Recently, the fluorescent bio-probe based on water-soluble boron-dipyrromethene (BODIPY) obtains enormous progress on structural optimization and functional modification, and becomes novel high-performance biological imaging materials owing to the development of hydrophilic modification. Focusing on the methods for improving the hydrophilicity of BODIPY, the water-soluble BODIPYs have been classified as ionic probe, electrically-neutral probe and amphiphilic probe. The research progress on the application of water-soluble BODIPY dyes in field of biology and medicine since 2006 has been summarized in this review, such as detection of necessary and pathogenicbiological chemical components, early detection and intervention of cancer, labelling drug delivery, marking specific organelles, real-time monitoring of biochemical and property changes with cells, andphotodynamic therapy. The merits of methods for improving the hydrophilicity and main issues of current studies have been summed up. The hypothesis for future directions has also been put forward.

Halogen ions play an important role in chemistry, biology and material. The concentration of fluoride in the organism directly affects its health. The halide materials often act as flame retardant to improve the ignition point for plastic and other polymer products. So it is of great significance to detect halogen ions. Chemosensors include colorimetric and fluorescent sensors, which have the advantages of good selectivity and high sensitivity. In recent years, some halogen ion chemosensors have been reported widely. According to the type of host and guest molecules, halgen ion chemosensors mainly include fluoride ion chemosensors, iodine ion chemosensors, dual channel chemosensors and functional chemosensors. In this paper, the progress of halogen ion chemosensors in recent years is reviewed, the synthetic strategies for them are summarized and the future research direction of halogen ion chemosensors is prospected.

Among the numerous bio-active species which are involved in the various chemical reactions in our body, reactive oxygen species (ROS) are a class of important biological species, which are oxidative. ROS can maintain the intracellular redox balance and are tightly related with the cell growth and death. Hence, the fluorescence detection of intracellular ROS has attracted wide attention. However, owining to the inherent features of ROS, such as the short lifetime and high reactivity, fluorescence analysis of ROS is always faced with some problems, like low selectivity and side reactions. Herein, the development of small molecular fluorescent probes for intracellular ROS over the past decade is summarized, and the design mechanisms and bio-applications of these probes are emphasized.

A novel CN^- chemosensor based N-4-pyridylcoumarin-3-carboxamide derivative Q1 was designed and synthesized. The recognition performance of sensor Q1 for ten different anions was studied by UV and fluorescence spectroscopy. When anions such as CN^-, F^-, Cl^-, Br^-, I^-, AcO^-, H₂PO₄^-,HSO₄^-,ClO₄^- and SCN^- were added to the mixed solution (DMSO/H₂O, V:V=9:1), addition of CN^- could increase the absorption peak of Q1 at 304 nm, and the corresponding fluorescence produced a strong emission peak at 431 nm. Q1 solution with CN^- emitted strong blue fluorescent that can be easily observed by naked eyes. The color changed (from colorless to faint yellow) and the "Turn-On" fluorescence behavior suggested that Q1 could detect CN^- by dual-channel. Happily, the fluorescent limit of detection (LOD) is 1.44×10^-8 mol/L, was lower than the specified content by World Health Organization (WHO) in drinking water. Based on all the experimental facts, we speculated that the possible identification mechanism was that the addition reaction took place between Q1 and CN^-, and it can also be confirmed by density functional theory (DFT). This result can be applied to the detection of CN^- in cherry kernel.

A turn-on probe, which exhibited highly selective and sensitive signaling behaviors toward Fe³⁺ over other common metal ions, has been synthesized and confirmed by ¹H NMR, ¹³C NMR, IR and MS. The addition of Fe³⁺ to the solution of probe induced a remarkable UV-Vis and fluorescence enhancement along with obvious color change detected by the naked eye. The reaction mechanism was also investigated and proposed as that the probe complexed Fe³⁺ via a 1:1 binding mode, and the subsequent complexation caused the ring-opening of the rhodamine spirolactam and thereby the changes of absorbance and fluorescence. These remarkable properties may allow Fe³⁺ to be detected directly in the presence of the other examined competing metal ions. Then, cells experiments showed that the probe could permeate through cell membranes and react to Fe³⁺ within living cells. Additionally, the probe was further used for detecting Fe³⁺ ions in living mouse which exhibited excellent fluorescence imaging.

Due to high selective coordination ability of phosphate anion to the Zn center of pincer type terpyridine zinc nitrate complexes, intriguing visual recognition of phosphate anion via selective metallo-hydrogel formation has been successfully realized. Based on this interesting result, a series of control experiments were conducted including the study on thermodynamic stability, rheological property and microscopic morphology of the metallo-hydrogel, a plausible mechanism of the discrimination was proposed.

