Fabrication fluorescent based sensors

Fluorescence resonance energy transfer (FRET) has also been used very often to design optical sensors. In this case, the sensitive layer contains the fluorophore and an analyte-sensitive dye, the absorption band of which overlaps significantly with the emission of the former. Reversible interaction of the absorber with the analyte species (e.g. the sample acidity, chloride, cations, anions,...) leads to a variation of the absorption band so that the efficiency of energy transfer from the fluorophore changes36 In this way, both emission intensity- and lifetime-based sensors may be fabricated. 

A microfluidic sensor to detect fluorescently labelled DNA was developed by Khur and co-workers [29], Photopatteming was obtained with carbene-generating photobiotin and allowed fabrication of homogeneous regions of immobilized biotin and the control of the spatial distribution of DNAs in a microchannel-flow-based sensor. 

In a related example, polyacrylamide hydrogel-based sensors functionalized with a thymine rich DNA which can simultaneously detect and remove mercury from water were fabricated [121]. Specifically, in the absence of Hg ", the DNA is in a random coil conformation, and the addition of SYBR Green I gives a weak fluorescence (Fig. 40a, yellow line). In the presence of Hg ", the DNA forms a hairpin structure yielding a ninefold emission increase. Using the naked eye, the... 

Wohltjen H, Barger WR, Snow AW, Jarvis NL (1985) A vapor-sensitive chemiresistor fabricated with planar microelectrodes and a Langmuir-Blodgett organic semiconductor film. IEEE Trans Electron Dev ED-32 1170-1174 Wolfbeis OS (1991) Fiber optic chemical sensors and biosensors, vol 1. CRC, Boca Raton, FL Wolfbeis OS (1992) Fiber optic chemical sensors and biosensors, vol 2. CRC, Boca Raton, FL Wolfbeis OS (2005) Materials for fluorescence-based optical chemical sensors. J Mater Chem 15 2657-2669 Wollenstein J, Plaza JA, Can6 C, Min Y, Bottner H, Tuller HE (2003) A novel single chip thin film metal oxide array. Sens Actuators B 93 350-355... 

A second sensor based on ELP was reported by Chen and co-woilcers (Gao et al., 2005). The ELP is fused to antibodies for a tumor marker (cancer antigen 19-9, CA 19-9) and subsequently used to inamobilise the antibodies to a surface. In this case, the temperature responsiveness of the ELP was used for the fabrication of the sensor detection occurred via the addition of a second, fluorescently labelled antibody to the tumor marker after the marker had been immobilised. This biosensor had a detection limit of 21 units/mL for CA 19-9. 

Describe in detail the fabrication and operation of one example for each of the following a) A conductometric sensor for the detection of organic vapors, b) An amperometric sensor for the same, c) A sensor interfaceable to a PC and usable as a detector in chromatography, d) A conductometric sensor for glucose, e) An amperometric sensor for the same, e) A potentiometric sensor for the same, f) A sensor whose sensitivity can be controlled electrically, g) A sensor incorporating an enzyme into the CP film wherein the enzyme concentration is precisely controllable, h) A sensor using an optical fiber probe and fluorescence-based detection. 

Sensitivity impacts upon the limit of detection and resolution of the device, making it a key performance parameter. Recently, several strategies have been developed in order to provide sensitivity enhancements for optical sensor platforms based on both optical absorption and fluorescence phenomena. These strategies are the result of rigorous theoretical analyses of the relevant systems and, combined with polymer processing technology and planar fabrication protocols, provide a viable route for the development of low-cost, efficient optical sensor platforms. 

The scientists from Hong Kong reported83 on a sol-gel derived molecular imprinted polymers (MIPs) based luminescent sensing material that made use of a photoinduced electron transfer (PET) mechanism for a sensing of a non-fluorescent herbicide - 2,4-dichlorophenoxyacetic acid. A new organosilane, 3 - [N,V-bis(9-anthrylmethyl)amino]propyltriethoxysilane, was synthesized and use as the PET sensor monomer. The sensing MIPs material was fabricated by a conventional sol-gel process. 

---