A near-infrared fluorescent probe for imaging of bisulfite in living animals and its application in food samples

Bisulfite (HSO₃^-) has been widely used as an antioxidant, enzyme inhibitor and antimicrobial agent in foodstuffs, pharmaceutical and beverages industries. It is also a signaling molecular in the cardiovascular and cerebrovascular systems. Nevertheless, a high level of HSO₃^- can cause allergic reactions and asthmatic attacks. Accordingly, the monitoring of HSO₃^- levels possesses momentous significance from the perspectives of biological technology and food security supervision. Herein, a near-infrared fluorescent probe LJ is rationally constructed for sensing HSO₃^-. The fluorescence quenching recognition mechanism was realized by the addition reaction of electron-deficient CC bond in probe LJ and HSO₃^-. Probe LJ revealed multifarious preponderances such as longer wavelength emission (710 nm), low cytotoxicity, larger Stokes shift (215 nm), better selectivity, higher sensitivity (72 nM) and short response time (50 s). Encouragingly, probe LJ can detect HSO₃^- in living zebrafish and mice in vivo by fluorescence imaging techniques. In the meantime, probe LJ was also successfully employed to semi-quantitatively detect HSO₃^- in real foodstuff samples and water samples by the "naked-eye" colorimetry without the help of any special instruments. More importantly, quantitative detection of HSO₃^- in practical food samples was achieved through a smartphone application software. Consequently, probe LJ is expected to provide an effective and convenient way for the detection and monitoring of HSO₃^- in organisms and for food safety detection, which has tremendous application potential.

Rewritable acidochromic papers based on oxazolidine for anticounterfeiting and photosensing of polarity and pH of aqueous media

Oxazolidine is a new category of stimuli-chromic organic compounds with unique characteristics in response to polarity, pH changes, water, light, and metal ions that were well-known as solvatochromism, acidochromism, hydrochromism, photochromism, and ionochromism, respectively. Therefore, oxazolidine derivatives have been developed for their potential applications in chemosensors, anticounterfeiting, and rewritable hydrochromic papers. In this study, various oxazolidine derivatives containing hydroxyl and naphthalene substituted groups were synthesized by using two different indolenine compounds. The synthesized oxazolidine derivatives were used for investigation of solvatochromism in different solvents, and also acidochromism in various pHs by using UV–Vis and fluorescence spectroscopies. In addition, the oxazolidine derivatives were coated on cellulosic papers using a layer-by-layer strategy to develop rewritable acidochromic papers for printing of security tags on cellulosic papers by using acidic and alkaline solutions as water-based inks. Therefore, the developed rewritable acidochromic papers could be used as security papers.

2,7-Diazapyrenes: a brief review on synthetic strategies and application opportunities

2,7-Diazapyrenes are promising azaaromatic scaffolds with a unique structural geometry and supramolecular properties. This core moiety and its derivatives with some N-methyl cations like N-methyl-2,7,-diazapyrenium, and N,N'-dimethyl-2,7-diazapyrenium attract special attention due to their challenging photophysical properties, especially in the context of interactions with DNA and some of its mononucleotides. This review focuses on the analysis of the main synthetic approaches to 2,7-diazapyrene and its functional derivatives employing various strategies under different reaction conditions. The opportunities of applications of 2,7-diazapyrenes, including their remarkable photophysical and supramolecular properties, DNA-bindings, in sensors, molecular electronics, supramolecular systems, and related areas are also highlighted.

Crystal structure of (4′E)-6′-(diethylamino)-2-[(E)-[(pyren-1-yl)methylidene]amino]-4′-{2-[(2E)-1,3,3-trimethyl-2,3-dihydro-1H-indol-2-ylidene]ethylidene}-1′,2,2′,3,3′,4′-hexahydrospiro[isoindole-1,9′-xanthene]-3-one, C54H48N4O2

C54H48N4O2, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 11.1883(5) Å, b = 13.5364(5) Å, c = 14.3412(5) Å, α = 105.885(3)°, β = 97.710(3)°, γ = 94.126(3)°, Z = 2, V = 2056.64(14) Å3, R gt (F) = 0.0685, wR ref (F 2) = 0.1606, T = 293(2) K.

