Sensing Platform For Detection Of L-Histidine Based On DNA Copper Nanoclusters

With the rapid development of the analytical science,analytical methods are improved to meet the requirement of the great changes.However,new nanomaterial-metal nanoclusters are studied by researchers.Metal nanoclusters are applied in various fields,such as environment,food,medicine,etc..The metal nanoclusters composed tens of metal atoms,which size was smaller than 2 nm.These ultra-small nanoclusters,including Au nanoclusters(AuNCs),silver nanoclusters(AgNCs),copper nanoclusters(CuNCs),platinum nanoclusters(PtNCs)have unique performace.Metal nanoclusters with more excellent fluorescence properties show unlimited application potential in biological cell imaging,disease diagnosis and treatment,biosensing,environmental monitoring and biological tracing.With the specific optical properties similar to AuNCs and AgNCs,it is expected to be an alternative to noble metal nanoclusters(gold,silver,copper nanoclusters).In recent years,DNA template copper nanometer cluster fluorescence sensor for the detection of biological substances is more and more widely.In this paper,a series of terminal deoxynucleotidyl transferase based fluorescence sensor platforms were constructed to polymerize the randomized strand to form a fluorescent signal with the T or poly-T single-stranded DNA.The main research work is performed as following:1.A fluorescent sensor is investigated based on terminal deoxynucleotidyl transferase(TdT)polymerized DNA for L-histidine(L-his)detection.Single strand DNA containing poly-thymine sequences are synthesized by TdT in the presence of dTTP.In blank control,poly-thymine sequences work as templates of copper nanoclusters due to the affinity between thymine and copper ions(II).Fluorescence intensity is enhanced when copper nanoclusters formed with reducing agents.In the presence of L-his,the imidazolyl group of L-his works as a chelating agent that forms copper/L-his chelated complex.Thus less copper ions are induced in poly-thymine sequences,and less copper nanoclusters are obtained to produce fluorescence signals.A good linear correlation was obtained between fluorescence change and the logarithm of the L-histidine concentration over the range from 5.0×10-9?5.0×10-4 mol·L-1.The detection limit was estimated as 3.420×10-9 mol·L-1.Compared with other methods of synthetic CuNCs,this method allowed to specifically determine L-histidine without template or labeling,which shows a good potential in biomedical and clinical analysis.2.A fluorescent sensor is investigated based on the signal amplification for L-histidine detection.In the absence of L-histidine,the DNAzyme structure was so stable that DNA template of the CuNCs synthesis were blocked in DNAzyme.The CuNCs synthesis was suspended leading fluorescence negative.In the presence of L-histidine,DNAzymes cleave the substrates specifically,and release the split substrates worked as DNA-CuNCs template.A good linear correlation was obtained between fluorescence change and the logarithm of the L-histidine concentration over the range from 4.000×10-9 to 4.000×10-5mol·L-1.The detection limit was estimated as 3.776 ×10-9 mol·L-1.And the recoveries were 96.58%?105.3%for the actual samples.Compared with the traditional method,this method allowed to specifically determine L-histidine without enzyme or labeling,which shows a good potential in clinical analysis.3.A fluorescent sensor is investigated based on Poly-T(Thymidine)single-stranded DNA-CuNCs for L-histidine(L-his)detection.Thymine has a good affinity for Cu2+ and Cu2+was reduced in the presence of sodium ascorbate to form copper nanoclusters.In the presence of L-his,the number of copper nanoclusters were decreased because of the chelating reaction between L-his and Cu2+.A good linear correlation was obtained between fluorescence change and L-his concentration over the range from 8.000×10-7 to 8.000×10-6 mol·L-1.The detection limit was estimated as 6.173×10-8 mol·L-1.And the recoveries were 96.54%?103%for the actual samples.This method allowed to specifically determine L-histidine without labeling and shows a good potential in clinical analysis.