A novel colorimetric and fluorescent probe for the highly selective and sensitive detection of palladium based on Pd(0) mediated reaction

A novel "turn-on" NIR fluorescent probe based on benzothianone for the detection of palladium species and its application in cell and zebrafish

The development of an efficient palladium probe holds significant application value, considering the detrimental impact of palladium contaminants on human health. Thus, it is critical to create a sensitive detection method. To this end, a fluorescent probe TM-TPA-Pd based on benzothianone structure was designed, using allyl carbonate as the Pd0 recognition unit. TM-TPA-Pd exhibited high sensitivity (1.4 eq), selectivity, near-infrared (NIR) fluorescence (798 nm), and low detection limit (0.46 μM) for Pd0 with a rapid "turn-on" fluorescence signal (5 min). Furthermore, TM-TPA-Pd has extremely low cytotoxicity and has been successfully applied to detecting cells and zebrafish, which has great potential for palladium detection in biological systems.

An activatable fluorescence probe for rapid detection and in situ imaging of β-galactosidase activity in cabbage roots under heavy metal stress

β-Galactosidase (β-gal), an enzyme related to cell wall degradation, plays an important role in regulating cell wall metabolism and reconstruction. However, activatable fluorescence probes for the detection and imaging of β-gal fluctuations in plants have been less exploited. Herein, we report an activatable fluorescent probe based on intramolecular charge transfer (ICT), benzothiazole coumarin-bearing β-galactoside (BC-βgal), to achieve distinct in situ imaging of β-gal in plant cells. It exhibits high sensitivity and selectivity to β-gal with a fast response (8 min). BC-βgal can be used to efficiently detect the alternations of intracellular β-gal levels in cabbage root cells with considerable imaging integrity and imaging contrast. Significantly, BC-βgal can assess β-gal activity in cabbage roots under heavy metal stress (Cd2+, Cu2+, and Pb2+), revealing that β-gal activity is negatively correlated with the severity of heavy metal stress. Our work thus facilitates the study of β-gal biological mechanisms.

Two-photon fluorescence probe for palladium with perchlorate induced quenching mechanism and its application in smartphone-based rapid detection

We propose a new approach for detecting palladium using a two-photon fluorescent probe quenched by perchlorate. This newly developed method has the potential to overcome some of the limitations of the currently available methods for detecting palladium. This article provides a detailed introduction to the design and synthesis of fluorescent probe, as well as the fluorescence performance in aqueous solutions. The results demonstrate the probe is highly sensitive, selective, and efficient in detecting palladium. The study also includes a thorough analysis of the quenching mechanism of the probe by perchlorate, and obtained different results from previous literatures. Moreover, the probe can easily identify and differentiate between palladium being present in the valence states 0, + 2/+ 4, and accomplish detecting palladium in convoluted solutions such as wastewater, environmental water, Hela cells and zebrafish. Due to its excellent performance, using self-developed optical device, the possibility of detecting palladium in aqueous solutions based on smartphone was explored.

Fluorescent and chromogenic organic probes to detect group 10 metal ions: design strategies and sensing applications

Group 10 metals including Ni, Pd and Pt have been extensively applied in various essential aspects of human social life, material science, industrial manufactures, medicines and biology. The ionic forms of these metals are involved in several biologically important processes due to their strong binding capability towards different biomolecules. However, the mishandling or overuse of such metals has been linked to serious contamination of our ecological system, more specifically in soil and water bodies with acute consequences. Therefore, the detection of group 10 metal ions in biological as well as environmental samples is of huge significance from the human health point of view. Related to this, considerable efforts are underway to develop adequately efficient and facile methods to achieve their selective detection. Optical sensing of metal ions has gained increasing attention of researchers, particularly in the environmental and biological settings. Innovatively designed optical probes (fluorescent or colorimetric) are usually comprised of three basic components: an explicitly tailored receptor unit, a signalling unit and a clearly defined reporter unit. This review deals with the recent progress in the design and fabrication of fluorescent or colorimetric organic sensors for the detection of group 10 metal ions (Ni(II), Pd(II) and Pt(II)), with attention to the general aspects for design of such sensors.