Methods for optical detection or sensing of L-cysteine with high selectivity and sensitivity have attracted increasing interest recently due to the potential association of L-cysteine to the fields of pathophysiology and clinical medicine. Recent advances since 2010 on reaction-based small molecule sensors as well as sensing ensembles constructed by metal complex and nanomaterials for optical sensing of L-cysteine were highlighted. The future advances in this field were also predicted and given at the end of this review.

A novel rhodamine B Schiff-base fluorescence probe 1 was synthesized and characterized by ¹H NMR, ¹³C NMR, MS and single-crystal X-ray analysis. The recognition properties of the probe 1 with Hg²⁺ ions were investigated in ethanol-water (V/V=7/3, HEPES 10 mmol/L, pH=7.0) by the UV-Vis spectrophotometry and the fluorescence spectrophotometry. The probe 1 showed remarkable "turn-on" fluorescent responses to Hg²⁺ with good selectivity over the other metal ions examined. The 1:1 binding model of probe 1 with Hg²⁺ was established by Job's plot and MS spectra. The probe can be applied to the quantitative analysis of Hg²⁺ with a linear range covering from 0 to 50 μmol/L. The fluorescence imaging experiments in MGC-803 living cells demonstrated that 1 could be used in biological systems to monitor Hg²⁺.

Ethyl 5-phenyl-2-(3-(trifluoromethyl)phenyl)-2H-1,2,3-triazole-4-carboxylate (EPFC), a newly synthesized compound, is used to study its structural properties and explore as a fluorescent probe for metal ions. EPFC was investigated in terms of structural, fluorescence spectroscopic, UV-Vis spectroscopic and theoretical analysis by using HF/6-31G(d), CIS/6-31G(d) and B3LYP/6-31G(d) methods, respectively. The corresponding product was characterized by NMR and HRESIMS methods. The interactions of the compound with 15 kinds of metal ions (Pb²⁺, Mn²⁺, K⁺, Na⁺, Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺, Zn²⁺, Ni²⁺, Hg²⁺, Li⁺ and Mg²⁺) were investigated by UV absorption spectroscopy and fluorescence spectroscopy. The quantum chemical values suggested that it is easy for EPFC to lose electron with weak electron accepting ability by frontier molecular orbital analysis. The calculated spectra were complimented with experimental measurements in great degree. In addition, a novel rhodamine B derivative containing 1,2,3-triazole unit, and REPFC was successfully designed and synthesized by the reaction between rhodamine B and EPFC. REPFC displayed more selectivity response to Hg²⁺ ion than other metal ions in N,N-dimethylformamide (DMF)-H₂O (V/V=1/1, pH 7.4) within a REPFC concentration range of 2.67×10^-5~4.67×10^-5 mol·L^-1 with an fluorescent enhancement and a rapid chemical reaction. The triazole appended colorless chemosensor turns to pink upon complex formation only with Hg²⁺ions even in the presence of other common metal ions and enables naked-eye detection. The coordination mechanism and turn on/off fluorescence for Hg²⁺ ions were well proposed by explaining Hg²⁺ inducing the ring-opened rhodamine B moiety. This study was an advancement for the application of 1,2,3-triazole compound and provides guidance for using simple and high-selectivity Hg²⁺ probes in aqueous solutions under physiological conditions.

The detection and fluorescent identification of some substances such as sLea/x in vivo can provide important reference for the diagnosis, treatment and prognosis of disease, molecular tracing and further research on the mechanism of related diseases. Therefore, the development and discovery of high selectivity and high sensitivity chemsensors is of great value. Due to the special structure, phenyl boronic acid compounds could interact and bind with sugar, catecholamine containing catechol structure, fluoride or alkali cyanide. So boronic acids could be develeped as fluorescence sensors selectively for related substances, while have the advantages of high selectivity, high efficiency, rapid analysis and so on. In recent years, boronic acid has been functioned with new materials such as nanoparticles and quantum dots to design novel sensors for better performance. In this paper, the recent progress in the study of boronic acid compounds in sensors is reviewed.

