The development of near-infrared fluorescent probes with low pKa, high selectivity, high photostability, and high sensitivity for lysosomal pH detection is of great importance. In the present work, we developed a novel near-infrared lysosomal pH probe (Lyso-hNR) based on a rhodamine derivative. Lyso-hNR showed fast, highly sensitive, and highly selective fluorescence response to acidic pH caused by the H+-induced structure changes from the nonfluorescent spirolactam form to the highly emissive open-ring form. Lyso-hNR displays a significant fluorescence enhancement at 650 nm (over 280-fold) from pH 7.0 to 4.0 with a pKa value of 5.04. Live cell imaging data revealed that Lyso-hNR can selectively monitor lysosomal pH changes with excellent photostability and low cytotoxicity. In addition, Lyso-hNR can be successfully used in tracking lysosomal pH changes induced by chloroquine and those during apoptosis. All these features render Lyso-hNR a promising candidate to investigate lysosome-associated physiological and pathological processes.

Two coumarin-based boron complexes (HBN and MBN) with aggregation-induced emission were designed and synthesized. The photophysical properties of the complexes were investigated in different solvents and in the solid state. Results showed that the inhibited C═N isomerization by N,O-chelated BF2 caused the significant enhancement of fluorescence in THF. In particular, the complexes displayed red-shifted emissions (>60 nm) in mixed solvents of CH3CN and water because of the aggregation-induced charge-transfer enhancement. In the solid state, the bright red emission appeared at 650 nm (620 nm), with a Stokes shift of 170 nm. Cell-imaging experiments indicated that the complexes have good membrane permeability and can be used as lysosome trackers.

•We designed a fluorescent probe (1) by integrating two reactive groups into coumarin.•Probe 1 can differentiate Cys and GSH based on different cascade reactions.•Probe 1 can be a useful tool for the selective detection of Cys and GSH in living cells.A fluorescent probe (1) for distinguishing amongst biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), is developed based on different cascade reactions. The key design feature of fluorescent probe 1 is the integration of two potential reaction groups for the thiol and amino groups of biothiols in one molecule. By reacting with the halogen atom and α, β-unsaturated malonitrile in probe 1, Cys, Hcy and GSH can generate a total of three main products with distinct photophysical properties. Probe 1 shows a strong fluorescence turn-on response to Cys with blue–green emission by using an excitation wavelength of 390 nm. At an excitation wavelength of 500 nm, probe 1 responds to GSH over Cys and Hcy and emits strong orange fluorescence. The discrimination of biothiols can be demonstrated by cell imaging experiments, indicating that probe 1 can be a useful tool for the selective imaging of Cys and GSH in living cells.Download high-res image (260KB)Download full-size image

In this work, two xanthene dyes (H-hNR and TF-hNR) have been synthesized by a convenient and efficient method. These two dyes exhibited deep-red and near-infrared emissions, high fluorescence quantum yields, and good photostability. Their structure–optical properties were investigated by X-ray crystal structure analysis and density functional theory calculations. Live cell imaging data revealed that H-hNR and TF-hNR could rapidly stain both A549 and HeLa cells with low concentrations. The excellent photophysical and imaging properties render them as promising candidates for use in live cell imaging.

•Four deep-red or near-infrared fluorescent dyes were designed and synthesized.•Carboxylic groups in the dyes improved water solubility and facilitated labeling.•The photophysical properties of the CPC dyes were investigated in details.•CPC1E and CPC2E could selectively stain lysosomes with good photostability.More and more attention has been paid to the design of new fluorescent imaging agents with good photostability and water solubility, especially those with emissions in the deep-red and near-infrared regions. In this work, we designed and synthesized four novel fluorescent dyes with deep-red or NIR fluorescence by hybridizing coumarin and pyronin moieties based on our previous work. Introduction of carboxylic acid in the dyes not only imparted the dyes with water solubility but also provided a versatile sensing platform for designing the fluorescent probes and sensors of biomolecules. The photophysical properties of these new dyes were investigated through absorption and fluorescence spectroscopy. Cell imaging experiments showed that esterification products could selectively stain lysosomes with good photostability, thereby indicating that they could be useful in the development of fluorescent probes for bioimaging.

