A highly sensitive sensor for colorimetric detection of palladium(II) in lysosomes and its applications

Considering the scarcity of palladium ion probes with subcellular organelle targeting, especially probes with near-infrared (NIR) emission wavelength fluorophores, our group has been working to overcome this problem and looking forward to providing potential practical tools for exploring the toxicity of palladium ions at the subcellular level. In this paper, a novel colorimetric and NIR fluorescent probe, BHCy-Pd, for the specific detection of palladium ions (Pd²⁺) in lysosomes via an internal charge-transfer (ICT) mechanism was designed and synthesized. As expected, BHCy-Pd exhibited a rapid, selective, and sensitive response for palladium with an ultralow limit of detection at 5.9 nM, accompanied by a distinct color change from purple to blue. Furthermore, BHCy-Pd can be made into a simple test strip for rapid and easy detection of Pd²⁺ in practical applications. Importantly, BHCy-Pd is capable of specific distribution in lysosomes, and thus can detect Pd²⁺ in real-time, thereby providing a potential tool for studying the cytotoxicity of Pd²⁺ ions at the subcellular level.

A new chromone based fluorescence probe for ratiometric detection of Pd2+

A new chromone based fluorescent probe (HMPM) is introduced for selective detection of Pd2+. The designed probe exhibits a ratiometric fluorescence enhancement which can be attributed to the ESIPT and/or...

Cu2+-selective NIR fluorescence sensor based on heptamethine cyanine in aqueous media and its application

A near-infrared (NIR) colorimetric fluorescence sensor, Cy7C3, based on heptamethine cyanine dye was synthesized for determining the presence of Cu²⁺ ions. The sensor showed highly sensitive fluorescence quenching toward Cu²⁺ ions in acetonitrile/buffer solution at physiological pH with long emission wavelength of 718 nm. Cy7C3 also provided an excellent selectivity to Cu²⁺ ions over other competing metal ions, with a low detection limit of 9 ppb, which was lower than the maximum concentration of Cu²⁺ ions in drinking water of U.S. EPA. Cy7C3 could achieve naked-eye detection of Cu²⁺ ions via the color change from blue to colorless, which allowed determination of Cu²⁺ ions in hydroponic fertilizers. Additionally, the sensor was developed to detect Cu²⁺ ions in HepG2 cancer cells via fluorescence imaging.

Sequential Detection of Palladium and Chromium Oxyanion by a Fluorescein Based Chemosensor in Mixed Aqueous Media

A new highly selective chemosensor, based on fluorescein-allyloxy benzene conjugate 1, was developed for the sequential detection of palladium and chromium oxyanions in a mixed aqueous media, and was studied by UV-visible and fluorescence spectroscopy. The sensing of palladium ions produces a chemodosimetric and ratiometric change in the emission band of 1 from 450 to 525 nm, followed by the sensing of chromate ions by 2 that quenches the emission band at 525 nm in a buffered H2O: DMF solution (9:1, pH = 7.4). The rate constants of palladium and chromate ions were found to be 8.6 × 105 M−1, 2.1 × 105 M−1, and 5.4 × 104 M−1 respectively. The chemosensor 1 has a palladium detection limit of 49 ppb while the sequential detection limit of chromate ions (CrO42− and Cr2O72−) were 127 and 259 ppb. The ratiometric change in the emission is produced due to the deallylation of 1 by palladium to produce 2 that restores the ESIPT (excited state intramolecular proton transfer) of the phenolic ring and enhances the electron transfer (ET) phenomenon from the phenolic group to fluorescein. The sequential binding of chromate ions to 2 inhibits the ESIPT and causes chelation enhanced quenching (CHEQ) of the fluorescence.

Development of a FRET-based ratiometric fluorescent probe to monitor the changes in palladium(ii) in aqueous solution and living cells

We have developed a new small-molecule based, mitochondrial-targeted ratiometric fluorescent palladium(ii) probe (CR-Pd). Fluorescence imaging shows that CR-Pd is suitable for the ratiometric visualization of palladium(ii) in living cells.

New palladium(ii) complexes with 3-(2-pyridyl)-5-alkyl-1,2,4-triazole ligands as recyclable C–C coupling catalysts

Compounds 4a–d revealed good catalytic activity and prospects for use as mesomorphic materials.

A near-infrared fluorescent probe based on chloroacetate modified naphthofluorescein for selectively detecting cysteine/homocysteine and its application in living cells

We have prepared a near-infrared (NIR) turn-on fluorescent probe (NFC) based on chloroacetate modified naphthofluorescein for specific detection of cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) and other amino acids (AAs) with the detection limits of 0.30 μM and 0.42 μM, respectively. The fluorescence intensity of the naphthofluorescein (NF) chromophore is modulated by an internal charge transfer (ICT) process. The probe NFC is readily available and weakly fluorescent, but of observably enhanced fluorescence after reacting with Cys or Hcy. We assumed and then demonstrated that the fluorescence off-on process involves a conjugate nucleophilic substitution/cyclization sequence. Furthermore, the probe has been successfully applied for detecting the total content of Cys and Hcy in human plasma and imaging in living cells with low toxicity.

