A New Method For The Enhancement Of Gold Nanoclusters And Tyrosine Fluorescence Signals

Fluorescent technology has widespread application in bioassay and medical detection,due to its high sensitivity,good reproducibility,real-time and visual detection.The relatively low fluorescence efficiency limits its application in highly sensitive detection,because of the low quantum yield of some fluorescence molecule.Thus,it is necessary to amplify the fluorescent intensity to highly improve the sensitivity of fluorescence detection.It still remains a practical challenge to amplify the fluorescent signal of current fluorescent technology.The developed fluorescence signal amplification techniques include metal enhanced fluorescence,aggregation induced enhanced luminescence and photonic crystal enhanced fluorescence.In this paper,two methods of fluorescence signal amplification are developed with the use of gold nanoclusters(AuNCs)and L-Tyrosine.In the first chapter,three methods of amplifying fluorescence signal,including metal enhanced fluorescence,aggregation-induced enhanced luminescence and photonic crystal-enhanced fluorescence are briefly introduced.And the mechanism of fluorecsence enhancement,research progress and application in analytical chemistry are summarized.In the second chapter,by taking advantage of the metal-enhanced fluorescence effect,a novel fluorescence enhancement system was designed to boost the fluorescence of AuNCs with AuNPs.AuNCs,a new type of luminescent nanomaterial,have a widespread application in biological imaging,sensing,catalysis and photonics,owing to good stability,low toxicity and good biocompatibility.However,the relatively low luminous efficiency limits their application in highly sensitive detection.Thus,it is necessary to amplify the fluorescence signal of the AuNCs to improve the sensitivity.Metal nanoparticles(NPs)with the surface plasmon resonances can dramatically affect the optical properties of nearby fluorescence molecules,resulting in an enhancement or quenching of fluorescence depending on the distance between the fluorescent molecules and the metal surface.On the basis of these,a metal-enhanced fluorescence system was constructed,and AuNPs were used to enhance the fluorescence of AuNCs.The effect of distance on the fluorescence intensity of AuNCs was investigated.And the distance between the AuNPs and AuNCs is controlled by the thickness of the silicon.The fluorescence intensity of AuNCs gradually increases with the increase of distance between AuNCs and AuNPs,when the distance is greater than 8 nm.A maximal enhancement of 3.7 times was observed with a shell thickness of 12 nm comparing to that of direct mixing of AuNCs with AuNPs.This finding can be utilized to develop a highly sensitive biosensor.Morever,this work opens a straightforward methodology for investigating the interaction between fluorescent metal NCs and NPs.In the third chapter,the mechanism of L-Tyrosine fluorescence enhancement was explored and a fluorescent analyses for detection of L-Tyrosine was developed based on the fact that fluorescence intensity of L-Tyrosine can be enhanced by nitrate ion.L-Tyrosine is a very important amino acid in the human body.A series of diseases can be induced by lacking of L-Tyrosine.Therefore,it is of significance to develop a simple,sensitive and convenient method for the detection of L-Tyrosine in the diagnostic and therapeutic of related diseases.L-Tyrosine almost has no fluorescence in alkaline conditions.In the presence of nitrate ions,the fluorescence intensity of L-Tyrosine will be significantly enhanced.The mechanism of the fluorescence enhancement of L-Tyrosine was explored through the fluorescence properties of the reaction product,dynamic light scattering analysis and transmission electron microscopy.The possible mechanism is that L-Tyrosine molecules was aggregated triggered by nitrate ion,which limits the free rotation of the carbon-carbon single bond in the L-Tyrosine molecule,resulting in aggregation-induced luminescence,and then boosted the fluorescence intensity of the L-Tyrosine.By taking advantage of interaction between L-Tyrosine and nitrate ion,a method for detection of L-Tyrosine was established.The fluorescence intensity of the reaction product at 407 nm was proportional to the concentration of L-Tyrosine in the range from 0.1 to 50.0 ?mol/mL with a detection limit of 49.0 nmol/mL.The method has the advantages of low cost,fast response and high sensitivity,which make the method very promising for detection of L-Tyrosine deficiency related diseases.In the fourth chapter,the two methods of amplifying the fluorescence signal was summarized,including the metal enhanced fluorescence and aggregation induced enhanced luminescence.A novel fluorescence enhancement system was established,in which AuNPs was used to boost the fluorescence of AuNCs.And,a new method for sensitive detection of L-Tyrosine was developed,because of the fluorescence intensity of L-Tyrosine can be enhanced by nitrate ion.