This paper reports on new applications of water- dispersible graphene quantum dots (GQDs) that we recently developed. The prepared GQDs not only show broad absorption in the visible spectrum from 400 to 700 nm, but can also serve as smart photosensitizers with high singlet oxygen (1O2) production under visible-light irradiation (≥420 nm). We showed that the prepared G QDs can potentially be used as a metal-free, visible-light-active, sensitized photocatalyst via e nergy transfer mechanism, in which the light energy was converted by GQDs to produce 1O2, which can kill nearby microorganisms and degrade organic dyes.本文提供了石墨烯量子点的应用新领域. 在此前的研究中, 我们发现以聚噻吩衍生物(PT2);为前驱物制备的石墨烯量子点在太阳光的照 射下可高效产生单线态氧. 本文进一步研究发现, 此类石墨烯量子点在模拟太阳光的照射下(大于420 nm);可以快速多次降解水中有机污染物 和高效灭杀细菌, 表明石墨烯量子点在环境保护领域拥有巨大的应用潜力.

A carbon dot-based fluorescence turn-on sensor for hydrogen peroxide (H2O2) with a photo-induced electron transfer mechanism was developed. The sensor exhibits good selectivity, sensitivity, and rapid response to H2O2 with a detection limit of 84 nM. The sensor maintains excellent sensing performance over a wide pH range.

We constructed an effective electron extraction layer (EEL) used for polymer solar cells by integrating one new kind of organic material of 4,4′-(1,4-phenylene) bis(2-phenyl-6-p-tolylnicotinonitrile) (p-PPtNT) and cesium carbonate (Cs2CO3) used as a compound EEL (CEEL). The CEEL based device exhibits an ideal PCE of 4.15%, corresponding to an enhancement 220% in contrast to that of control device without EEL, which is also comparable to that of ZnO based device. Our analyses indicated that the remarkably improved PCE for CEEL based device is mainly ascribed to the Ohmic contact and the negligible electron extraction barrier at cathode/active layer by inserting CEEL.

Aminobenzofuran-fused rhodamine dyes (AFR dyes) containing an amino group were constructed by an efficient condensation based on 3-coumaranone derivatives. AFR dyes exhibited significantly improved properties, including deep-red and near-infrared emissions, a large Stokes shift, good photostability, and wide pH stability. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium assay experiments show that these AFR dyes are biocompatible for their low cytotoxicity to both A549 and HeLa cells. Cell imaging data reveal that AFR1, AFR1E, and AFR2 are mainly located in the mitochondria, while AFR3 is a lysosome tracker. As far as we know, NIR AFR3 is the longest fluorescent rhodamine derivative containing the amino group. These amino group-containing AFR dyes hold great potential in fluorogenic detection, biomolecule labeling, and cell imaging.

•A new polythiophene-based chemosensor for streptomycin has been developed.•PT3 displays colorimetric and fluorescent dual-responses toward streptomycin.•The sensing mechanism may be the conformational change of PT3 induced by streptomycin binding.A colorimetric and fluorescent dual-responses chemosensor (PT3, a water-soluble polythiophene) for streptomycin was designed and synthesized. The structure of PT3 was characterized by using infrared spectroscopy, 1H NMR and gel-permeation chromatography analyses. The conformational change of PT3 induced by streptomycin resulted in the red shift of absorption spectra and fluorescent quenching. Moreover, PT3 showed excellent selectivity for streptomycin over other antibiotics and biomolecules. PT3 could quantificationally detect streptomycin in the range of 2–70 μM with a detection limit of 0.2 μM (116 ppb), which is lower than the maximum residue limit defined by World Health Organization (200 ppb).