A water-soluble near-infrared fluorescent probe for specific Pd2+ detection

Palladium (Pd) is widely used in chemistry, biology, environmental science etc., and Pd²⁺ is the most plenitudinous oxidation state of the Pd that can exist under physiological conditions or in living cells, which could have adverse effects on both our health and environment. Thus, it is of great significance to monitor the changes of Pd²⁺. Hence, a novel near-infrared fluorescent probe M-PD has been developed for selective detection of Pd²⁺ based on naphthofluorescein in this work. The result demonstrated that M-PD exhibited favorable properties for sensing Pd²⁺ such as excellent water solubility, high selectivity and sensitivity. And the limit of detection was estimated as 10.8 nM, much lower than the threshold in drugs (5-10 ppm) specified by European Directorate for the Quality Control of Medicines. More importantly, detection and recovery experiments of Pd²⁺ in aspirin aqoeous solution and soil are satisfactory. In addition, M-PD has also been successfully used for near-infrared fluorescence imaging of Pd²⁺ in living cells, indicating that the probe has better feasibility and application potential in the determination of Pd²⁺.

A fluorescence ‘turn-on’ chemodosimeter for the specific detection of Pd2+by a rhodamine appended Schiff base and its application in live cell imaging

Allylether-Rhodamine selectively invites Pd²⁺from mixture of other cations and Pd(0) in H₂O-MeCN medium and exhibits maroon emission due to C(allyl)-O bond cleavage and opening of spirolactam ring. The LOD is 50 nM at pH 7. Imaging Pd²⁺species in living cells under physiological conditions is achieved.

Molecular engineering of a dual emission near-infrared ratiometric fluorophore for the detection of pH at the organism level

A near-infrared ratiometric fluorophore (NIR-HBT) was rationally designed and constructed by expanding both the excitation and emission wavelength of the classical ratiometric fluorophore 2-(benzothiazol-2-yl)phenol (HBT) into the near-infrared region. The NIR-HBT was easily synthesized by incorporating the HBT module into the hemicyanine skeleton and showed evident NIR ratiometric fluorophore characteristics. Further application of the new fluorophore for pH detection demonstrated that NIR-HBT possesses superior overall analytical performance and NIR-HBT was successfully applied for detection of acidosis caused by inflammation in living animal tissue, which indicated the potential application value of NIR-HBT in biological imaging and sensing.

A depropargylation-triggered spontaneous cyclization based fluorescent “turn-on” chemodosimeter for the detection of palladium ions and its application in live-cell imaging

A novel depropargylation-triggered spontaneous cyclization reaction based fluorescent turn-on chemodosimeter for the detection of palladium ions has been rationally designed and developed.

A colorimetric and fluorescent dual probe for palladium in aqueous medium and live cell imaging

A colorimetric and fluorescent dual probe for palladium species was rationally developed by combining the resorufin fluorophore with allyl chloroformate.

Long-wavelength analyte-sensitive luminescent probes and optical (bio)sensors

Long-wavelength luminescent probes and sensors become increasingly popular. They offer the advantage of lower levels of autofluorescence in most biological probes. Due to high penetration depth and low scattering of red and NIR light such probes potentially enable in vivo measurements in tissues and some of them have already reached a high level of reliability required for such applications. This review focuses on the recent progress in development and application of long-wavelength analyte-sensitive probes which can operate both reversibly and irreversibly. Photophysical properties, sensing mechanisms, advantages and limitations of individual probes are discussed.

A new turn on Pd(2+)-specific fluorescence probe and its use as an imaging reagent for cellular uptake in Hct116 cells

A new coumarin-rhodamine conjugate is used as a specific probe for Pd(2+) ions and this could even delineate Pd(II) from Pd(0) or Pd(IV) in aqueous buffer medium (pH ∼ 7). Laser confocal microscopic studies reveal that efficient cellular internalization of this reagent helps in imaging the cellular uptake of Pd(2+) as low as 0.1 ppm in Hct 116 cells. This reagent could even be used for estimation of Pd(2+) in human urine samples.

Highly selective and sensitive fluorescence chemosensor for the detection of palladium species based on Tsuji-Trost reaction

A new chemosensor 7-nitro-2,1,3-benzoxadiazole-4-allyl-N-(thiophen-2-ylmethyl)carbamate (NBDTC) was synthesized and utilized for palladium detection based on the Tsuji-Trost reaction. NBDTC displayed specific and ratiometric fluorescent responses toward palladium species. The chemosensor showed more than 50-fold enhancement in fluorescence intensity with the presence of PEG400 and palladium because NBDTC can be transformed to NBDT under palladium-catalyzing Tsuji-Trost reaction. NBDTC displayed high selectivity and sensitivity for palladium species with the detection limit of 1.13×10(-9) M.

