Construction And Application Of MIP-ECL Sensors Based On Polydopamine-p-phenyldiboric Acid Nanocomposite In Flavonoid Analysis

Electrochemiluminescence（ECL）has double advantage of optical analysis and electrochemical analysis.It is simple,rapid and high-sensitive due to no external light source required and reducing the light scattering and noise.In recent years,developing new and efficient nano-scale organic emitters（NOEs）to construct ECL sensors,which can effectively improve the detection sensitivity and extend the linear dynamic range,is the frontier direction of ECL analysis.At the same time,molecularly imprinted polymers（MIPs）,which are used as the recognition elements of chemical sensors,can eliminate the interference from other analogues on luminescence signals and help to solve the selectivity defects of ECL sensors since only the target molecules can bind with ECL reagents in such case.However,due to the lack of theoretical guidance,the selecting of imprinting system has defects of high cost,long preparation time and poor experimental effect.Molecular simulation technology based on computer technology and quantum chemistry theory can guide the choice of molecular imprinting system in theory and improve the synthesis efficiency,which is particularly important for the establishment of molecular imprinting system.In this paper,two kinds of MIPs with baicalin or quercetin as the template were prepared by a precipitation polymerization.At the same time,polydopamine-p-phenyldi-boric acid nanocomposite（PDA-PBA）with high luminous efficiency were synthesized as well.Then two MIP-ECL sensors were constructed for the determination of baicalin and quercetin by using MWCNTs-NH₂/AuNPs/MIPs/PDA-PBA/GCE as the working electrodes.On the other hand,molecular dynamics（MD）simulation was used to design baicalin molecular imprinting system and measure the active sites of the template molecule and functional monomer through their electron cloud distribution.This work not only makes a meaningful practical exploration and theoretical guidance for the development of MIP-ECL sensors,but also provides a new idea and method for the rapid and accurate detection of the two targets in real samples.The research work of this paper includes the following four parts:1.The properties and luminescence mechanism of NOEs are briefly summarized;The types and application of chemically modified electrodes are introduced;The formation of MIPs and the coupling modes molecular imprinting technique with ECL analysis are reviewed emphatically.2.Baicalin molecularly imprinted polymer（b-MIP）and polydopamine-p-phenyldiboric acid nanocomposites were synthesized.A MIP-ECL sensor for the determinaiton of baicalin was constructed with the as-prepared MWCNTs-NH₂/AuNPs/b-MIP/PDA-PBA/GCE as the working electrode and potassium persulfate as the co-reactant.The effects of pH value,concentration of K₂S₂O₈,concentration of PBS buffer solution,potential window,scan rate and the number of b-MIP layers on ECL signal were investigated.The results showed that under the optimized conditions,ECL intensity and the logarithm of baicalin concentration showed a good linear relationship in a certain range.The linear range was 1.0×10^-8～1.0×10^-3g/mL,and the detection limit（3σ）was1.28 ng/mL.The method was applied to the determination of baicalin in Qingkailing granules and urine with the recoveries of 95.0～107.2%.3.Molecularly imprinted polymer（q-MIP）was synthesized using quercetin as template molecule.Then a MIP-ECL method for the determination of quercetin was established by using MWNTs-NH₂/AuNPs/q-MIP/PDA-PBA/GCE as the working electrode,based on the obvious sensitization of quercetin on the ECL of PDA-PBA-K₂S₂O₈ coreaction system.The effects of pH value,concentration of K₂S₂O₈,concentration of phosphate buffer solution（PBS）,potential window,scan rate and the number of q-MIP layers on ECL signal of the system were investigated.The results showed that under the optimal conditions,ECL intensity and the logarithm of quercetin concentration had a good linear relationship in a certain range,the linear range was1.0×10^-8～1.0×10^-4 g/mL,and the detection limit（3σ）was 2.75 ng/mL.The method was applied to the determination of quercetin in two kinds of tea,and the recoveries were97.0～104.0%.4.The baicalin molecular imprinting system was designed by molecular dynamics（MD）simulation,and the optimal functional monomer,crosslinking agent and solvent were selected.The molecular electrostatic potentials（MEPs）of baicalin and acrylamide（AM）were calculated and their active sites were measured through the electron cloud distribution.