| Urea, as a common substance that widely founded in the variety environment and its content is bound to have effect on the environment. Urea in the water is an indicator for monitoring the public health; urea in the soil becomes a reflection of the performance of the soil. In addition, urea which is also an important substance exists in the serum and urine, is also the one of markers in the kidney function, decompensated heart failure and other diseases. Nowadays, the common detection technology could not satisfy the actual demands. So to develop a method of accurate, fast, good specific recognition as well as high sensitivity is necessary.Based on better selective molecularly imprinted technology combining with nanoparticle doption , a molecularly imprinted electrochemical sensor used in sensitively evaluating urea had been flexibly constructed, and various characterization techniques were used for investigating the mechanics during the preparation and response procedure of the proposed sensor.First of all, an urea electrochemical sensor was developed based on chitosan molecularly imprinted films which prepared by potentiostatic electrodepositing of chitosan in the presence of urea followed by eluting with 0.1 mol/L KCl for 20 min. The redox response of [Fe(CN)6]3-/4- indictor for indirectly test electro performance for the sensor. As our expectation, the urea MIP electrochemical sensor showed equilibrium adsorption time of 12 min, excellent selectivity to urea among the structural similarities and co-existences, high linear sensitivity to urea in the range from 1.0×10-8 ~ 4.0×10-5 mol/L with a detection limit of 5.0 nmol/L. Furthermore, the recoveries ranged from 96.3% to 103.3% offered great potential for clinical diagnosis applications.Then, a urea imprinted electrochemical sensor doping with CdS quantum dots was constructed. The results showed that, in the case of the same preparation conditions, the optimized doping concentration was 3.0×10-4 mol/L (in Cd2+ dollars), the sensor could be favorable set up. The sensor equilibrium adsorption time for urea was 5 min, linear response range: 5.0×10-12 ~ 4.0×10-10 mol/L and 5.0×10-10 ~ 7.0×10-8 mol/L, detection limit was found to be 1.0 pmol/L. Compared with the undoped sensor, it had a more sensitive response, wider linear range and lower detection limit, highlighted the effect of CdS quantum dots. Moreover, significant specific recognition, excellent anti-interference ability, high recovery results (90.7% to 105.6%), good regeneration performance and long lifetime provide feasibility to the early diagnosis for the disease related with urea marker. Finally, varieties of characterization techniques for discuss the mechanism of undoped / doped CdS quantum dots urea molecular imprinted electrochemical sensor. Attenuated total reflection - infrared spectroscopy (ATR-IR) and X-ray diffraction (XRD) results showed that the urea and chitosan could be combined mainly by hydrogen bonds; CdS quantum dots doped into the membrane interacted with chitosan by electrostatic interactions. Energy dispersive spectroscopy (EDS), ATR-IR and XRD test indicated that the three substances can be modified on the Au electrode surface via co-electrodeposition, confirmed the feasibility of the preparation of the urea molecularly imprinted electrochemical sensors. Scanning electron microscope (SEM) revealed that an imprinted electrochemical sensor which matched the urea with size, shape, spatial configuration and interaction was successfully synthesis. Electrochemical impedance spectroscopy (EIS) and other electrochemical experiments results demonstrated that, not only a molecularly imprinted sensor's successful preparation but also the promoting effect of electron transfer by CdS quantum dots. Thermodynamics and kinetic results showed that the sensor consistent with the Langmuir adsorption model, and the fitting data further illustrated that the urea molecularly imprinted electrochemical sensor had good specific recognition to its template molecular. |
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