Biosensors Based On MoS₂ Nanosheets And Mo,S Codoped Carbon Dots

The rapid development of medical technology puts forward new challenges to medical diagnosis technology.The early prediction and diagnosis of some serious diseases,especially cancer,are the keys of effective treatment.Therefore,simple,rapid and sensitive detection of diseases tumor biomarker is of great importance for the screening,diagnosis and prognosis evaluation of various diseases.At present,most of protein tumor markers are detected via immunoassay method.However,this method suffers from some problems such as high cost,poor stability,time-consuming immobilizing processes and complex detection procedures,due to the use of antibodies and enzymes.Thanks to the rapid development of nanoscience and nanotechnology,biosensors based on nanomaterials have drawn considerable attractions and become the forefront of bioanalysis field,because of possessing advantages of low-cost,high sensitivity,facile fabrication and fast response.One challenge in the field of biosensor is how to make the most of the characteristics and advantages of different nanomaterials to design and establish high-performance new sensors for biomolecules detection,and investigate the reaction process and mechanism at the micro-nano level.In this paper,based on the different physical and chemical properties of aptamer,MoS₂ nanosheets?NSs?and Mo,S co-doped carbon quantum dots,we designed and fabricated a series of biosensors for monitoring disease markers.At the same time,the sensing process and mechanism were investigated.The main contents can be summarized as follows:?1?First,using the strategy of carcinoembryonic antigen?CEA?competing with MoS₂ NSs to combine its aptamer probe,a biosensor for rapid and sensitive detection of tumor marker CEA was developed.CEA detection is significantly important for the screening,diagnosis and prognosis evaluation of various gastroenteric tumor.In the proposed“OFF-ON”fluorescent biosensor,MoS₂ NSs with high quenching efficiency combined with well discrimination ability toward aptamer and aptamer/protein afforded the biosensor easy construction,fast detection and high sensitivity.The sensing platform exhibited good reproducibility,selectivity and high sensitivity for CEA in a broad range of 100 pg/mL-100 ng/mL with the detection limit of 34 pg/mL.?2?To further broaden the scope of the biosensor model based on aptamers probe/MoS₂ NSs,a biosensor for detecting breast cancer-specific tumor marker CA15-3 was developed.Furthermore,the mechanism of action between ssDNA and MoS₂ NSs was investigated in detail.The surface interaction between ssDNA and MoS₂ NSs was explored by adsorption and desorption experiments.The results indicated that van der waals force played a crucial role in DNA adsorption by MoS₂NSs.The fundamental study of biointerface science on ssDNA and MoS₂ NSs will facilitate their potential applications in various fields.Additionally,it was proved by determination of fluorescence lifetime experiment and temperature effect experiment that the quenching of organic dye Cy5 labelled on ssDNA by MoS₂ NSs was attributed to fluorescence resonance energy transfer.Based on the extraordinarily high quenching efficiency of MoS₂ NSs to aptamer probe and different adsorption affinity of MoS₂ NSs toward aptamer and aptamer/carbohydrate antigen 15-3?CA15-3?,an aptameric biosensor was fabricated for the detection of CA15-3.The fabricated biosensor not only displayed high sensitivity with the detection limit of 0.0039 U/mL?S/N=3?,but also exhibited good stability and selectivity.?3?Based on catalytic activity of MoS₂ NSs nanozyme and aptamer controllable MoS₂ NSs nanozyme activity,a colorimetric biosensor was developed for the detection of CEA in a sensitive and facile manner.As a candidate of natural enzyme,the intrinsic low activity of some nanozymes limits their applications in the fabrication of biosensor.In this work,the peroxidase-like activity of MoS₂ NSs was dramatically enhanced through ssDNA modification,which was 4.3-times higher than that of bare MoS₂ NSs.Such an enhancement of catalytic activity is mainly ascribed to the increased affinity of ssDNA/MoS₂ NSs complex toward substrate TMB,further accelerating electron transfer from TMB to H₂O₂.On the basis of aptamer tuned MoS₂NSs nanozyme activity,we developed a convenient,affordable and instrument-free portable test kit by rooting aptamer/MoS₂ NSs system into agarose hydrogel to visually monitor CEA.Importantly,our work illuminates the feasibility of using aptamer to enhance catalysis of nanozymes and their application potential for label-free and visual detection of aptamer targeted biomolecules.?4?With assistance of MoS₂ powder,the Mo,S co-doped carbon quantum dots?Mo-CDs?with high peroxidase mimetic catalytic activity were synthesized.Combining the enzyme-like properties of Mo-CDs and the catalytic properties of cholesterol oxidase,a cascade colorimetric biosensor was designed and established for the detection of cholesterol in serum.In this chapter,to improve the enzyme-like activity of nano-enzymes,MoS₂ powder was introduced into the resources of the synthesis of carbon dots,and then the mixture was sonicated.Finally,the co-doping of Mo and S in carbon dots was achieved by one-step solvothermal method.The Mo-CDs possess a robust peroxidase-like activity,which can easily catalyze 3,3,5,5-tetramethylbenzidine?TMB?to produce a blue oxidized TMB in the presence of H₂O₂.The Mo,S doping in the carbon dots?CDs?notably boosted the yield of CDs and might facilitate the electron transfer between TMB and H₂O₂,which further enhance the catalytic activity of CDs.The constructed biosensor exhibited excellent selectivity and high sensitivity for cholesterol in the range of 0.01-1.0 mM along with the detection limit as low as 7?M.The total cholesterol concentration in serum sample was measured with satisfactory results and the results could be read out by naked eye,indicating the potential application in clinical diagnosis and preparation of portable test kit.