荧光传感方法检测爆炸物的研究进展

爆炸物检测是当前国际安全中迫切关注的问题之一。在过去的几十年中,大量的荧光传感材料用于荧光传感检测气态、液态和固态爆炸物见诸于报道。近年来,为了实现爆炸物的快速响应、高灵敏和高选择性的检测,研究工作者大力开发了各种新型荧光材料。这篇综述总结了近年来用于爆炸物检测的先进荧光材料,详尽、系统、重点地介绍了共轭聚合物、荧光小分子、超分子体系、具有聚集诱导发光效应的活性材料及静电纺丝纳米材料等各种荧光材料在爆炸物检测中的应用,展望了荧光传感方法在爆炸物检测领域的应用前景。     

Synthesis and Applications of Red‐Emissive Carbon Dots

Carbon dots (CDs), a new class of fluorescent carbon nanoparticles (less than 10 nm in size), have been widely applied in various fields, including sensors, bioimaging, catalysis, light‐emitting devices (LEDs), and photoelectronic devices, owing to their unique properties such as low toxicity, bio‐compatibility, high photostability, easy surface modification, and up‐conversion fluorescence, over the past decades. Recently, multiple‐color‐emissive CDs, especially red‐emissive CDs (RCDs), have drawn much attention owing to their unique advantages, like the ability to penetrate the animal bodies without the disturbance of strong tissue autofluorescence, multiple‐color fluorescence displaying or sensing, and the capacity to be one essential component to obtain white LED (WLED). In this review, we focused on the progress of recently‐emerging RCDs in the past five years, including their synthetic methods (hydrothermal, solvothermal, reflux condensation and microwave techniques), influencing factors (precursors, solvents, elements doping, surface chemistry) and various applications (bioimaging, sensor, photocatalysis and WLEDs), with a perspective on the future advancements.     

Sensing of 2,4,6‐Trinitrotoluene (TNT) and 2,4‐Dinitrotoluene (2,4‐DNT) in the Solid State with Photoluminescent RuII and IrIII Complexes

A series of metal–organic chromophores containing Ru^II or Ir^III were studied for the luminometric detection of nitroaromatic compounds, including trinitrotoluene (TNT). These complexes display long‐lived, intense photoluminescence in the visible region and are demonstrated to serve as luminescent sensors for nitroaromatics. The solution‐based behavior of these photoluminescent molecules has been studied in detail in order to identify the mechanism responsible for metal‐to‐ligand charge‐transfer (MLCT) excited state quenching upon addition of TNT and 2,4‐dinitrotoluene (2,4‐DNT). A combination of static and dynamic spectroscopic measurements unequivocally confirmed that the quenching was due to a photoinduced electron transfer (PET) process. Ultrafast transient absorption experiments confirmed the formation of the TNT radical anion product following excited state electron transfer from these metal complexes. Reported for the first time, photoluminescence quenching realized through ink‐jet printing and solid‐state titrations was used for the solid‐state detection of TNT; achieving a limit‐of‐quantitation (LOQ) as low as 5.6 ng cm^?2. The combined effect of a long‐lived excited state and an energetically favorable driving force for the PET process makes the Ru^II and Ir^III MLCT complexes discussed here particularly appealing for the detection of nitroaromatic volatiles and related high‐energy compounds.     

Fluorescence quenching study of humic‐fraction‐modified silica gel in a solid state after association with a variety of pesticidal analytes in hexane and acetonitrile

In this paper, we investigate the fluorescence quenching of acidic humic‐fraction‐modified silica gel in the solid state after association with a variety of pesticidal analytes in hexane and acetonitrile. The percentage of fluorescence quenching is found to be dependent on the contact time and linearly on the number of moles of analyte involved in the association process. However, any π–π complexation interaction arising from the acidic aromatic ring on the analyte due to the derivatization of a bulky electron‐withdrawing group is not observed. Also, any mechanism leading to adsorption or any quenching process occurring as a result of the steric hindrance obtained by a theoretical interaction simulation is not observed. The Fourier transform infrared (FTIR) data and simulation results, instead, suggest that electron‐rich atoms on the analyte, such as oxygen, sulfur, nitrogen, and phosphorus, are responsible for fluorescence quenching, following dipole–dipole interaction with the humic‐fraction‐modified adsorbent.     

