Desigins And Applications Of Differential Molecularly Imprinted Polymers Based Optical Sensors

Molecularly imprinted polymers（MIPs）,as artificial antibodies,have imprinting sites matching the template molecules in shape,size and functional groups,which can simulate the antigen-antibody recognition process to selectively enrich template molecules.Compared with natural antibodies,MIPs have the advantages of low cost and good stability.Various analytical methods have been used in combination with MIPs.During the enrichment process,besides the specific adsorption between the imprinted cavities and the template molecules,there is still inevitable non-specific adsorption on the outside surface MIPs for the template and other species,which reduces the accuracy of experimental results.In this thesis,the differential strategy is proposed to eliminate the influence of interferents,which greatly improves the anti-interference ability of the MIPs-based analytical method.1.Enhancing anti-interference ability of molecularly imprinted ratiometric fluorescence sensor via differential strategyThe non-specific adsorption of interferents onto the outside surface of molecularly imprinted polymers（MIPs）particles is disadvantageous for selective determination of the template molecules.Based on the fact that the responses of non-imprinted polymers（NIPs）and MIPs particles to non-template molecules are similar,the anti-interference ability of MIPs sensor can be much improved via differential strategy,demonstrated by bovine hemoglobin（BHb）determination.The MIPs for BHb were prepared via surface imprinting and sol-gel process,with graphene quantum dots@SiO₂/Cd Te quantum dots（GQDs@SiO₂/CdTe QDs）for ratiometric fluorescence measurements.By using a weight factor of 1.283 to compensate the lower specific surface area in NIPs particles,the differential ratiometric fluorescence signal between MIPs and NIPs channels to 2.00μmol/L ovalbumin and phycocyanin were equivalent to BHb at the concentration of 0.025 and 0.014μM,which are only about 11%and 5.8%of the interference level in the normal ratiometric fluorescence method,respectively.The differential ratiometric fluorescence measurement was also performed in a smartphone-based device for field analysis of BHb in urine samples,with the linear range of 0.05-4μmol/L and the detection limit of 13nmol/L.2.A smartphone-based ratiometric fluorescence and absorbance dual-mode device and primary inner filter effect correction.Multi-signal assays offer the advantage to improve the accuracy and diversity by integrating the merits of each output.In the widely used colorimetric and fluorometric dual-mode,the fluorescent intensity and absorbance signals are usually measured by a lab spectrofluorometer and a spectrophotometer.Herein,a smartphone-based device which is able to measure simultaneously the ratiometric fluorescence and absorbance signals was designed.Its analytical performance is demonstrated by the determination of Rhodamine B（RhB）.In a three-channel cuvette,the detection cell（with test solution）was sandwiched between two light intensity measurement cells（with RhB standard solution）.Under the irradiation of the excitation light of 550 nm,the fluorescent images of the three cells were captured by the camera in a smartphone.The ratiometric fluorescence and the absorbance at 550 nm are obtained according to the brightness ratio of the middle cell and the third cell to the first one,respectively.The dual-mode of fluorescence and absorbance can widen the detection range,with the limit of detection for RhB of 3.2 nmol/L in ratiometric fluorescence mode and 0.38μmol/L in absorbance outputs,respectively.Importantly,the possible inner filter effect at the excitation wavelength of the fluorescence can be corrected according to the absorbance signal,improving the accuracy of determination.The dual-mode portable device was used to determine RhB in combination with differential molecularly imprinting strategy to improve further the anti-interference ability.3.Investigation the specific adsorption behavior of the imprinted cavities within MIPs via a differential strategyImprinted cavities are the cornerstones for recognition specificity of MIPs,but the investigations related to their recognition behavior are usually included part of inevitable non-specific adsorption on the outside surface of MIPs.Herein,we reported a differential strategy to distinguish the specific adsorption of template molecules into imprinted cavities and non-specific adsorption,by using the non-specific adsorption on non-imprinted polymers couple as the reference.By using MIPs of malachite green（MG）as the model,the adsorption isotherm and kinetics of MG into the imprinted cavities are demonstrated to follow the Langmuir isotherm and pseudo-second-order kinetics models,respectively.The equilibrium constant and maximum adsorption capacity of MG into imprinted cavities within MIPs are 241.2 L/g and 24.97 mg/g via the specific adsorption,83.53 L/g and 11.92 mg/g for the non-specific adsorption onto surface,respectively.A smartphone-based analytical device with rotating seven colorimetric tubes was fabricated to measure the absorbance on-line,monitoring simultaneously the amounts of MG adsorbed in six channels without terminating adsorption processes.The pure specific recognition by imprinted cavities within MIPs enhances the anti-interference ability and sensitivity for MG determination.The smartphone-based absorbance device with an optical path of 10 cm was applied to the field determination of MG in actual water samples,with the detection limit of 1.1μg/L and the recovery in the range of 94.1～105%.The difference in volume of eluent has little influence on absorbance measurement in the portable absorbance device,providing convenience in accurate field analysis.4.Differential MIPs electrochemiluminescence sensor for dopamineIn the presence of S₂O₈^2-as the coreactant,graphite phase carbon nitride（g-C₃N₄）can be generated strong cathodic electrochemiluminescence（ECL）signals.As dopamine（DA）can quench the ECL of the g-C₃N₄-S₂O₈^2-system,an ECL sensor for DA can be fabricated.To improve the detection sensitivity and selectivity of this method,multi walled carbon nanotubes and titanium oxide were first used to enhance the strength of ECL.And MIPs numbrane for DA was fabricated by using DA as the template and chitosan as the film-forming agent.The as-prepared ECL sensor is used as the model to test the adaptability of differential MIPs strategy in ECL sensors.It was shown that the ECL intensities of MIPs and NIPs are in linear relations of the logarithm of DA concentration.The differential MIP strategy is only suitable for deducting the ELC intensity from of interferents in the absence of DA.When DA was coexisted with interferents,especially for unknown species,the ECL intensity difference between MIPs and NIPs cannot be used as the analysis signal.To implement the differential MIPs strategy,the linear relation betweenf the ECL intensity and the logarithm of DA concentration is converted to the linear relation betweenf the DA concentration and the exponential of the ECL intensity.Then,the differential strategy is used to enhance further the the anti-interference ability of the MIPs-based ECL sensor.Under optimized experimental conditions,the differential ratiometric ECL MIPs based sensor showes a good linear correlation with DA in the concentration range of 10 pmol/L to 1 nmol/L,with a detection limit of 5.6 pmol/L.