A Colorimetric Chloramphenicol Assay Based On Gold Nanoparticles Functionlized By Aptamer

Chloramphenicol(CAP)as the first synthetic antibiotic has been widely used in clinic,animal husbandry and aquaculture.However,it has been found to cause many diseases,which are extremely risky to human health.Thus,building a method to monitor the concentration of CAP in water to alarm contamination of CAP is significant.Because of the super sensitive localized surface plasmon resonance(LSPR)of gold nanoparticles(GNPs),GNP-based colorimetric assays have attracted considerable attention in a broad range of field,especially in environmental monitoring.Furthermore,aptamer has excellent affinity and specificity for targets and can easily functionalize GNPs.Thus,a novel aptamer&GNPs-based colorimetry was established to detection the concentration of CAP in water environment.The main results were as follow:1.The CAP aptamer was modified by a sequence of 5 adenosine groups to anchor on the surface of GNPs to synthesize the probes(polyA-Apt@GNPs).PolyA-Apt@GNPs were tested by UV-Vis absorption spectra,TEM,ectrophoresis,ultrasonic-tolerance test,salt-tolerance test and detecting ability test.Then,the results shows the binding between polyA-Aptamer and GNPs is strong,and polyA-Apt@GNPs has the high stability and excellent responding rate and signal.2.A competitive colorimetry has been established to detect CAP.It is based on the competitive capture for two compounds,viz.CAP(which can not directly cause a significant signal change of polyA-Apt@GNPs in acid environment)and D-(-)-threo-2-Amino-l-(4-nitrophenyl)-1,3-propanediol(CAP-base,which can directly cause a significant signal change of polyA-Apt@GNPs in acid environment).The capture of CAP-base triggers the aggregation of modified GNPs in salt-containing solution,and this causes the solvent a color change from red to purple.However,in the presence of CAP and CAP-base,the capture of CAP weakens this color change by a competing process for capture.Thus,the concentration of CAP is associated with the degree of deaggregation of GNPs and can be quantified by the ratio of absorbance at 620 nm and 520 nm.After optimizing concentration of probe,sample pH value,molar ratio(aptamer/GNPs)of probe,ionic strength and concentra-tion of CAP-base,the assay has a 22 nM limit of detection(LOD),and the response is linear in the range of 0.20 to 3.20 ?M CAP concentration.This assay was successfully applied to the determination of CAP in spiked environmental water samples.3.Based on the different chemical structural in primary(1°)amine and secondary(2°)amine between CAP-base and CAP,the mechanism is supposed.When polyA-Apt@GNPs captures the target,it will have 3 kinds of probability:(1)polyA-Apt@GNPs tends to aggregate due to the decrease of absolute value of ?potential if the charge of the target is positive;(2)polyA-Apt@GNPs dose not change if the charge of the target is neutral;(3)polyA-Apt@GNPs tends to prevent aggregating due to the decrease of absolute value of ? potential if the charge of the target is negative.Then the test of polyA-Apt@GNPs detecting CAP and CAP-base in both acid and basic environment and detecting complementary ssDNA in acid environment and the test of ? potential of polyA-Apt@GNPs captured CAP-base have proved the mechanism partly.Conceivably,owing to the mechanism,this method has a wide scope in that it may be applied to a wide range of analytes if respective aptamers are available.