New nano materials-based optical sensor for application in rapid detection of Fe(II) and Pd(II) ions

For the analytical determination of Fe(II) and Pd(II) concentrations, a novel optical sensor based on spectrophotometric technique was used. The optical sensor was prepared by direct immobilization of a novel synthesized chromophore, 5-amino-phenanthrolin-3 formyl salicylic acid, onto nanocellulose. Human vision can identify the color associated with Fe II ions, and spectrophotometric methods can measure it with detection and quantification limits of 0.239 and 0.796 ppb, respectively. Pd(II) detection and quantification limits were 0.318 ppb and 1.06 ppb, respectively. The effects of various parameters on the detection of Fe(II) or Pd(II) ion content were investigated and optimized. The optical phenanthroline-nanocellulose (5-Phen) sensor could be reproduced multiple times and used with a higher capacity each time. The results demonstrated that the 5-Phen sensor could measure Fe(II) in human blood serum accurately and successfully even without any pre-concentration.

Imaging mitochondrial palladium species in living cells with a NIR iridium(III) complex

The wide use of palladium (Pd) raises the concern about environmental pollution and human diseases, evoking the need for the development of detection methods for Pd species. However, the development of near-infrared (NIR) luminescence probes for subcellular Pd species remains challenging. In this work, we presented a NIR iridium(III) complex-based luminescence probe for the detection of Pd⁰ species through incorporating an allyl group and amino group into the N^N ligand. We found that the probe was capable of detecting Pd⁰ species with a limit of detection (LOD) of 0.5 μM. Importantly, cell imaging experiments showed that the probe is applicable for visualizing mitochondrial Pd⁰ ions in living cells, which are also suitable for Pd(II) species. To the best of our knowledge, this is the first NIR luminescence imaging probe for the detection of mitochondria Pd species in living cells, paving the way for studying subcellular distributions and related toxicity analysis of exogenous Pd species in living cells.

A new ratiometric switch "two-way" detects hydrazine and hypochlorite via a "dye-release" mechanism with a PBMC bioimaging study

A new ratiometric fluorescent probe (E)-2-(benzo[d]thiazol-2-yl)-3-(8-methoxyquinolin-2-yl)acrylonitrile (HQCN) was synthesised by the perfect blending of quinoline and a 2-benzothiazoleacetonitrile unit. In a mixed aqueous solution, HQCN reacts with hydrazine (N₂H₄) to give a new product 2-(hydrazonomethyl)-8-methoxyquinoline along with the liberation of the 2-benzothiazoleacetonitrile moiety. In contrast, the reaction of hypochlorite ions (OCl^-) with the probe gives 8-methoxyquinoline-2-carbaldehyde. In both cases, the chemodosimetric approaches of hydrazine and hypochlorite selectively occur at the olefinic carbon but give two different products with two different outputs, as observed from the fluorescence study exhibiting signals at 455 nm and 500 nm for hydrazine and hypochlorite, respectively. A UV-vis spectroscopy study also depicts a distinct change in the spectrum of HQCN in the presence of hydrazine and hypochlorite. The hydrazinolysis of HQCN exhibits a prominent chromogenic as well as ratiometric fluorescence change with a 165 nm left-shift in the fluorescence spectrum. Similarly, the probe in hand (HQCN) can selectively detect hypochlorite in a ratiometric manner with a shift of 120 nm, as observed from the fluorescence emission spectra. HQCN can detect hydrazine and OCl^- as low as 2.25 × 10^-8 M and 3.46 × 10^-8 M, respectively, as evaluated from the fluorescence experiments again. The excited state behaviour of the probe HQCN and the chemodosimetric products with hydrazine and hypochlorite are studied by the nanosecond time-resolved fluorescence technique. Computational studies (DFT and TDDFT) with the probe and the hydrazine and hypochlorite products were also performed. The observations made in the fluorescence imaging studies with human blood cells manifest that HQCN can be employed to monitor hydrazine and OCl^- in human peripheral blood mononuclear cells (PBMCs). It is indeed a rare case that the single probe HQCN is found to be successfully able to detect hydrazine and hypochlorite in PBMCs, with two different outputs.

