The Research For Liquid-phase Colorimetric Assay Based On Special Organic Indicator

Colorimetric biosensor is the important part of biosensors that combined the sensing technology and biological detection principle has been widely used in medical sensing,environmental monitoring and food agriculture.In recent years,the colorimetric sensing strategy related reports have been emerged in an endless stream.In this paper,several colorimetric biosensor platforms based on organic indicator are designed and successfully applied to the analysis of life-related substances and environmental pollution monitoring.This thesis consists of four parts which its the main contents are as follows:1.First,the development and application of organic indicator were introduced.And then,the research and progress of visual sensing were introduced in detail.Last,the detection and significance of visualization methods in amino acids and nitrite were expounded.2.We present a simple yet facile colorimetric indicator-displacement assay for cysteine in aqueous solution with a sensitive optical readout,based on the competitive binding affinity between the 1-?2-pyridylazo?-2-napthol?PAN?indicator and cysteine target for the host Zn²⁺.In the absence of cysteine,Zn²⁺ can induce an appreciable yellow-to-pink color change for PAN solution through the formation of PAN-Zn²⁺ complex.However,adding cysteine to above PAN-Zn²⁺ complex solution resulted in a ligand exchange reaction between PAN and cysteine,with about 57 nm blue shift in the absorbance maximum?from 527 nm to 470 nm?,accompanied by an obvious color change of the solution from pink to yellow.The obtained indicator-displacement assay provide good detecting performance for cysteine with a detection limit of 7.3 ?M?S/N =3?by a UV/vis spectrometer as well as with a good linear range from 25 to 1000 ?M.More importantly,the proposed sensing system could be successfully used to the fabrication of a colorimetric INHIBIT logic gate,and converted into the test paper and image capture analytical devices for onsite visual determination of cysteine in practical applications.3.In this work,we proposed a naked-eye colorimetric strategy for simultaneous detection of cysteine and lysine based on 3,3',5,5'-tetramethylbenzidine?TMB?system in a neutral condition?p H 7.0?.Based of the fact that Ag⁺ could oxidize 3,3',5,5'-tetramethylbenzidine?TMB?to oxidized TMB?ox TMB?and induce a blue color solution corresponding to an absorption peak centered at 652 nm,thus the adding of cysteine or lysine to formation of different product results in the blue color fading to colorless quickly or change to scarlet,respectively.With this strategy,the limit of detection in experimental measurement for cysteine and lysine is 2.5 ?M and 3.9 ?M,respectively.And the selectivity can also be guaranteed among the other amino acid.4.We herein present a three-in-one platform for colorimetric sensing,fluorimetric sensing and electrochemical sensing,enabled by 3,3',5,5'-Tetramethylbenzidine?TMB?oxidation.TMB is the most common chromogenic substrate for colorimetric assay and the oxidation of TMB has great utility in bioanalysis such as peroxidase/peroxidase mimetic-based biosensing.First,the nitrite can oxidize 3,3',5,5'-tetramethylbenzidine?TMB?to develop a yellow color in aqueous solution,the linear dynamic range for the concentrations of nitrite is between 8.3 ?M to 116.7 ?M along with a limit of detection?LOD?of about 1.2 ?M?calculated LOD as 3?/slope?.Then,the nitrite can quenching the fluorescence of 3,3',5,5'-tetramethylbenzidine?TMB?in aqueous solution,the linear dynamic range for the concentrations of nitrite is between 1.6 ?M to 113.3 ?M along with a limit of detection?LOD?of about 5.6 n M?calculated LOD as 3?/slope?.Finally,we also investigate electrochemical performance,the linear dynamic range for the concentrations of nitrite is between 0.17 ?M to 75 ?M along with a limit of detection?LOD?of about 58.9 n M?calculated LOD as 3?/slope?.Especially,three different readout of TMB is well-achieved using three different assays in a same system.By employing a joint experimental study,we reveal that the unique performance of TMB.