Colormetric Detection Of Amino Acids Based On Gold Or Silver Nanoparticles

In recent decades,noble nanoparticles materials have been widely used in the fileds of biology,material and medicine(especially AuNPs and AgNPs)due to their specific properties including magnetic,optical,and catalytic characteristics.The mechanism based on the anti-aggregation of Au nanoparticles is commonly used to detect target species.On the other hand,modifying the organic molecules onto the surface of noble metal nanoparticles cannot only enchance the water solubility but the sensing selectivity and sentivity.In our work,the assays based on the inhibition of Au nanoparticles and functionalized Ag nanoparticles have been established to successfully accomplish the quantitative determination of Methionine,Glutathione and Histidine.The major contents are shown as follows:(1)The detertmination of methionine(Met)concentration based on the anti-aggregation of Au nanoparticles.Since melamine(Mel)can induce the aggregation of AuNPs and the adding of Met can inhibit the aggregation of it,we built up an assay to detect Met quantificationally.It can be easily observed with the naked eye.A good linear relationship between ratio of the absorbance and the concentretion of Met in the range of 0 to 1.0 ?M with limit of detection(LOD)24.5 nM was presented.This method is successfully applied to determine Met concentration in serum and urine samples.(2)Selective detection of glutathione(GSH)based on the pH regulation of AuNPs in the prescence of 2-Mercapto-1-methylimidazole(MMI).A certain concentration of MMI which is used as aggregation reagent was added into AuNPs,resulting in the color changed from wine red to blue.However,the increasing concentrations of GSH can gradually weaken the aggregation extent of AuNPs.And under the same p H,other animo acids which included –SH can not have the same effect.Therefore,the method can detect GSH over other compounds with high selectivity.The process of anti-aggregation of AuNPs can be monitored by an ultraviolet-visible spectrophotometer and the naked eyes.A linear relationship between the intensity ratio A650 nm/A520 nm and the GSH concentration is obtained(R2 = 0.998)with a LOD of 12.0 nM.(3)A simple and lower-cost assay with high sensitivity for the GSH detection is introduced based on the anti-aggregation of AuNPs.The interaction between Cys and AuNPs results in the aggregation of AuNPs accompanied by a color changes from red wine to purple,which can be monitored by UV-visible spectrometer to realize the quantification of GSH.There was a good linear relationship between ratio of the absorbance ratio A650 nm/A520 nm and the concentretion of GSH in the range of 1.0 to 1.0 ?M with detection limit of 20.3 nM.The established method has been applied to the determination of GSH in serum and urine samples.(4)Colorimetric test for Histidine(His)using silver nanoparticles modified with sulfanilic acid(SAA).The presence of His results in a visually detectable gradual color changes from bright yellow via orange to purple.The mechanism is assumed to be mainly due to electrostatic interaction,strong ?-? stacking,and hydrogen bonding between SAA and His.The assay has a 52.7 nM detection limit in the 0 to 3.5 ?M concentration range.The method could also be applied to detect polyhistidine-tagged cysteine(His-HisHis-His-His-His-Cys)and the concentration can be quantified down to 5.57 nM,which links the method to His-tag technology.