Fluorescent imaging technology has received great attention owing to their advantageous features in high sensitivity, relatively simple operations and real-time living cells, tissue and in vivo imaging. Compared with one-photon confocal imaging, two-photon confocal imaging offers considerable advantages such as high resolution, deep-tissue depth, lower tissue auto-fluorescence and so on. As typical D-π-A two-photon dyes, 1,8-naphthalimide dyes have wide application in two-photon imaging for enzyme, reactive carbon species, reactive oxygen species, reactive nitrogen species, biothiols and ions due to their advantages such as high photostability, large Stokes/anti-Stokes shifts. According to the mechanisms of intramolecular charge transfer, photoinduced electron transfer and fluorescence resonance energy transfer, etc., the application in two-photon imaging of 1,8-naphthalimide dyes is summarized and emphasized.

^aEngineering and Research Center for Southwest Bio-pharmaceutical Resources of National Education Ministry of China, Guizhou University, Guiyang 550025) (^bKey Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang 550025) (^cCollege of Tobacco Science, Guizhou University, Guiyang 550025

A series of hexahydroquinazolin-2-amine-based derivatives have been designed and synthesized from renewable isolongifolanone. Their solid states exhibited an enhanced emission and a dark green to bright yellow color range. In addition to good thermal stability, their solid-state fluorescence is not readily restricted by multiple conventional factors such as long term UV irradiation, increasing operated pressure and elevated heating temperature. In contrast to the derivatives which undergo serious aggregation-caused quenching (ACQ), the dimethylamino-substituted derivative 1-6,6,10,10-tetramethyl-4-(4'-(N,N-dimethylamino)phenyl)-5,7,8,9,10,10a-hexahydro-6H-6a,9-methanobenzo[h]quinazolin-2-imino)methyl)naphthalen-2-ol (3e) demonstrate obvious aggregation-induced emission (AIE) characteristics. Moreover, these fluorescent derivatives were also used for specific and sensitive sensing of Zn²⁺ ion in aqueous solutions. Then, their photophysical mechanisms were obtained by the density functional theory calculations. These probes were successfully applied to image Zn²⁺ ion in pollen grains of Althaea rosea.

A novel fluorescent probe L with long wavelength emission and large Stokes shift was designed and synthesized based on 1,4-diethyl-7-hydroxytetrahydroquinoxaline-6-carboxaldehyde. The color of L was changed from yellow to pink and colorless upon addition of Cu²⁺ and Co²⁺ respectively in dimethylsulfoxide (DMSO), which illustrated that probe L could recognize Cu²⁺ and Co²⁺ by naked eyes. The complex L-Cu²⁺ could recognize H₂S with fluorescence "OFF-ON" in DMSO/H₂O (V:V=7:3, HEPES, 1×10^-2 mol/L, pH=7.4). The test strip assay showed that the L-Cu²⁺ pretreated test strip showed obvious color changes toward different concentrations of H₂S, which indicated that H₂S could be rapidly detected by naked eyes and fluorescent double channel. In addition, the molecular target of compound L can be searched by utilizing the reverse docking method in Discovery Studio (DS) software. Then, docking analysis was performed using CDOCKER module of DS, and it was found that molecule L has a good combination to 2x0v protein (P53_human). Therefore, it is expected to be applied in the medicine field.

It is well-known that cyanide anion (CN^-) is a hypertoxic anion, which can cause adverse effects in both environment and living beings. Thus, it is highly desirable to develop strategies for detecting cyanide, especially in aqueous medium and food. However, due to the short half-life of free cyanide, long analysis time and interference from other competitive anions are general challenges for accurate monitoring of cyanide. Taking advantage of the special nucleophilicity of cyanide, a new colorimetric and fluorescent sensor (Q1-2) was synthesized based on naphtho[2,1-b]furan-2-carbonyl chloride and 2-aminobenzimidazole which designed by tuning the intramolecular hydrogen bonding to affect the π-conjugated efficiency. Upon the addition of cyanide anion, the probe displayed a red-shift in absorption spectra and the fluorescence decreased immediately with the detection limit of 8.0769×10^-7 and 1.0510×10^-9 mol/L, respectively. Other anions gave nearly no interference. Furthermore, Q1-2 was successfully applied to the naked eye identification for cyanide in the visible light and under the UV lamp in food samples and silica gel plates.

