Study On Carbon Based Fluorescence Sensing And Biochemistry Inspired Detection

Biochemical sensors are devices used to analyze organic/inorganic molecules in the environment,food and living organisms.It is mainly composed of three parts:the detector,which is used to identify the target analyte signal;the converter,which converts the detected signal into a useful output;the signal processor,which analyzes and processes the output signal.In the past decades,fluorescent nanosensors have received more attention than other analytical technologies because of their outstanding advantages,such as rapid response,easy operation,higher sensitivity and selectivity.Therefore,fluorescent nanosensors are used for the highly sensitive detection of various analytes(such as drugs,proteins,markers,metal ions,and biomolecules).However,there are still some challenges in the development of fluorescent nanosensors:1)Semiconductor quantum dots usually contain toxic heavy metals(such as cadmium and lead),which greatly limits their sensing applications due to the potential environmental hazards and high costs;2)Dye-doped fluorescent nanomaterials are not only harmful to the environment but also easy to degrade,which affects their detection accuracy;3)Similar substances in real samples are easy to cause strong interference to fluorescent nanosensors;4)Relatively low fluorescence quantum yield.In view of this,based on the preparation of a variety of carbon-based polymorphic fluorescent nanomaterials,this paper fully studied their surface morphology,chemical bonds and optical properties,then constructed several fluorescent nanosensing platforms for the detection of metal ions,biomolecules and proteins with highly sensitivity.The main research contents of this paper are as follows:1.In order to improve the fluorescence quantum yield,a facile and universal method was successfully developed to converge the fluorescence of carbon dots(CDs).This method is suitable for most fluorescent materials with low quantum yield.Specifically,the CDs-doped composites fluorescent microspheres were prepared using an in-situ growth method,in which the silica(Si O₂)spheres were used as the carriers.The as-prepared CDs-Si O₂ spheres composites(CS)have excellent characteristics such as high fluorescence quantum yield,easy separation and modification.Firstly,the CS composites were used to construct an"on-off-on"mode fluorescent sensing platform for the detection of iron ions(Fe³⁺)and pyrophosphate(PPi),with the detection limits of8.1?M and 5?M,respectively.Then we found that in an alkaline environment,dopamine(DA)was easily oxidized to quinone structure which could cause the fluorescence quenching of the CS composites.Based on this foundation,we developed a multifunctional sensor platform for the detection of Urea and Urease.As we know,urea can be hydrolyzed in the presence of urease to produce OH^-,which increases the p H value of the surrounding environment,thereby promoting the quenching of the fluorescence of the CS composites by DA.After optimized conditions,the detection limits of urea and urease are 1.67?M and 0.002 mg/m L,respectively.Finally,in order to further improve the sensitivity of detection,we covalently coupled red-emitting gold nanoclusters(Au NCs)to the surface of the CS composites,successfully synthesized CS-Au NCs(CSA)which exhibited two fluorescence emissions.It was found that the addition of Ag⁺could significantly enhance the fluorescence of Au NCs while the fluorescence of the CS composites would not be affected.In summary,the CSA ratiometric fluorescent probes demonstrated high selectivity and sensitivity for the detection of Ag⁺.Under optimized conditions,the detection limit of Ag⁺was as low as1.6 n M,which was significantly better than that of a single Au NCs probe.2.A novel dual-emission ratiometric fluorescent probe based on carbon dots(CDs)and 7-amino-4-methylcoumarin(AMC)was constructed for the highly sensitive detection of dopamine(DA).The coupling was carried out through the amide reaction between the carboxyl groups on the surface of CDs and the amino groups on the surface of AMC.The resultant nanohybrid(CDC)exhibits two fluorescence emission peaks simultaneously,under a single excitation wavelength.When the system presented DA,the photoinduced electron transfer effect can effectively quench the fluorescence intensity of CDs and AMC.Thus could achieve highly sensitive detection of DA by monitoring the ratiometric ratio change in fluorescent intensity.The linear response range of the constructed ratiometric fluorescent probe was in the range of 0–33.6?M,and the detection limit was 5.67 n M.Compared with the single fluorescent probe,the constructed dual-emission ratiometric fluorescent probe has higher sensitivity and selectivity,which is expected to find potential applications in biomedical dopamine detection.3.A"turn-on"mode multi-signal assay strategy was developed to monitor the alkaline phosphatase(ALP)activity.Through preliminary experiments,carbon-containing nanoparticles(CNPs)were successfully prepared via p-aminophenol(AP)and diethylenetriamine(DETA)at lower temperatures.Inspired by the alkaline phosphatase(ALP)-triggered a specific catalytic reaction which can be hydrolyzed to produce AP,we constructed an in-situ detection of ALP system which can simultaneously generate fluorescence and colorimetric signals.By optimizing the reaction parameters,the detection limits for both fluorometric and colorimetric were both 0.05 m U/m L.Moreover,this method can be applied to the screening of ALP inhibitors,and is expected to provide an effective way for early diagnosis of diseases.4.For the first time,a facile,rapid and visual detection multi-channel fluorescence sensing platform is proposed for highly sensitive detection of epinephrine(Ep),norepinephrine(NE)and levodopa(L-DOPA).This method only needs to mix ethylenediamine(EDA)with different concentrations of Ep,NE,and L-DOPA,and the detection can be completed within 10 minutes.Moreover,in order to improve the sensitivity and the recognition ability of visual detection,different dual-emission ratiometric fluorescent probes were constructed for quantitative detection of Ep,NE,and L-DOPA,which has shown high-sensitivity and high-selectivity,the detection limits were 18.9,85.5,and 9.7 n M,respectively.It is believed that the detection strategy we proposed can provide a theoretical basis and more possibilities for the field of biosensing and early diagnosis of diseases.