Selective Determination Of Tetracycline Based On Molecularly Imprinted Technique And Development Of Electrochemical Analyzer

Due to the overuse of tetracycline antibiotics as veterinary drugs and feed additives in livestock or aquaculture industry, the residue of tetracycline antibiotics in environment have lead to serious consequences, such as arising antibiotic-resistant bacterias, allergic symptoms in humans and environmental pollution. Thus, it is important to control the use of antibiotics and restrict its abuse. Traditional determination techniques for tetracycline antibiotics include immunoassays, microbiological inhibition tests, and chemical-physical methods (e.g., liquid chromatographic analysis and capillary electrophoresis). However, microbiological tests are relatively time consuming and nonspecific. The chemical-physical methods depend on large equipment and complicated procedure for sample pre-treatment. Therefore, these methods are not suitable for on-site or routine analysis. Electrochemical techniques have been proposed as a promising method for the measurement of environmental pollutants. Its have some advantages, such as fast, simple and inexpensive equipment. However, low selectivity of this method confined its use in routine analysis. Molecularly imprinted technique (MIT) is a polymeric method, which has made great development in the past few decades. Molecularly imprinted polymer (MIP) can provides specific binding sites for template molecules, which match the template specifically by spatial structures and functional groups. Besides, MIP also has some other unique properties, such as predetermination, selectivity, and high chemical and physical stability. It is expected that combination of MIT and electroanalysis will achieve sensitive and selective determination for tetracycline (TC). Based on this guideline, some works were carried out as follows:(1) Gold microelectrode was prepared by electrodeposited gold colloids with micro-nano structure on tungsten tip, whose parameters were optimized. This electrode was used to detect tetracycline by cyclic voltammetry. The oxidation peak currents were linearly related to TC concentrations in the range of 1 to 100 mg L-1. The detection limit was 0.09 mg/L (S/N=3). However, selectivity of this electrode to TC was low in co-existing of chlorotetracycline.(2) MIP modified electrodes were fabricated through photo- and thermal-polymerization, respectively. The characterization results of SEM, FTIR and CVs demonstrated that polymer was uniformly modified on the surface of Pt particle modified titanium (Pt/Ti) substrate, and the binding sites were successfully formed in MIP. In the electrochemical determination of tetracycline hydrochloride by photo-initiated MIP electrode, the linear range was from 0.4 to 20 mg L-1, and the detection limit was 0.12 mg L-1 (S/N=3). The imprinted ratio is 20.7,16.9 and 13.6 to CAP, CTC and OTC, respectively. In the electrochemical determination of TC by thermal-initiated MIP electrode, the linear range was in from 0.1 to 10 mg L-1, and the detection limit was 0.026 mg L-1 (S/N=3). The imprinted ratio is 12.1 and 18.7 to CTC and CAP respectively. Therefore, the combination of MIT with electroanalysis improved the selectivity for TC in electrochemical determination.(3) Multi-wall carbon nanotubes (MWNTs) was used as supporting material in fabrication of MIP electrode. TEM, SEM, CVs and EIS were used to characterize the modified electrode. The results demonstrated that the electro-transfer ability from the binding sites to surface of the electrode was improved. When using glass carbon electrode as substrate, the relationship between peak current and TC concentration was linear in the range from 0.1 to 40 mg L-1 and the detection limit was 0.04 mg L-1 (S/N=3). The imprinted ratio is 4.1,6.3 and 6.4 to OTC, CAP and nafcillin, respectively. When using Pt/Ti as substrate, the linear range was in TC concentration range from 0.01-50 mg L-1, and the detection limit was 0.008 mg L-1 (S/N=3). The imprinted ratio is 9.2 and 16.7 to CTC and CAP respectively. In this study, the use of MWNTs increased binding sites on surface of MIP electrode. The determination limit and linear range for TC were improved.(4) Analyzer for TC based on molecularly imprinted technique was developed using amperometric method. In the electrochemical determination for TC by analyzer, MIP electrode was applied as working electrode. The linear range was from 0.01-50 mg L-1, and the detection limit was 0.008 mg L-1 (S/N=3).In this study, electroanalysis and molecularly imprinted based technique were combined in determination of tetracycline. Molecularly imprinted technique improved the selectivity for TC determination. The use of MWNTs as supporting material further increased the sensitivity and linear range of MIP sensor. At last, a kind of analyzer for TC was developed, which has high sensitivity and selectivity for TC determination. It is expected that the sensor could be used in on-line detection in the future.