Research On Optical And Electrochemical Biosensing Based On Two-dimensional Nanomaterials

Biosensing technology has attracted huge attraction in biological analysis and biomedicine due to its easy operation,rapid response,high selectivity and low cost.It has become the research frontier of the biotechnology.With the rapid development of science and technology,the understanding of the nature has gone from micro to nano level.Nanomaterials present different optical,electronic and magnetic properties from their bulk materials because of their small size effect,surface effect,quantum size effect and macroscopic quantum tunneling effect.By aplplying the intrinsic property of nanomaterials and combining the modification of biomolecules,novel nanomateial-based sensing platforms can be fabricated and used for biosensing applications in many fields including clinical diagnoses,food safety and environment monitoring,greatly promoting the development of bioscience and biomedicine.One of the key questions is how to make the most of the advantages of different nanomaterials to build novel nanomaterial-based optical and electrochemical sensing platforms for biological analysis and to study the reaction process and mechanism.The thesis can be devided into five parts.1.Ultrathin Ta2NiS5 nanosheet-based bioseneor for fluorescence detection of DNARapid and ultra-sensitive detection has always been a great challenge in molecular diagnostics.Concerning this issue,a novel fluorescent sensing platform is designed based on single-layer ternary chalcogenide nanosheet?Ta₂NiS₅?.For the first time,the high-yield and scalable production of ultrathin 2D ternary chalcogenide nanosheets?e.g.Ta₂NiS₅?in solution is achieved by exfoliating their layered microflakes.The size of resulting Ta₂NiS₅ nanosheets ranges from tens of nanometers to few micrometers.Importantly,the production yield of single-layer Ta₂NiS₅nanosheets is very high,ca.86%.As a proof-of-concept application,a novel fluorescence sensing platform is designed for the detection of DNA with excellent selectivity and high sensitivity?with detection limit of 50 pM?based on the different affinities towards single-stranded DNA?ssDNA?and double-stranded DNA?dsDNA?of Ta₂NiS₅ nanosheet and high fluorescence quenching ability.2.Ultrathin Ta2NiS5 nanosheet-based biosensor accompanied by exonuclease III-regulated target cyclic amplification for detection of single nucleotide polymorphismSingle nucleotide polymorphisms?SNPs?are agents of various diseases such as cancers,Alzheimer disease,and diabetes.Therefore,methods to discriminate SNPs are of significant importance as the first step for the disease prediction and clinical diagnosis.For the first time,we report that the ternary chalcogenide nanosheet exhibits different affinity towards oligonucleotides with different lengths and efficiently quenches the fluorescence of dye labeled DNA probes.Based on these findings,as a proof-of-concept application,the ternary chalcogenide nanosheet is used as a target cyclic amplification biosensor,showing high specificity in discriminating single-base mismatch.This simple strategy is fast and sensitive for the SNP detection with ultralow detection limit of unlabeled target?250 fM?and high discrimination ratio?5%?in the mixture of perfect match?mutant-type?and single-base mismatch?wild-type?target.Importantly,this sensing method is extensively compatible for the SNP detection in clinical samples,making it a promising tool for the mutation-based clinical diagnostic and genomic research.3.PtS2 nanodots-based sensor for highly sensitive non-enzymatic glucose detectionGlucose detection is of great importance in various fields ranging from biomedical applications to fuel cells.Development of simple and fast glucose biosensor with excellent sensing performance is a great challenge in clinical medicine.To address this,a novel electrochemical sensing interface is designed for glucose detection based on transition metal dichalcogenide nanodots?PtS₂?.PtS₂ nanodots are successfully fabricated by exfoliating their layered microflakes though electrochemical Li-intercalation and exfoliation method.Considering the good conductivity and high specific surface area of PtS₂ nanodots,a novel non-enzymatic glucose sensor is fabricated and applied to novel non-enzymatic glucose detection.The as prepared PtS₂ nanodots based glucose sensor displays excellent electrocatalytic activity with fascinating sensitivity up to 671.7?A mM^-1 cm^-2,outstanding detection limit of 0.2?M,short response time?within 10 s?and significant specificity for glucose detection.Furthermore,the sensor exhibits excellent storage stability and reproducibility.Note that the as designed glucose sensor shows attractive feasibility for real sample analysis.The novel material exhibits excellent electrochemical performance and easy preparation,making it a promising candidate in the development of highly sensitive non-enzymatic glucose sensor.4.C₃N₄ nanoribbon-based“off-on”fluorescent biosensor for detection of citrateCitrate is a critical metabolite that is involved in various biological systems and can serve as biomarker for prostate cancer prediction and diagnosis.A novel“off-on”fluorescent biosensor is designed based on C₃N₄ nanoribbons for citrate detection.In the prescence of Cu²⁺,the fluorescence of C₃N₄ nanoribbons can be quenched because of the photoinduced electron transfer.With the addition of C₆H₅O₇^3-,the interaction of Cu²⁺and C₃N₄ nanoribbons is inhibited by the strong chelation between Cu²⁺and C₆H₅O₇^3-,resulting in the fluorescence recovery.The designed sensing platform displays excellent selectivity and good liner detection range with a detection limit of 0.78?M.Moreover,the novel“off-on”fluorescent biosensor can be applied for C₆H₅O₇^3-detection in living cells due to its good biocompatibility and low cytotoxicity,showing great potential for in vivo detection.5.Plasmonic nanobiosensor based on hairpin DNA for detection of trace oligonucleotides biomarker in cancersMicroRNAs?miRNAs?,a class of small,endogenous,noncoding RNA molecules,can serve as biomarkers for potential applications in cancer diagnosis,prognosis,and prediction due to its abnormal expression.As a result,a novel label-free biosensor with nanometer scale is prepared and employed in the detection of trace oligonucleotides based on the localized surface plasmon resonance?LSPR?.The dielectric constant on the surface of DNA modified gold nanoparticle would change when probe single-strand DNA hybridized with target oligonucleotides,which resulted in the notable red shift of scattering peak position.The biosensor with excellent selectivity can be used in a real-time monitoring hybridization process.Notably,this method can provide label-free detection of DNA and miRNA at single nanoparticle level with limit of detection up to 3 nM.Due to the advantages of LSPR scattering spectra,single nanoparticle biosensor can be designed for trace cancer-relevant miRNAs detection in the future.