Water-soluble fluorescent probes for bisulfite and viscosity imaging in living cells: Pyrene vs. anthracene

We have designed two mitochondria targetable probes P-Py and P-An by the π-conjugation of polyaromatic hydrocarbons (pyrene vs. anthracene) with 4-dimethylamino pyridinium. They present an amphiphilic property with excellent solubility in the common polar and non-polar solvents. Both of them demonstrated a significant fluorescence response to bisulfite in Tris-HCl buffer solutions (5 mM, pH = 7.4). By a combination of fluorescence, UV-vis, time-resolved emission, ¹H NMR, and ESI-MS, their sensing mechanisms have been elaborated to be a Michael addition. Notably, P-Py also exhibits a sensitivity to the viscosity change with a Stokes shift of 140 nm, due to the restriction of C-C bond rotation. By taking advantages of its good water solubility, low toxicity, and high mitochondrial target, the dual responses of P-Py to exogenous SO₂ derivatives and viscosity change in mitochondria were explored by confocal fluorescence microscopy.

A Novel Fluorescence Probe for the Reversible Detection of Bisulfite and Hydrogen Peroxide Pair in Vitro and in Vivo

The detection of changes in the reactive oxygen species (ROS)/reactive sulfur species (RSS) couple is important for studying the cellular redox state. Herein, we developed a 1,8-naphthalimide-based fluorescence probe (NI) for the reversible detection of bisulfite (HSO₃ ^- ) and hydrogen peroxide (H₂ O₂ ) in vitro and in vivo. NI has been designed with a reactive ethylene unit which specifically reacts with HSO₃ ^- by a Michael addition reaction mechanism, resulting in the quenching of yellow fluorescence at 580 nm and the appearing of green fluorescence at 510 nm upon excitation at 500 nm and 430 nm, respectively. The addition product (NI-HSO₃ ) could be specifically oxidized to form the original C=C bond of NI, recovering the fluorescence emission and color. The detection limits of NI for HSO₃ ^- and NI-HSO₃ for H₂ O₂ were calculated to be 2.05 μM and 4.23 μM, respectively. The reversible fluorescence response of NI towards HSO₃ ^- /H₂ O₂ couple can be repeated for at least five times. NI is reliable at a broad pH range (pH 3.0-11.5) and features outstanding selectivity, which enabled its practical applications in biological and food samples. Monitoring the reversible and dynamic inter-conversion between HSO₃ ^- and H₂ O₂ in vitro and in vivo has been verified by fluorescence imaging in live HeLa cells, adult zebrafish and nude mice. Moreover, NI has been successfully applied to detect of HSO₃ ^- levels in food samples.

A novel fluorescent probe based on a triphenylamine derivative for the detection of HSO3- with high sensitivity and selectivity

A novel highly active fluorescence chemical sensor (TBQN) for HSO₃^- was synthesized by the Knoevenagel reaction based on triphenylamine-benzothiazole as a new fluorophore. The probe possessed good selectivity toward HSO₃^- and anti-interference ability with common ions. The fluorescence and UV-vis spectra of the TBQN probe were significantly changed after the addition of HSO₃^-. At the same time, the probe solution released obvious green fluorescence. Moreover, the limit of detection for HSO₃^- was calculated to be 3.19 × 10^-8 M. The TBQN probe displayed a rapid response to HSO₃^- and it took about 3 min to complete the recognition. The detection mechanism is the nucleophilic addition reaction between HSO₃^- and -C[double bond, length as m-dash]C- in the probe molecule. The π-conjugation and ICT (intramolecular charge transfer) transition in the TBQN molecule were destroyed by this addition, which resulted in the change of the fluorescence before and after the addition of HSO₃^-. Then, the mechanism was verified by theoretical calculations, ¹H NMR measurements and mass spectroscopy. In addition, the probe showed low cytotoxicity and could be used for biological imaging in RAW264.7 cells.

Real-Time Visualization and Monitoring of Physiological Dynamics by Aggregation-Induced Emission Luminogens (AIEgens)

Physiological dynamics in living cells and tissues are crucial for maintenance and regulation of their normal activities and functionalities. Tiny fluctuations in physiological microenvironments can leverage significant influences on cell growth, metabolism, differentiation, and apoptosis as well as disease evolution. Fluorescence imaging based on aggregation-induced emission luminogens (AIEgens) exhibits superior advantages in real-time sensing and monitoring of the physiological dynamics in living systems, including its unique properties such as high sensitivity and rapid response, flexible molecular design, and versatile nano- to mesostructural fabrication. The introduction of canonic AIEgens with long-wavelength, near-infrared, or microwave emission, persistent luminescence, and diversified excitation source (e.g., chemo- or bioluminescence) offers researchers a tool to evaluate the resulting molecules with excellent performance in response to subtle fluctuations in bioactivities with broader dimensionalities and deeper hierarchies.

