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

•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.

In our work, we investigated the interactions between a small molecule, folic acid, and biological cells through the interaction of folic acid and folate receptors using a laser scanning confocal imaging-surface plasmon resonance (LSCI-SPR) system. The changes of SPR peaks and cell concentration had good linear relationships, and fluorescence imaging provided further data. The detection limit was as low as 1.0 × 103 cells per mL, and linear coefficients were 0.95206, 0.95454, 0.94287, 0.98711, and 0.99228 for mouse lymphoma (L5178Y TK+/−) cells, mouse lymphoma (EL4) cells, mouse T lymphocytes (Cl.Ly 1+2−/9) cells, human lung cancer (A549) cells, and human oral epidermis carcinoma (KB) cells, respectively. The results indicated that the LSCI-SPR system has potential future application in analyzing small molecule–biological cell affinity and in acquiring quantitative parameters.

•Based on ESIPT and PET mechanisms, a novel fluorescent probe has been developed.•In aqueous solution, the probe displays high sensitivity and good selectivity to H2S.•This probe has been successfully applied to detect intracellular H2S in living cellsThe O-2,4-dinitrobenzensulfonate of 1,3-bis(bispyridin-2ylimino)isoindolin-4-ol has been developed as a novel red-emitting fluorescent probe for the detection of H2S. The dinitrobenzenesulfonate moiety in the probe both prohibits the excited state intramolecular proton transfer process and produces a photo-induced electron transfer process, which renders the probe non-fluorescent in the absence of the analyte. In the presence of H2S a specific H2S-mediated cleavage reaction converts the probe into 1,3-bis(bispyridin-2-ylimino)isoindolin-4-ol which exhibits a strong red fluorescence with a large Stokes shift (218 nm) via an excited state intramolecular proton transfer process upon excitation. It's noteworthy that this new probe shows good selectivity and sensitivity to H2S over glutathione, cysteine and homocysteine. Moreover successful detection and imaging of intracellular H2S in living cells was achieved. To our knowledge this is the first application of this type of fluorescent probe for intracellular H2S detection.Utilizing 2,4-dinitrobenzensulfonyl unit (DNBS) as a recognition group, a novel red-emitting fluorescent probe, BPI-DNBS, was developed for the selective detection of H2S with a 218 nm Stokes shift. It's noteworthy that this H2S fluorescent probe displays a good selectivity against biothiols, which makes it successful to image intracellular H2S in living cells.

A novel red (λmaxem = 632 nm) fluorescent probe based on 3-hydroxyflavone was designed and synthesized for thiol recognition with high sensitivity and excellent selectivity. Application of the probe for selective detection of intracellular thiols has been successfully demonstrated.

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 highly sensitive and selective 1,8-naphthyridine-based fluorescent chemodosimeter for Zn2+ has been designed, synthesized, and applied to the detection of intracellular Zn2+.

A C3-symmetric Schiff-base example of the new simple, low cost, highly water soluble, and sensitive turn-on fluorescent Zn2+ chemosensor is described. The sensor was successfully applied to the detection of intracellular Zn2+. Moreover, the sensor could also serve as a potential recyclable component in sensing materials. Notably, the color change is so obvious that all of the recycling process can be seen clearly by the naked eye.

A highly sensitive and selective 1,8-naphthyridine-based fluorescent chemodosimeter for Zn2+ has been designed, synthesized, and applied to the detection of intracellular Zn2+.