The Design And Application Of Fluorescent Probe Based On Ligand-Stabilized Silver Nanoclusters/Nanoparticles

Metal nanomaterial?Au,Ag,Cu,Fe,and Pt-based species?,a key element in the fast developing nanotechnology,possesses unique properties,such as surface plasmon resonance,fluorescence,electrochemistry,and catalysis and so on.Silver nano material is a type of ligand-stabilized Ag structure with 1-100 nm in size.According to their sizes,silver nanomaterial used usually involves two kinds,such as fluorescent silver nanoclusters?AgNCs?and silver nanoparticles?AgNPs?as nanoquencher.Compared with organic dyes suffering photobleaching and semiconductor quantum dots with large size and toxicity,silver nanoclusters stabilized by DNA?DNA/AgNCs?have a lot of advantages,such as small size,facile synthesis,tunable emission,high photostabilization,and good biocompatibility,applying to chemical analysis,biomedicine,and environmental monitoring and so on.However,conventional single emitter still suffers from low brightness and photostabilization.The paper investigates the preparation of fluorescent silver nanocluster pair intergrowth via assembly of two emitters,and studies in detail optical properties and the fluorescence enhancement mechanism of silver nanocluster pair intergrowth modulated by different DNA templates.Based on target-induced structure controllable silver nanocluster pair intergrowth and assembly of silver nanocluster pair intergrowth and quencher,we have constructed some fluorescent probes based on DNA/AgNCs,realizing the exquisite combination of target recognition and silver nanocluster fluorescence enhancement and avoiding the requirement for covalent modification in traditional fluorescent probe.Different from AgNCs,larger-size AgNPs as a nanoquencher for fluorophore is an important element in fluorescent probe design,and possesses high quenching efficiency,green synthesis,and low cost.Using carbon dots?C--dots?-stabilized AgNPs?C-dots/AgNPs?as quencher,we have developed a fluorescent probe,which is low-cost,label-free,and simple.1.The synthesis and fluorescence enhancement mechanism of silver nanocluster pair intergrowth.Using different spacers with different base numbers and arrangement for linking yellow and NIR emitters,the obtained silver nanocluster pair intergrowth produce enhanced fluorescence compared with single emitter.The templates with spacer containing polythymine with different base numbers can produce length-dependent fluorescence enhancement of AgNCs.Among them,S-T15 with 15 nt thymine spacer produces the highest fluorescence intensity in 15 min and fluorescence enhancement ratio up to-850 fold relative to one emitter.Spacers containing different base composition?such as polythymine,polyadenine,polyguanine,and polycytosine?and selection of emitter affect optical properties?absorption and emission spectra?,morphology characteristics and homogeneity of AgNCs.It is noting that the fluorescence enhancement mechanism of DNA/AgNCs is consistent with ligand-metal-metal-charge-transfer?LMMCT?.2.Design of fluorescent molecular beacon probe based on silver nanocluster pair intergrowth.The changes in primary and second structure of the template for forming AgNCs can quench or enhance fluorescence.Based on target-induced change in the structure of silver nanocluster pair intergrowth,two kinds of novel probes can be developed,such as silver nanocluster linear molecular beacon?AgNC-LMB?and proximity-dependent fluorescence light-up probe.Linear molecular beacon?LMB?is a single stranded DN A containing adjacent fluorophore and quencher,the presence of target and exonuclease can make fluorophore far away from quencher,leading to recovery of fluorescence.Based on AgNCs as fluorophore and target recognition site as quencher,using fluorescent silver nanocluster pair intergrowth resulting from recovery of template flexibility due to destroy of target binding site by target DNA and exonuclease III,we have developed a novel AgNC-LMB for DNA detection.NanoCluster Beacons?NCBs?is the probe where target-induced proximity of G enhancer and darkish emitter can lead to fluorescence enhancement.Combining fluorescence enhancement from silver nanocluster pair intergrowth with NCB concept,we have developed a versatile proximity-dependent probe based on light-up DNA/AgNCs.Zirconium ion(Zr⁴⁺),target DNA,and ATP enable formation of silver nanocluster pair intergrowth with detectable fluorescence enhancement via-PO₃^2--Zr⁴⁺-PO₃^2-structure,complementary base pairing,and aptamer conformal change,respectively.Compared with traditional FRET-based fluorescent probes,our label-free designed ones are simple-operation and low-cost.3.Fluorescent probes based on assembly of silver nanocluster pair intergrowth and quencher.The fluorescent AgNCs as fluorophore can be quenched by gold nanoparticles?AuNPs?and metal ions(Cu²⁺).Using target-induced fluorescence increase of AgNCs away from quencher,we design the fluorescent probes based on combination of silver nanocluster pair intergrowth and quencher,such as surface plasmon-enhanced energy transfer?SPEET?between AgNCs and AuNPs for DNA detection and Cu²⁺-mediated "on-off" silver nanocluster switch for detection of pyrophosphate?PPi?and alkaline phosphatase?ALP?.Absorption peak and distance proximity are indispensable for occurrence of SPEET.Based on SPEET between AgNCs?555 nm excitation peak?and AuNPs?520 nm absorption peak?,using control of SPEET by salt-induced different aggregation of AuNPs due to different binding ability of single stranded?ssDNA?and doubled stranded DNA?dsDNA?to the surface of AuNPs,we have developed a novel label-free fluorescent probe for label-free detection of specific DNA.The label-free,enzyme-free,and thermal cycle-free method contributes to development of simple,cost-effective,and convenient sensors.Cu²⁺ disturbs the accurate formation of AgNCs,resulting in the quenching of fluorescence of AgNCs.PPi allows the strong combination of Cu²⁺and PPi,leading to the fluorescence recovery.ALP can transform PPi into orthophosphate?Pi?,free Cu²⁺ can re-quench fluorescence of AgNCs.Using the target-induced "on-off" switch,PPi and ALP can be detected with detection limit of 112.69 nM and 0.005 U/mL,respectively.The proposed method is label-free,seperation-free,simple,and cost effective.4.The synthesis of silver nanoparticles stabilized by carbon dots and its application for glucose detection.Different from fluorescent AgNCs,larger AgNPs?>2 nm?can act as nanoquencher.Using C-dots as ligand,the synthesized C-dots/AgNPs can quench fluorescence of C-dots.H₂O₂ from the hydrolysis of glucose by glucose oxidase?GOx?can etch AgNPs.The destruction of AgNPs can make the fluorescence of C-dots recover,leading to the quantitative assay for glucose with detection limit of 1.39?M.The simple,low-cost,highly sensitive,and perfectly selective method has a potential for the accurate detection of glucose level in serum.