•A new method for investigating biological cell–protein interactions was reported.•The method used a laser scanning confocal imaging–surface plasmon resonance system.•SPR sensor chip was prepared by modification of mouse normal IgG on the Au film.•The fluorescence enhanced with increasing concentration of cells and fit well with SPR signal.A new method for investigating biological cell–protein interactions was developed by using a laser scanning confocal imaging–surface plasmon resonance (LSCI–SPR) system. Mouse normal IgG was modified on the SPR chip. The suspension mouse lymphocyte cancer cells (L5178Y cells) labeled by Hoechst33342 freely flowed into the surface of the SPR sensor chip. By changing the concentration of the cells, the fluorescence images and the SPR signal were synchronously recorded in real time. The red fluorescence points in the imaging region increased with increase in the concentration of the mouse lymphocyte cancer cells and fit well with the change in the SPR signal. Different suspending cells were chosen to investigate cell–protein interactions through antigen–antibody reactions on the biological cell surfaces through binding detection. This method has potential application in cell biology and pharmacology.

3-Phenylthiophene-based water-soluble copolythiophenes (CPT9) were designed for colorimetric and fluorometric detection of lysophosphatidic acid (LPA) based on electrostatic interaction, hydrophobic interaction, and hydrogen bonding. Other negatively charged species gave nearly no interference, and the detection limit reached to 0.6 μM, which is below the requisite detection limits for LPA in human plasma samples. The appealing performance of CPT9 was demonstrated to originate from the multipoint interaction-induced conformational change of conjugated backbone and weakened electron transfer effect. To our best knowledge, this is the first polythiophene based optical sensor which displays emission peak red-shift followed with fluorescence enhancement.Keywords: biosensors; colorimetric; conjugated polythiophene; electron transfer; lysophosphatidic acid; ratiometric fluorescent;

We developed a new fluorescent sensor (PPC-S) for Hg2+ based on the aggregation-induced emission (AIE) of pyrazolo[3,4-b]pyridine-based coumarin chromophore (PPC-O). Given the desulfurization reaction with Hg2+, AIE inactive PPC-S can be transformed into PPC-O with AIE activity, which can be employed for the fluorescence turn-on detection of Hg2+ with satisfactory selectivity and sensitivity in aqueous solutions.

A water-soluble, polythiophene-based colorimetric sensor was designed for selective and sensitive detection of carbenicillin in HEPES buffer solution. Quaternized quinine was linked to thiophene through bis-functionality benzyl group, which can interact with carbenicillin via electrostatic interaction and geometric match effect. The sensor exhibited a colorimetric signal change upon the addition of carbenicillin because of the formation of more nonplanar structures. However, the addition of other beta-lactam antibiotics or dicarboxylic acids into the sensor solution caused no obvious changes in absorbance intensity ratio. This result may be attributed to the cavity formed by the semi-rigid framework of PTQ2, which is suitable for the special binding with carbenicillin. This novel sensor can effectively distinguish carbenicillin from other beta-lactam antibiotics and has a wide linear range response in HEPES buffer solution. Linear calibration curves are obtained with 0 to 18 μmol/L of HEPES buffer solution, with a limit of detection of 0.54 μmol/L.

A series of deep red fluorescent dyes (CR1 to CR3) was developed via introduction of a coumarin moiety into the rhodamine molecular skeleton. The novel dyes possessed the individual advantages of coumarin and rhodamine derivatives, and the emission wavelength was extended to the deep red region (>650 nm) due to the extension of fused-ring conjugate structure simultaneously. To illustrate its value, we designed and conveniently synthesized a series of novel deep red bioimaging dyes (CR1E to CR3E) by esterification of CR1 to CR3, which could selectively stain mitochondria. They were superior to the MitoTrackers for mitochondrial staining in terms of large Stokes shift, excellent contrast for imaging, high photostability, and low cytotoxicity. Furthermore, the fluorescence of the coumarin moiety and rhodamine-like fluorophore could be switched like classical rhodamine. Thus, they could be used as an effective platform in constructing fluorescence sensors. Based on this fact, we constructed a novel ratiometric sensor (CR1S) for Hg2+ with good selectivity that could be successfully applied to the imaging of Hg2+ in living A549 cells. This design strategy is straightforward and adaptable to various deep red dyes and sensing platforms by simply introducing different fluorophores.

