Synthesis And Application Of Molecularly Imprinted Films On The Surface Of Carbon Nanomaterials

Molecular imprinting technology is an emerging scientific technology that appeared in the early 1980s,and it uses the target molecule as a template.Based on heating,redox and other methods,monomer is initiated,crosslinking agents form polymers around the template molecule,and then the template is eluted to obtain a polymer with a three-dimensional cavity.Since the polymer simulates the principle of antigen-antibody recognition,it is also termed as a plastic antibody.Compared with antigen-antibody,the polymer has the advantages of high temperature resistance,acid and alkali resistance,high stability,and low synthesis cost.Carbon materials are widely used in the fields of catalytic degradation,biological analysis,and catalytic hydrogen production due to their simple preparation,low cost,and good stability.However,the selectivity and anti-interference ability are still a challenging problem for the sensors constructed by carbon materials.This problem can be solved by molecularly imprinted polymers that has high selectivity for the target molecules.In this work,molecularly imprinted membranes were synthesized on the surfaces of two carbon nanomaterials,namely graphite phase carbonitride material?g-C₃N₄?and carbon dots?C-dots?,and used for biosensing application.The details are as follows:1.A molecularly imprinted membrane using 3,3^?,5,5^?-tetramethylbenzidine as a template was synthesized on the surface of g-C₃N₄ and used as a photooxidation nanozyme to construct a colorimetric sensing method for detecting L-cysteine.In traditional nanozyme biosensor applications,the surface of the nanozyme is active and easily interacts with biomolecules.Hence,the sensing processed were uasally interfered by the biological sample matrix,making accurate analysis of the biological sample difficult.MIP-g-C₃N₄ has a TMB binding site inside,allowing the oxidation reaction to proceed inside the polymer,thus isolating the contact between g-C₃N₄ and the biological sample,and improving the anti-interference ability of g-C₃N₄,especially in serum samples?about 1,000 times?.Using scavengers of different active species?ROS?,the oxidation mechanism of g-C₃N₄ was verified.It was concluded that·O₂^?plays a leading role in the photooxidation process.The UV-vis spectrophotometry was used to compare the oxidation activity the selectivity to different color-developing substrate of g-C₃N₄ and MIP-g-C₃N₄.The results showed that the oxidation ability of MIP-g-C₃N₄was more than 4 times higher than that of g-C₃N₄,and it had a good selectivity for TMB.The measurement of the Michaelis constant?K_m?and the maximum reaction rate(?_max)of the nanozyme further indicated that MIP-g-C₃N₄ increased the oxidation activity of g-C₃N₄.Finally,nanozymes are used for colorimetric detection of L-cysteine.The experimental results showed that the nanozyme had a good response signal to L-cysteine,the linear response range of detection was 1-20?M,and the detection limit was 0.2?M.The recovery values was 91.6-94.1%for the detection of L-cystine in serum samples.Therefore,this method is expected to be used for the detection of L-cysteine in actual biological samples.2.The C-dots-induced synthesis of molecularly imprinted polymer with controllable film thickness was constructed by light.Based on the high fluorescence and photocatalytic activity of C-dots,it can be used as a fluorescent donor and an initiator for polymerization.Firstly,the molecularly imprinted membrane was synthesized by light induction.The formation of the polymer on the surface of C-dots can be proved by UV-vis spectroscopy and the morphology analysis of the C-dots and polymer-encapsulated C-dots composite material.In order to verify the controllability of the film thickness,six kinds of composite materials were synthesized under different irradiation time?0.5-2 h?.The fluorescence resonance light scattering and dynamic light scattering proved that the polymer particle size can gradually increase with the growth of irradiation time.This enhancement indicated that the thickness of the polymer film can be controlled by the length of irradiation time,and the thickness of the film was quite thin,only 12-22 nm.Moveover,the fluorescence test showed that the polymer film prepared by this method had little effect on the fluorescence of carbon dots,and the fluorescence decreased only 6.6%after the polymer is wrapped,so it can be used as a good fluorescence donor.Finally,The molecularly imprinted polymer?MIP-C-dots?with tetracycline as a template were synthesized,and it was found that the fluorescence of C-dots can be quenched well by the tetracycline adsorbed into the MIPs pores,which is due to the thickness of the molecularly imprinted film synthesized by photosensitization is extremely thin,which is more conducive to the energy transfer between donor and acceptor during fluorescence resonance energy transfer.The light-induced synthesis of MIP-C-dots provides a new idea for the construction of fluorescence resonance energy transfer sensing system.