 

Other alternatives for the construction of CNT based FETs have been explored. For example, carbon nanotube branches with Y shape can be used directly as transistors where the modulation of the current from an ON to an OFF state is presumably mediated by the defects and the morphology of the junction (see Fig. 19) [170, 171]. Carbon nanotube based FETs can be gated by an electrode immersed in a solution, or by charged molecules in solution (proteins, DNA, etc.) which opens a huge field of applications in sensors [172-176] (see Fig. 20). Their ability to operate under biological conditions allows their direct use or integration into biological systems [177]. 

The physiological importance of nitric oxide should also be mentioned. It plays an important role in smooth muscle relaxation, platelet inhibition, neurotransmission, immune regulation, and penile erection (Nobel Prize in 1998 for the discovery of its role in the cardiovascular system). The importance of NO in biological systems stimulated the development of electrochemical sensors and the investigation of the electrochemical behavior of that compound. 

Development of biological sensors coupled to microprocessors or compu ters for process control and monitoring of biological systems (including humans). 

One method to realize the taste sensor may be the utilization of similar materials to biological systems as the transducer. The biological membrane is composed of proteins and lipids. Proteins are main receptors of taste substances. Especially for sour, salty, or bitter substances, the lipid-membrane part is also suggested to be the receptor site [6]. In biological taste reception, taste stimulus changes the receptor potentials of taste cells, which have various characteristics in reception [7,8]. Then the pattern constructed of receptor potentials is translated into the excitation pattern in taste neurons (across-fiber-pattem theory). 

In the present study, therefore, lipid membranes were used as transducers of taste information. Artificial lipid materials, such as dioleyl phosphate (DOPH) or dioctadecyl-dimethyl-ammonium, were used to construct a lipid membrane and responses of electrical potential and resistance of the membranes were measured [9-15]. It was confirmed that the lipid membranes could discriminate five primary taste substances. Moreover, they could detect the interactions between taste substances observed in biological systems. The response properties were different in different types of lipids. If a hydrophobic part of a lipid was different, taste substances which can be detected were different. These facts indicate that the taste sensor can be realized by the use of various kinds of lipid membranes as transducers. 

The present sensor could easily discriminate between some kinds of commercial drinks such as coffee, beer and aqueous ionic drinks (Figure 11) [22], Since the standard deviations were 2 mV at maximum in this experimental condition, these three output patterns are definitely different. If the data are accumulated in the computer, any food can be easily discriminated. Furthermore, the taste quality can also be described quantitatively by the method mentioned below. In biological systems, patterns of frequency of nerve excitation may be fed into the brain, and then foods are distinguished and their tastes are recognized [4-8]. Thus, the quality control of foods becomes possible using the taste sensor, which has a mechanism of information processing similar to biological systems. 

---