A novel sensor molecule 2-hydroxyl-1-naldehyde-N-(4-aminophenyl)-1,8-naphthalimide (H1) based on functionalized naphthalimide Schiff Base derivative was synthesized. H1 was characterized by ¹H NMR, ¹³C NMR and HRMS. Furthermore, its fluorescence properties were studied in dimethyl sulfoxide (DMSO)/H₂O (V:V=7:3) solutions. Its maximum emission wavelength was 496 nm. The solution of H1 has yellow-green fluorescence under the UV lamp (365 nm). H1 showed fluorescence-colorimetric dual channel identification ability for Fe³⁺. With the addition of various metal ions into the H1 solution, only Fe³⁺ caused the fluorescence of the H1 quenching and the color disappeared. Other cations such as Ag⁺, Ca²⁺, Ba²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cu²⁺, Mg²⁺ and Hg²⁺ could not induce similar response. The results of anti-disturbance experiment demonstrated that other cations can not interfere in the detection of Fe³⁺. H1 has good sensitivity for Fe³⁺, the fluorescence and UV-Vis detection limits of the H1 for Fe³⁺ are 3.04×10^-8 and 2.71×10^-6 mol·L^-1, respectively. Finally, the test strips based on the H1 were prepared, which could conveniently and efficiently detect Fe³⁺ in water.

Fluoride ion is an anion with the high electronegativity and the smallest radius. It has important application in all aspects of daily life. In this paper, based on the cleavage of Si-O bond induced by fluoride ions, a novel derivative of perylene B which contains four silicon oxygen bond was designed and synthesized, and this fluorescent chemosensor could recognize F^- with good selectivity and high sensitivity. The probe molecule had a fast response time for F^- and the sensing procedure could be completed in about 1 min, and the detection limit of F^- of the probe molecule B reached 3.5×10^-8 mol·L^-1.

A novel fluorescent "turn-on" probe 7-(dibutylamino)-2'-((2-hydroxybenzylidene)amino)-3-methyl-1-phenyl-1H-spiro[chromeno[2,3-c]pyrazole-4,1'-isoindolin]-3'-one (SCPz-S) with Schiff base structure was designed and synthesized, and characterized by ¹H NMR, ¹³C NMR and high resolution mass spectrometry (HRMS). The UV-Vis and fluorescence spectra were used to investigate the ions recognition capability of probe SCPz-S. It was excavated that the probe SCPz-S has a dual colorimetric and fluorescence response to CN^- in THF/H₂O (V:V=1930:50, 5 mmol/L Tris-HCl, pH=7.4). After adding CN^-, the system of probe SCPz-S will change from colorless to yellow, and fluorescence enhance 1060-fold at 575 nm. The sensor SCPz-S also has good anti-interference ability and a wide pH range from 3 to 12 applicable. Its LOD for CN^- is 1.121×10^-8 mol/L, and the recognition mechanism has been investigated.

Porous organic polymer fluorescence materials have the characteristics of high porosity and outstanding fluorescence properties. The function of fluorescence sensing is given when the skeleton has binding sites with specific analytes, such as nitroaromatic explosives (NAEs), metal ions, anions, gases, organic solvents, etc. In this paper, according to the different types of porous organic polymer materials (POPs), namely the amorphous porous organic polymer materials, crystal porous metal organic framework materials (MOFs) containing coordination bond, and crystal covalent organic framework materials (COFs), the new progress of the POPs fluorescence materials in recent years is reviewed. Especially, the design and synthesis based on functional organic molecules, and their fluorescence sensing applications, are introduced in details. In the future, continuing to design new types of fluorescent COFs from the molecular level is a development direction of highly efficient and recyclable fluorescence chemosensors for detecting NAEs, metal ions, anions, etc.

A novel pH probe 7-(4'-(dimethylamino)benzylidene)-isolongifolanone (DB) was designed and synthesized from isolongifolanone and characterized by ¹H NMR, ¹³C NMR, and MS. The recognition properties of the probe towards H⁺ were investigated by UV-Vis and fluorescence spectroscopy. The results showed that DB exhibited highly selective and sensitive fluorescence response towards H⁺ ion, and the fluorescence intensity decreased linearly in a relatively low range of acidic pH. In addition, the recognition ability of DB towards H⁺ was not affected by various metal ions. The fluorescence intensity of DB had a linear relationship in the acidic pH range of 1.0～3.5, I=174.134pH－47.836, R=0.9936. DB was also sensitive to change in surrounding trifluoroacetic acid (TFA) vapor. Moreover, the pH probe was successfully applied to imaging extreme acidity in HeLa cells.

