Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
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Polymerization <strong>and</strong> Applications <strong>of</strong> <strong>Biodegradable</strong> Polyesters<br />
observable responses. A key advantage <strong>of</strong> CP-based sensors is the potential <strong>of</strong> the CP to<br />
exhibit collective properties that are sensitive to very minor chemical or physical changes.<br />
The most important aspect <strong>of</strong> biosensor is how to combine the electrical component (i.e., CP)<br />
with the biological recognition components. An effective <strong>and</strong> widely used approach was to<br />
immobilize bioactive molecules in or on CPs. 141-143<br />
Physical adsorption is the simplest way to introduce bioactive molecules on CPs for<br />
biosensors. For example, glucose oxidase was directly adsorbed onto PPy for a biosensor<br />
which can detect glucose from concentrations <strong>of</strong> 2.5 to 30 mM using dimethylferrocene as an<br />
electron transfer mediator. 144 However, this method is not reliable because the amount <strong>of</strong> the<br />
absorbed compound is not repeatable <strong>and</strong> this immobilization is not stable. 145 An alternative<br />
way is to entrap the biomolecule into the polymers substrate. For example, poly(3,<br />
4-ethylenedioxythiophene) (PEDOT) exhibited a 5% shrinkage in thickness when it is rinsed<br />
with ethanol, which can be utilized to incorporate horseradish peroxidase. 146 Besides enzymes,<br />
this method has also been used for immobilization <strong>of</strong> antibodies <strong>and</strong> DNA. 147-149 Just like<br />
the absorption method, this approach also has some limitations such as denature <strong>of</strong> the<br />
proteins <strong>and</strong> the low accessibility <strong>of</strong> analytes to the sensing element. Moreover, entrapment<br />
methods need a high concentration <strong>of</strong> the biomolecule (~0.2-3.5 mg/mL), which is not<br />
suitable for industry application due to the higher cost.<br />
Compared to entrapment <strong>and</strong> absorption, affinity binding seemed to be more stable<br />
bonding techniques. The avidin-biotin complex was the most studied affinity binding pair due<br />
to the extremely specific <strong>and</strong> high-affinity interactions between biotin <strong>and</strong> the glycoprotein<br />
avidin (Ka = 1 × 10 15 mol -1 L). 150 This method requires the synthesis <strong>of</strong> biotinylated CPs<br />
firstly. For example, the pyrrole monomers was copolymerized with biotinylated hydrophilic<br />
pyrrole monomers with different PEG lengths as spacer arms to create the bonding site. 151<br />
And the amount <strong>of</strong> anchored avidin can be tuned by the biotin density or the length <strong>of</strong> the<br />
PEG spacer in the copolymer. There are also other affinity binding complexes that have been<br />
studied for the immobilization <strong>of</strong> DNA onto CP surfaces. For example, a unique intercalator<br />
(i.e., a molecule that inserts itself into double-str<strong>and</strong>ed DNA)-based immobilization technique<br />
has been developed. 152 Target DNA str<strong>and</strong>s are detected when they form DNA duplexes with<br />
labeled DNA probes <strong>and</strong> are subsequently immobilized by the affinity binding <strong>of</strong> the<br />
intercalator, which is covalently bound to PPy. And more importantly, the detection limits can<br />
lower to 1 pg/mL.