Polythiophene sensors

A modular and flexible approach to polythiophene sensors based on the polymerization of a thiophene-activated ester has been reported (Bernier et al. 2002). Subsequent reaction of the pol5mierized NHS ester with a variety of diamines permits the synthesis of sensors for different analytes from a common platform. For example, reaction of the NHS polymer with an aminomethyl-modified 15-crown-5 derivative yielded a polymer that underwent color changes in the presence of alkah cations (Fig. 12.14). 

Polythiophene Sensors (8,49, 50). In order to gain information concerning the type of interaction between polymer sensing material and analyte vapor, we have performed preliminary studies with a non-doped regioregular poly(3-hexylthiophene) (Rieke Metals Inc.) sensor, since the conformation of polythiophene chains is known to be potentially sensitive to external stimuli which are frequently accompanied by measurable changes in their Vis/UV spectra (60). 

We had initially limited our studies to polypyrrole based sensors with several different chemically inert VOCs and to polythiophene sensors with toluene analyte. However, because of the relatively low sensitivity of the polypyrrole sensors and because of photosensitivity of the polythiophene sensors we have recently directed our attention to a new type of oligomer of aniline which we have recently synthesized and characterized (67, 62). 

Conducting polymers Polythiophene Sensor/array of sensor based on block copoly-mers of poly thiophenes nanostructures fabri-cated through ink-jet printing on prefabricated electrode Ethanol 10 ppm fin all analytes i2-24... 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

First, the above-mentioned sensors have major drawbacks, as the detection and recognition event is a function of the nature and characteristics of the side chains, and the side chain functionalization of the CP requires advanced synthesis and extensive purification of numerous monomeric and polymeric derivatives. Second, this generation of sensors primarily employed optical absorption as the source for detection, resulting in lower sensitivity when compared with other sensing systems for biological processes. However, the use of fluorescence detection within these sensing systems could justify continued development. More recent examples include a fluorescent polythiophene derivative with carbohydrate functionalized side chains for the detection of different bacteria [15] and novel synthesis schemes for ligand-functionalization of polythiophenes [16]. 

Marsella MJ, Swager TM (1993) Designing conducting polymer-based sensors - selective ionochromic response in crown-ether containing polythiophenes. J Am Chem Soc 115 12214-12215... 

Polythiophenes (PTs)/CNTs composites have emerged as an intriguing system for use as photovoltaic devices and field effect transistors [57]. Swager and Bao independently reported methods for the assembling of PTs/CNTs systems and showed their great potential as transparent conductive films [58]. Another interesting application arises from the possibility to functionalize the polythiophene backbone for applications as chemical sensors [134]. 

Sensitive, cationic, water-soluble polythiophenes have been utilized for biosensing. Leclerc et al. have created affinitychromic sensors with such polymers for transducing a variety of recognition events such as those between... 

The imidazolium salt functionalized polymer 12 also functions as an iodide sensor, rapidly changing color in the presence of sodium iodide (Ho and Leclerc 2003). Iodide-mediated aggregation was highly sensitive to the length of the side chain coimecting the imidazolium salt to the polythiophene backbone. A variety of... 

Paid K, Leclerc M. Functionalized regioregular polythiophenes towards the development of biochromic sensors. Chem Commun 1996 2761-2762. 

Chiral conjugate polymers such as polythiophenes with an optically active substituent in the 3 position have been studied for use in optoelectronic devices, sensors, and catalysis (Nilsson et al., 2004). These materials show activity based on their chiral behaviors, which can be influenced by solvent or temperature. Flelical biomolecules can be used to induce chirality in optically inactive polythiophenes (Ewbank et al., 2001). Nilsson et al. (2004) extended this to use a positively charged random-coil peptide conjugated with a... 

Chang JB, Liu V, Subramanian V, Sivula K, Luscombe C, Murphy AR, Liu J, Frechet JMJ. (2006) Printable polythiophene gas sensor array for low-cost electronic noses. / Appl Phys 100 014506. 

Polythiophene (PT) 20 can be regarded as a hybrid structure of cis-polyacetylene and sulfur, where the incorporation of the heteroatom leads to a much higher environmental stability of PT compared with that of PA [131], The outstanding physical and bulk properties make PT a desirable material for device applications like sensors, energy storage, solar cells, LEDs, NLO devices, and more [132], Due to the large number of possible technical applications, much effort has been made to tailor the properties of PT by synthesis. 

When constructing biosensors, which are to be used continuously in vivo or in situ, maintaining sensor efficiency while increasing sensor lifetime are major issues to be addressed. Researchers have attempted various methods to prevent enzyme inactivation and maintain a high density of redox mediators at the sensor surface. Use of hydrogels, sol-gel systems, PEI and carbon paste matrices to stabilize enzymes and redox polymers was mentioned in previous sections. Another alternative is to use conductive polymers such as polypyrrole [123-127], polythiophene [78,79] or polyaniline [128] to immobilize enzymes and mediators through either covalent bonding or entrapment in the polymer matrix. Application to various enzyme biosensors has been tested. 

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