The Applications Of Colorimetric Method In Biothiols And Heavy Metal Ions Determination

Biological thiols,including cysteine?Cys?,glutathione?GSH?and homocysteine?HCys?,the levels of these biothiols in human body are directly associated with various diseases,and play essential roles in pathological processes and biochemical pathways.Heavy metal ions are common environmental pollutants widely distributed in water,soil and food,these heavy metal ions are harmful to the human health when the concentration is out of range.Therefore,a simple,feasible,and highly sensitive method is needed for biothiols and heavy metal ions detection.In this dissertation,we developed facile,rapid,and highly sensitive colorimetric sensors,and investigated the application of these methods in cysteine,glutathione,homocysteine and silver ion.The main points are outlined as follows:1.We proposed a novel colorimetric sensor for biothiols determination based on the I^--H₂O₂-3,3',5,5'-tetramethylbenzidine?TMB?system.I^-could catalyze the oxidation of TMB to form the blue oxidized TMB?ox-TMB?in the presence of H₂O₂.This induced an absorption peak centered at 652 nm in the UV-vis absorption spectrum.The addition of biothiols could decolorize ox-TMB,which led to a decrease of the absorbance at 652 nm.Our analytical method displays good performance to biothiols under the optimum experimental conditions with low detection limit for Cys,HCys and GSH with 0.1,5 and 0.5?M,respectively.In addition,this system in the experiment was not affected by interference of other amino acids,so the developed method is sensitivity and selectivity.Compared with previous reports,this direct approach reveals a few advantages like simple,time-saving and environmentally friendly.Finally,this technique provides a excellent platform for successful detection of biothiols in human plasma,exhibiting its promising potentials for biomedical sensing.2.A facile colorimetric sensor has been fabricated for the detection of silver ion based on L-cysteine functionalized gold nanoparticles.In this study,several experimental conditions that may affect the sensitivity of this method were optimized prior to the test,and then under the optimal conditions,we have investigated the aggregation rate of the Au NPs by tuning the concentrations of silver ions.When cysteine was added into the system,cysteine bound onto the surface of Au NPs through the formation of Au-S bonds and caused the aggregation of Au NPs,which resulted in the red color of Au NPs solution turning to blue,and a new absorption band at 640 nm occurred in the UV-vis spectrum.Silver ion has very strong affinity towards cysteine,which made cysteine desorption from the Au NPs surface.Thus,the introduction of Ag ion was able to prevent the aggregation of the Au NPs,and the color of Au NPs solution changed from blue to red.Furthermore,this proposed method does not need necessary sophisticated instrumentation,making it simpler,more time-saving and cost-effective.This method also was not affected by interference of other ions.The colorimetric strategy would open a new avenue for other metal ions by modifying various specific ligands onto the Au NPs that selectively bind target metal ions.