•A hemicyanine sensor was synthesized for the ratiometric detection of pH fluctuation.•The linear reversible ratiometric response ranges from pH 7.0 to 8.8 and 6.0 to 9.0.•pH fluctuation was tracked via fluorescence imaging with low dark toxicity.It is highly demanded and challenging to develop small-molecular fluorescent sensors for the ratiometric detection of pH fluctuation. A ratiometric fluorescent pH sensor was constructed by integrating a pH-sensitive fluorophore with a pH-insensitive hemicyanine group. Its linear and reversible ratiometric fluorescent response from pH 7.0 to 8.8 and 6.0 to 9.0 respectively makes this sensor suitable for the practical tracking of pH fluctuation in live cells. With this sensor, stimulated pH fluctuation has been successfully tracked in a ratiometric manner via fluorescence imaging with low dark toxicity.With a ratiometric fluorescent pH sensor, stimulated pH fluctuation has been successfully tracked in a ratiometric manner via fluorescence imaging with low dark toxicity.

It is significant to develop probes for rapid, selective, and sensitive detection of highly toxic hydrazine in both environmental and biological science. In this work, under mild conditions, through the electrostatic attraction between negatively charged CDs and positively charged hemicyanine molecules, a novel ratiometric fluorescent probe containing CDs and a hemicyanine derivative was fabricated for reliable, selective, and sensitive sensing of hydrazine. This nanohybrid system possesses dual emission peaks at 550 and 610 nm under a single excitation wavelength of 530 nm. The addition of hydrazine to CDs–hemicyanine nanohybrid solution results in complete fluorescence quenching of the hemicyanine derivative, while the orange fluorescence of CDs remains constant. Furthermore, the CDs–hemicyanine nanohybrid system shows high selectivity toward hydrazine over other various species, including some nucleophilic species, metal ions and anions. The limit of quantification (LOQ) was 0–1 mM and the detection limit was as low as 8.0 μM.

It is significant for cell physiology to keep the homeostasis of pH, and it is highly demanded to develop ratiometric fluorescent sensors toward pH. In this work, under mild condition, through the electrostatic interaction between carbon nanodots (CDs) and organic molecules, two novel ratiometric fluorescence hybrid nanosensors were fabricated for sensing acidic pH. These nanohybrid systems possess dual emission peaks at 455 and 527 nm under a single excitation wavelength of 380 nm in acidic pH condition. With the increasing of pH, the fluorescence of the 1,8-naphthalimide derivative completely quenches, while the blue fluorescence of CDs keeps constant. Furthermore, the CDs−organic molecular nanohybrids exhibit excellent anti-disturbance ability, reversible pH sensing ability, and a linear response range in wide pH range respectively. Besides the ability to target lysosome, with one of the nanosensor, stimulated pH change has been successfully tracked in a ratiometric manner via fluorescence imaging.Download high-res image (127KB)Download full-size imageUnder mild condition, through the electrostatic interaction between carbon nanodots (CDs) and organic molecules, two novel ratiometric fluorescence hybrid nanosensors were fabricated for sensing acidic pH. The ability to target lysosome, with one of the nanosensor, stimulated pH change has been successfully tracked in a ratiometric manner via fluorescence imaging.

•A highly selective fluorescent probe for hydrazine shows off-on property.•The probe can quantitatively detect hydrazine in the concentration range from 0 to 20 μM.•The detection limit on fluorescence response of the probe can be as low as 140 nM.It is crucial to develop highly sensitive and selective probes toward hydrazine because it is a class of highly toxic and pollutant compound. Herein, using fracture of carbon carbon double bond and dissociation of amide by hydrazine, a novel off-on fluorescent probe was developed for hydrazine. The probe can quantitatively detect hydrazine in concentration range from 0 to 20 μM with the LOD of 140 nM. Further, it displayed excellent selectivity and anti-interference ability over many neutral molecules, metal ions, anions, and biological species. The ability to target lysosome and the response of hydrazine to this probe in a living cell was successfully tracked via fluorescence imaging.It is crucial to develop highly sensitive and selective probes toward hydrazine because it is a class of highly toxic and pollutant compound. Herein, using fracture of carbon carbon double bond and dissociation of amide by hydrazine, a novel off-on fluorescent probe was developed for hydrazine. The probe can quantitatively detect hydrazine in concentration range from 0 to 20 μM with the LOD of 140 nM. Further, it displayed excellent selectivity and anti-interference ability over many neutral molecules, metal ions, anions, and biological species. The response of hydrazine to this probe in a living cell was successfully tracked via fluorescence imaging.Download high-res image (123KB)Download full-size image

