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

Aggregation-Induced Emission Phosphorescence Featured Au-Ag Coordination Polymer with a Diphosphine N-Heterocyclic Carbene Ligand for Highly Sensitive Detection of Cr(VI)

Luminescent materials with aggregation-induced emission (AIE) characteristics have been recognized as highly selective and sensitive probes for the detection of toxic metal ions in recent years. In this paper, a Au-Ag cluster-based coordination polymer [Au3Ag3(L)2(CN)6(H2O)2]n [1, L = 1,3-bis((diphenylphosphanyl)methyl)-4,5-dihydro-imidazolylidene] was prepared by in situ generation of the diphosphine N-heterocyclic carbene (PCNHCP)-type ligand L in the presence of the corresponding metal salts. Compound 1 exhibited 530 nm phosphorescence under 380 nm excitation with a QY of 6.30% and a lifetime (τ) of 7.14 μs in the solid state. 1 showed good AIE behavior in the mixture of MeOH/H2O while the best aggregation state (fwater = 90%, QY = 6.79%, τ = 6.70 μs) exhibited selective and sensitive emission quenching toward Cr(VI) ions. Ultralow detection limits of 9.7 ppb (w/w) for Cr2O72- and 17.9 ppb (w/w) for CrO42- were achieved.

Silver nanoprism-mediated colourimetric sensing probe for efficient detection of Pd(II) and Pt(II) ions in water and reuse of formed bimetallic nanoprisms

Sensitive and selective methods for detecting Pd(II) and Pt(II) ions in water are crucial for environmental monitoring and remediation. Although traditional methods for detection of Pd(II) and Pt(II) ions are accurate and sensitive, they face substantial challenges due to high costs, reliance on specialised equipment and limited field applicability, thereby presenting notable limitations. In this study, we introduce a novel colourimetric sensing probe designed specifically to identify Pd(II) and Pt(II) ions in aqueous solutions. This probe utilises the enhanced chemical stability of Ag nanoprisms achieved through Pd or Pt deposition on their surfaces. Our approach features exceptionally low limits of detection of 2.6 nM for Pd(II) and 0.3 nM for Pt(II), indicating an impressive detection range. Furthermore, the probe's ease of use, cost-effectiveness and compatibility with both naked eye and UV-Vis spectrophotometric detection make it a selective, reliable and affordable option for point-of-care analysis. Beyond its impressive sensitivity for ion detection, this methodology offers the additional benefit of enabling the on-demand synthesis of customised bimetallic catalysts. The synthesised Ag/Pd and Ag/Pt bimetallic nanoprisms demonstrate promising catalytic potential for environmental remediation. This advancement paves the way for efficient recycling and reuse of valuable Pd(II) and Pt(II) ions in various catalytic applications.

Novel activated NIR-II fluorescence/Ratio photoacoustic probe for dual-modality accurate imaging of palladium ions overload in mouse liver

Palladium contaminants can pose risks to human health and the natural environment. Once Pd2+ enters the body, it can bind with DNA, proteins, and other macromolecules, disrupting cellular processes and causing serious harm to health. Therefore, it becomes critical to develop simple, highly selective and precise methods for detecting Pd2+in vivo. Here, we have successfully developed the first activated second near-infrared region fluorescence (NIR-II FL) and ratio photoacoustic (PA) probe NYR-1 for dual-modal accurate detection of Pd2+ levels. NYR-1 is capable of rapidly (< 60 s) and sensitively detection of Pd2+ in solution, providing switched on NIR-II FL920 and ratio PA808/PA720 dual-mode signal change. More notably, the probe NYR-1 was successfully used for non-invasive imaging of Pd2+ overload in mouse liver by NIR-II FL/Ratio PA dual-modality imaging technology for the first time. Thus, this work opens up a promising dual-modal detection method for the precise detection of Pd2+ in organisms and in the environment.

Indium nanocubes based recyclable fluorescent chemosensor for sustainable environmental monitoring: pH-induced fluorescence transition and selective detection of Pd(II) ions

Rapid modern industrialization and urbanization have escalated heavy metal pollution, with palladium (Pd2+) raising significant concerns due to its extensive usage in catalysis, hydrogen storage, and electronics, thereby imposing substantial risks on the environment and human health. In this study, we report a highly fluorescent indium nanocubes based chemosensor (InNCs) functionalized with perylene tetracarboxylic acid (PTCA) and 4-(pyridyl)ethenyl benzene (PEB). The InNCs exhibited emission maximum at 415 nm (λex ∼ 350 nm) with robust chemical and photo-stability, and acted as a fluorogenic probe for selective recognition of Pd2+ in aqueous medium. The fluorescence sensing properties of InNCs were thoroughly assessed via different techniques including steady-state absorption, emission and time-resolved emission spectroscopic methods. Among the various competitive analytes, only Pd2+ could induce a significant fluorescence quenching in the probe. This "turn-off" fluorescence sensing demonstrated a remarkably low LoD of ∼65 nM. Notably, with the addition of EDTA, the probe displayed good recyclability upto 4 cycles. The sensory probe was successfully employed as a reusable platform to estimate Pd(II) in different real water and soil samples with considerable accuracy (∼ 5-10 % error). Moreover, the probe exhibited a pH-induced fluorescence transition, indicating its potential to be applied as a pH sensor. The Pd(II) binding and pH-sensing mechanisms have also been elucidated through density functional theory (DFT) calculations.

