Liquid Crystal Catalysis-SERS/RRS/Abs Aptamer Determination Of Oxytetracycline And Other Organic Pollutants

The unique fluidity and anisotropy of liquid crystals（LCs）allowed the molecular arrangement on the surface of LCs to change and adjust with the changes of external environmental conditions such as light,heat,and magnetism,thus showed wonderful physical and chemical properties.Therefore,LCs are often utilized as the excellent responsive materials in environmental analysis and biochemical analysis.Current research on LCs in the field of analytical chemistry often focused on the fluorescence polarization analysis triggered by the response events,and there have little application in nanocatalytic spectroscopy.LCs are also excellent catalysts for some chemical reactions.If LCs were used as catalysts for specific indicator reactions and combined with spectroscopic techniques,new spectroscopic analysis methods can be established and the application range can be broadened.In this paper,a novel RRS/SERS/Abs sensing platform was successfully established to detect environmental pollutants based on the catalytic effect of LCs the mediation of aptamers,and the specific recognition of target molecules by aptamers.The molecular behavior of LCs was discussed by molecular spectroscopy and particle size analysis,and a reasonable catalytic mechanism was proposed.The details are as follows:Three small molecule thermotropic liquid crystals,4-hexyloxybenzoic acid（HXB）,4-heptyloxybenzoic acid（HPB）and 4-cyano-4’-pentylbiphenyl（5CB）,were used as research objects and their molecular behavior in the temperature range of 25-75°C was explored.The experimental results showed that the LCs molecules will gradually aggregate into large size nanoparticles（NPs）with catalytic activity.Among the three LCs,5CB was the most thermally sensitive and the abundant surface electrons of 5CB can promote the electron transfer of redox reactions,thus showed strong catalytic effect on nanoindication reactions.When there is an Bisphenol A aptamer(Apt _BPA),it can be adsorbed on the surface of LCNPs by electrostatic interaction to inhibit its catalytic activity.When BPA is added,it can combine with Apt _BPA to form an Apt _BPA-BPA complex so that the catalytic activity of LCNPs is restored.The reaction rate of Na H₂PO₂-HAu Cl₄ was accelerated,and the concentration of Au NPs with RRS signal increased.When the BPA concentration is in the range of 0.005-0.05 ng m L-~1,the RRS signal increased linearly with the BPA concentration,and an bpa RRS analysis method can be established.By changing the types of aptamers,we tried to detect oxytetracycline（OTC）,tetracycline（TEC）,melamine（MA）and sulphadimidine（SDM）,and found that they still have good applicability.The detection ranges are 0.25-3.0 ng m L^-1,5-15 ng m L^-1,0.01-4.0 ng m L^-1and 2.5-10 ng m L^-1 respectively.After adding Victoria Blue 4r（VB4r）to the reaction system,Au NPs were used as a SERS substrate,and it can generate a strong SERS signal,which changes with the concentration of Au NP.According to the SERS signal changing with BPA concentration,a new SERS method for BPA is established.It has a linear range of 0.001-0.0125ng m L^-1 and a detection limit of 0.2 ng L^-1.In addition,the HPB-HAu Cl₄-Na H₂PO₂ assay system can also perform effective Abs detection for OTC in the concentration range of 1.0-7.50ng m L^-1.Through the investigation of interfering ions and the detection of actual samples,it is found that the method is feasible and provides a reference for the analysis method of detecting trace organic pollution in the environment.In third section,the traditional nematic liquid crystal 5CB was employed as the template and to load Au NPs on the surface to synthesize Au/5CB nanocomposites.The catalytic performances of Au/5CB,5CB,Au NPs and Cu₂O NPs were studied through the Cu（II）indicator reaction.Through research and analysis,the catalytic performance was mainly affected by electron distribution on surface.As excellent electron donors,Au NPs were uniformly distributed on the surface of Au/5CB with uniform particle size,shape and high degree of dispersion,which greatly improved the catalytic performance of Au/5CB and promotes the electron transfer and the formation of Cu₂O crystal nucleis which were conducive to the catalytic amplification of the reaction.In addition,Au/5CB also showed good thermal stability and salt tolerance.Through experiments,Apt _OTCcan inhibit the catalytic effect of Au/5CB,thereby inhibit the occurrence of the Cu（II）reaction.After adding OTC,it reacted explicitly with Apt _OTC to bind to each other,and Apt _OTC desorbed from the surface of Au/5CB.Then the catalytic activity of Au/5CB recovered,and the Cu（II）indicator reaction was accelerated.The Au NPs produced in the system increased,and the RRS signal gradually increased.Based on this principle,a linear equation related to OTC concentration and RRS signal intensity can be established so as to achieve the purpose of detecting OTC.Because the Au NP generated by the reaction can be used as a SERS substrate,after the addition of VB4r probe molecules,the SERS effect can occur,and the signal will increase as the concentration of Au NPs increases.Therefore,when the OTC concentration is in the range of 0.05-1.0 ng m L^-1,the system’s SERS signal increased linearly,the detection limit is 0.02 ng m L^-1,and the correlation coefficient is 0.9972.Good results have been achieved by applying the established RRS analysis methods to actual environmental water detection.This work provides a new idea for the application of LCs to the analysis of environmental pollutants.