Study Of The Application Of Fluorescence "off-on" Strategy In The Detection Of Thiols Small Molecules

In the field of small molecule detection,to determine whether a detection method is appropriate,it is often investigated for its sensitivity and selectivity for target molecules,time-consuming and other factors.Among many current analysis methods,the fluorescence analysis method has the above advantages.Fluorescence analysis refers to the analysis method established based on the measurement of the fluorescence spectrum of the compound,and the qualitative and quantitative analysis can be performed by using the characteristic spectrum of the substance.In order to overcome the limitation of direct fluorescence analysis method in the scope of application,and expand its scope of application.At present,based on mechanisms such as Fluorescence resonance energy transfer（FRET）and Inner filter effect（IFE）,a series of new fluorescence analysis methods have been established.Among them,sensors of the fluorescent"off-on"strategy means that the fluorescence intensity of the fluorescent substance is quenched under the action of the quencher.When the detected substance is added,the quenching system constructed is destroyed,so that the system fluorescence gradually recover.In order to achieve sensitive and specific quantitative analysis of the detected substance.In general,traditional fluorescent luminophores such as organic fluorescent dye probe molecules often have disadvantages such as high sensitivity to the environment and prone to photobleaching.Therefore,it is particularly important to find more stable and excellent fluorescent materials.With the development of nanotechnology era,some excellent fluorescent nanomaterials came into being.Such as carbon dots（CDs）,broadly refers to those nanoparticles with a particle size less than 10nm,composed of carbonized carbon cores and heteroatoms attached to organic functional groups.As a novel fluorescent luminescent material,CDs have the advantages of excellent photostability,low toxicity,biocompatibility,etc.,making it widely used in bioimaging,biosensing,photocatalysis,optoelectronics and other fields.Based on the above theoretical knowledge,this article uses traditional carboxyfluorescein dye-labeled oligonucleotide molecules（FAM-T15）,blue fluorescent nitrogen,sulfur co-doped carbon dots（N,S-CDs）and yellow fluorescent boron and nitrogen co-doped carbon dots（B,N-CDs）as fluorescent signals,and manganese dioxide nanosheets（MnO₂ NS）,silver nanoparticles（AgNPs）,and permanganate（Permanganate,MnO4^-）were used as quenchers,respectively.Several fluorescence quenching systems were constructed,and it was found that different fluorescence quenching systems have different responses to some thiols small molecules.Based on the fluorescent"off-on"strategy,fluorescence analysis methods for detecting thiol small molecules such as glutathione（GSH）,biothiol（GSH/Cys/Hcy）,captopril（Cap）,and thiourea（TU）were established in turn.The detailed information is listed as follows:1 Detection of GSH based on FAM-T15/MnO₂ NS"off-on"strategy.The single-stranded oligonucleotide（FAM-T15）labeled with a fluorescent dye probe molecule can bind well to the surface of manganese dioxide nanosheets（MnO₂ NS）,thereby generating energy transfer and used to construct a fluorescence quenching system.Experiments have found that when glutathione（GSH）molecules are present,GSH can reduce and destroy MnO₂ NS,causing it to decompose and fragment.As a result,the constructed fluorescence quenching system is destroyed,FAM-T15 adsorbed on the surface of MnO₂ NS is released freely,and the fluorescence is restored.The fluorescence intensity of the system gradually increases with the increase of GSH concentration.By investigating relationship between the fluorescence increase value（ΔI）and the concentration of GSH,a fluorescence analysis method of GSH is established based on the"off-on"strategy.This method has a good linear relationship in the range of GSH concentration of 6.0?200?M,the detection limit（3?）is 3.5?M,and it has been successfully used in the detection of human serum samples,with a recovery efficiency of 96.9%?103.1%.Relative standard deviation（RSD）is less than 4.3%.This fluorescence“off-on”strategy based on FAM-T15/MnO₂ NS provides a new method choice for rapid fluorescence detection of GSH.2 Detection of biothiols based on an"off-on"strategy for N,S-CDs/AgNPs pH-dependent.Very close structure and property similarities among biothiols,such as glutathione（GSH）,cysteine（Cys）,and homocysteine（Hcy）,present a major challenge to achieve their discriminative detection.In this contribution,a nanomaterial surface energy transfer（NSET）system was established to discriminate GSH from Cys and Hcy with the photoluminescence（PL）“switch-on”response.The nanosensor was constructed using nitrogen and sulphur co-doped carbon dots（N,S-CDs）and silver nanoparticles（AgNPs）through assembling an energy transfer-based quenching system,featuring the pH-promoted distinct PL“switchon”response.Under neutral conditions,only Cys and Hcy can encapsulate AgNPs,leaving little chance for N,S-CD binding on the surface of AgNPs,which can lead to PL signal recovery,and the total quantity of Cys and Hcy can be determined.However,at pH 3.0 all three kinds of biothiols can lead to the PL signal recovery and the total quantity of GSH,Cys,and Hcy can be determined,due to the similar slopes and intercepts of their calibration curves.Thus,the concentration of GSH could be further calculated and the strategy was successfully applied for the detection of GSH in human serum,demonstrating its potential in bioanalysis and significance in addressing biological and medicinal requirements.3 Detection of Cap or TU based on B,N-CDs/MnO4^-fluorescence quenching system"off-on"strategy.Captopril（Cap）is an angiotensin-converting enzyme（ACE）inhibitor that has a significant antihypertensive effect on many types of hypertension.Thiourea（TU）and its derivatives,commonly used as fungicides,herbicides,etc.,tend to cause residues in food,and have the potential to cause allergies and hypothyroidism.Therefore,it is of great significance to develop fast,simple and sensitive detection methods for their detection.In this work,we synthesized boron and nitrogen co-doped carbon dots（B,N-CDs）by a simple hydrothermal synthesis method,with o-phenylenediamine（o-PD）and tetraformylbenzeneboronic acid（4-FPBA）as precursors.They are high stability,good water solubility,and yellow fluorescence.That we found permanganate ions（MnO4^-）can effectively quench the fluorescence of B,N-CDs through the mechanism of internal filtration effect in the later.In the presence of Cap or TU,MnO4^-is reduced to Mn²⁺,and the fluorescence of B,N-CDs restored.Therefore,based on the“off-on”strategy of the fluorescence quenching system of B,N-CDs/MnO4^-,rapid fluorescence detection of Cap and TU is achieved,with Cap and TU in the concentration range of 0.5?30?M,5?100?M,respectively.The detection limits（3?）are 180.5 nM and 40.7 nM,respectively.This method can be used for the detection of Cap and TU residues in food preparations.The recovery efficiency were in the range of 92.45?102.6%and 93.27?102.9%,respectively,and the relative standard deviation（RSD）was less than 5.0%.