In recent years, designing and synthesizing fluorescent nanoprobes with good biocompatibility, stable optical properties and low cytotoxicity are research hotspots in the biomedical field. The novel tetraphenylethene-based fluorescent probe (TPE-Rho) was synthesized by reaction of 1,1,2-triphenyl-2-(4-formylphenyl)ethene with 2-(4-oxo-3-phenyl-1,3-thia-zol-2-ylidene)malononitrile. After the aggregation-induced emission (AIE) characteristics of TPE-Rho were investigated, TPE-Rho dots with uniform particle size distribution were obtained through a modified nanoprecipitation method by using Pluronic F-127 (amphiphilic surfactant) as the encapsulation. TPE-Rho dots have excellent optical property such as strong yellow fluorescence, good stability and long Stokes shift (ca. 200 nm), and have little effect on cell growth activity. Then, TPE-Rho dots were utilized to stain live SK-Hep1 cells and LoVo cells, the staining region and fluorescent intensity were analyzed. The experimental results show that TPE-Rho dots have no significant effect on cell viability, and can stain live cells and selectively act on the cytoplasm. Thus, it can be confirmed that TPE-Rho dots has good biocompatibility, low cytotoxicity, high cell membrane permeability, and good stability, therefore it can be used as a viable cell staining agent.

Cdc25B has become the important target for curing cancer owing to its over expression in kinds of cancers. Compounds containing phenanthroline moiety have become research objectives on the DNA fluorescence probes or the new curing agents for their excellent fluorescence property and bioactivities. Twelve novel 1,2,4-triazine scheleton phenanthroling derivatives ARTP1～ARTP12 were first designed and synthesized, the structures of ARTP1～ARTP12 were characterized successfully by means of IR and NMR. The inhibitory activities of ARTP1～ARTP12 against Cdc25B were evaluated. The results show that nine target molecules exhibit excellent inhibitories, four molecules behave better activities than the contrast reference Na₃VO₄ indicating that they may be used as Cdc25B inhibitors. Meanwhile, three novel complexes Co-ARTP-5, Co-ARTP-6 and Co-ARTP-10 were first afforded by the reaction of the excellent inhibitory active compounds ARTP5, ARTP6 and ARTP10 with Co³⁺ respectively. The structures of the three complexes were confirmed through IR, UV-Vis, ¹H NMR and fluorescence spectra. The interaction modes between the complexes and CT-DNA were explored. As a result, the excitation peaks of the complexes show a red shift and the complexes interact with CT-DNA through the insert mode. The binding constants K_b are (2.12±0.20)×10⁵, (3.29±0.20)×10⁵and (1.50±0.20)×10⁵ L·mol^-1, respectively, and it occurs strong fluorescene quenching. The complexes are expected to be the DNA fluorescence probes.

Chiral compounds play an essential role in asymmetric synthesis, biology, medical field and pharmacology. It is necessary to establish fast, sensitive and high enantioselective chiral analysis methods. Chiral sensors, which could determine the absolute configuration and the value of enantiomeric excess of enantiomers, have the advantages of simple, rapid, sensitive and real-time. Herein, the review is focused on the recent progress of chiral fluorescent sensors, circular dichroism sensors, UV-Vis sensors, NMR sensors and MS sensors. Their characteristics, sensing mechanism and applications in chiral recognition are reviewed, and the prospects of chiral sensors are also discussed.

A novel carbazole-based Schiff base derivative L was synthesized and evaluated for the property of selective detection of HSO₄^- ion in aqueous medium. N-(9-Ethyl-carbazol-3-yl)-1-methyl-1-(4-nitrophenyl)-methanimine (L) selectively recognized HSO₄^- ion in CH₃CN-H₂O (V:V=9:1) via the hydrolysis reaction of Schiff bases to elicit a distinct visual colour change from orange to colorless with a significant blue fluorescence under the UV lamp. The fluorescence enhancement phenomenon caused by HSO₄^- ion did not change in the presence of other anions. The sensing mechanism of probe L for HSO₄^- had been investigated by Job's plot, ¹H NMR titration spectra and HRMS spectrum. The detection limit for the HSO₄^- ion was determined as 1.91×10^-8mol·L^-1. The compound L can be used as a highly selective and sensitive colorimetric, and fluorescent turn-on probe for HSO₄^-.

The endoplasmic reticulum, a subcellular organelle, plays an important role in the life activities of mammalian cells. Therefore, visualizing the endoplasmic reticulum, and further examining its active substances, microenvironments and physiological processes have important guiding value for the diagnosis and treatment of related diseases. In recent years, the design and synthesis of endoplasmic reticulum-targetable fluorescent probes have received more and more attentions. Currently, reported endoplasmic reticulum-targetable fluorescent probes mainly include simple endoplasmic reticulum imaging, metal ions, small molecule material, big molecule material, microenvironments, etc. This article summarizes and describes the design and synthesis of the reported endoplasmic reticulum-targetable fluorescent probes, analyzes the application of endoplasmic reticulum fluorescent probes in the study of cellular physiological processes, and prospects the development trend of endoplasmic reticulum-targetable fluorescent probes.

