MIP-Based Sensing

In another work lacosamide based MIPs of methacrylic acid monomers were used for the solid-phase extraction of the template from rat plasma before LC analysis and the results revealed a recovery of over 98% for the SPE and the LOD and LR of the method were evaluated to be 0.03 pg mL and 0.1-100 pg mL [244]. B. B. Prasad et al. reported the MIP-based SPE of epinephrine and detection of the same through an MIP based sensing device in plasma cerebrospinal fluids. They reported the reaction of functionalized multiwalled carbon nanotubes (MWCNTs-COCl)] as a monomer with N-hydroxy phenylmaleimide and used glycoldimethylacrylate as the cross-linking agent. The LOD of the hyphenated method was reported to be 0.002 ng mL [245]. In another study M. Moein and co-workers developed MIP cartridges to be used in combination with HPLC for facile analysis of human insulin in plasma and urine. They used insulin as the template, in the reaction between meth-acrylicacid monomer and ethylene eglycol dimethacrylate cross-linker. The reaction initiation was achived by 2,2/-azobisisobutyronitrile. The overal results showed LODs of 0.2 ng mL in plasma and 0.03 ng mL in urine with recovery factors over 87% [246]. 

So far, pharmaceutical compounds with more than one MIP-based sensing device were covered. The following lines will include the target species which have been the subject of fewer investigations. For the ease of access, the cases are sorted in alphabetical order. 

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. 

Other detection methods have been used in optical MIP sensing systems. An MIP-based chemiluminescent flow-through sensor was developed for the detection of 1,10-phenanthroline (Lin and Yamada 2001). A metal complex was used to catalyze the decomposition of hydrogen peroxide and form the superoxide radical ion that can... 

The present chapter critically encompasses developments and achievements reached in MIP-based selective sensing combined with optical, piezoelectric (PZ) and electrochemical signal transduction. General procedures of MIP preparation along with methods of MIP immobilization for chemosensor fabrication are presented. Protocols of analyte determination involving measurement complexities, like template presence or absence, have been addressed in detail. Moreover, analytical parameters, such as detectability, sensitivity, selectivity, linear dynamic... 

Interestingly, the analytes of smaller sizes than that of the functional monomer used for MIP preparation were determined based on the MIP-PZ sensing. For instance, acetaldehyde was determined by using the methacrylate functional monomer for MIP preparation [154]. The fabricated MIP-PZ chemosensor was 11-fold more selective for acetaldehyde than for acetone. 

Preparation of an MIP-based composite is a valuable method for immobilization of MIP on the transducer surface. For instance, a carbon-based material, such as graphite, is mixed in this procedure with MIP particles to form a composite [173]. This composite and transducer surface (graphite) is then brought in contact to enhance binding of the sensing element and the conducting substrate. The most important aspect of this procedure is that abrasive polishing can readily renew the surface of the chemosensor. 

MIP films are polymerized on flat surfaces. Surfaces derivatized with polymerizable groups are preferred since they allow covalent attachment to the surface. MIP films are attractive as sensing elements in MIP based sensors [112]. 

In an early approach towards MIP-based sensors using capacitance measurement, thin MIP membranes were prepared by in situ polymerization of MAA/ EDMA and then sandwiched as a sensing layer in afield effect device a capacitance decrease was observed due to specific binding of the template L-phenylalanine anilide [103]. Recently, two promising alternative approaches towards ultrathin MIP films for capacitive sensors had been reported electropolymerization of phenol for imprinting of phenylalanine [74], and photo-initiated graft copolymerization of AMPS/MBAA for imprinting of desmetryn [82] and creatinine [83] (cf Sections III.C.2, III.C.3). 

Fluorescence-based sensing systems offer the possibility of high levels of sensitivity and MIPs containing reporter molecules have been the subject of considerable research. There are two ways in which this may be achieved within MIPs. The simpler of the two is simply imprinting a molecule with inherent fluorescence, as demonstrated by Matsui et al. in the imprinting of cinchonidine and cinchonine. More challenging is the placement of a... 

Figure 15 Schematic presentation of MIP-based electrochemical sensing of glucose.

Morphin sensors based on MIPs have also been described [432,439,441]. Amperometric morphine sensors based on morphin imprinted poly(3,4-ethylene-dioxythiophene), which catalyze morphine oxidation and lowers the oxidization potential on an indium tin oxide (ITO) electrode, is an example. The same MIP has been used in the form of immobilized molecular particles for the same purpose. In one report, rather uniform MIP microspheres were prepared through precipitation polymerization to produce more active surface area. Poly(3,4-ethylenedioxythiophene) was utilized to immobilize the MIP particles, prepared through the reaction between methacrylic acid monomers and trimethylolpropane trimethacrylate crossHnkers in the presence of morphin, on indium tin oxide (ITO) glass [441]. Another microfluidic amperometric MIP-based morphin sensing system, using 3,4-ethylenedioxythiophene monomers, has also been reported in the literature [439]. 

Promethazine sensing devices based on MIPs include an MIP-based potentiometric sensor which was reported to be applicable in the concentration range of 5.0 X 10" - 1.0 X 10 M, with an LOD 1.0 X 10 M [409] and an MIP-modified carbon phase electrode with two linear response ranges of 4 x 10 -lx 10 M and 1 x 10 - 1 X 10" M and a detection limit of 2.8 x 10 M [381]. Propranolol detection has also been reported through MIP-based phosphorescent probes using tetrabromobisphenol A and diphenylmethane 4,4 -diisocyanate as functional monomers in tetrahydrofuran [380], and an MIP-based ion-selective sensor with a narrow linearity range of 10 -10" M [360]. 

MIP-based tramadol sensing devices include the highly selective MWCNTs carbon paste electrode modified with molecularly imprinted polymers with differential pulse voltammetric detection. The device had a linear response range of 10 to 10" M [350]. The other report was on an MIP-electrochemical sensor prepared by coating SiO, Fe O, as the core and the supporting material, with an MIP based on ethyleneglycol dimethacrylate as the crosslinker and functional monomers. The MIP-modified particles prepared this way were eventually incorporated into the modified carbon paste electrode, which was used for cyclicvoltammetry of the analyte within a linear range of 0.01-20 pmolL-i [366]. 

Metal nanoparticles have also been included into MIPs. Such particles can be used, for example, as nanoantennae for the enhancement of electromagnetic waves (plasmonic enhancement). It has been shown by He et al. [122] that a thin layer (20-120 nm) of testosterone-imprinted silica could be synthesized around 350 nm silver particles in a controlled way. The composite material showed specific binding of the testosterone target. Matsui et al. [123] reported a molecularly imprinted polymer with immobilized Au nanoparticles as a sensing material for spectrometry. The sensing mechanism is based on the variable proximity of the Au nanoparticles... 

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