| Biomolecules participate in the regulation of various physiological processes in organisms and maintain the normal operation of the life system.The abnormal expression of some important biomolecules has been confirmed to be closely associated with the occurrence and development of some diseases.Therefore,the construction of accurate and sensitive biosensing platforms is significant to medical diagnosis,drug development and disease treatment.Compared with the traditional analytical methods,optical sensing methods based on nano-materials have the advantages of high sensitivity,good selectivity and fast response.Quantum dots are nanocrystals with a size smaller than or close to the exciton Bohr radius and a diameter less than 10 nm.Compared with traditional organic fluorescent dyes,quantum dots have the characteristics of wide absorption spectra,narrow and symmetrical emission spectra,large Stokes shift and strong photobleaching resistance.In addition,the fluorescence properties of quantum dots can be adjusted by changing their size,morphology,composition and surface groups.As new fluorescent nanomaterials,silicon quantum dots（Si QDs）and molybdenum disulfide quantum dots（Mo S2 QDs）show great potential in the construction of biosensing platforms due to the advantages of high fluorescence intensity,good biocompatibility and low toxicity.Herein,Si QDs and Mo S2 QDs with different optical properties were synthesized and combined with other molecules or nanomaterials to construct fluorometric and colorimetric dual-mode sensing platforms for the detection of lots of biomolecules.Details are as follows:In the first chapter,we briefly introduced two kinds of common nanomaterials in the construction of nano-biosensing platforms,Si QDs and Mo S2 QDs,including their synthesis methods,basic characteristics and applications in various fields.On this basis,we expounded the research content and significance.In the second chapter,we constructed a fluorometric and colorimetric dual-mode sensing system based on p H-stable Si QDs and p H-sensitive 4-nitrophenol（4-NP）for the detection of p H or urease.Firstly,blue fluorescent Si QDs were prepared via an aqueous-phase synthesis method.As the p H of the system gradually increased,the absorption peak of 4-NP at 400 nm increased and overlapped quite well with the fluorescence excitation spectrum of Si QDs.Thus,the fluorescence of Si QDs was effectively quenched by 4-NP.The fluorescence and absorption intensities could be used to accurately quantify p H value.Urease could specifically hydrolyze urea to generate carbon dioxide and ammonia,causing an obvious increase of the p H value of the system.Therefore,the above dual-mode p H sensing system could also be utilized to quantitatively detect urease.The linear ranges of the fluorometric and colorimetric methods for urease detection were both 2-40 U/L.The limits of detection were 1.67U/L and 1.07 U/L,respectively.Moreover,the dual-mode system has been successfully exploited in the detection of urease in human saliva.In the third chapter,we constructed a thrombin aptasensor based on catalytically active gold nanoparticles（Au NPs）and fluorescent Si QDs.The thrombin aptamer-modified gold nanoparticles（S1-Au NPs）could catalytically reduce4-nitrophenol（4-NP）to 4-aminophenol（4-AP）.Thrombin could specifically combine with its aptamer to form a G-quadruplex structure,which masked the surface-active catalytic sites of Au NPs and restrained the reduction of 4-NP.In this process,the absorption peak of 4-NP increased and the fluorescence of Si QDs was greatly quenched.The linear ranges of the fluorometric and colorimetric aptasensor for thrombin detection were 0.5-30 n M and 0.3-30 n M,respectively.The limits of detection were 0.15 n M and 0.13 n M,respectively.With the advantages of cost-effectiveness,simplicity of operation and broad applicability,this aptasensor has been successfully applied in the detection of thrombin in human serum.In the fourth chapter,we constructed a dual-signal sensing system based on copper-doped Si QDs（Cu-Si QDs）and single-stranded DNA-modified copper-manganese oxide nanosheets（Cu Mn O2 NSs@ss DNA）for the detection of tannin acid（TA）.Cu Mn O2 NSs@ss DNA could catalyze H2O2 to produce reactive oxygen species,which could oxidize 3,3’,5,5’-tetramethylbenzidine（TMB）.The oxidation product（ox TMB）had an obvious UV-vis characteristic absorption peak and could quench the fluorescence of Cu-Si QDs.The introduction of TA inhibited the catalytic oxidation of TMB,leading to the decreased absorption peak and the recovered fluorescence.The detection method had excellent sensitivity and selectivity.The linear ranges of fluorometric and colorimetric method for TA detection were0.05-1.8μM and 0.1-1.2μM,respectively.The limits of detection were 0.018μM and0.077μM,respectively.In addition,the method has been successfully used for TA determination in antibacterial ointment and white wine samples.In the fifth chapter,we designed a novel dual-mode ratiometric fluorometric and colorimetric sensing system based on Mo S2 QDs and rhodamine B（Rh B）by combining the exonucleaseⅢ（ExoⅢ）-assisted recycling amplification strategy with the magnetic separation technique for the determination of KRAS gene.As the target DNA,KRAS gene could hybridize with the hairpin DNA and initiate the exonuclease III-assisted recycling amplification.The output DNA（o DNA）served as a bridge to link magnetic beads labeled with ss DNA1（MBs-ss DNA1）to gold nanoparticles modified with ss DNA2（Au NPs-ss DNA2）.After magnetic separation,the remaining Au NPs-ss DNA2 could catalyze the reduction of Rh B by Na BH4.When the KRAS gene concentration increased,the concentration of Au NPs-ss DNA2 in the solution decreased and the reduction of Rh B was inhibited.In this process,the fluorescence of Rh B enhanced while the fluorescence of Mo S2 QDs as a reference signal kept unchanged.Meanwhile,the absorption peak of the Mo S2 QDs/Rh B sensing platform gradually increased.The fluorometric and colorimetric dual-mode sensing methods displayed excellent selectivity for KRAS gene determination with the limits of detection of 0.22 p M and 0.41 p M,respectively.By combining signal amplification strategy and magnetic separation technology,this method effectively eliminated background interference and improved the sensitivity.In addition,the sensing system has been successfully applied to the detection of KRAS gene in human serum.In the sixth chapter,we constructed a fluorometric and colorimetric dual-mode biosensor for Pax-5a gene detection based on zinc-doped Mo S2 QDs（Zn-Mo S2 QDs）and G-quadruplex/hemin complex by using the exonuclease-assisted recycling amplification.Pax-5a gene could hybridize with the hairpin DNA and the formed duplexes could be cleaved by exonucleaseⅢ（ExoⅢ）to release the output DNA（o DNA）.Guanine-rich DNA sequence（G-rich DNA）and magnetic beads（MBs）labeled with the capture DNA（c DNA）could hybridize with o DNA to form the MBs-c DNA/o DNA/G-rich DNA complex.The remaining G-rich DNA in the supernatant through magnetic separation could bind hemin to produce G-quadruplex/hemin complex.The complex had peroxidase-like activity and could catalyze the oxidization of 3,3’-diaminobenzidine（DAB）.The generated brown oxidation product（ox DAB）had a distinct UV-vis characteristic absorption peak and could quench the fluorescence of Zn-Mo S2 QDs.The detection limits of Pax-5a gene by fluorometric and colorimetric methods were 0.52 p M and 1.12 p M,respectively.Furthermore,this sensing system has been successfully applied to Pax-5a gene determination in human serum samples,which had broad prospects in biochemical analysis and clinical diagnosis.In the seventh chapter,we systematically summarized the contents of this paper and discussed the development of Si QDs and Mo S2 QDs in the future. |
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