Polymorph‐Dependent Solid‐State Fluorescence and Selective Metal‐Ion‐Sensor Properties of 2‐(2‐Hydroxyphenyl)‐4(3H)‐quinazolinone

2‐(2‐Hydroxy‐phenyl)‐4(3H)‐quinazolinone (HPQ), an organic fluorescent material that exhibits fluorescence by the excited‐state intramolecular proton‐transfer (ESIPT) mechanism, forms two different polymorphs in tetrahydrofuran. The conformational twist between the phenyl and quinazolinone rings of HPQ leads to different molecular packing in the solid state, giving structures that show solid‐state fluorescence at 497 and 511 nm. HPQ also shows intense fluorescence in dimethyl formamide (DMF) solution and selectively detects Zn²⁺ and Cd²⁺ ions at micromolar concentrations in DMF. Importantly, HPQ not only detects Zn²⁺ and Cd²⁺ ions selectively, but it also distinguishes between the metal ions with a fluorescence λ_max that is blue‐shifted from 497 to 420 and 426 nm for Zn²⁺ and Cd²⁺ ions, respectively. Hence, tunable solid‐state fluorescence and selective metal‐ion‐sensor properties were demonstrated in a single organic material.     

Strong Fluorescent Smart Organogel as a Dual Sensing Material for Volatile Acid and Organic Amine Vapors

An L ‐phenylalanine derivative ( C12PhBPCP ) consisting of a strong emission fluorophore with benzoxazole and cyano groups is designed and synthesized to realize dual responses to volatile acid and organic amine vapors. The photophysical properties and self‐assembly of the said derivative in the gel phase are also studied. C12PhBPCP can gelate organic solvents and self‐assemble into 1 D nanofibers in the gels. UV/Vis absorption spectral results show H‐aggregate formation during gelation, which indicates strong exciton coupling between fluorophores. Both wet gel and xerogel emit strong green fluorescence because the cyano group suppresses fluorescence quenching in the self‐assemblies. Moreover, the xerogel film with strong green fluorescence can be used as a dual chemosensor for quantitative detection of volatile acid and organic amine vapors with fast response times and low detection limits owing to its large surface area and amplified fluorescence quenching. The detection limits are 796 ppt and 25 ppb for gaseous aniline and trifluoroacetic acid (TFA), respectively.     

A Reusable DNA Single‐Walled Carbon‐Nanotube‐Based Fluorescent Sensor for Highly Sensitive and Selective Detection of Ag+ and Cysteine in Aqueous Solutions

Here we report a reusable DNA single‐walled carbon nanotube (SWNT)‐based fluorescent sensor for highly sensitive and selective detection of Ag⁺ and cysteine (Cys) in aqueous solution. SWNTs can effectively quench the fluorescence of dye‐labeled single‐stranded DNA due to their strong π–π stacking interactions. However, upon incubation with Ag⁺, Ag⁺ can induce stable duplex formation mediated by C–Ag⁺–C (C=cytosine) coordination chemistry, which has been further confirmed by DNA melting studies. This weakens the interactions between DNA and SWNTs, and thus activates the sensor fluorescence. On the other hand, because Cys is a strong Ag⁺ binder, it can remove Ag⁺ from C–Ag⁺–C base pairs and deactivates the sensor fluorescence by rewrapping the dye‐labeled oligonucleotides around the SWNT. In this way, the fluorescence signal‐on and signal‐off of a DNA/SWNT sensor can be used to detect aqueous Ag⁺ and Cys, respectively. This sensing platform exhibits high sensitivity and selectivity toward Ag⁺ and Cys versus other metal ions and the other 19 natural amino acids, with a limit of detection of 1 nM for Ag⁺ and 9.5 nM for Cys. Based on these results, we have constructed a reusable fluorescent sensor by using the covalent‐linked SWNT–DNA conjugates according to the same sensing mechanism. There is no report on the use of SWNT–DNA assays for the detection of Ag⁺ and Cys. This assay is simple, effective, and reusable, and can in principle be used to detect other metal ions by substituting C–C base pairs with other native or artificial bases that selectively bind to other metal ions.     

Large scale synthesis of red emissive carbon dots powder by solid state reaction for fingerprint identification

Red emissive carbon dots(CDs) powder was synthesized on a large scale from phloroglucinol and boric acid by a novel solid state reaction with yield up to 75%. This method is safe and convenient, for it needs neither high pressure reactors nor complicated post-treatment procedures. The as-prepared carbon dots powder exhibited strong red fluorescence with excitation-independent behavior. XPS measurement and PL spectra suggest that such red fluorescence arise from boron-doped structures in CDs, which increases along with the boron concentration on CDs surface but decreases when the concentration quenching effect takes place. To overcome the aggregation induced fluorescence quenching of the solid CDs powder,the conventional methods are dispersing CDs into a large amount of inert substrates. But our present work provides a new strategy to realize strong red fluorescence of CDs in solid state. As a result, such carbon dots powder works well for latent fingerprint identification on various material surfaces.     

