Fluorescence Detection Of L-Cysteine Based On Nucleic Acid Probes Or Carbon Quantum Dots

Fluorescence analysis method,a significant composition of analytical chemistry,is widely used in scientific research,biomedicine and so on.L-Cysteine(Cys)containing reducing thiol is closely related to human health.In this paper,2-aminopurine(2-AP)modified DNA(H 2-AP)and nitrogen-doped carbon quantum dots derived from polyethyleneimine(PQDs)and reduced carbon quantum dots(Y-CQDs)are used to construct fluorescent probes for the detection of Cys.The main contents are as follows:(1)An efficient and sensitive fluorescence analysis assay for the detection of Cys was established based on H 2-AP.H 2AP contains two thymine(T)-T mismatches.After adding Hg²⁺,H 2-AP forms a stable neck-ring structure DNA from single stranded DNA(ss DNA)due to the formation of T-Hg²⁺-T mismatch structure.Cys can extract Hg²⁺from the T-Hg²⁺-T mismatch structure,resulting neck-ring structure DNA to return to ss DNA.Exo I specifically hydrolyzed ss DNA and released 2-AP with a strong fluorescence.By comparing the fluorescence intensity after and before adding Cys,the sensitive detection of Cys was realized.Under the best experimental conditions,the linear range of 0.4-400 n M(R²=0.997)and the detection limit of 0.16n M were realized.However,other amino acids wirhout redyctive sulfur groups could not increase the fluorescence intensity.Satisfactory results were obtained by using this sensor in actual sample testing,which indicated that this mehod possess a broad application prospects in food,environment and medical analysis.(2)Blue-emission nitrogen doped carbon quantum dots(PQDs)were synthesized from polyethyleneimine(PEI)by a one-step hydrothermal method.An bond was constructed between Cu²⁺and the nitrogen and oxygen functional groups on the surface of PQDs,which not only quenched the fluorescence of PQDs but also changed the UV-vis signals.The color of the solution was also changed(colorlss to blue)accordingly.After adding Cys,Cys captured Cu²⁺through the Cu-S bond and restored the fluorescence of PQDs.At the same time,the absorption peak at 272 nm obviously shifted to blue,and the color of the solution quickly recovered from blue to colorless.A weak signal was obtained after adding other biothiols.Although the sensitivity of this method is not high,it realized the dual-signal and rapid detection of Cu²⁺and Cys,and successfully constructs an"AND"logic gate based on the multi-signal response.Finally,this method is not only simple,cheap and stable,but also suitable for the detection of Cu²⁺and Cys in actual samples.(3)Reducing carbon quantum dots,named Y-CQDs,were synthesized from O-phenylenediamine and ethylene glycol by a simple and low cost hydrothermal method.A fluorescent logic gate for the detection of Au³⁺and biothiols was constructed based on Y-CQDs.In this logic gate,obvious fluorescence quenching was recorded after adding the first input-Au³⁺.Au³⁺was rapidly reduced to Au nanoparticles(Au NPs)by Y-CQDs with reducibility,the presence of nitrogen/oxygen functional groups on the surface of Y-CQDs was responsible for the complex of Y-CQDs/Au NPs and quenched their fluorescence through fluorescence energy resonance transfer(FRET).With this signal-off process,the linear range of 0-16?M and the detection limit of 59n M were achieved for the detection of Au³⁺in tap water.In addition,up addition of biothiols in the Y-CQDs/Au³⁺solution as the second input,the fluorescence intensity recovered significantly due to Au NPs were caught by biothiols through strong Au-S bonds.The changes of fluorescence signal were obtained in the Y-CQDs/Au³⁺sensing system,which exhibited good linear ships in the range of 0-20?M,0-20?M and 4-12?M for L-cysteine(Cys),DL-homocysteine(Hcy)and L-glutathione(GSH),respectively.The detection limits were calculated as 0.58?M for Cys,0.58?M for Hcy and 0.62?M for GSH.