Construction Of Fluorescent Probes For The Detection Of Metal Ions In Food And The Environmental Samples Based On Carbon Dots

As an emerging carbon-based fluorescent material,carbon dots?CDs?refer to a nearly spherical nanoparticle with the size less than 10 nm.Compared to traditional semiconductor quantum dots,organic dyes and inorganic luminescent materials,CDs not only inherit the low toxicity of carbon-based materials,but also own unique opticaltunability,lightbleachingresistance,goodwatersolubilityand biocompatibility.Therefore,CDs are widely applied to the fields of biological imaging,chemical sensing and photoelectric conversion.In terms of the preparation of CDs,the complexities of synthesis and limitation of large-scale preparation are problems that cannot be ignored.The development of a fast,green and effective preparation method still needs to be fostered.In terms of application,poor selectivity and difficulty in on-site detection are also a tough nut to crack.It is urgent to explore a facile way on how to break the limitations of CDs in the application of ions detection.Take all above problems into consideration,this paper focus on searching an appropriate way to solve the problems.The detailed research contents are listed below:1.Nitrogen doped carbon dots?N-CDs?with a product yield of up to 56%were prepared by a solid phase method.In this part,citric acid was used as the carbon source and histidine was utilized as the nitrogen source.The N-CDs show a high selective response to Cu²⁺.It is speculated that the fluorescence quenching may result from the behavior of sharing electron pairs between the nitrogen-containing groups of N-CDs and Cu²⁺.Therefore,a fluorescent probe for detecting Cu²⁺was constructed and applied to detect Cu²⁺in complex matrices such as urine,environmental water and juice samples.The recoveries were between 96%and 102%.2.The polymer dots?PDs?for detecting Co²⁺and Mn²⁺were prepared by one step microwave-assisted method.Ethylenediamine was selected as the nitrogen source and polyvinyl alcohol was used as the carbon source.The processability and viscosity of polyvinyl alcohol also provided the basis and possibilities for the preparation of self-film forming polymer dots?FPDs?.The bright fluorescence of PDs can be distinctly quenched by cobalt ion(Co²⁺)and manganese ion(Mn²⁺).For Co²⁺,the linear range was from 3.4 to 50.0?mol L^-11 and 46.7 to 600.0?mol L^-11 with the limit of lowest detection?LOD?of 1.0?mol L^-1.The LOD of Mn²⁺was 0.4?mol L^-11 in the range of 1.5-100.0?mol L^-1.The FPDs were obtained via dropping PD solution on quartz glass.The bright blue fluorescence of FPDs can be obviously quenched by Co²⁺and Mn²⁺.This part may provide an efficient and flexible approach to the application of on-site detection.3.The blue fluorescent polymer dots?B-PDs?were synthesized with polyethyleneimine and succinic acid through a simple and rapid microwave-assisted method.The preparation conditions,structural characteristics and optical properties of the B-PDs were investigated.The B-PDs showed good bonding properties to iron ion(Fe³⁺).Therefore,a fluorescent probe for selectively detecting Fe³⁺was constructed.In order to further explore the application of the B-PDs,the study of Sudan dyes were carried out.It was found that the fluorescence of the B-PDs was apparently quenched by Sudan dyes.Therefore,a probable approach for detection of Sudan dyes based on the B-PDs was proposed.This part may give a way to extend the application of B-PDs.