An effective approach to develop targetable and responsive fluorescent probes for imaging of organelles based on cresyl violet scaffold

Fluorescent probes combined with confocal microscopy are recognized as a powerful tool for imaging living cells and even organelles due to their high sensitivity and resolution. However, many of analyte-activatable and organelle-targetable fluorescent probes are developed via tedious attempts, and a relatively predictable method to design such probes is still lacking. Herein, we put forward an effective synthetic strategy to construct both targetable and responsive probes for organelles based on the cresyl violet scaffold. The approach allows access to a variety of organelle-targeting fluorescent probes for an analyte of interest via introducing the corresponding targeting and recognition groups to the 5- and 9-positions of cresyl violet, respectively. The potency of the approach is exemplified by its application to develop four cresyl violet-based fluorophores with different organelle-targeting groups, and a mitochondrion-targeting ratiometric probe capable of imaging Pd⁰ in living cells.

Novel Boronate Probe Based on 3-Benzothiazol-2-yl-7-hydroxy-chromen-2-one for the Detection of Peroxynitrite and Hypochlorite

Derivatives of coumarin, containing oxidant-sensitive boronate group, were recently developed for fluorescent detection of inflammatory oxidants. Here, we report the synthesis and the characterization of 3-(2-benzothiazolyl)-7-coumarin boronic acid pinacol ester (BC-BE) as a fluorescent probe for the detection of peroxynitrite (ONOO-), with high stability and a fast response time. The BC-BE probe hydrolyzes in phosphate buffer to 3-(2-benzothiazolyl)-7-coumarin boronic acid (BC-BA) which is stable in the solution even after a prolonged incubation time (24 h). BC-BA is slowly oxidized by H2O2 to form the phenolic product, 3-benzothiazol-2-yl-7-hydroxy-chromen-2-one (BC-OH). On the other hand, the BC-BA probe reacts rapidly with ONOO-. The ability of the BC-BA probe to detect ONOO- was measured using both authentic ONOO- and the system co-generating steady-state fluxes of O2•- and •NO. BC-BA is oxidized by ONOO- to BC-OH. However, in this reaction 3-benzothiazol-2-yl-chromen-2-one (BC-H) is formed in the minor pathway, as a peroxynitrite-specific product. BC-OH is also formed in the reaction of BC-BA with HOCl, and subsequent reaction of BC-OH with HOCl leads to the formation of a chlorinated phenolic product, which could be used as a specific product for HOCl. We conclude that BC-BA shows potential as an improved fluorescent probe for the detection of peroxynitrite and hypochlorite in biological settings. Complementation of the fluorescence measurements by HPLC-based identification of oxidant-specific products will help to identify the oxidants detected.

A highly sensitive fluorescent probe for ozone based on coumarin-benzothiazole derivative

Ozone is widely used in daily life, but studies have shown that O3 can damage human trachea and lungs, leading to diseases such as asthma, emphysema, and bronchitis. Therefore, it is of great significance to develop a simple and efficient detection method for monitoring O3 in living cells. In this study, 3-(but-3-en-1-yl)-2-(7-(but-3-en-1-yloxy)-2-oxo-2H-chromen-3-yl)benzo[d]thiazol-3-ium (BCT) as a new type of water-soluble fluorescent probe was synthesized by substitution reaction of 4-bromo-1-butene and hydroxycoumarin-benzothiazole derivatives, which can specifically detect ozone in aqueous solution. The interaction of ozone on the probe can be completed within 20 min, the fluorescence intensity is significantly enhanced, and it has the advantages of high sensitivity (detection limit LOD = 43 nM). The influence of pH on the fluorescent performance of BCT shows that the probe with super stability under weak alkali and acidic environment, which provides the necessary conditions for its detection of ozone in physiological system detection. Therefore, BCT is expected to become an effective tool for detecting ozone in cellular organisms.