Ultrasensitive near-infrared fluorescence-enhanced probe for in vivo nitroreductase imaging

Nitroreductase (NTR) can be overexpressed in hypoxic tumors, thus the selective and efficient detection of NTR is of great importance. To date, although a few optical methods have been reported for the detection of NTR in solution, an effective optical probe for NTR monitoring in vivo is still lacking. Therefore, it is necessary to develop a near-infrared (NIR) fluorescent detection probe for NTR. In this study, five NIR cyanine dyes with fluorescence reporting structure decorated with different nitro aromatic groups, Cy7-1-5, have been designed and explored for possible rapid detection of NTR. Our experimental results presented that only a para-nitro benzoate group modified cyanine probe (Cy7-1) could serve as a rapid NIR fluorescence-enhanced probe for monitoring and bioimaging of NTR. The structure-function relationship has been revealed by theoretical study. The linker connecting the detecting and fluorescence reporting groups and the nitro group position is a key factor for the formation of hydrogen bonds and spatial structure match, inducing the NTR catalytic ability enhancement. The in vitro response and mechanism of the enzyme-catalyzed reduction of Cy7-1 have been investigated through kinetic optical studies and other methods. The results have indicated that an electro-withdrawing group induced electron-transfer process becomes blocked when Cy7-1 is catalytically reduced to Cy7-NH2 by NTR, which is manifested in enhanced fluorescence intensity during the detection process. Confocal fluorescence imaging of hypoxic A549 cells has confirmed the NTR detection ability of Cy7-1 at the cellular level. Importantly, Cy7-1 can detect tumor hypoxia in a murine hypoxic tumor model, showing a rapid and significant enhancement of its NIR fluorescence characteristics suitable for fluorescence bioimaging. This method may potentially be used for tumor hypoxia diagnosis.

A simple and effective fluorescent probe based on rhodamine B for determining Pd2+ ions in aqueous solution

It is demonstrated that the mechanism of the probe to Pd²⁺ and images under a UV lamp.

A colorimetric and ratiometric fluorescent probe for detection of palladium in the red light region

We synthesized a colorimetric and ratiometric red-light emissive chemosensor with high selectivity and sensitivity towards palladium species.

A near-infrared chemodosimeter with Pi-selective colorimetric and fluorescent sensing and its application in vivo imaging

A near-infrared colorimetric and fluorescent chemosensor for detecting phosphate ion (Pi) has been developed. The practical utility of this chemosensor was demonstrated by employing it to detect Pi in Paramecium and C. elegans.

A ratiometric fluorescent probe for determining Pd2+ ions based on coordination

An aniline-rhodamine-based ratiometric fluorescent probe (RI) was designed and synthesized. , the metal coordinating chromophoric ligand, exhibited high selectivity and sensitivity for Pd(2+) ions with a detection limit of 73.8 nM. This method of Pd(2+) detection had a 10 min response time.

Development and bioorthogonal activation of palladium-labile prodrugs of gemcitabine

Bioorthogonal chemistry has become one of the main driving forces in current chemical biology, inspiring the search for novel biocompatible chemospecific reactions for the past decade. Alongside the well-established labeling strategies that originated the bioorthogonal paradigm, we have recently proposed the use of heterogeneous palladium chemistry and bioorthogonal Pd⁰-labile prodrugs to develop spatially targeted therapies. Herein, we report the generation of biologically inert precursors of cytotoxic gemcitabine by introducing Pd⁰-cleavable groups in positions that are mechanistically relevant for gemcitabine’s pharmacological activity. Cell viability studies in pancreatic cancer cells showed that carbamate functionalization of the 4-amino group of gemcitabine significantly reduced (>23-fold) the prodrugs’ cytotoxicity. The N-propargyloxycarbonyl (N-Poc) promoiety displayed the highest sensitivity to heterogeneous palladium catalysis under biocompatible conditions, with a reaction half-life of less than 6 h. Zebrafish studies with allyl, propargyl, and benzyl carbamate-protected rhodamines confirmed N-Poc as the most suitable masking group for implementing in vivo bioorthogonal organometallic chemistry.

A naked-eye and ratiometric near-infrared probe for palladium via modulation of a π-conjugated system of cyanines

The modulation of π-conjugated electrons in cyanine dyes can result in a ratiometric fluorescence change with a large Stokes shift (270 nm), especially for realizing palladium detection in aqueous samples using indicator paper and in living cells by ratiometric mode.