The oxidation state of a protein observed molecule-by-molecule.

We report the observation of the redox state of the blue copper protein azurin on the single-molecule level. The fluorescence of a small fluorophore attached to the protein is modulated by the change in absorption of the copper center via fluorescence resonance energy transfer (FRET). In our model system, the fluorescence label Cy5 was coupled to azurin from Pseudomonas aeruginosa via cysteine K27C. The Cy5 fluorescence was partially quenched by the absorption of the copper center of azurin in its oxidized state. In the reduced state, absorption is negligible, and thus no quenching occurs. We report on single-molecule measurements, both in solution by using fluorescence correlation spectroscopy (FCS) combined with fluorescence intensity distribution analysis (FIDA), and on surfaces by using wide-field fluorescence microscopy.     

纤维素接枝改性芴-苯和咔唑-苯共聚物及其对硝基芳烃的检测

采用Suzuki偶联反应将合成的芴-苯和咔唑-苯共聚物接枝到经化学改性的纸纤维素上,制备了可用于硝基芳烃检测的传感纸纤维素.荧光猝灭研究显示,由于两种传感纸纤维素具有的大比表面积和孔道结构有利于2,4-二硝基甲苯(DNT)蒸气分子的快速扩散,因此二者比薄膜态具有更高的荧光猝灭效率.荧光猝灭的可逆性研究显示,两种传感纤维素经过四次猝灭-恢复循环后,对DNT气态分子依然具有较高的猝灭效率,表明制备的纸纤维素具有良好的荧光猝灭可逆性和稳定性.     

A highly selective multifunctional Zn‐coordination polymer sensor for detection of Cr (III), Cr (VI) ion,and TNP molecule

A new coordination polymer based on the 4‐(2,2′;6′,2″‐tripyridyl)‐4′‐1,2‐phenyl dicarboxylic acid (H₂tbda), namely, [Zn (tbda)]_n ( 1 ), features a one‐dimensional binuclear chain structure and exhibits the excellent luminescence in pH range of 3‐12 in aqueous solution. Particularly, compound 1 shows the remarkable selectivity, anti‐interference, and recyclability for sensing Cr (III) ion through the fluorescence enhancement. Meanwhile, compound 1 can also serve as a sensor for detecting the trace amounts of Cr (VI) ion and 2,4,6‐trinitrophenol (TNP) with high selectivity and recyclability through the fluorescence quenching effect. Furthermore, the detection mechanisms of compound 1 as a fluorescence sensor for different analytes have been explored in detail.     

Femtogram Detection of Explosive Nitroaromatics: Fluoranthene‐Based Fluorescent Chemosensors

Herein we report a novel fluoranthene‐based fluorescent fluorophore 7,10‐bis(4‐bromophenyl)‐8,9‐bis[4‐(hexyloxy)phenyl]fluoranthene ( S₃ ) and its remarkable properties in applications of explosive detection. The sensitivity towards the detection of nitroaromatics (NACs) was evaluated through fluorescence quenching in solution, vapor, and contact mode approaches. The contact mode approach using thin‐layer silica chromatograp‐ hic plates exhibited a femtogram (1.15 fg cm^?2) detection limit for trinitrotoluene (TNT) and picric acid (PA), whereas the solution‐phase quenching showed PA detection at the 2–20 ppb level. Fluorescence lifetime measurements revealed that the quenching is static in nature and the quenching process is fully reversible. Binding energies between model binding sites of the S₃ and analyte compounds reveal that analyte molecules enter into the cavity created by substituted phenyl rings of fluoranthene and are stabilized by strong intermolecular interactions with alkyl chains. It is anticipated that the sensor S₃ could be a promising material for the construction of portable optical devices for the detection of onsite explosive nitroaromatics.     