•A colorimetric and ratiometric fluorescent probe was synthesized for hydrazine.•The limit of quantification (LOQ) value was 0–120 μM.•The detection limit could be as low as 1.6 μM.•The probe displays little dark toxicity under physiological temperature.It is significant to develop probes for rapid, selective, and sensitive detection of the highly toxic hydrazine in both environmental and biological science. In this work, under mild condition, a novel colorimetric and ratiometric fluorescent probe (probe 1) was synthesized. Probe 1 with a chemoselective reaction mediated by hydrazine in which the diethyl malonate moiety was transformed into an aldehyde group exhibited high sensitivity and good selectivity in hydrazine recognition. Probe 1 can quantitatively detect hydrazine in concentration range from 0 to 120 μM with the LOD of 1.6 μM. Further, it displayed good selectivity and anti-interference over many species including some nucleophilic species, anions and metal ions. The ratiometric fluorescence change of this probe upon addition of hydrazine in living cells has been successfully demonstrated. Furthermore, the probe displays low dark toxicity under physiological temperature.The ratiometric fluorescence change of the probe upon addition of hydrazine in living cells has been successfully demonstrated and displays little dark toxicity under physiological temperature.Figure optionsDownload full-size imageDownload high-quality image (120 K)Download as PowerPoint slide

•A Cr3+ selective fluorescent “off-on” and lifetime-based chemosensor was synthesized.•The chemosensor was capable of quantitatively detect the concentration of Cr3+ by a dramatically enhanced fluorescence.•The 'in situ' prepared Cr3+ complex showed high selectivity and sensitivity toward S2−.•The calculated low detection limit (LOD) value is as low as 307 nM for S2−.•The lifetime changed from 4.95 to 4.89 ns upon the addition of Cr3+, and further increased to 5.88 ns upon addition of S2−.A novel 1,8-naphthalimide-based chemosensor was designed and synthesized for rapid recognition of Cr3+. The desired sensor showed off-on fluorescent and lifetime-based response upon Cr3+ and S2− in solution, on test paper and in cells. With the intensity-based method, the limit of quantification (LOQ) value was 0–5.5 × 10−5 M and the detection limit could be as low as 0.60 ppm. The 'in situ' prepared Cr3+ complex can recognize S2− among a series of common anions with high selectivity and sensitivity, the LOD can be as low as 307 nM. The lifetime of the sensor changes from 4.95 to 4.89 and further to 5.88 ns upon addition of Cr3+ and S2− in turn.The fluorescence and lifetime change of the chemosensor and the 'in situ' prepared Cr3+ complex upon addition of Cr3+ and S2− on test paper and in living cells have been successfully demonstrated.

Based on 8-hydroxyquinoline, a 1,8-naphthalimide-derived colorimetric and fluorescent probe was synthesized for naked-eye and fluorescent recognition of F− (from both tetrabutylammonium fluoride and NaF) with high sensitivity and excellent selectivity. The probe can be employed to detect F− quantitatively within certain concentration range, and the detection limit could be as low as 1.8 μM for tetrabutylammonium fluoride and 9 μM for NaF. With this probe, the tests for fluorine contents in tap water, water sample from Eyebrow Lake and several brands of toothpastes were successfully performed.Based on 8-hydroxyquinoline, a 1,8-naphthalimide-derived probe was synthesized for F− (from tetrabutylammonium fluoride and NaF) naked-eye and fluorescent recognition with high sensitivity and excellent selectivity, the detection limit could be as low as 1.8 μM for tetrabutylammonium fluoride and 9 μM for NaF.

