It is crucial for cell physiology to keep the homeostasis of pH, and it is highly demanded yet challenging to develop luminescence resonance energy transfer (LRET)-based near-infrared (NIR) ratiometric luminescent sensor for the detection of pH fluctuation with NIR excitation. As promising energy donors for LRET, upconversion nanoparticles (UCNPs) have been widely used to fabricate nanosensors, but the relatively low LRET efficiency limits their application in bioassay. To improve the LRET efficiency, core/shell/shell structured β-NaGdF4@NaYF4:Yb,Tm@NaYF4 UCNPs were prepared and decorated with hemicyanine dyes as an LRET-based NIR ratiometric luminescent pH fluctuation-nanosensor for the first time. The as-developed nanosensor not only exhibits good antidisturbance ability, but it also can reversibly sense pH and linearly sense pH in a range of 6.0–9.0 and 6.8–9.0 from absorption and upconversion emission spectra, respectively. In addition, the nanosensor displays low dark toxicity under physiological temperature, indicating good biocompatibility. Furthermore, live cell imaging results revealed that the sensor can selectively monitor pH fluctuation via ratiometric upconversion luminescence behavior.

•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

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 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

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.

•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.

•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.

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 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.

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 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.

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+.

A multifunctional fluorescent chemosensor for Al3+ and Cu2+ has been developed, which displays a dual-model and on–off fluorescence response upon addition of Al3+ and Cu2+ respectively. The fluorescence signals of the chemosensor can be restored with F− and ethylenediaminetetraacetic acid (EDTA) disodium for Al3+ and Cu2+, showing that the binding of the chemosensor and Al3+/Cu2+ is chemically reversible. The ‘in situ’ prepared Al3+ complex (1·Al) showed high selectivity toward F−, which can be applied to distinguish F− from Cl−, Br− and I−. Moreover, the fluorescence emission intensity of the ‘in situ’ prepared Cu2+ complex (1·Cu) is increased with the addition of Al3+, demonstrating that 1·Cu could be a good off–on Al3+ sensor candidate.

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+.

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.