A colorimetric and fluorescent turn-off chemosensor for fluoride based on novel naphthalene-fused boron dipyrromethene (BODIPY) 5 was designed and synthesized. In various anions, only upon addition of fluoride, the UV-Vis absorption peak of probe 5 red-shifted 100 nm, reaching the near infrared (NIR) region. Thus, it can be used as naked-eye detector for fluoride ion. In the fluorescence test, upon addition of fluoride, the fluorescence of probe 5 quenched significantly. Confocal fluorescence microscopy experiments demonstrate that 5 can be used for monitoring fluoride in living cells.

A new turn-off probe 6 was synthesized from bis(pyridin-2-ylmethyl)amine and truxene derivatives, and its structure was confirmed by ¹H NMR and HRMS. The recognition behaviors of 6 to various metal ions were investigated and the results show that 6 exhibited good selectivity and high sensitivity to Cu²⁺ and Ni²⁺ with good anti-interference. The probe 6 presented apparent fluorescence quenching in DMF/H₂O (V/V=8/2, pH=7.0) solution toward Cu²⁺ and Ni²⁺. HRMS analysis showed a 1:1 binding stoichiometry between 6 and Cu²⁺ or Ni²⁺. The detection limit for Cu²⁺ and Ni²⁺ was calculated to be 28 and 41 nmol/L, respectively. The detection limit of 6 for Cu²⁺ and Ni²⁺ was far lower than the maximum allowable level of World Health Organization (WHO) limit for drinking water.

Nitroxyl (HNO), which is the one-electron reduced and further protonated form of nitric oxide, plays important biological functions. A lysosome-targeted dual-photon HNO fluorescent probe (Lyso-HNO), which contains 4-(2-amino-ethyl)morpholine as lysosomal-targetable groups, 1,8-naphthalimide as two-photon fluorophore and triphenylphosphine as HNO reaction site, was synthesized and characterized. The recognition behaviors of Lyso-HNO to HNO were investigated. The results showed that Lyso-HNO exhibited good selectivity and sensitivity to HNO with fast response,. and the detection limit of Lyso-HNO to HNO was estimated to be 202 nmol·L^-1. The probe can be applied to bioimaging exogenous lysosomal HNO by two-photon fluorescence confocal microscopy.

Aerogel is a kind of gel materials, of which the fluid phase is gas. Aerogel has the characteristics of low density and high porosity, and has a wide application prospects. In this work, a rapid solvents exchange method was developed, and using in-situ secondary extraction, rapid solvents exchange in aerogel preparation was achieved through the miscibility and immiscibility of ethanol-dichloromethane-water. Combined with hydrophobic treatment and vacuum drying, hydrophobic silica aerogel was obtained. The aerogel had a low density and a contact angle with water of 155.8°. The aerogel can load various organic fluorescent probe dyes, which can effectively avoid the fluorescence quenching caused by the aggregation of the probe molecules, which it will expand the practical application range of the organic fluorescent probes in wider fields.

Reactive nitrogen and reactive oxygen are chemical substances with strong biological activity. In human cells, peroxides can be generated due to enzymatic or non-enzymatic processes. Abnormal levels of peroxide can cause oxidative damage and aging and various diseases such as cardiovascular disease, neurological diseases, Alzheimer's disease, Parkinson's disease and even cancer. In order to effectively cure these diseases, health workers must find the source of the problem. Currently, there is no better way to detect reactive oxygen species and reactive nitrogen. Fluorescence spectrometry in recent years becomes the preferred method for the majority of researchers for detecting active oxygen and reactive nitrogen. Therefore, the development of selective recognition and high sensitivity molecular fluorescent probes to achieve effective detection of reactive nitrogen and reactive oxygen species is of great significance. On one hand, molecular fluorescent probe detecting and imaging technology has excellent characteristics such as high sensitivity, strong selectivity, small damage and good cell compatibility. On the other hand, fluorescent probes play an important role in the pathophysiological process of reactive nitrogen and reactive oxygen species. Therefore, the fluorescent probe method is widely used in the fields of biology and medicine. However, due to the inherent specificity of reactive nitrogen and reactive oxygen species, it has become an urgent problem for researchers, such as high reactivity, short cycle, etc. In order to overcome the shortcomings of fluorescent probe analysis, researchers are constantly striving to find better active fluorescent probes for the detection of reactive nitrogen and reactive oxygen species. Recent evolutions in the development of molecular fluorescent probes for the detection of active nitrogen and reactive oxygen species and cell imaging work are reviewed. Finally, a new type of molecular fluorescent probe is proposed to be used for the challenge of active nitrogen and active oxygen detection, and the future development direction and prospect.