•The nano film showed sensitivity and selectivity toward Fe3+ and further toward PPi.•The film shows a distinct color change from colorless to pink.•The sensor can detect Fe3+ quantitatively in concentration range of 100–2000 μM.•The calculated low detection limit (LOD) value could be 1.19 μM for Fe3+.•The intensity at 564 nm linearly decreases with PPi concentration from 50 to 3000 μM.•The calculated low detection limit value is 1.75 μM for PPi.Novel rhodamine and quinoline-functionalized nano film was prepared by copolymerization and electrospinning. Propenyl monomer of rhodamine and quinoline was synthesized and then copolymerized with methyl methacrylate via solution polymerization. This prepared copolymer was electrospun into nano film, as a solid-state sensor, which exhibits highly selective recognition of Fe3+ ions over various environmentally and biologically relevant metal ions and anions with a distinct color change from colorless to pink in very fast response time (<1 min). The sensor can detect Fe3+ quantitatively in concentration range of 100–2000 μM, and the calculated low detection limit (LOD) value could be 1.19 μM for Fe3+. As the resultant product, the Fe3+-contaminated nano film showed recovered color change by extra addition of pyrophosphate P2O74− (PPi) solution. It was found that the absorption intensity at 564 nm of the Fe3+-contaminated nano film linearly decreases with PPi concentration from 50 to 3000 μM with LOD value of 1.75 μM. In addition, both the nano films before and after Fe3+-contaminating are reusable for the detection of Fe3+ and PPi, respectively.Novel rhodamine-functionalized electrospun film was synthesized and utilized as colorimetric chemosensor for Fe3+ and further for PPi for the first time. This prepared copolymer was electrospun into nano film, as a solid-state sensor, which exhibits highly selective recognition of Fe3+ ions with a distinct color change from colorless to pink in very fast response time (<1 min). As the resultant product, the Fe3+-contaminated nano film showed recovered color change by extra addition of PPi solution.

Vesicles of a noncovalent dumbbell-shaped amphiphilic triblock copolymer were formed by self-assembly of host-guest inclusion between β-cyclodextrin containing poly(ethylene oxide) (β-CD-PEO) and adamantyl group containing polystyrene (AD-PS-AD) in solution. Addition of water into the copolymer resulted in the formation of new bowl-shaped and vesicle morphologies by adjusting not only ratio of solvents (THF dioxane or DMF) but also the length of the PS middle block in the guest polymer, which was ascribed to the large compound micelles (LCMs). The continuous phase of PS was composed of an assembly of reversed micelles (PEO core and PS corona) with hydrophilic PEO chains surrounding the structure at the polymer/aqueous solution interface in the larger compound micelles.

It is important to develop probes for rapid, selective, and sensitive detection of highly toxic benzenethiols in both environmental and biological science. In this work, based on the selective cleavage reaction by benzenethiols under mild conditions, a novel naphthalimide-based fluorescent probe was designed and synthesized for the rapid recognition of benzenethiols with excellent selectivity and anti-interference over other various species including some nucleophilic species, aliphatic thiols, anions and metal ions. The limit of quantification (LOQ) value was 0–4.0 μM and the detection limit could be as low as 10.3 nM. The fluorescence enhancement of this probe upon addition of benzenethiol on test paper and the application of the probe for selective detection in water samples and living cells have been successfully demonstrated.

A novel naphthalimide-based fluorescent probe was designed and synthesized for thiol recognition with high sensitivity and excellent selectivity. The probe can detect thiol quantitatively in a concentration range of 0–6.0 μM and the detection limit could be as low as 1.6 nM. The fluorescence enhancement of this probe upon addition of Cys on test paper and the application of the probe for selective detection of intracellular Hcy, GSH and Cys have been successfully demonstrated.

Based on 1,8-naphthalimide, a novel multifunctional colorimetric and fluorescent probe was designed and synthesized for basic pH and F− naked-eye and fluorescence recognition with high sensitivity and excellent selectivity. The probe can detect F− quantitatively in a concentration range of 0–16.7 μM and 0–20 μM in different methods, and the detection limit could be as low as 25 nM for F−. The detection of F− on chromatography plates and the preliminary application of the probe to detect fluoride contents in toothpaste have been successfully demonstrated.

A mononuclear zinc complex is shown to act as a highly selective naked-eye-based chemosensor for pyrophosphate (PPi) in aqueous solution. Based on the keto–enol transformation process, addition of PPi made the color of the sensor complex change from red to colorless. Moreover, electrospun nanofibers from the mononuclear zinc complex could detect PPi on site and in real-time and the color of the nanofibers changes rapidly after they were immersed in an aqueous solution of pyrophosphate.