Pyrene based materials as fluorescent probes in chemical and biological fields

Molecules that experience a change in their fluorescence emission due to the effect of fluorescence enhancement upon binding events, like chemical reactions or a change in their immediate environment, are regarded as fluorescent probes.

Photocytotoxicity of heavy-atom-free thiobarbituric acid functionalized pyrene derivatives against MCF-7 cancer cells

Two thiobarbituric acid-functionalized pyrene derivatives (P1, P2) have been synthesized to explore the photophysical properties and photodynamic activity of dyes of this type. Both compounds exhibit an intense intramolecular charge transfer (ICT) band at ca. 470 nm, which is absent in the spectra of the precursor. P1 and P2 exhibit singlet oxygen generation on irradiation with light with moderate singlet oxygen yields of 0.36 and 0.32, respectively, in DMSO. P1 showed better photodynamic activity against MCF-7 cells with an IC₅₀ value of 18.3 μM under illumination at 455 nm for 60 min with a Thorlabs M455L3 LED (330 mW.cm^-2).

Selective immediate detection of Cu2+ by a pH-sensitive rhodamine-based fluorescence probe in breast cancer cell-line

A biocompatible fluorogenic chemosensor (N-(3-carboxy acryloyl)) rhodamine B (RHA) comprising a furan-2,5-dione receptor and a rhodamine fluorophore via an iminohydrazine crosslinker has been prepared for more scrutinizing optical properties and utilization in molecular imaging of living cells. The consequences indicated that RHA not only is a good pH indicator in acidic media but also can be used as a great sensitive fluoroionophore with high selectivity. The fluorescence emission of the molecule RHA is quite stable in the presence of 15 diverse cations, 18 anions (especially H₂PO₄^-, S², and F^-), and 5 amino acids with the different functional group as a model, except Cu²⁺ ions with observable emission intensity changing. The Cu²⁺ probe has a dual functional effect, an "on-off" mechanism in solvent media, and an "off-on" mechanism in Phosphate Buffered Saline (PBS) in acidic pH conditions. The detection limits for Cu²⁺ in acetone-water media was 0.69 μM and 0.18 μM in pH = 5.0. Moreover, RHA can fluorescently and colorimetrically image Cu²⁺ ions in acidic and neutral pH with low cytotoxicity in living cells.

A lysosome specific, acidic-pH activated, near-infrared Bodipy fluorescent probe for noninvasive, long-term, in vivo tumor imaging

Long-term, in vivo, fluorescent cell tracking probes are useful for understanding complex cellular processes including tissue regeneration, communication, development, invasion, and cancer metastasis. A near-infrared fluorescent, water-soluble probe is particularly important for studying these biological events and processes. Herein, a lysosome specific, near-infrared Bodipy probe with increased fluorescent intensity in the acidic, lysosome environment is reported. This Bodipy probe is packaged in a nanoparticle using DSPE-PEG₂₀₀₀. The resulting nanoparticle is intravenously delivered to a tumor xenograft, where the fluorescent Bodipy becomes useful for non-invasive, long-term, in vivo fluorescent tumor imaging for periods greater than 36 days. These long-term, in vitro and in vitro tracking data indicate that the described Bodipy nanoparticles hold great potential for monitoring biological processes.

A turn-off fluorescence probe based on terpyridine for pH monitoring

A new pH-dependent fluorescence probe 2,8-bis((E)-4-([2,2':6',2″-terpyridin]-4'-yl)styryl)-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (TBPTP) based on Tröger's base (TB) bound to terpyridine was designed and synthesized. Photophysical properties and titration experiments of TBPTP were investigated by absorption and fluorescence spectroscopy. TBPTP exhibited high sensitivity in an acidic environment with the working pH range 7.2-2.5, especially having a good liner response to pH changes in the range 2.5-4.3, which suggested that TBPTP is a good candidate for pH monitoring.