A 3-hydroxyflavonoid esters HFBA was synthesized by the reaction of 2-hydroxyacetophenone with p-methyl benzaldehyde, and its structure was characterized by NMR and high resolution mass spectrometer. The recognition behaviors of HFBA to hydrazine were investigated and the results show that HFBA exhibits good selectivity and sensitivity to N₂H₄ with fast response and good anti-interference ability in DMSO/PBS buffer (pH=7.4). Furthermore, the detection limit of HFBA for hydrazine was estimated to be 0.11 μmol/L, and the probe HFBA was successfully applied for the imaging of hydrazine in living cells.

Sulfhydryl compounds, such as cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and so on, play an important role in the normal human physiological processes. Molecular fluorescent probes have attracted much attention of scholar in the detection of sulfhydryl compounds, since it has the advantage of good selectivity, high sensitivity, good biocompatibility and real-time in situ monitoring. At present, the design of thiol-based fluorescent probes is mainly based on the strong nucleophilicity of sulfhydryl groups. In this paper, the synthesis of fluorescent probes for detecting sulfhydryl compounds, which was reported from 2013 to 2018, is reviewed based on the different mechanism of the reaction between fluorescence probe and sulfhydryl, including Michael addition, cyclization of aldehyde groups, sulfonamides or sulfonates of the lysis, natural chemical linkage and so on. The detection limit of the probe, response time, equivalence ratio were elaborated.

Endoplasmic reticulum (ER) is an important organelle in eukaryotic cells and participates in the synthesis and secretion of various proteins, glycogen, lipids, and cholesterol substances. It is surrounded by a single membrane in the cytoplasm, which is a three-dimensional mesh structure formed by flat cysts, membrane tubes, and bubbles. Research on the physiological morphology of ER can facilitate the resolution of certain metabolic diseases. Due to the good optical properties and outstanding specific localization, fluorescent probe technology has been widely used in structural investigation and activity tracking of organelles. The ER fluorescent probes can be divided into two types, one is a single functional ER localization probe, the other is a multi-functional ER probe, which has multiple functions of locating and detecting active species in ER, the morphology and environment of ER. In this article, the structure, function and biological application of ER fluorescent probes in recent years are summarized and reviewed. Various localization mechanisms of ER fluorescent probes are described. The development trend of ER fluorescent probes in life science research is prospected.

Fluorescence detection based on excited state intramolecular proton transfer (ESIPT) using reaction-based probes has attracted considerable attention in the scientific community as they offers promising advantages, including high selectivity, high sensitivity and large Stoke shift. The representative examples of design strategies, mechanism of actions, existing challenges and future developments for reaction-based ESIPT fluorophores reported in the last ten years are reviewed.

A novel benzimidazole-hydrazone derivative,N'-(2-hydroxy-1-naphthyl)methylene-2-[2-(4-methylphenylsulfonyl-methyl)-1H-benzoimidazol-1-yl]acetohydrazide (L), was synthesized and characterized by IR, ¹H NMR, ¹³C NMR, HRMS and elemental analysis. The recognition properties of L for anions were studied by naked eye, ultraviolet-vis and fluorescence spectroscopy. The results showed that the color of the solution changes from colorless to bright yellow upon addition of F^-, AcO^- and H₂PO₄^- to the CH₃CN solution of compound L. The solution of L emitted yellow fluorescence after the addition of F^- and AcO^- under the UV lamp (λ=365 nm). It indicated that compound L can be used as a probe for the naked eye to recognize F^-, AcO^- and H₂PO₄^-. The experimental results of UV and fluorescence spectroscopy showed that the probe L can recognize F^- and AcO^- with high selectivity and sensitivity. The binding constants (K_a) of probe L to F^- and AcO^- were 4.25×10³ and 2.96×10⁴ L·mol^-1, respectively. The detection limits (DL) were 3.63×10^-7 and 8.51×10^-8 mol·L^-1, respectively. The stoichiometry of complexation between L and F^-/AcO^- was 1:1, which was supported by the Job's plot and density functional theory (DFT) calculations. The mechanism of binding of L with F^-/AcO^- was established by ¹H NMR titration. The results showed that compound L can be used as a colorimetric and fluorescent probe for detecting F^- and AcO^-.