Previous reports of fluorescent sensors for alcohols based on charge-transfer character of their excited state are based on mono-, di-, and tetra-phosphonate cavitands, which are capable of selecting analytes through shape/size selection and various specific H-bonding, CH−π, and cation–dipole interactions. To contrast, color changes based on absorption properties of the ground state are more suitable for direct observation with the naked eye. Three sensitive and selective colorimetric sensors for C1–C4 alcohols have been developed on the basis of alcohol-mediated ground-state intramolecular proton transfer. Reverse proton transfer induced by water achieves a fully reversible reaction. In addition, the solvent color indicates alcohol concentration.

•Two colorimetric and off–on fluorescent rhodamine-based sensors were synthesized.•The sensors display high selectivity towards Al3+ and Cu2+ with only minimal interference from other ions.•The detection mechanism involves a ring-opening process as a consequence of metal complex formation.•The binding of sensors and metal ions is chemically reversible with F− or EDTA.Based on Rhodamine B, two Al3+/Cu2+-selective chemosensors were synthesized, which display a high selectivity for Al3+ and Cu2+ among environmentally and biologically relevant metal ions. A 1,8-Naphthyridine modified rhodamine derivative can detect Al3+ in ethanol with off–on fluorescence behavior, and detect Cu2+ in aqueous solution with colorimetric method. The 8-Hydroxyquinoline-based rhodamine sensor can detect Al3+ in ethanol with both off–on fluorescence and colorimetric methods. The detection mechanism involves a ring-opening process as a consequence of metal complex formation. Job's plots and a time-of-flight mass spectral study indicated that each chemosensor chelated Al3+/Cu2+ with 1:1 stoichiometry. The binding of the chemosensors and Al3+/Cu2+ is chemically reversible by the addition of F−/EDTA solution, respectively.

Compared with other fluorescent probes, ratiometric fluorescence responses are more attractive because the ratio between the two emission intensities can be used to measure the analyte concentration and provide a built-in correction for environmental effects. A highly selective and sensitive ratiometric fluorescent probe for Fe3+ was synthesized, which exhibits an enhanced fluorescence with a large red-shift in emission from 361 to 455 nm upon addition of Fe3+. The red-shift of the emission peak can be ascribed to the reformed orbital, and the increase of emission intensity may be ascribed to the inhibition of the rotation of C–C bonds between each two aromatic rings.Graphical abstractA highly selective and sensitive ratiometric fluorescent probe for Fe3+ was synthesized, which exhibits an enhanced fluorescence with a large red-shift in emission from 361 to 455 nm upon addition of Fe3+. Highlights► A ratiometric fluorescent probe for Fe3+ was synthesized. ► The probe exhibits an enhanced fluorescence with a red-shift upon addition of Fe3+. ► Inhibition of the rotation of C–C bonds was possible detection mechanism for Fe3+.

Multilayer films composed of azide-functional polymer and polyphenylene dendrimer-stabilized gold nanoparticles with alkynes in their peripheries have been fabricated using a layer-by-layer (LBL) approach via “click” chemistry. This method permits facile covalent linking of the polymer/nanoparticle interlayers in the mixture of DMF and water, which provides a general and powerful technique for preparing uniform nanoparticle (NP) thin films. The deposition process is linearly related to the number of bilayers as monitored by UV–vis spectroscopy. The multilayer structure and morphology have been characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle.

A highly fluorescent chemosensor based on 1,8-naphthyridine with high sensitivity and selectivity toward Ni2+/Cu2+ over other cations both in aqueous solution over a wide pH range (4–10) and in cellular environments was developed. Counteranions such as acetate, sulfate, nitrate, and perchlorate have no influence on the detection of such metal ions. Ethylenediamine showed high selectivity toward the in situ-prepared Cu2+ complex over the Ni2+ complex, which can be applied to distinguish Ni2+ and Cu2+. The Ni2+-induced fluorescence on–off mechanism was revealed to be mediated by intramolecular charge transfer from the metal to the ligand, while that by Cu2+ involves intramolecular charge transfer from the ligand to the metal, as confirmed by picosecond time-resolved fluorescence spectroscopy and time-dependent density functional theory calculations.

