Application Of Fluorescent Nanoprobes Based On The MXenes In Biosensing

In recent years,two-dimensional nanomaterials have attracted intensive attention because of their unique physical and chemical properties.Among them,the new two-dimensional nanomaterial transition metal carbon/nitride?MXenes?has superior electrical conductivity(2400 S cm^-1),high specific surface area(98 m² g^-1)and efficient photothermal conversion efficiency?nearly 100%?,which has been widely used in energy storage and biomedical engineering.As the first discovered MXenes material,Ti₃C₂ MXenes shows strong absorption in the wavelength range of 300-900nm,and can quench the fluorescence of various fluorophores by fluorescence resonance energy transfer?FRET?,which can be used as an efficient and broad-spectrum fluorescence quencher.When the lateral sizes of Ti₃C₂ MXenes are reduced to several nanometers,Ti₃C₂ quantum dots?Ti₃C₂ QDs?can be obtained with photoluminescence properties.Ti₃C₂ QDs show good dispersion,biocompatibility and photostability,along with tunable emission wavelength and high quantum yield.In this paper,on the basis of the excellent photochemical properties of Ti₃C₂ MXenes and Ti₃C₂ QDs,fluorescent nanoprobes were constructed for the application in the field of biosensing.The specific research work is as follows:1.The development of a fluorescent nanoprobe for glucose sensing based on Ti₃C₂ MXenes and nitrogen-doped carbon dots?N-CDs?.When polyacrylic acid modified Ti₃C₂ MXenes?PAA-Ti₃C₂?was mixed with nitrogen-doped carbon dots?N-CDs?,PAA-Ti₃C₂ can quench the fluorescence of N-CDs by FRET.H₂O₂ produced from the oxidization of glucose by glucose oxidase?GOx?can undergo redox reaction with PAA-Ti₃C₂ and induce the degradation of PAA-Ti₃C₂ sheets,which restores the fluorescence of N-CDs.As a result,a"turn-on"fluorescent assay for the sensing of glucose was developed.With the use of the proposed probe,a linear response to glucose ranging from 0.5 mM to 10 mM with the limit of detection as low as 0.2 mM,was achieved.In addition,the probe was further used for the analysis of glucose in actual blood with good accuracy and stability.The recovery rate was from 98.6%to104.8%,with the standard deviation ranging from1.9%to 3.1%.2.A fluorescent probe for the selective detection of p-nitrophenol?p-NP?was developed based on the Ti₃C₂ QDs.The absorption spectrum of p-NP has a large overlap with the excitation and emission spectra of Ti₃C₂ QDs,and thus the fluorescence of Ti₃C₂ QDs can be efficiently quenched by p-NP through the internal filtration effect?IFE?.The experimental results showed that the fluorescence quenching rate of p-NP to Ti₃C₂ QDs was linearly related to the concentration of p-NP in the range of 0.1-200?M.With the use of the probe,a detection limit of 0.1?M for p-NP was obtained,which was lower than the p-NP standard for drinking water defined by the US Environmental Protection Agency.3.A sensitive assay for the detection of alkaline phosphatase?ALP?was developed by introducing the Ti₃C₂ QDs into the colorimetric detection system of ALP.In the traditional colorimetric detection method for ALP,ALP catalyzed the dephosphorylation of p-nitrophenol phosphate?p-NPP?to produce p-NP with color,and the activity of ALP can be measured by monitoring the change of the absorption spectra.The introduction of Ti₃C₂ QDs converts the color signal of p-NP into a more sensitive fluorescent signal of Ti₃C₂ QDs,reducing the detection limit by an order of magnitude(0.02 U L^-1).Furthermore,the method was further applied in the identification of embryonic stem cells?ESCs?based on the differences of ALP activity in different cells.