Preparation Of Xanthine Polypyrrole Molecularly Imprinted Electrochemical Microsensors And Its Performances

The amount of xanthine （XA） in human body is closely connected with health,as the environment it presence is complex and it has many coexisting substances,constructed a method which can be used to quick, sensitive, and accuratedetermination of XA, is meaningful for the rapid and effective diagnosis of relativedisease.Because electrochemical sensor has the advantage of high sensitivity, easy tominiaturization and automation, it becomes a practical means of the early diagnosisfor disease. The surface area of microelectrode is very small, so it can be applied tothe rapid detection of a small area on real-time test system. The molecularlyimprinted polymers （MIPs） based electrochemical sensor combines the specificselectivity to a specific target molecule （template molecule） which is benefited frommolecularly imprinted technique with the sensitive electrochemical analysis detectors.And the enhancement of nanomaterial has improved the limited sensitivity ofmicrosensor.Hereby, the molecularly imprinted polymers were constructed on the surface ofcarbon fiber microelectrode （CFME）, and MIPs microsensor of XA was prepared,then it will realize the highly selective and highly sensitive detection of xanthine. Thefollows are the concrete work:（1） Optimal preparation conditions and analytical performance of MIPsmicrosensor were studied here. In the competitive reaction with its common structuralsimilarity and coexistence, a satisfactory molecularly binding selectivity of XA wasobtained with an imprinting factor （IF） of6.63. Though the imprinting effect of thisMIPs microsensor is similar to conventional MIPs sensor, its adsorption equilibriumtime is shorter and kinetic constant is smaller. There is a linear response to theconcentration of XA in a certain ranges under the optimized conditions. The rangesare from4.0×10^-6M to6.0×10^-5M and8.0×10^-5M to2.0×10-3M with adetection limit of2.5×10-7M. Meanwhile, good stability （RSD,3.2%, n=10） andreproducibility （RSD,2.0%, n=10） were observed and recoveries ranged from94.2% to108.4%were calculated when applied to XA determination in real blood serumsamples.（2） The electrochemical signal of XA is weak, and its content in human body islow. On this basis, a new XA electrochemical microsensor was constructed based ongraphene （GR） doped polypyrrole （PPy） molecularly imprinted films. TheGR-MIP/CFME significantly improved the electrochemical responses for XA. Theoxidation peak current of XA was well-proportional to its concentration in the rangefrom2.0×10-8to8.0×10^-6M and1.0×10^-5to3.0×10^-4M. The detection limit is5.0×10^-9M which was reduced by two orders of magnitude of MIP/CFMEs’.Furthermore, the prepared imprinted sensor still retain excellent specific recognitionto XA with an IF of15.4and the microsensor has faster response, stronger affinitywhen compares to MIP/CFME.（3） The scanning electron microscope （SEM）, X-ray-diffraction spectroscopy（XRD）, Fourier transform infrared spectroscopy （FTIR）, Raman spectroscopy andelectrochemical impedance spectroscopy （EIS） were used to characterize thepreparation, the morphology and structural properties of the MIPs. Through thecharacterization of SEM, FTIR and XRD confirmed that the PPy-GO and PPy-GRnano-complexes have been formed on the surface of CFME. The structure of the GRdoped composite were researched by Raman spectroscopy and XRD, and thepreparation of MIPs doped by GR were explained here. The EIS, CV, DPV and CCwere employed to further investigate the special recognition of MIPs microsensor totemplate molecule and reveal the enhancing effect of molecularly imprintedmicrosensor doped by GR.