Trivalent chromium (Cr³⁺) plays an important role in the metabolismof fats, nucleic acids, carbohydrates and proteins. Moreover, Cr³⁺ is considered to be a carcinogen and is extremely harmful to humans. Therefore, Cr³⁺ fluorescent probe L was synthesized by reaction of 8-hydroxyquinolinaldehyde with thiocarbazone. The probe L showed high selectivity towards Cr³⁺ ion through the color of solution changed from colorless to yellow for naked-eye detection and significant fluorescence intensity enhanced in CH₃CN/H₂O (V:V=1:2, Tris buffer 50 mmol/L, pH=7.3) solution. The 1:1 binding stoichiometry between probe and Cr³⁺ was determined from Job's plot, fluorescence titration, ESI-MS and density functional theory (DFT) calculations. The association constant (K_a) and the detection limit for Cr³⁺ were found to be to be 1.00×10⁵ and 2.85×10^-7 mol/L, respectively. Moreover, bioimaging experiments showed that L could sense Cr³⁺ ion in living cells with a fluorescence enhancement signal.

Cyanide ion has strong toxicity for mammals, because it can affect many normal function of body, such as blood vessels, visual, as well as central nervous system, heart, endocrine and metabolic system. In addition, the cyanide salts are widely used in the production of human life, especially in electroplating and plastic manufacturing, mining, gold and silver leather industry, metallurgy, etc., which resulting in the pollution of environment. Therefore, the artificial cyanide selective receptor or fluorescent sensor has attracted widely attention in the field of anionic recognition. Due to the advantages of simple synthesis method, low cost, fast response, colorimetry and/or fluorescence change before and after reaction with cyanide, chemical sensors have been deeply studied by many researchers in the past decades. Based on the reaction of cyanide ions in different media, the research progress of cyanide sensors is summarized since 2010 from four aspects:(1) identification of cyanide in pure organic phase, (2) identification of cyanide ions in aqueous media, (3) identification of cyanide ions in pure water phase, and (4) identification of cyanide ions in solid phase. These sensors for cyanide in solution and solid material test and detect cyanide by naked eyes, which realizes the convenient, fast and real-time detection of cyanide in environmental and food samples.

Hydrazine (N₂H₄) is a highly toxic biochemical reagent with the capability of mutagenic, teratogenic and carcinogenic. For accurately monitoring the concentration of N₂H₄ in the environment and life, two FRET (fluorescence resonance energy transfer)-based dual-emissive ratiometric fluorescent probes (FRET-1/2) were designed and synthesized. The structures of both probes were charactered by ¹H NMR, ¹³C NMR and HRMS. The results prove that both probes exhibit good selectivity and sensitivity to N₂H₄ and can be used for detecting N₂H₄ in water samples.

2-(1'-Acetyl-ferrocenyl) benzothiazole (FcSO) probe was synthesized by the acetylization reaction of 2-ferrocenyl benzothiazole, which was obtained from the cyclization reaction of ferrocenecarboxaldehyde with 2-aminothiophenol. Crystal and molecule structures of FcSO probe were characterized by spectra methods and X-ray single crystal diffraction analysis. The recognition ability to Al³⁺, Cr³⁺, Fe³⁺ ions of FcSO probe was researched by three analytical methods of UV-Vis, fluorescence and electrochemistry. The results show that the recognition to Al³⁺, Cr³⁺, Fe³⁺ ions of FcSO probe is effective via three channels, and the detection limits of FcSO probe to Al³⁺, Cr³⁺, Fe³⁺ ions are 7.456×10^-6, 3.72×10^-6 and 1.35×10^-5 mol/L, respectively. ¹H NMR research results indicate that the acetyl, ferrocenyl and benzothiazole groups of FcSO probe play important roles in recognizing Al³⁺, Cr³⁺, Fe³⁺ ions.

The multifunctional fluorescent probes can detect a plurality of anions and cations or other small molecules. These probes can greatly improve the detection efficiency and reduce the analysis cost with respect to the mono-analyte fluorescent probes. Thus, they have attracted much attention in recent years. According to their molecular structural characteristics, the reported multifunctional fluorescent probes are divided into three types as organic small molecules, polymers and metal-organic complexes. The new progress on their molecular design, synthesis and detecting application is reviewed on the viewpoint of sensing objects and performances. The developing potential of multifunctional fluorescent probes is envisioned also, and the probes capable of simultaneously identifying multiple analytes in the same system should be highlighted in the future