High‐Level Incorporation of Silver in Gold Nanoclusters: Fluorescence Redshift upon Interaction with Hydrogen Peroxide and Fluorescence Enhancement with Herbicide

High‐level incorporation of Ag in Au nanoclusters (NCs) is conveniently achieved by controlling the concentration of Ag⁺ in the synthesis of bovine serum albumin (BSA)‐protected Au NCs, and the resulting structure is determined to be bimetallic Ag₂₈Au₁₀‐BSA NCs through a series of characterizations including energy‐dispersive X‐ray spectroscopy, mass spectroscopy, and X‐ray photoelectron spectroscopy, together with density functional theory simulations. Interestingly, the Ag₂₈Au₁₀ NCs exhibit a significant fluorescence redshift rather than quenching upon interaction with hydrogen peroxide, providing a new approach to the detection of hydrogen peroxide through direct comparison of their fluorescence peaks. Furthermore, the Ag₂₈Au₁₀ NCs are also used for the sensitive and selective detection of herbicide through fluorescence enhancement. The detection limit for herbicide (0.1 nm ) is far below the health value established by the U.S. Environmental Protection Agency; such sensitive detection was not achieved by using AuAg NCs with low‐level incorporation of Ag or by using the individual metal NCs.     

Colorimetric and Fluorescent Chemosensors for the Detection of 2,4,6‐Trinitrophenol and Investigation of their Co‐Crystal Structures

A full account of our studies of 2,4,6‐trinitrophenol (TNP) sensing is provided. A series of chemosensors 2 , 3 , 4 , 5 with a variety of aromatic chromophores for specific recognition of TNP has been designed and then realized through the fluorescence “on/off” mechanism. These chemosensors demonstrated highly selective, sensitive, and fluorescent quenching of TNP with remarkable visual changes through the intramolecular charge‐transfer (ICT) process. Their host–guest interactions were investigated by ¹H NMR spectroscopic titrations and their corresponding co‐crystal structures, which showed that the 1:1 host–guest complexes were formed by multiple hydrogen‐bond interactions in solution or in the solid state. The origins of the significant affinity demonstrated during the fluorescence recognition process were further disclosed through DFT calculations of corresponding compounds.     

New Dual Fluorescent Probe for Simultaneous Biothiol and Phosphate Bioimaging

The simultaneous detection of relevant metabolites in living organisms by using one molecule introduces an approach to understanding the relationships between these metabolites in healthy and deregulated cells. Fluorescent probes of low toxicity are remarkable tools for this type of analysis of biological systems in vivo. As a proof of concept, different naturally occurring compounds, such as biothiols and phosphate anions, were the focus for this work. The 2,4‐dinitrobenzenesulfinate (DNBS) derivative of 9‐[1‐(4‐tert‐butyl‐2‐methoxyphenyl)]‐6‐hydroxy‐3H‐xanthen‐3‐one (Granada Green; GG) were designed and synthesized. This new sulfinyl xanthene derivative can act as a dual sensor for the aforementioned analytes simultaneously. The mechanism of action of this derivative implies thiolysis of the sulfinyl group of the weakly fluorescent DNBS‐GG by biological thiols at near‐neutral pH values, thus releasing the fluorescent GG moiety, which simultaneously responds to phosphate anions through its fluorescence‐decay time. The new dual probe was tested in solution by using steady‐state and time‐resolved fluorescence and intracellularly by using fluorescence‐lifetime imaging microscopy (FLIM) in human epithelioid cervix carcinoma (HeLa) cells.     

HCl/NH_3敏感的卟啉-二氧化硅反蛋白石光子晶体荧光传感器

将反蛋白石结构的光子晶体引入到腐蚀性气体检测体系,制备得到卟啉-二氧化硅反蛋白石光子晶体(TPP-SiO_2IOPCs)荧光传感器。相对于空白样,TPP-SiO_2IOPCs传感器实现了氯化氢(HCl)气体检测信号200倍的增强,这主要归因于反蛋白石型光子晶体的大孔结构和慢光子效应。同时,TPP-SiO_2IOPCs传感器对于HCl气体的猝灭效率可达75%,比空白样的提高了25%,而且经HCl气体处理后的传感器通入氨气(NH_3)后,初始的荧光强度几乎完全恢复。在HCl和NH_3条件下进行5个循环后,TPP-SiO_2IOPCs传感器表现出良好的可重复使用性。该研究对于发展高效的荧光传感器提供了新的思路。     

Highly Selective “Turn‐On” Fluorescent and Colorimetric Sensing of Fluoride Ion Using 2‐(2‐Hydroxyphenyl)‐2,3‐dihydroquinolin‐4(1 H)‐one based on Excited‐State Proton Transfer

A simple, highly selective and sensitive colorimetric system for the detection of fluoride ion in an aqueous medium has been developed using 2‐(2‐hydroxyphenyl)‐2,3‐dihydroquinolin‐4(1 H)‐one. This system allows selective “turn‐on” fluorescence detection of fluoride ion, which is found to be dependent upon guest basicity. An excited‐state proton transfer is proposed to be the signaling mechanism, which is rationalized by DFT and TD‐DFT calculations. The present sensor can also be applied to detect fluoride levels in real water samples.     

