New Biosensing Research Based On Target-Mediated Assembly Of SERS Gold Nanoparticles

With the deeper fundamental understanding and the advances in nanofabrication techniques,the surface enhanced Raman scattering?SERS?applications have expanded across many fields of science including materials science,life science and environmental science.Compared to other optical-based analytical methods including UV-vis and fluorescence,SERS technique provides the advantages of abundant spectral information,narrow line signatures and little or no sample pretreatment etc.Considering some target-activated the aggregation of gold-nanoparticles generating SERS of the Raman dye,a series of novel SERS biosensors have been developed with simple,fast,high sensitivity and stability.Firstly,a novel SERS biosensor based on enzyme-activated plasmonic coupling for specific detection of Uracil-DNA Glycosylase?UDG?has been developed.UDG is a high conserved damage repair enzyme which can specifically excise Uracil residue in the base excision repair?BER?pathway which keeps the normal genomic sequence.The abnormal UDG activity in human cells may cause some diseases such as cancer and neurodegeneration disease.We designed a hairpin-like structure contained a Uracil base in the stem and modified on the surface of the gold nanoparticles?AuNPs?as SERS probe.The target of UDG recognizes and excises the base of Uracil forming an AP site.Consequently,the AP site is then cleaved by Endo IV,which destroyed the stability of the hairpin-like structure,thus generating a free-stretched single-stranded DNA on the surface of Au-nanoparticles.Lastly,the single chain can be degraded from 3'-terminus step by step with the Exo I,resulting in the aggregation of the Au-nanoparticles that yield uniformly distributed hot spots.This strategy has the trait of simple,fast,homogeneous reaction,high sensitivity and specificity.Under optimal conditions,this biosensor exhibits ultrasensitive detection of UDG activity with detection limit of 4.29×10^-4 U m L^-1 and a detection range of 5 orders of magnitude.This provides a facile method about BER research and relevant molecular diagnostic and drug screening.Secondly,we constructed a target-activated assembly of AuNPs biosensor for ATP detection.This strategy relies on the special target-aptamer binding along with the catalytic hydrolysis of Exo ?,leading to the aggregation of AuNPs.This nanomachine is constructed by three kinds of nucleic acid strands on the surface of AuNPs by Au-S bond.In the presence of ATP,the target ATP will combine its aptamer with high specificity,inducing the DNA Walker released from the duplex structure to initiate the Nanomachine.Consequently,the liberated DNA Walker will hybridize with DNA Track at 3'terminus forming the blunt end,which could be digested with Exo ? from 3' to 5' of DTs of duplex until released DNA Walker again.Lastly,the DNA Walker is able to walk along the 3-D track by Exo ? cleaving the DNA Track at each step.As a result,the AuNPs will lose the protection of the DNA on the surface after Exo ? cleaved and form aggregation each other under the condition of high salt environment.The aggregation of the AuNPs significantly enhanced SERS signal of Raman dye due to the extremely powerful electromagnetic field.The limit of detection of this concept is 0.288 pM,which up to ultrasensitive and specificity for ATP detection.Finally,a kind of biosensor was constructed which was based on the replacement of miR-21 to start the nanomachine to detect miR-21.In this method,the nanomachine was consisted with three kinds of nucleic acid including DNA Walker,DNA Track and Protect probe.Then the mixed hybridization solution and DNA Track were combined to modify the AuNPs.In the presence of miR-21,it will combine with the Protect probe and release the DNA Walker.Then,the DNA Walker will hybridize with the DNA Track forming the duplex structure.At last,the AuNPs will lose the protection of the DNA on the surface after Exo ? cleaved and form aggregation each other under the condition of high salt environment.Hence,this strategy may represent a simple,fast,label-free platform for ATP detection.