Study Of Novel Biosensing Methods Based On Fluorescent Carbon Nanomaterials

Carbon dots(C-dots)and graphene quantum dots(GQDs)recently emerge as superior and universal fluorophores because of their unique combination of a number of key merits,including excellent photostability,small size and biocompatibility,These glowing carbon nanocrystals provide unprecedented opportunities for bioimaging and optical sensing.In preface part,we give a short introduction on properties,preparation and functionalization of CDs and GQDs.Then we summarize their applications in biological fluorescence probes.Inspired by these researches,We use the characteristics and advantages of these two types of materials to build biosensors,That can achieve the determinantion of biomolecules.The main contents and described as follows:1.A novel,sensitive and selective biosensors was developed for the detection of hemoglobin(HGB)based on the quenched fluorescence of CDs.Under the experimental conditions,the limit of detection for HGB was as low as 0.12 nmol/L.The method was utilized to detect HGB in human urine and human blood samples with satisfactory results.The static quenching mechanism of this system was further investigated by UV–vis absorption spectrometry and FT-IR spectrometry.2.GQDs coupled to gold nanoparticles(AuNPs)are viable “off-on” fluorescent probes for L-cysteine.Under the experimental conditions,the limit of detection for L-cysteine was as low as 0.32 nmol/L.It was applied to the detection of L-cysteine in human urine and human plasma samples and gave satisfactory results.The fluorescence of GQDs was quenched by AuNPs through fluorescence resonance energy transfer(FRET).The fluorescence of GQDs was converted back to an “on”status by adding L-cysteine which bound to AuNPs.3.A ratiometric fluorescent nanosensor for ultrasensitive and highly selective recognition of horseradish peroxidase(HRP)was reported for the first time.DAP was the oxidation product of o-phenylenediamine(OPD)that acted as the cosubstrate ofHRP.Upon the addition of HRP,OPD could be catalytically oxidized to phenazine-2,3-diyldiamine(DAP),then the fluorescence intensity corresponding to DAP at 553 nm increased dramatically with a simultaneous fluorescence quenching of af-GQDs at 440 nm,resulting in a ratiometric fluorescent nanosensor toward HRP.Under the experimental conditions,the limit of detection for HRP was as low as 0.21fmol/L.The reaction mechanism of this system was further investigated by a variety of spectral methods.The enzymatic activity of HRP was further evaluated.4.A ratiometric nanosensor for label-free and highly selective recognition of DNA was reported in this work,by employing fluorescent CDs and ethidium bromide(EB).When EB was present,the fluorescence of CDs was quenched effectively due to the electron transfer process between CDs and EB.Upon the addition of DNA,thefluorescence of EB at 592 nm was enhanced dramatically but the fluorescence intensity of CDs at 424 nm stayed almost constant,leading to a ratiometric detection of DNA.Under the experimental conditions,the limit of detection for DNA was as low as 0.47 mmol/L.The reaction mechanism of this system was further investigated by a variety of spectral methods.5.A label-free and ratiometric fluorescent nanosensor for ultrasensitive determination of human telomere DNA based on amino-functionalized graphene quantum dots(af-GQDs)coupling catalytic G-quadruplex/hemin DNAzyme for the first time.DAP was the oxidation product of o-phenylenediamine(OPD)that acted as the cosubstrate of G-quadruplex/hemin DNAzyme.Upon the addition of human telomere DNA,OPD could be catalytically oxidized to DAP,then the fluorescence intensity corresponding to DAP at 553 nm increased dramatically with a simultaneous fluorescence quenching of af-GQDs at 440 nm,resulting in a ratiometric fluorescent nanosensor toward human telomere DNA.Under the experimental conditions,the limit of detection for human telomere DNA was as low as 25 fmol/L.The reaction mechanism of this system was further investigated by a variety of spectral methods.