The Application Of Gold/silver Nanomaterials In Fluorescence Sensing And Analysis

Precious metals are non-ferrous metals including gold,silver,platinum and other elements.Due to their special physical properties?high density,high conductivity,high electron affinity?,they have widely used in electronics,chemical,medical and other fields.Precious metal nanomaterials refer to new materials prepared by nanotechnology with a size below 100 nm and different physical and chemical properties than traditional nanomaterials.The optical,magnetic and catalytic properties depended on size make precious metal nanomaterials a hot spot in the field of analytical chemistry.The use of precious metal nanomaterials represented by gold nanoparticles?AuNPs?and silver nanoclusters?AgNCs?is more important in fluorescence sensors.Great progress has been made.AuNPs have good stability and special bio-affinity,no cytotoxicity.They are generally prepared by chemical reduction using chloroauric acid.The reduction methods mainly include ascorbic acid reduction method,sodium citrate reduction method,white phosphorus reduction method and citric acid-sodium citrate reduction method.The AuNPs synthesized by different kinds of reducing agents have different particle sizes,and the AuNPs can be conveniently prepared under the experimental conditions according to different purposes and requirements.AgNCs are composed of several to several tens of silver atoms and have fluorescent properties,which have attracted great attention in the fields of chemistry,biology and materials science.However,the generally synthesized water-soluble silver nanoclusters have poor stability.Therefore,adding a suitable template to control the growth of nanoclusters to synthesize stable silver nanoclusters is the key to developing silver nanoclusters as fluorescent probes.Currently,templates used as synthetic silver nanoclusters include dendrimers,various types of polymers,small molecule compounds that can be complexed with metal ions,DNA,and proteins.Among them,the DNA templated AgNCs?DNA-AgNCs?have received great attention due to their unique properties.In this research paper,three kinds of fluorescence sensors have been constructed based on AuNPs and DNA-AgNCs.Three fluorescent platforms have been developed for the determination of glutathione reductase?GR?,bleomycin and quinolones,respectively.The details are as follows:?1?Graphene quantum dots?GQDs?and gold nanoparticles?AuNPs?were combined for probing GR activity.The main probing mechanism is based on the following facts:?1?The fluorescence of GQDs can be quenched by AuNPs through fluorescence resonance energy transfer?FRET?.?2?Reduced glutathione?GSH?can protect AuNPs from being aggregated and enlarge the inter-particledistance between GQDs and AuNPs,which subsequently produces the fluorescent signal recovery.?3?AuNPs has much weaker affinity towards oxidized glutathione?GSSG?in contrast to GSH.?4?GR cancatalyze the reduction of GSSG into GSH in the presence of coenzyme?-nicotinamide adenine dinucle-otide 2'-phophate hydrate?NADPH?.Based on these facts,a turn-on fluorescent assay for GR has thusbeen developed based on the GQDs-AuNPs system.The proposed assay can allow for the evaluation of GRactivity in the range of 0.0050-0.13 mU/mL,with a minimum detectable concentration of 0.0050 mU/mL.Besides,this GQDs-AuNPs based GR assay was successfully applied for screening the inhibitor of GR activity byusing 1,3-bis?2-chloroethyl?-1-nitrosourea?BCNU?as a model.?2?The authors describe a molecular beacon-based fluorescent probe for the determination of the cancer drug bleomycin?BLM?.The probe was tagged with DNA-templated silver nanoclusters?DNA-AgNCs?and guanine-rich sequences?GRSs?at two terminals serving as signal reporter with a loop.In the absence of the BLM-iron?II?complex[BLM-Fe?II?],the probe has a hairpin shape and displays strong fluorescence because the AgNCs are close to the GRSs.In the presence of the BLM-Fe?II?complex,it will selectively cleave the probe at the 5'-GC-3'scission site of the loop.This displaces the AgNCs away from the GRSs and causes a decrease in fluorescence,best measured at excitation/emission wavelengths of 565/623 nm.This effect enables BLM to be detected with a detection limit as low as 33 pM,which was 1-3 orders of magnitude more sensitive than most of the previous reports.?3?DNA-AgNCs were successfully utilized as novel fluorescent probes for the detection of quinolones for the first time.The as-prepared DNA-AgNCs exhibited strong emission at 596 nm,which could be quenched by Cu²⁺ions.The addition of quinolones caused restoration of fluorescence intensity of the DNA-AgNCs-Cu²⁺system.This detection protocol exhibited excellent sensitivities for four kinds of quinolones.For instance,the linear ranges were from 20to 100 nM for nalidixic acid with the limit of detection?LOD?2.0 nM,from 5 to 120 nM for cinoxacin with the LOD 1.2 nM,from 5 to 100 nM for ciprofloxacin with the LOD 1.0 nM,and from 1 to 60 nM for moxifloxacin with the LOD 96 pM,respectively.Benefiting from high sensitivity,satisfactory recoveries were obtained for trace detection of quinolones in real samples,such as tablets and human urine.