Colorimetric Sensors For Conformational Recognition Of Fatty Acids And Their Applications

Fatty acid is a class of carboxylic acids with long aliphatic chains,which are usually derived from triglycerides or phospholipids.Fatty acids are important dietary sources of fuel for body because,when metabolized,they yield large quantities of ATP.Based on the fat chain,fatty acids can be divided into saturated fatty acids and unsaturated fatty acids.Related studies have found that part of the saturated fatty acids will increase the body's serum cholesterol levels,and there is a close relationship between cholesterol levels and the incidence of cardiovascular disease.At the same time,the trans unsaturated fatty acids concluded in the unsaturated fatty acids are also harmful to human health,the probability of cardiovascular and cerebrovascular disease is 3-5 times than the saturated fatty acids,it can also induced cancer,type 2 diabetes,allergies Disease.In addition,long-chain fatty acids cannot cross the blood–brain barrier(BBB)and so cannot be used as fuel by the cells of the central nervous system.Based on the significant impact of fatty acids on human health,the identification of species and conformation for fatty acids is of great significance.Traditional fatty acid analysis methods include high performance liquid chromatography(HPLC),capillary electrophoresis(CE),gas chromatography(GC)and mass spectrometry(MS)are usually time-consuming,high cost as a result of requirement for sophisticated instrumentation,complex operation and cannot achieve real-time detection and so on.In recent years,colorimetric sensors based on its strengths of online,real-time,simple and fast operation have applied in analysis of metal ions,biological macromolecules and medical imaging and so forth.But in the application of fatty acids' recognition is still relatively rare.Thus,this paper is devoted to construction of three new colorimetric sensors applied to the identification of fatty acids.This paper mainly includes the following four aspects:(1)The first chapter reviews the importance and research progress of fatty acid recognition and the application status of gold nanoparticles sensors.(2)The second chapter,there are differential complexation between Ag+ and distinct type of fatty acid,while colorless TMB(tetramethyl benzidine)solution can be oxidized to blue by silver ions.Based on the above findings,a new method for the colorimetric identification of fatty acid based on TMB chromogenic agent was constructed.First of all,the experimental parameters in the system was optimized,including the concentra-tion of silver nitrate,TMB concentration,the incubating time,the reaction temperature.Then,the sensitivity of the sensing system and the change of the fatty acid composition under different heating time were investigated under the optimized experimental conditions.Finally,the recognition effect of the sensing system on the standard and the actual samples was explored.The results showed that the colorimetric sensor established by TMB chromogenic agent has the advantages of high sensitivity,wide linear range,simple easy to use and strong visualization,and has achieved good results in the identification of actual sample.(3)The third chapter constructed a colorimetric sensor based on spherical gold nanoparticles and studied its applicability to the actual system.The gold nanoparticles were prepared by sodium citrate reduction.The spherical gold nanoparticles were characterized by UV-Vis absorption spectrophotometer and transmission electron microscopy(TEM).The sensitivity and detection limits of the gold nanoparticles sensor were investigated.The results show that the colorimetric sensor based on gold nanoparticles towards fatty acids has anti-interference ability,high degree of visualization,wide linear range,beside,it can identify the fatty acid in the actual sample.(4)The fourth chapter,as we all known,nanomaterials show unique properties in physics and chemistry due to the characteristics of quantum size effect,surface effect,small size effect and tunneling effect and so on.As a special nanomaterial,gold nanorods(GNRs)possess unique transverse surface plasmon resonance(TSPR)and longitudinal surface plasmon resonance(LSPR)because of their anisotropism.Based on the correlation between the LSPR absorption peaks of GNRs and their corresponding absorbance with analyte,GNRs were firstly synthesized through a seed-mediated method,the yellow TMB2+ produced by Ag+ oxidation can etch GNRs along the longitudinal axis under the acidic conditions,which resulted in the decrease of the aspect ratio of GNRs,blue shift and significant changes of color in the solution.The different complexing ability between different types of fatty acids and silver ions made the different etching process of gold nanorods,achieving the colorimetric recognition of fatty acids.Based on this phenomenon,a non-aggregation GNRs colorimetric sensor for rapid determining fatty acids has been designed.The results showed that the colorimetric sensor based on gold nanorods has a wide range of color,a high degree of visualization,good stability,good selectivity and so on,and was able to recognize fatty acid in the actual sample.