Fabrication And Application Of Differential Molecularly Imprinting Polymers Electrochemical Sensors

Molecularly imprinting polymers（MIP）have the similar properties as biological antibodies to recognize and enrich selectively template molecules.By combining with MIP,the selectivity and sensitivity of the chemical/biosensors can be improved.However,compared with natural biological probes,there is still an obvious gap in the recognition selectivity of MIP to target molecules.Great efforts have been made to prepare MIP with better recognition selectivity and improve the anti-interference ability of MIP sensors.But the progress is slow.The imprinting factors,as a parameter to describe the recognition selectivity of MIP,is usually 1.5～7.The main factor which limits the further improvement the selectivity of MIP sensors is the non-specific adsorption of interferents on MIP surface.As shown in many references,the adsorption amounts of an interferent on MIP and non-imprinted polymers（NIP）are strongly related.If NIP is used as a reference to eliminate the interference caused by the non-specific adsorption of interferent on MIP,the selectivity of MIP sensor is expected to be improved significantly.In this thesis,the differential strategy is used to develop MIP electrochemical sensors.The main contents are listed below.1.Differential MIP capacitance sensor for dopamine determinationBy using o-phenylenediamine as functional monomer and dopamine（DA）as template,MIP membrane with selective recognition cavities to DA was electropolymerized on the surface of glassy carbon electrode（GCE）for DA determination.As the imprinting factor of MIP/GCE is only 4.19,the selectivity of MIP capacitive sensor for DA was not very high,resulting considerable interference in the determination of DA due to the non-specific adsorption of interferents on MIP/GCE.Lucky,the influence level of an interferent can be measured from the response value of NIP/GCE.Thus,the responses difference between MIP/GCE and NIP/GCE is a useful analytical signal to eliminate effectively the interference due to the non-specific adsorption of interferents on the surface of MIP/GCE.It is shown that interference level is reduced by more than one order of magnitude in the differential capacitance sensor,improving significantly the selectivity of MIP capacitance sensor for DA determination.In addition,the baseline drift of capacitance sensor is also suppressed in the differential detection model.Under the experimental conditions,the differential sensor is used to determine DA,with the linear range of 0.1～2.5μM and the detection limit of 6.8 n M.The good anti-interference ability of the differential MIP sensor is helpful in the determination of DA in actual samples.2.Determination of 4-acetaminophen and sulfadiazine by differential MIP voltammetric sensorsBy using pyrrole as functional monomer and 4-acetylaminophenol（AP）template,MIP membrane with selective recognition cavities to AP was electrochemically polymerized on the surface Ni₂P/GCE.It was shown that the as-prepared MIP_AP/Ni₂P/GCE has a sensitive current response to AP at the peak potential ca.0.42 V,with the detection limit of 0.016μM.Although the imprinting factor of the prepared MIP_AP is as high as 6.13,the anti-interference ability of the sensor is still not good enough.It is important to eliminate the interference from the non-specific adsorption of interferents on the surface of MIP_AP for the determination of AP.For example,the current response from 20μM ascorbic acid（AA）on MIP_AP/Ni₂P/GCE is equivalent to 5.2μM AP.Similarly,MIP membrane for sulfamerazine（SMR）was electrochemically polymerized on Ni₂P/GCE using pyrrole as functional monomer.The as-prepared MIP_SMR/Ni₂P/GCE exhibits sensitive current response to SMR,with the peak potential at 0.89 V,and the detection limit of0.025μM.The imprinting factor of the as-prepared MIP_SMR is 5.82,limiting the anti-interference ability of the sensor.For example,the presence of 20μM sulfamethoxazole（SMZ）was determined falsely as 4.7μM SMR by the MIP_SMR/Ni₂P/GCE.Because MIP_AP/Ni₂P/GCE and MIP_SMR/Ni₂P/GCE are prepared by the same electrochemical polymerization processes using pyrrole as functional monomer,they have the same chemical composition and similar specific surface area.Accordingly,the non-specific adsorption behavior of the interferents on MIP_AP and MIP_SMR is expected to be near the same.In a differential model,the current response of MIP_SMR/Ni₂P/GCE at 0.42 V is used to estimate the interference level of interferents in AP measurement.By using current response difference between MIP_AP/Ni₂P/GCE and MIP_SMR/Ni₂P/GCE at 0.42 V as the analytical signal,the differential current response from 20μM of AA is only equivalent to 0.25μM AP,with the interference level only 4.8%of that in the conventional detection mode.Similarly,the interference level in the determination of SMR can be measured by the current response of MIP_AP/Ni₂P/GCE at 0.89 V.By using the current response difference between MIP_SMR/Ni₂P/GCE and MIP_AP/Ni₂P/GCE at 0.89 V as the analytical signal,the differential current response from 20μM SMZ is only equivalent to 0.33μM SMR,being 7.1%of the interference level in the conventional detection mode.Importantly,in the determination of two anlaytes,NIP is not need in the differential strategy.Moreover,the specific surface area of MIP film is basically the same,which can significantly improve the anti-interference ability of the determination method without additional experimental steps.In addition,the adsorption isotherms of AP and SMR on MIP and NIP membranes were measured by quartz crystal microbalance to calculate the imprinting factor.And the linear range of the calibration curves of MIP voltammetric sensors was discussed.Finally,the proposed analytical method was applied to determine AP and SMR in actual meat samples,with the recovery in the range of 94～105%.