Construction Of Sulfur Quantum Dot Composite Fluorescent Sensor For Detection Of Disease Markers

Sulfur quantum dots（SQDs）with excellent optoelectronic properties,water and chemical stability,and low toxicity are a new class of quantum dots,which have been successfully used in biochemical sensing,bioimaging,optical devices,and photocatalysis.At present,the research of SQDs in biochemical sensing mainly focuses on the detection of metal ions,or through metal ion fluorescence signaling for the detection of small molecule organic compounds;and the detection of analytes based on the principle of fluorescence quenching-recovery.However,their application scope is limited due to the less number of groups on the surface of SQDs that recognize organic substances and biological macromolecules.In addition,the fluorescence quantum yield of SQDs is low due to the fluorescence burst caused by its surface defects.In order to improve the quantum yield of SQDs and broaden their applications,new methods for preparing SQDs and constructing various composites based on SQDs are proposed in this paper.The prepared SQDs were used for fluorescence sensing to develop for fluorescent sensing detection of Hg²⁺,2,6-dipicolinate（DPA）,sialic acid（SA）,H₂O₂,alkaline phosphatase（ALP）and glycoproteins.The main contents of this paper are as follows:（1）This chapter introduces the preparation method and luminescence mechanism of SQDs,and focuses on the application progress of SQDs;the classification of disease markers and the application of fluorescence sensing in disease markers are summarized.（2）In order to solve the problem that the preparation process of SQDs depends on the etchant and the size of quantum dots is not easy to control,in this paper,the SQDs with stable luminescence properties were prepared by hydrothermal method using polyethylene glycol（PEG）-400 as passivator and sublimed sulfur powder as sulfur source.Utilizing the feature that Hg²⁺can quench the fluorescence of SQDs,a high sensitivity detection of Hg²⁺was realized;since DPA and SQDs can compete to adsorb Hg²⁺,DPA can be indirectly detected,and both have low limit of detection.SQDs had a limit of detection of 0.15μM for Hg²⁺and a limit of detection of 1.24μM for DPA.The established method was applied to the detection of Hg²⁺and DPA in real samples,the recoveries were 88.92-116.92%and99.78-108.00%,and the relative standard deviations were 2.54-3.44%and 4.71-5.54%,respectively.（3）In order to improve the selectivity and sensitivity of sulfur quantum dots,a preparation method of phenylboronic acid-functionalized SQDs（B-SQDs）was established,and SA was selectively detected by the phenylboronic acid-alizarin red S（ARS）system.First,SQDs were modified with aminosiloxanes,followed by condensation acylation to graft 4-carboxyphenylboronic acid onto the surface of quantum dots,resulting in phenylboronic acid-functionalized SQDs.The binding of ARS to B-SQDs quenched the blue fluorescence of B-SQDs,and the red fluorescence of ARS was generated.Based on the principle that SA can displace ARS from the ARS-phenylboronic acid complex,when SA was added,the fluorescence of B-SQDs recovered and the red fluorescence of free ARS was quenched.The ratio of B-SQDs and ARS fluorescence response signals was linearly correlated with SA in the range of 1-70μM,R²=0.992,and the limit of detection was 0.54μM.（4）In order to improve the sensitivity and accuracy of detection,a dual emission fluorescence sensor（SQDs/Cu NCs）was constructed by combining red fluorescence-emitting copper nanoclusters（Cu NCs）and blue fluorescence-emitting SQDs.The study found that the fluorescence intensity of SQDs in the composites decreased significantly,which was mainly caused by the internal filtering effect（IFE）between SQDs and Cu NCs.When SQDs/Cu NCs were placed in H₂O₂solution,the fluorescence of Cu NCs was quenched and the fluorescence of SQDs recovered,which was due to the oxidation of Cu（0）in Cu NCs by H₂O₂.The SQDs/Cu NCs were applied to the detection of H₂O₂in exhaled breath condensate,and the spiked recoveries and relative standard deviations were 101-109%and 2.39-5.07%,respectively.（5）In order to improve the selectivity and luminous efficiency,Zn（II）was first combined with SQDs,and then the surface Zn（II）induced growth to form a metal-organic framework（ZIF-8）shell to obtain the composite material of ZIF-8 packaged SQDs（SQDs@ZIF-8）.Using SQDs@ZIF-8 for the detection of ALP,it was found that the fluorescence of SQDs@ZIF-8 could be effectively quenched when ALP and the substrate,2-phospho-L-ascorbic acid trisodium salt（AAP）,coexisted.In the range of 0.15～50 U/L,the fluorescence intensity had a good linear relationship with ALP,and its detection limit was0.04 U/L.In addition,SQDs@ZIF-8 was used for colorimetric detection of ALP,and the UV absorption intensity was linearly correlated with ALP in the range of 10-200 U/L.The combination of the above two detection methods can significantly broaden the detection range.（6）According to the research results of the previous chapter,this chapter used a metal-organic framework（Eu-MOF-B（OH）₂）containing phenylboronic acid and rare earth elements to encapsulate SQDs,and SQDs@Eu-MOF-B（OH）₂with core-shell structured was synthesized by layer-by-layer assembly method.Taking advantage of the feature that boronic acid groups can selectively bind to glycoproteins,when SQDs@Eu-MOF-B（OH）₂interacted with glycoproteins,the fluorescence of Eu-MOF-B（OH）₂was quenched,while the fluorescence of SQDs was not affected.The ratiometric fluorescence sensor was used for the detection of alpha-fetoprotein,and its fluorescence ratio at 616 nm and 420 nm showed a good linear relationship with alpha-fetoprotein in the range of 10-500 n M,and the limit of detection was 6.44 n M.In summary,a variety of fluorescent sensors based on SQDs were prepared in this paper,and the detection of various disease markers with high sensitivity and high selectivity was realized.