Explosives Sensing by Using Electron‐Rich Supramolecular Polymers: Role of Intermolecular Hydrogen Bonding in Significant Enhancement of Sensitivity

We demonstrate here that supramolecular interactions enhance the sensitivity towards detection of electron‐deficient nitro‐aromatic compounds (NACs) over discrete analogues. NACs are the most commonly used explosive ingredients and are common constituents of many unexploded landmines used during World War II. In this study, we have synthesised a series of pyrene‐based polycarboxylic acids along with their corresponding discrete esters. Due to the electron richness and the fluorescent behaviour of the pyrene moiety, all the compounds act as sensors for electron‐deficient NACs through a fluorescence quenching mechanism. A Stern–Volmer quenching constant determination revealed that the carboxylic acids are more sensitive than the corresponding esters towards NACs in solution. The high sensitivity of the acids was attributed to supramolecular polymer formation through hydrogen bonding in the case of the acids, and the enhancement mechanism is based on an exciton energy migration upon excitation along the hydrogen‐bond backbone. The presence of intermolecular hydrogen bonding in the acids in solution was established by solvent‐dependent fluorescence studies and dynamic light scattering (DLS) experiments. In addition, the importance of intermolecular hydrogen bonds in solid‐state sensing was further explored by scanning tunnelling microscopy (STM) experiments at the liquid–solid interface, in which structures of self‐assembled monolayer of the acids and the corresponding esters were compared. The sensitivity tests revealed that these supramolecular sensors can even detect picric acid and trinitrotoluene in solution at levels as low as parts per trillion (ppt), which is much below the recommended permissible level of these constituents in drinking water.     

Fluorescence Sensor with A New ON1–OFF–ON2 Switching Mechanism Using the Excited State Intermolecular Proton Transfer Reaction of An Anthracene‐diurea Compound

A new photoreaction mechanism of “Three‐state molecular switch” fluorescence sensor based on ON¹‐OFF‐ON² sequence was achieved by anthracene‐diurea compound, which was designed using two phenylurea groups and one anthracene, 9,10BtDSPUA. Photochemical properties of 9,10BtDSPUA and interaction between 9,10BtDSPUA and anion were investigated in detail by absorption, ¹H NMR, fluorescence, and fluorescence decay measurements. While the fluorescence of 9,10BtDSPUA in DMSO (ON¹) was quenched in the presence of low concentration of acetate anion (OFF), fluorescence enhancement occurred by the addition of high concentration of acetate anion (ON²). This compound forms complex with acetate anion through hydrogen bonding interaction in the ground state resulted in tautomer formation by excited state intermolecular proton transfer (ESIPT) on irradiation. Whereas single coordination of acetate anion to anthracene‐diurea compound may cause fluorescence quenching, full coordination may cause fluorescence enhancement due to suppressing ESIPT. This suppressing ESIPT was occurred by electron‐donating resonance effect between two urea moieties. This study is the first example of ON¹‐OFF‐ON² fluorescence sensor for concentration detection of acetate anion.     

Multi‐Use NBD‐Based Tetra‐amino Macrocycle: Fluorescent Probe for Metals and Anions and Live Cell Marker

Ligand L (4‐(7‐nitrobenzo[1,2,5]oxadiazole‐4‐yl)‐1,7‐dimethyl‐1,4,7,10‐tetra‐azacyclododecane) is a versatile fluorescent sensor useful for Cu^II, Zn^II and Cd^II metal detection, as a building block of fluorescent metallo‐receptor for halide detection, and as an organelle marker inside live cells. Ligand L undergoes a chelation‐enhanced fluorescence (CHEF) effect upon metal coordination in acetonitrile solution. In all three complexes investigated the metal cation is coordinatively unsaturated; thus, it can bind secondary ligands as anionic species. The crystal structure of [Zn L Cl](ClO₄) is discussed. Cu^II and Zn^II complexes are quenched upon halide interaction, whereas the [Cd L ]²⁺ species behaves as an OFF–ON sensor for halide anions in acetonitrile solution. The mechanism of the fluorescence response in the presence of the anion depends on the nature of the metal ion employed and has been studied by spectroscopic methods, such as NMR spectroscopy, UV/Vis and fluorescence techniques and by computational methods. Subcellular localization experiments performed on HeLa cells show that L mainly localizes in spot‐like structures in a polarized portion of the cytosol that is occupied by the Golgi apparatus to give a green fluorescence signal.