Dimethylaniline functionalised pyrene fluorophores; dual colour pH switching in solution and self-assembled monolayers

A pyrene charge transfer fluorophore with three ionizable N,N-dimethylaniline moieities was explored as an interfacial pH switch. The parent carboxylate compound and the thiolated derivative were shown by spectroscopy combined with DFT calculation to be successively and reversibly protonated. Protonation leads to progressive decrease of intensity of the 550 nm centered N,N-dimethylaniline to pyrene charge transfer emission which on protonation of the third site, leads to extinction of this transition and evolution of an intense blue (450 nm) pyrene-centered emission. Concomitant loss of the charge transfer absorbance was observed and the changes are reversed on neutralization of pH. A self-assembled monolayer of the thiolated derivative was prepared on gold and found from voltammetry of ferricyanide/ferrocyanide probe to form close packed monolayers. The probe voltammetry, label-free electrochemical impedance spectroscopy of the film was monitored as a function of pH and progressive, but reversible protonation steps were reflected in decreasing film resistance. The Stokes shift of the probe prevents self-quenching so a broad, charge transfer fluorescence centered around 540 nm was recorded for the self-assembled monolayer where as per solution, progressive and reversible reduction in intensity was observed. The facile assembly, impedance and optical switching make these materials potentially interesting as on-off or two colour on-off-on fluorescence switches with potential applications in logic gates or in responsive surface applications.

A photostable Si-rhodamine-based near-infrared fluorescent probe for monitoring lysosomal pH during heat stroke

Heat stroke is a symptom of hyperthermia with a temperature of more than 40 °C, which usually leads to all kinds of physical discomfort and even death. It is necessary to study the mechanism of action of heat stroke on cells or organelles (such as cytotoxicity of heat) and the processes of cells or organelles during heat stroke. Recent studies have shown that there is a certain correlation between heat stroke and lysosome acidity. In order to clarify their relationship, Lyso-NIR-pH, a photostable Si-rhodamine-based near-infrared fluorescent probe, was developed for sensing pH changes in lysosomes during heat stroke in this paper. For Lyso-NIR-pH, a morpholine group is employed as the lysosome-targeting unit and a H⁺-triggered openable deoxylactam is employed as the response unit to pH. Lyso-NIR-pH can detect pH with a high selectivity and a sensitivity, and its pK_a is 4.63. Lyso-NIR-pH also has outstanding imaging performances, such as excellent lysosome-targeting ability, low autofluorescence and photostable fluorescence signal, which are in favor of long-term imaging of pH with accurate fluorescence signals. Moreover, we successfully applied Lyso-NIR-pH to monitor lysosomal pH increases induced by chloroquine and apoptosis in live cells. Finally, we successfully applied Lyso-NIR-pH for monitoring changes of lysosomal pH during heat stroke. These results confirmed that Lyso-NIR-pH is a powerful tool to monitor pH change in lysosomes and study its possible effects.

Recent Advances in Aggregation-Induced Emission Chemosensors for Anion Sensing

The discovery of the aggregation-induced emission (AIE) phenomenon in the early 2000s not only has overcome persistent challenges caused by traditional aggregation-caused quenching (ACQ), but also has brought about new opportunities for the development of useful functional molecules. Through the years, AIE luminogens (AIEgens) have been widely studied for applications in the areas of biomedical and biological sensing, chemosensing, optoelectronics, and stimuli responsive materials. Particularly in the application of chemosensing, a myriad of novel AIE-based sensors has been developed to detect different neutral molecular, cationic and anionic species, with a rapid detection time, high sensitivity and high selectivity by monitoring fluorescence changes. This review thus summarises the recent development of AIE-based chemosensors for the detection of anionic species, including halides and halide-containing anions, cyanides, and sulphur-, phosphorus- and nitrogen- containing anions, as well as a few other anionic species, such as citrate, lactate and anionic surfactants.

Mega-stokes pyrene ceramide conjugates for STED imaging of lipid droplets in live cells