Hetarenocoumarins based on 7-hydroxy-3-(benzothiazol-2-yl)coumarin

The syntheses of angular hetarenocoumarins, namely chromeno[8,7-e][1,3]oxazin-2-ones and furo[2,3-h]chromen-2-one, have been accomplished starting from 7-hydroxy-3-(benzothiazol-2-yl)-coumarin using aminomethylation and formylation reactions.

A Near-infrared Fluorescent Probe of Dicyanoisophorone Derivatives for Selective Detection and Fluorescence Cellular Imaging of Palladium

Palladium (Pd) has been acknowledged to be a rare inner transition metal, which plays a pivotal role in many fields. This article focuses on developing a safe and effective near-infrared fluorescent probe, MW-PD, which would make a great contribution to the detection of palladium residue in drugs, especially trace residues. The fluorescent probe was rationally designed by combining the dicyanoisophorone fluorophore with an allyloxycarbonyl group. Based on the Tsuji-Trost reaction, the probe exhibited high selectivity and sensitivity toward Pd (0) over other common metal ions with a low detection limit (8.0 nM). Moreover, MW-PD showed biocompatibility and was successfully applied to imaging Pd (0) in Hela cells.

Whey peptide-encapsulated silver nanoparticles as a colorimetric and spectrophotometric probe for palladium(II)

Silver nanoparticles (AgNPs) coated with whey peptides are shown to be a useful optical nanoprobe for the highly sensitive determination of Pd(II). The peptidic surface of the AgNPs works as a molecular receptor for the rapid detection of Pd(II) via a color change from dark yellow to orange/red along with a spectral red-shift with a gap about 120 nm. The effect is caused by the formation of a coordination complex between Pd(II) and the peptide ligands. This results in the aggregation of AgNPs and an absorbance spectral shift from 410 to 530 nm. The absorbance response is linear in the range 0.1 to 1.3 μM Pd(II) with a low detection limit of 115 nM. The nanoprobe responds within a few minutes and is not interfered by other metal ions except for Mg(II). The probe potentially can be applied to the determination of Pd(II) contamination in the products of Pd(II)-catalyzed organic reactions and in pharmaceutical settings. Graphical abstractSchematic representation of the nanoprobe for Pd(II). (a) Synthesis of whey peptide-coated silver nanoparticles (AgNPs), (b) the nanoprobe design for Pd(II) detection, (c) HR-TEM imaging and elemental mapping, (d) quantitative determination of Pd(II) (Inset shows colorimetric results).

An umbelliferone-derivated fluorescent sensor for selective detection of palladium(II) from palladium(0) in living cells

Palladium (Pd) has drawn worldwide attentions because its connections to industry, chemistry, biological material and public health. Quantitative and selective detection tools for Pd and its ion forms are in urgent necessity. Here an umbelliferone derivative Umb-Pd2 was provided as a small, steady, safe and selective sensor for detecting Pd(II). It indicated advantages including sensitive (LOD 1.1 nM), wide pH tolerance (5.0-10.0), applicable linear range (0-1.8 equivalent) and low toxicity. The most attractive point was its explicit selectivity towards Pd(II) from Pd(0) in both independent and coexistence systems. This distinguishing ability was further utilized in imaging in living cells, raising this work as a rare and important example among all the published papers on palladium sensing. Thus, Umb-Pd2 supplied a potential approach for further improvement and applications in both daily chemistry and public health.

