A review of recent developments in fluorescent sensors for the selective detection of palladium ions

A comparative study of the physiological and biochemical properties of tomato (Lycopersicon esculentum M.) and maize (Zea mays L.) under palladium stress

There is great concern about the environmental impact and toxicity of palladium (Pd) because of its widespread use in automotive catalytic converters and other applications. Pd migrates and transforms in the environment and is absorbed by plant roots where it affects plant growth and eventually enters the food chain. Here we explored the effects of Pd on the physicochemical and biochemical characteristics of C3 (tomato) and C4 (maize) plants. We measured physicochemical and biochemical properties, including chlorophyll, protein, soluble sugar, antioxidant enzymes, malondialdehyde, proline, and root activity, in tomato and maize seedlings after cultivation in different concentrations of PdCl₂ solution (0, 0.2, 0.5, and 1 mM) in order to observe how Pd stresses them. Results showed that, with increasing Pd concentration, chlorophyll a and chlorophyll b contents and root activity decreased. Meanwhile, malondialdehyde, proline, protein, and soluble sugar contents increased. After cultivation in 1 mM PdCl₂, the Pd contents in the roots, stems, and leaves of tomato seedlings were 12.389, 1.132, and 0.206 mg/g, respectively. In general, Pd has significant effects on the physiological and biochemical properties of both tomato and maize. Additionally, tomato seedlings were more sensitive to Pd stress, photosynthesis in maize was less inhibited by Pd and the antioxidant capability of maize was stronger. These results indicated that maize (C4 plant) exhibited a higher tolerance to Pd than tomato (C3 plant). Pd migration in tomato was observed and the translocation factor (TF) was calculated. The values of TF_stem/root, TF_leaf/root, TF_leaf/stem, and TF_shoot/root were 0.09, 0.02, 0.18, and 0.11 in tomato seedlings, respectively. Pd accumulated most in the roots, followed in turn by stems, leaves, and only trace amount of Pd was transferred into shoots.

A colorimetric chemosensor for quantification of exchangeable Cu2+ in soil

Chemosensors have already demonstrated potential for the detection and imaging of metal ions in solutions and biological systems, however, their applications to soil analysis are limited. This study explores the potential of utilizing a chemosensor for the detection of exchangeable Cu²⁺ in soils via qualitative (solution visual color change) and quantitative (UV-Vis spectrophotometry) approaches. Montmorillonite and kaolin clays were doped with Cu(NO₃)₂ solutions from 2.5 to 50 mM, and contaminated soil samples were collected from a historic copper mine. The exchangeable Cu²⁺ was extracted using a standard CaCl₂ cation exchange approach, and the Cu²⁺ concentration in the resulting solutions determined by UV-Vis spectrophotometry, using a chemosensor, and compared to traditional ICP-MS analysis. Analytical results showed that the chemosensor provided a visual response in contaminated soils at concentrations of 25 μM and quantitative detection to concentrations of 1 μM using UV-Vis spectrophotometry. This work demonstrates the first reported chemosensor for exchangeable Cu²⁺ with application to soil systems.

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).

Two-Dimensional Metal-Organic Framework Nanosheets as a Dual Ratiometric and Turn-off Luminescent Probe

Current research on metal-organic framework (MOF) luminescent sensing probes focuses on the design of three-dimensional bulk-sized MOFs that in return limits their up-close interactions with targeted guest molecules. In this work, we report a two-dimensional (2D) copper-based metal-organic framework, namely, AUBM-6, synthesized via solvothermal method from isonicotinic acid linker and copper(II) ion. The resulting 2D-layered MOF crystals were highly fluorescent in their exfoliated form and, therefore, explored for detecting several solvents, where a ratiometric selectivity was shown toward acetone. Metal ion sensing was also performed, by which fluorescent detection was observed to have the highest turn-off quenching efficiency toward Pd²⁺.

Simple fabrication of a carbaldehyde based fluorescent “turn-on” probe for the selective and sole detection of Pd2+: application as test strips

A simple fluorescent “turn-on” probe (DHMC) has been designed for selective and sole detection of Pd²⁺.

Fluorescence sensing and intracellular imaging of Pd2+ ions by a novel coumarinyl-rhodamine Schiff base

Coumarinyl-rhodamine, HCR, served as an extremely selective sensor for Pd²⁺ ions in ethanol/H₂O (8 : 2, v/v, HEPES buffer, pH 7.2) solution and the limit of detection (LOD) was 18.8 nM (3σ method).

Structural, Luminescent and Thermal Properties of Heteronuclear PdII⁻LnIII⁻PdII Complexes of Hexadentate N₂O₄ Schiff Base Ligand

New Pd^II–Ln^III–Pd^II complexes of hexadentate N₂O₄ Schiff base ligand (H₄L: N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diamino-2,2-dimethylpropane) with Eu (1), Tb (2), Er (3) and Yb (4) ([Pd₂Eu(H₂L)₂NO₃](NO₃)₂∙2H₂O∙2CH₃OH 1, [Pd₂Ln(H₂L)₂H₂O](NO₃)₃∙3H₂O, where Ln = Tb 2, Er 3, [Pd₂Yb(H₂L)₂H₂O](NO₃)₃∙5.5H₂O 4) were synthesized and characterized structurally and physicochemically by thermogravimetry (TG), differential thermogravimetry (DTG), differential scanning calorimetry (DSC) and luminescence measurements. The compounds 1–4 are built of cationic heterometallic Pd^II–Ln^III–Pd^II trinuclear units. The palladium(II) centers adopt a planar square geometry occupying the smaller N₂O₂ cavity of the Schiff base ligand. The lanthanide(III) is surrounded by two Schiff base ligands (eight oxygen atoms) and its coordination sphere is supplemented by a chelating bidentate nitrate ion in 1 or by a water molecule in 2–4. The complexes have a bent conformation along the Pd^II–Ln^III–Pd^II line with valence angles in the ranges of 162–171°. The decomposition process of the complexes results in mixtures of: PdO, Pd and respective lanthanide oxides Eu₂O₃, Tb₂O₃, Tb₄O₇, Er₂O₃, Yb₂O₃. The luminescent measurements show low efficiency intramolecular energy transfer only in the complex of terbium(III) (2).