•We reported an ultrasensitive and selective detection for Hg2+ ions using LSCI-SPR.•The principle of the LSCI-SPR sensor is the specific coordination between Hg2+ and thymine bases.•The fluorescence quenching for rhodamine-labeled ssDNA fitted well with the changes in SPR.•The detection limit was as low as 0.01 ng/ml for Hg2+ ions in ultrapure and tap water.•This LSCI-SPR sensor showed excellent selectivity over a spectrum of interference metal ions.An ultrasensitive and selective detection of mercury (II) was investigated using a laser scanning confocal imaging-surface plasmon resonance system (LSCI-SPR). The detection limit was as low as 0.01 ng/ml for Hg2+ ions in ultrapure and tap water based on a T-rich, single-stranded DNA (ssDNA)-modified gold film, which can be individually manipulated using specific T–Hg2+–T complex formation. The quenching intensity of the fluorescence images for rhodamine-labeled ssDNA fitted well with the changes in SPR. The changes varied with the Hg2+ ion concentration, which is unaffected by the presence of other metal ions. The coefficients obtained for ultrapure and tap water were 0.99902 and 0.99512, respectively, for the linear part over a range of 0.01–100 ng/ml. The results show that the double-effect sensor has potential for practical applications with ultra sensitivity and selectivity, especially in online or real-time monitoring of Hg2+ ions pollution in tap water with the further improvement of portable LSCI-SPR instrument.

A novel chromo- and fluorogenic sensor, 4-(4-dimethylaminostyryl)-1-hexadecylpyridinium (DSHP) for lysophosphatidic acid (LPA) was successfully developed by incorporating a long alkyl chain into the cyanine molecule. DSHP shows excellent selectivity and high sensitivity towards LPA with a detection limit of about 7.09 × 10−7 M based on electrostatic and hydrophobic interactions between the sensor and LPA. Upon addition of LPA ranging from 0 to 7.5 × 10−4 M, DSHP displays an ‘on–off–on’ fluorescence response and obvious colour change. Good linear relationships between the fluorescence intensity and LPA concentrations were achieved in the fluorescence quenching ranges of 0–28 μM and 34–52 μM, which could be attributed to the combined effects of the photoinduced electron transfer and LPA-induced aggregation of the sensor molecules.

A novel visible colorimetric sensor (L1) with high selectivity for fluoride ion based on coumarin has been synthesized by a simple modification of our earlier report. The chemosensor L1 shows an obvious color change from yellow to blue upon addition of fluoride ion with a large red shift of 145 nm in acetonitrile, and without interference of other anions such as Cl−, Br−, I−, NO3−, H2PO4−, HSO4−, and AcO−. The investigation of 1H NMR spectrum titration indicates the proposed mechanism is that F− first establishes a hydrogen bonding interaction with L1, and then the formation of [F–H–F]− induces deprotonation.Graphical abstractHighlights► We report a novel visible colorimetric chemosensor L1 based on our previous works. ► L1 shows an obvious color change from yellow to blue upon addition of fluoride ion. ► L1 exhibits highly selective recognition of fluoride ion via the N–H deprotonation.

A carbon dot-based fluorescence turn-on sensor for hydrogen peroxide (H2O2) with a photo-induced electron transfer mechanism was developed. The sensor exhibits good selectivity, sensitivity, and rapid response to H2O2 with a detection limit of 84 nM. The sensor maintains excellent sensing performance over a wide pH range.