Chemosensors/chemical sensor

In parallel with improvements in chemical sensor performance, analytical science has also seen tremendous advances in the development of compact, portable analytical instruments. For example, lab-on-a-chip (LOAC) devices enable complex bench processes (sampling, reagent addition, temperature control, analysis of reaction products) to be incorporated into a compact, device format that can provide reliable analytical information within a controlled internal environment. LOAC devices typically incorporate pumps, valves, micromachined flow manifolds, reagents, sampling system, electronics and data processing, and communications. Clearly, they are much more complex than the simple chemo-sensor described above. In fact, chemosensors can be incorporated into LOAC devices as a selective sensor, which enables the sensor to be contained within the protective internal environment. Figure 5... 

Another distinction should be made (independently of the fluorescence aspects) between chemical sensors (also called chemosensors) and biosensors. In the former, the analyte-responsive moiety is of abiotic origin, whereas it is a biological macromolecule (e.g. protein) in the latter. 

Although the construction of sensors for external physical stimuli, such as light, heat or pressure, is relatively simple, it becomes more complicated when the target stimuli come from atoms or molecules. These types of sensors are often referred to as chemical sensors or chemosensors and biochemical sensors or biosensors (see below in Sects. 1.2 and 1.3). For the latter types, a sensing material should be used that can respond to the presence of the target analyte. This response may or may not be obviously true with vague information. Hence, chemo- and biosensors should be... 

As far as chemical sensors are concerned, colorimetric chemosensors for anions based on calix[4]pyrrole (16-18, 22-31) showed strong binding to the fluoride anion. Receptors (29-31) are the first naked-eye detectable chemosensors that are able to discriminate between different anionic substrates as a result of detectable colour changes. On the other hand, the fluorescence of the receptors (16-18, 22-28) is quenched significantly in the presence of anionic guests. 

Chemical sensors are by definition small, inexpensive and preferably hand-held devices, capable of continuously monitoring chemical constituents in liquids or gases. MIP sensors usually consist of an imprinted sensitive layer and a transducer to convert the chemical information, in real time, into an electrical or optical signal which is further evaluated electronically [12]. Figure 21.1 shows the set-up of chemosensors and two typical mass-sensitive devices. 

Fig. 7.18.1 The concept of physical chemo-sensors replacing traditional chemosensors a) conventional chemical sensor b) array im plementation of a physical chemosensor, in...

Fluorescent probes have been extremely useful in elucidating biochemical mechanisms and processes inside of living cells via fluorescent microscopy. This technique is particularly valuable because it is non-destructive and the probes can be observed in real time over the course of cellular events. Fluorescent probes fall into two main classes chemosensors and biosensors. Biosensors are fluorescently labelled proteins, most often antibodies. These types of probes have the disadvantage of poor cell permeability, but can be generated with specificity for any macromolecule against which an antibody can be raised. Chemical sensors are typically based on synthetic compounds and have been used in cells mainly to quantify the concentration of certain... 

PEBBLEs are water-soluble nanoparticles based on biologically inert matrices of cross-linked polymers, typically poly(acrylamide), poly(decylmethacrylate), silica, or organically modified silicates (ORMOSILs), which encapsulate a fluorescent chemo-sensor and, often, a reference dye. These matrices have been used to make sensors for pH, metal ions, as well as for some nonionic species. The small size of the PEBBLE sensors (from 20 to 600 nm) enables their noninvasive insertion into a living cell, minimizing physical interference. The semipermeable and transparent nature of the matrix allows the analyte to interact with the indicator dye that reports the interaction via a change in the emitted fluorescence. Moreover, when compared to naked chemosensors, nanoparticles can protect the indicator from chemical interferences and minimize its toxicity. Another important feature of PEBBLEs, particularly valuable in intracellular sensing applications, is that the polymer matrix creates a separate... 

One constant problem for crown ether based sensors in vivo is the ubiquitous presence of chemical species that will compete with the target analyte for the sensor binding site. For sensors incorporating [18]crown-6 this especially problematic as sodium, potassium, ammonium and hydronium (H30+) cations are all attracted to the threefold symmetry of the crown s cavity. Protonated terminal amines, including amino acids and peptides, can also interfere with analyte detection. It is therefore all the more pleasing when a crown ether based sensor is developed that does not bind to biologically common cations. This is the case for a saxitoxin chemosensor reported by Gawley, LeBlanc and co-workers [24],... 

Figure 13.4 Typical design principle of lanthanide complex-based chemosensors based on binding of an analyte (an) (a) directly influencing the Ln(III) luminescence, (b) influencing photophysical properties of the ligand, and (c) addition of a sensitizing analyte onto a poorly luminescent lanthanide-containing sensor [1]. (Reproduced from J.C.G. Bunzli and C. Piguet, Taking advantage of luminescent lanthanide ions, Chemical Society Reviews, 34, 1048-1077, 2005, by permission of The Royal Society of Chemistry.)...

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