The Study Of Detection Antibiotics Residues In Food Based On Colorimetric Aptasensor

Aptamer was used as a signal recognition element in the design of molecular probes due to its structure flexibility.Its structure was changed or restructured after interacting with the target molecule,which were ones of the best choices for signal transmission.Compared with antibodies,aptamers can not only efficiently and specifically bind to targets,but also have many unique advantages,such as strong affinity,high stability,and easy preparation.Although these optical aptasensors based nanomaterial have been increasingly used for food safety testing,they also have some shortcomings that greatly limit their practical applications.Most reported optical aptasensors require complex modification.The detection process was complicated and depend special equipment as signal reading.Among them,including colorimetric aptasensors based on gold nanoparticles(AuNPs),the interface of aptamer chain could be modified to obtain covalent coupling and fixation on its surface to achieve satisfying detection limit,but the status inevitably causes the cost of testing increases,and not be satisfyed point-of care testing.Therefore,in order to further expand the application of aptamers in food safety detection,established and developed the optical aptasensing systems that are simpler,faster,higher sensitivity and better selectivity still have high scientific and reality significance.The research will be carried out in the following aspects to solve the above defects:A label-free,rapid response colorimetric aptasensor for sensitive detection of CAP was proposed,which was based on the strategy of ss-DNA-modified AuNPs aggregation assisted by lanthanum(La3+)ions.The AuNPs generated color change monitored by red,green and blue(RGB)analyzed by smart phone imaging APP.La3+,as a trigger agent,strongly combined with the phosphate groups of the surface of ss-DNA-AuNPs probe,which helps create AuNPs aggregation and the color change of AuNPs from red to blue.On the contrary,when mixing with CAP,the aptamer(Apt)bound to CAP to form a rigid structure of the Apt-CAP complex,and La3+ attached to the phosphate groups of the complex,which prevents the aptamer binding the surface of the AuNPs.As a result,the color of the AuNPs changed to violet-red.Finally,UV-vis absorption spectrum and the smart phone imaging APP were employed to determine CAP with a lower detection limit of 7.65 nM and 5.88 nM,respectively.The proposed strategy featuring high selectivity and strong anti-interference ability for detection of CAP in practical samples was achieved.It's worth mentioning that the simple and portable colorimetric aptasensor will be used for facilitating on-site detection of food samples.In order to further extend the above design conception,the signal amplification was achieved through enzymatic reactions to improve the sensitivity of detection.We designed a simple,high selectivity colorimetric aptasensor.It regulated the catalytic activity of PDA@Pt@AuNPs by the concentration of Apt-CAP complex to achieve the detection of CAP.When CAP was absent in the system,due to the nitrogen and oxygen protonation in an acidic environment,the bases of Apt usually were electrostatically repelled with the polydopamine(PDA)covered by PDA@Pt@AuNPs.Thus,Apt cannot be tightly adsorbed on the surface of PDA@Pt@AuNPs,result on the activity of PDA@Pt@AuNPs was no inhibitory.But,when CAP is present,After Apt binding specifically to CAP and happening conformationally flips,it's exposed the negatively charged phosphate group.The formed Apt-CAP complex can be tightly attached to the surface of PDA@Pt@AuNPs by electrostatic attraction,which prevents the contact between the active site of PDA@Pt@AuNPs and the chromogenic substrate,caused the catalytic activity inhibition.The strategy showed remarkable selectivity and anti-interference ability for detection of CAP in actual samples.The detection limit obtained 5.48 nM in 0-350 nM.The mobile phone imaging analysis was combined with proposed strategy and achieved satisfactory detection results,which effectively promoting the development of routine inspections of food safety.In addition,proposed strategy was used nanoenzyme catalysis to effectively avoid the false phenomenon caused by non-specific aggregation of precious metal nanomaterials which broadens the performance development.In order to achieve multiple targets of the detection requirement,we devise a novel colorimetric aptasensor for multiplex antibiotics based on an ss-DNA fragment coordinately controlling AuNPs aggregation.The multifunctional aptamer(Apt)was elaborately designed to be adsorbed on AuNPs surfaces acting as a binding element for antibiotics and a molecular switch.CAP and tetracycline(TET)were selected as the model antibiotics.When one kind of antibiotics was added,the specifically recognized fragment of Apt can bind to it and dissociated,and the non-specific one coordinately controls AuNPs aggregation under high-salt conditions.Hence,different color changes of AuNPs solution can be used as the signal readout.The aptasensor exhibited remarkable selectivity and sensitivity for separate detection of TET and CAP,and the detection limits are estimated to be 32.9 and 7.0 nM,respectively.The analysis with the absorption spectroscopy and the smartphone were applied to detect antibiotics in real samples with consistent results and desirable recoveries.