Establishment Of Piezoelectric Sensor Based On Enrofloxacin Molecularly Imprinted Polymers

Enrofloxacin(ENRO) is a quinolones antibiotic. Due to the strong antibacterial activity, wide distribution and low price, ENRO is widely used for the animal breeding and veterinary diagnosis. However, the side effects of the ENRO residues in the animal derived food would cause seriously damage to human health, and even pathogens resistance for pathogenic bacteria. Therefore, it is imperative to synthesize a new type of function materials for the enrichment and separation of the ENRO residues accurately and quickly in animal derived food, and further to establish a new technique with good selectivity and high sensitivity, thereby enabling simple detect the ENRO antibiotic residues succinctly.Molecular imprinting technology(MIT) is a process including the polymerization of an imprinted molecule interacted with functional monomers, cross-linking agents in the specific solvent to synthesize the molecularly imprinted polymers(MIPs), which has the particular adsorptivity and selectivity to the imprinted molecule. MIPs is also a novel polymer material with the expected structure and properties. Quartz crystal microbalance(QCM) based on quartz crystal converter is a detection device to analyze the quality and concentration of the analyte by the piezoelectricity converting quality signal into frequency signal. The combination of MIT and QCM could develop a novel sensor with high sensitivity and resolution for the real time online monitoring of analyte by using the predetermination, recognition and practicability of MIPs.In this paper, ENRO was chosen as a template molecule, 2-vinyl-4,6-diamino-1,3,5-triazine(VDAT), 4-Vinylpyridine(4-Vpy), acrylamide(AM), and trifluoromethacrylic acid(TFMAA) were viewed as the functional monomers, ethylene glycol dimethacrylate(EDMA), pentaerythritol triacrylate(PETA), and trimethylolpropane trimethacrylate(TRIM) were selected as the cross-linking agents, and acetonitrile, chloroform, tetrahydrofuran, water, toluene, and methanol were taken as the solvents. The functional monomer, molar ratio, cross-linking agent, and solvent of the ENRO-MIPs system were optimized by the density functional theory(DFT) at the B3LYP/6-31G(d,p) level. Then, we selected the functional monomer, molar ratio, cross-linking agent, and solvent of the ENRO-MIPs system via the adsorption experiments. The calculated results revealed that the ENRO-TFMAA complex with the molar ratio of 1:7 owned the lowest binding energy, the strongest interaction of hydrogen bond, and the most stable composition; EDMA was the best cross-linking for the preparation of ENRO-MIPs; acetonitrile was the most appropriate solvent to improve the adsorption properties of ENRO-MIPs.ENRO-MIPs were synthesized using precipitation polymerization and characterized utilizing series of adsorption experiments to investigate its binding capacity for ENRO and the structure analogues on the basis of the computational simulation results. The results indicated that ENRO-MIPs reached the maximum saturated adsorption capacity after 180 min. Analysis of the Scatchard plot showed that the binding sites of ENRO-MIPs to ENRO contain two binding sites, the dissociation constant(Kd) and apparent maximum adsorption quantity(Qmax) were Kd1 = 490.44 mg/L, Qmax1 = 46.76 mg/g and Kd2 = 991.08 mg/L, Qmax2 = 79.23 mg/g, respectively. The absorption amount of ENRO-MIPs to ENRO was higher than those of ciprofloxacin(CIP) and ofloxacin(OFL), emerging a stronger specific selective adsorption ability. The average particle diameters of ENRO-MIPs(220 nm) was lager than that of NIPs(190 nm), and the thermostability of ENRO-MIPs was excellent before 300℃. In addition, infrared spectrum analysis results demonstrated the polymerization between the template molecule ENRO and the functional monomer TFMAA was hydrogen bonding interaction.The ENRO-MIPs piezoelectric sensor was established according ENRO-MIPs modifying the QCM electrode via the entrapping method, in which polyvinyl chloridem(PVC) and tetrahydrofuran were selected as the investment material and solvent, respectively. The detection conditions were optimized. Then the ENRO-MIPs piezoelectric sensor was applied to monitor the content of ENRO in the chicken sample. The results indicated that the sensor display an excellent response when the mass ratio of membrane material, the volume of coatings, and the testing PH were 3:1, 15 μL, and 7, respectively. The regression equation of the sensor was y =-2.616x- 25.816(R2 = 0.9987) with the ENRO standard concentrations of 10 ~ 800 ng/mL under the optimized conditions, and the corresponding limit of detection(LOD) was 18.72 ng/mL. Furthermore, the recovery of ENRO in the chicken sample was 95.78% ~ 98.83% with 5 times cyclic utilization for the sensor.