A fluorescent probe for carbon monoxide based on allyl ether rather than allyl ester: A practical strategy to avoid the interference of esterase in cell imaging

Pd⁰-mediated Tsuji-Trost reaction is a practical strategy to design fluorescent probes for carbon monoxide (CO) sensing, and in such reaction CO can reduce Pd²⁺ to Pd⁰ in-situ and remove allyl groups on fluorophores. In most of these probes, esters are commonly used to link allyl on fluorophores. We found that the ester groups could be hydrolyzed by esterase activity of fetal bovine serum (FBS), while FBS is a requisite in cell culture, and the hydrolysis could interfere the Pd⁰-mediated Tsuji-Trost reaction. In this study, we synthesized a fluorescent probe (Cou-CO) using allyl ether as reaction site rather than allyl ester. Cou-CO is non-fluorescence, and could react with CO under the presence of Pd⁰ to form Cou with strong fluorescence, and the maximum excitation and emission wavelengths of Cou are 464 nm and 495 nm respectively. Cou-CO shows excellent selectivity to CO and could avoid the effect of FBS with the limit of detection for CO is 78 nm. Finally, Cou-CO was successfully applied for imaging of CO in living cells.

A new turn-on fluorescent probe for the detection of palladium(0) and its application in living cells and zebrafish

A new “turn-on” fluorescent probe 1 for the detection of Pd⁰ has been designed and synthesized.

A lysosome targetable fluorescent probe for palladium species detection base on an ESIPT phthalimide derivative

A novel lysosome-targetable phthalimide fluorescent probe was designed for detecting palladium based on ESIPT for signal transduction. The fluorescent probe conjugating with allylcarbamate displayed weak fluorescent due to the ESIPT process hinder by allylcarbamate. But with the addition of palladium, the ESIPT emission was recovery though the palladium-catalyzed deallylation reaction and the fluorescence intensity exhibited 40-fold enhancement at 511 nm. In addition, the probe showed excellent selectivity, high sensitivity, fast responds and low limit detection for palladium with a larger Stoke-shift. Moreover, the targetable probe was also successfully applied for detecting palladium in lysosomes of living cells. Hence, the probe though ESIPT modulation is a promising for monitoring palladium in practical samples.

A new colorimetric, near-infrared fluorescent probe for rapid detection of palladium with high sensitivity and selectivity

A new type of colorimetric, fluorescent palladium (Pd) probe characterized with beaconing fluorescence signal in the quiet near-infrared (NIR) region (centered ~ 717 nm), recognition response time of approximately 3 min, limit of detection (LOD) down to 5.1 ppb, and excellent recognition specificity over a wide range of interfering metal cations was developed. It is believed that the probe underwent sequential Pd⁰-mediated oxidative addition and reduction elimination reactions, yielding typical D-π-A molecular skeleton of the final reaction product capable of intramolecular charge transfer (ICT). The benzothiazole moiety of the probe molecular skeleton is believed to play a vital trole in shifting the beaconing fluorescence signal to the quiet NIR region and accelerating the Pd⁰ recognition process of the probe via the formation of the fluorescent reaction product with largely extended π-delocalization. With unique advantages, the fluorescent probe we developed will find practical applications for detecting residual Pd with concentration below the safety margin in pharmacy and biomedical engineering.

Readily Available Fluorescent Probe for Carbon Monoxide Imaging in Living Cells

Carbon monoxide (CO) is an important gasotransmitter in living systems and its fluorescent detection is of particular interest. However, fluorescent detection of CO in living cells is still challenging due to lack of effective probes. In this paper, a readily available fluorescein-based fluorescent probe was developed for rapid detection of CO. This probe can be used to detect CO in almost wholly aqueous solution under mild conditions and shows high selectivity and sensitivity for CO with colorimetric and remarkable fluorescent turn-on signal changes. The detection limit of this probe for CO is as low as 37 nM with a linear range of 0-30 μM. More importantly, this probe (1 μM dose) can be conveniently used for fluorescent imaging CO in living cells.

Highly selective fluorescence detection of Pd2+/4+ species based on a catalyzed aromatic Claisen rearrangement

A highly selective chemodosimeter based on 1,8-naphthalimide for Pd^2+/4+ species via a Claisen rearrangement was developed with a detection limit of 1.4 μM.