A fluorescent color/intensity changed fluoranthene derivative chemosensor for Fe3+ has been prepared and confirmed by 1H-NMR, 13C-NMR, HRMS, and crystal data, which displays a high selectivity and antidisturbance for Fe3+ among environmentally and biologically relevant metal ions. Fluorescence studies show that fluorescent emission peak blue shifts about 100 nm with fluorescent intensity enhancing 75-fold, indicating a Fe3+-selective dual-emission behavior. Further study demonstrates the detection limit on fluorescence response of the sensor to Fe3+ is down to 10−7 M range. The fluorescence signals of chemosensor can be restored with o-phenanthroline, showing the binding of chemosensor and Fe3+ is really chemically reversible.Highlights► A fluorescent color/intensity fluoranthene-based chemosensor for Fe3+ is described. ► Compound 3 shows blue shift about 100 nm, intensity indicates 75-fold enhanced. ► Detection limit is down to 10−7 M range. ► Compound 3 can detect Fe3+ ions through dual-emission fluorescent behavior. ► The fluorescence signals can be restored with o-phenanthroline.

A pyrene derivative has been synthesized as a visible light excitable fluorescent chemodosimeter which exhibits “on–off” and “green–red” fluorescence behavior for Ni2+ and Pb2+ with different reaction speed, respectively, and its sensing ability toward metal cations and counter ions was investigated in detail. The high selectivity of the ‘in situ’ prepared Ni2+ and Pb2+ complexes toward EDA and the reaction speed difference provide two new effective methods for distinguishing between Ni2+ and Pb2+.

Water-soluble starlike polymers containing concentrated carboxyl groups were conveniently synthesized via the combination of “click” chemistry and atom transfer radical polymerization. The starlike polymer was composed of a shorter polyacrylate main chain and longer poly(acrylic acid) side chains. Alkyne and azide groups were introduced to the structure units of the main chain by esterification and the chain end of the side chain by substitution reaction of NaN3 to bromine, respectively. By click chemistry between alkyne and azide group, well-defined starlike polymers were obtained. FT-IR, gel permeation chromatography, and 1H NMR were used to characterize the resulting polymers. Aggregation behavior demonstrated by transmission electron microscopy was observed when the starlike polymers were dispersed in water at pH 7.0–7.5. Using the starlike polymers as templates, water-soluble silver nanoclusters mainly consisting of Ag2 supported by the generated nanoparticles and carboxyl groups were successfully synthesized. Also, their optical properties and morphology were characterized by UV–vis absorption spectra and TEM.

An “off-on” Zn2+ and “on-off” Cu2+ fluorescent chemosensor C was designed and synthesized. The binding of C and Zn2+/Cu2+ is chemically reversible by the addition of EDTA disodium solution; moreover, the fluorescence emission signal of ZnC decreased with the addition of Cu2+, demonstrating that ZnC could detect Cu2+via metal displacement.

A fluoranthene based fluorescent chemosensor 2-(7,10-diphenyl-fluoranthen-8-yl)-pyridine (B) which shows excellent selectivity towards Fe3+ is described. Upon addition of FeCl3 into the ethanol solution of B, it exhibits a great decrease of emission intensity against environmental and biological samples. Further experiments demonstrate that Fe(NO3)3 has the similar influence as FeCl3 on the emission spectra of B while Fe2(SO4)3 has no influence on that of B.Fluorescent chemosensor B shows excellent selectivity towards Fe3+, no fluorescence change was found even when the amount of these alkali and alkaline earth metal ions was at a high concentration of 6 mM.Highlights► A fluoranthene-based fluorescent Fe3+-chemosensor B is synthesized. ► B can detect Fe3+ against competing metal ions through ON–OFF fluorescent behavior. ► Either Fe(NO3)3 or FeCl3 can quench the emission of B while Fe2(SO4)3 cannot.

An “off-on” Zn2+ and “on-off” Cu2+ fluorescent chemosensor C was designed and synthesized. The binding of C and Zn2+/Cu2+ is chemically reversible by the addition of EDTA disodium solution; moreover, the fluorescence emission signal of ZnC decreased with the addition of Cu2+, demonstrating that ZnC could detect Cu2+via metal displacement.

It is important to develop probes for rapid, selective, and sensitive detection of highly toxic benzenethiols in both environmental and biological science. In this work, based on the selective cleavage reaction by benzenethiols under mild conditions, a novel naphthalimide-based fluorescent probe was designed and synthesized for the rapid recognition of benzenethiols with excellent selectivity and anti-interference over other various species including some nucleophilic species, aliphatic thiols, anions and metal ions. The limit of quantification (LOQ) value was 0–4.0 μM and the detection limit could be as low as 10.3 nM. The fluorescence enhancement of this probe upon addition of benzenethiol on test paper and the application of the probe for selective detection in water samples and living cells have been successfully demonstrated.