Detection Of Genes Via Lateral Flow Biosensors Of Diseases Based On CdTe QD-DNA Probes

With the genes of various diseases have been learned,detection of nucleic acid could realize the early detection and perform better than detection of antigen or antibody.However,at the early stage of disease,the number of deoxyribonucleic acid is trace amount.In order to amplify the detection signal,different kinds of nucleic acid amplification techniques and novel nano materials have been involved in testing schemes.There are two main methods of nucleic acid amplification techniques,non-enzyme displacement cycle and enzyme digestion cycle.In terms of nano materials,such as,nanocluster,up-conversion luminescent material,quantum dot(QD)and so on,which have been applied in gene detection.At present,gene detection could not be suitable for household or using in rural and poverty areas,because developed test methods need expensive instruments and rigorous operating conditions.Therefore,the increasing number of scholar are dedicating effort to designing low-cost,easy operable and portable biosensors,especially,lateral flow strip sensors exactly match these characteristics.The principle of test strips is the liquid sample could migrate on the paper by utilizing capillarity of micropore.Then,the signal probe would be captured or not,when it flows to test line and control line which were immobilized on nitrocellulose membrane.Finally,the qualitative or semi-quantitative determination would be realized by testing absence or presence of signal or strong or weak of signal.In recent years,gold nanoparticles are the most common signaling molecules of later flow assay,and detection of antigen or antibody,human chorionic gonadotropin(HCG),heavy metal and virus have been applied maturely to lateral flow assay.The main significance of our works is for employing QDs and nucleic acid amplification technologies on lateral flow biosensors to finish more expedient,wide and accurate test of diseases.Moreover,it is tremendous helpful for point of care and postoperative monitoring.This study includes following two main contents:(1)Designed and constructed a fluorescent lateral flow biosensors based on CdTe QD-DNA probes and DNA strand displacement cycle amplification.As a novel nanomateral,QDs are more biocompatible which could combine with more biomolecules to enhance the sensitivity and accuracy of biosensors.There were two haiphin DNA(H1 and H2,H2 had been modifcaed with CdTe QDs)acted as probes in this work.The target(HIV-DNA)could initiate the unfolding of H1's haipin structure and partly mathch with H1.Then,unmatched H1 would motivate the unfolding of H2 and complement more with H2.Therefore,the target would be unwinded from H1 and cycle to next reaction for converting into a number of QD-double strand DNA(QD-dsDNA)nano-structure,which could be captured by test line.These two probes would not complementary paring without Target.Finally,testing the fluorescent signal of CdTe QDs upon test line to determinate the gene of human immunodeficiency virus(HIV-DNA)quantitatively,the detection range of 1 pM to 10 nM and the limit of detection(LOD)as low as 0.76 pM(S/N = 3).In addition,the suggested scheme could also detect any nucleotide sequence or protein and virus which has aptamers.By the way,this method could eliminate the hook effect,because the reporter probe was not connected with capture probe by the target.Therefore,this strip biosensor could be applied to practical application prospectively.(2)Constructed a dual-signal detection based on QDs and AuNPs via lateral flow strips.The target gene(Escherichia coli special DNA)could hybridize with QD-DNA probe and drive the other sequence unwind,which matched with the probe partly.Then,this sequence would hybridize with Au-haipin DNA.When the sample flows to the test zone,these two probe would be captured respectively.Finally,test the decrease of the fluorescent signal from QDs and the increase of color from AuNPs(Au nanoparticles)for realizing dual-signal detection.As conventional reporters,AuNPs own high-noticeable color.However,they are used for qualitative or semi-quantitative detection mostly.As novel nanomaterals,QDs have high specific surface area and great biocompatibility,so they could enhance the sensitivity of sensors.But,detections of fluorescent signal need expensive instruments and could not realize colorimetric assays.Therefore,it is significant to reach a method combine the color detection with fluorescence detection based on paper sensors.