The Preparation Of Ratiometric Sensor Based On Carbon Dots,Gold Nanoclusters And Their Application Study

Ratiometric fluorescent assay technique is a kind of analytical method based on two or more fluoresense signal changes.It has aroused great attention by researchers in the fields of micro-molecule analysis,cell imaging,in-vivo diagnosis due to the various advantages such as high sensitivity and eminent capability of anti-interference.Developing the ratiometric fluorescent probe based on nano-fluorescent material has become the current hotspot.Therefore,a novel ratiometric fluorescent probe was developed based on nitrogen-doped carbon dots,which applied to selective detection of Fe³⁺.Another ratiometric pH fluorescent probe was prepared based on gold nanoclusters available in the laboratory.The specific research is showed as below:1.The nitrogen-doped carbon dots（CDs）with fine stability,high quantum yield,were obtained with ascorbic acid and polyethylene glycol diamines.The CDs were then characterized with transmission electron microscope（TEM）,UV-vis spectroscopy,Fluorescence（FL）spectroscopy,and FT-IR spectroscopy.The ratiometric fluorescent probe was then built by conjugating rhodamine B isothiocyanates（RhB）to the surface of the CDs,which applied to selective detection of Fe³⁺.The results show that,the ratios（I399/I577）in light intensity between the light scattering（LS）of CD and the FL of RhB display a good linear relationship with the Fe³⁺concentrations ranging from 0.01 μmol/L to 1.2 μmol/L,the linear equation is I399（CDs）/I577（RhB）= 0.256 + 0.379 C（C: μmol/L）,and the correlation coefficient is 0.996,with a detection limit of 6 nmol/L.The detection mechanism of this sensor is due to the surface passivation and the enlargement of the CDs when FePO4 deposited on the CDs,the FL intensity and LS intensity of CDs show a rising trend and the FL intensity of RhB basically remains unchanged.Furthermore,the practicability of this ratiometric florescent probe has been proved with a high recovery of 97.2% to108.8% when applied to detect the Fe³⁺in practical water sample.2.A gold nanoclusters（BSA-Au NCs）using the bovine serum albumin（BSA）as a coating reagent were prepared according to the previous reports.They were then conjugated with fluorescein isothiocyanate（FITC）to form a ratiometric pH probewith good selectivity and specificity.The nanospheres BAF@PEI were prepared when surrounded the ratiometric pH probe with Polyethyleneimine（PEI）.The as-prepared ratiometric nanospheres have been characterized by TEM,UV-vis,FL,FT-IR.The resuls showed that the diameter of the ratiometric nanospheres are about60 nm.The emission wavelength at 522 nm and 604 nm,respectively derived from FITC and BSA-Au NCs,with the excitation wavelength at 365 nm.Between the pH of4.0 to 10.0,the FL intensity of FITC show a rising trend while the FL intensity of BSA-Au NCs remain mostly the same with the increase of pH.Meanwhile,when the pH cycles among 5.0 and 9.0,the nanoospheres show a great reversibility to pH.The nanosphere is proved to have a low cytotoxicity by MTT assay.It is promising to be further applied in biomarkers and imaging.