Lipid droplets are dynamic subcellular organelles that participate in a range of physiological processes including metabolism, regulation and lipid storage. Their role in disease, such as cancer, where they are involved in metabolism and in chemoresistance, has emerged over recent years. Thus, the value of lipid droplets as diagnostic markers is increasingly apparent where number and size of droplets can be a useful prognostic. Although diverse in size, LDs are typically too small to be easily enumerated by conventional microscopy. The advent of super-resolution microscopy methods offers the prospect of detailed insights but there are currently no commercial STED probes suited to this task and STED, where this method has been used to study LDs it has relied on fixed samples. Here, we report a pyrene-based ceramide conjugate PyLa-C17Cer, that stains lipid droplets with exceptionally high precision in living cells and shows excellent performance in stimulated emission depletion microscopy. The parent compound PyLa comprises a pyrene carboxyl core appended with 3,4-dimethylaminophenyl. The resulting luminophore exhibits high fluorescent quantum yield, mega-Stokes shift and low cytotoxicity. From DFT calculations the Stokes shifted fluorescent state arises from a dimethylaminophenyl to pyrene charge-transfer transition. While the parent compound is cell permeable, it is relatively promiscuous, emitting from both protein and membranous structures within the living mammalian cell. However, on conjugation of C17 ceramide to the free carboxylic acid, the resulting PyLa-C17Cer, remains passively permeable to the cell membrane but targets lipid droplets within the cell through a temperature dependent mechanism, with high selectivity. Targeting was confirmed through colocalisation with the commercial lipid probe Nile Red. PyLa-C17Cer offers outstanding contrast of LDs both in fluorescence intensity and lifetime imaging due to its large Stokes shift and very weak emission from aqueous media. Moreover, because the compound is exceptionally photochemically stable with no detectable triplet emission under low temperature conditions, it can be used as an effective probe for fluorescence correlation spectroscopy (FCS). These versatile fluorophores are powerful multimodal probes for combined STED/FCS/lifetime studies of lipid droplets and domains in live cells.

A chemosensor with a paddle structure based on a BODIPY chromophore for sequential recognition of Cu2+ and HSO3−

In this study, a highly selective chemosensor ML based on a BODIPY fluorescent chromophore was synthesized for sequential recognition of Cu²⁺ and HSO₃⁻ in a CH₃OH/H₂O (99 : 1 v/v) system, which contained three recognition sites and its structure characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor ML showed an obvious “on–off” fluorescence quenching response toward Cu²⁺ and the ML-Cu²⁺ complex showed an “off–on” fluorescence enhancement response toward HSO₃⁻. The detection limit of the sensor ML was 0.36 μM to Cu²⁺ and 1.4 μM to HSO₃⁻. In addition, the sensor ML showed a 1 : 3 binding stoichiometry to Cu²⁺ and the recovery rate of ML-Cu²⁺ complex identifying HSO₃⁻ could be over 70%. Sensor ML showed remarkable detection ability in a pH range of 4–8.

A highly selective chemosensor based on a BODIPY chromophore for sequential recognition of Cu²⁺ and HSO₃⁻.

A FRET-based two-photon probe for in vivo tracking of pH during a traumatic brain injury process

Traumatic brain injury (TBI) is a cause of neurodegenerative diseases accompanied by intracellular pH decrease. Herein, a FRET-based ratiometric two-photon fluorescent pH probe is designed to monitor pH change and understand TBI process.

Multifunctional fluorescent leucomalachite green derivatives for chemodosimetric detection of Fe3+, specific imaging of lipid droplets and intracellular pH monitoring

Fluorescent leucomalachite green derivatives detect micromolar concentrations of Fe³⁺, specifically stain lipid droplets in live cells and monitor intracellular pH variations in microorganisms.

A mitochondria-targeted and deep-red emission ratiometric fluorescent probe for real-time visualization of SO2 in living cells, zebrafish and living mice

A mitochondria-targeted and red-emissive ratiometric fluorescent probe for fast imaging of SO₂ in living cells and zebrafish has been developed, and the changes of SO₂ in living mice have been visualized in real time with this probe.

Differential calixarene receptors create patterns that discriminate glycosaminoglycans

A well-designed fluorescence displacement sensing array based on calixarene receptors realizes the discrimination of glycosaminoglycans.

Detection of SO2 derivatives using a new chalco-coumarin derivative in cationic micellar media: application to real samples

A new probe ChC16 was synthesized and studied as a turn-on fluorescent probe, based on a Michael addition mechanism for sensing SO₂ derivatives, which is favored in the presence of cationic micellar media such as cetylpyridinium bromide (CPB).

A benzimidazole-based highly selective colorimetric and far-red fluorometric pH sensor for intracellular imaging

A turn-on fluorescent probe (E)-4-(2-(1H-benzo[d]imidazol-2-yl)vinyl)-N,N-diphenylaniline (BVD) was facilely synthesized via the ethylene bridging of triphenylamine and benzimidazole.