Isatin-Schiff base functionalized graphene oxide as a highly selective turn-on fluorescent probe for the detection of Pd(II) via photoinduced electron transfer pathway

We investigated the use of isatin-Schiff base functionalized graphene oxide (ISBGO) as a selective fluorescent chemosensor for the detection of palladium ions. Selectivity tests indicated that over 23 metal ions tested, ISBGO (λex = 340 nm, λem = 504 nm) showed the highest affinity for Pd(II), displaying a 10.1-fold enhancement. Also, interference tests proved that in the presence of both Pd(II) and other metal ions, there was still high fluorescence intensity and no considerable quenching occurred. According to DFT and TD-DFT calculations, photo-induced electron transfer (PET) is responsible for the turn-on response produced by the chemosensor. Coordination of Pd(II) with ISBGO in fact blocks PET from imine nitrogen of 3-iminoindolin-2-one moiety to the benzene ring, which in turn leads to a turn-on response. In addition, Job's plot analysis and Benesi-Hildebrand approach suggest that ISBGO preferably forms a 1:1 complex with Pd(II) with an association constant of 1.020 × 105 M-1. Moreover, FT-IR spectroscopy and DFT study showed that amide oxygen and imine nitrogen of 3-iminoindolin-2-one moiety acted as binding sites of ISBGO. High sensitivity, fast response, great degree of sensitivity, short life time, low detection limit of 32 nM combined with high association constant (Kf) of 1.020 × 105 M-1 and increased fluorescence quantum yield (Φf) of roughly 1.5-fold in the presence of Pd (II), highlight the role of ISBGO as an excellent probe for sensing Pd(II) in aqueous solution.

A near-infrared emitting "off-on" fluorescent probe for bioimaging of Pd(Ⅱ) ions in living cells and mice

BACKGROUND

The surging consumption of palladium in modern industry has given rise to its accumulation in the ecosystem, posing conspicuous toxicity to aquatic organisms and human health. The investigation of palladium in biological systems is highly demanded for the in-depth understanding of its dynamics and behaviors. Fluorescence imaging serves as a powerful approach to assess palladium species in biological systems, and currently most of the sensing probes are applicable to living cells. Effective tracking of palladium species in living organisms is challenging, which requires sufficient hydrophilicity and imaging depth of the probes.

RESULTS

Based on an intramolecular charge transfer (ICT) mechanism, a distyryl boron dipyrromethene (BODIPY) derivative (DISBDP-Pd) has been prepared for the near-infrared (NIR) fluorescence imaging of Pd2+ ions. Two additional methoxy triethylene glycol (TEG) chains could serve as flexible and hydrophilic moieties to enhance the aqueous solubility and cell permeability of the extended conjugate. Solution studies revealed that DISBDP-Pd exhibited a NIR fluorescence enhancement signal exclusively to Pd2+ ions (detection limit as low as 0.85 ppb) with negligible interference from Pd0 species and other closely related metal ions. Computational calculations have been performed to rationalize the binding mode and the mechanism of action. Fluorescence imaging assays have been conducted on A549 human non-small cell lung carcinoma cells and mouse models. Exhibiting negligible cytotoxicity, DISBDP-Pd demonstrated concentration-related fluorescence enhancement signals in response to Pd2+ ions in living cells and mice.

SIGNIFICANCE

DISBDP-Pd exhibits advantages over many small molecule palladium probes in terms of satisfactory aqueous solubility, high sensitivity and selectivity, and biocompatible NIR emission property, which are particularly favorable for the sensing application in biological environments. The design strategy of this probe can potentially be adopted for the functionalization of other BODIPY probes implemented for NIR fluorescence bioimaging.

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.

A colorimetric and fluorescent signaling probe for assaying Pd2+ in practical samples

We developed an optical signaling probe to detect Pd2+ ions in Pd-containing catalyst and drug candidate. The Pd2+ signaling probe (Res-DT) was readily prepared by reacting the versatile fluorochrome resorufin with phenyl chlorodithioformate. In a phosphate-buffered saline solution (pH 7.4) containing sodium dodecyl sulfate (SDS) as a signal-boosting surfactant, Res-DT exhibited a pronounced colorimetric response with a chromogenic yellow to magenta shift, leading to a substantial increase in the fluorescence intensity. The Pd2+ signaling performance of Res-DT was attributed to the Pd2+-promoted hydrolysis of the dithioate moiety. The probe displayed high selectivity toward Pd2+ ions and remained unaffected by commonly encountered coexisting components. Moreover, the detection limit of Res-DT for Pd2+ ions was 10 nM, and the signaling was achieved within 7 min. Furthermore, to demonstrate the real-world applicability of Res-DT, a Pd2+ assay was performed in Pd-containing catalyst and drug candidate using an office scanner as an easily accessible measurement device. Our results highlight the prospects of Res-DT as a tool to detect Pd2+ ions in various practical samples, with potential applications in catalysis, medicine, and environmental science.

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.

Colorimetric Paper-Based Analytical Devices (PADs) Backed by Chemometrics for Pd(II) Detection

This paper presents the development of cheap and selective Paper-based Analytical Devices (PADs) for selective Pd(II) determination from very acidic aqueous solutions. The PADs were obtained by impregnating two cm-side squares of filter paper with an azoic ligand, (2-(tetrazolylazo)-1,8 dihydroxy naphthalene-3,6,-disulphonic acid), termed TazoC. The so-obtained orange TazoC-PADs interact quickly with Pd(II) in aqueous solutions by forming a complex purple-blue-colored already at pH lower than 2. The dye complexes no other metal ions at such an acidic media, making TazoC-PADs highly selective to Pd(II) detection. Besides, at higher pH values, other cations, for example, Cu(II) and Ni(II), can interact with TazoC through the formation of stable and pink-magenta-colored complexes; however, it is possible to quantify Pd(II) in the presence of other cations using a multivariate approach. To this end, UV-vis spectra of the TazoC-PADs after equilibration with the metal ions solutions were registered in the 300-800 nm wavelength range. By applying Partial Least Square regression (PLS), the whole UV-vis spectra of the TazoC-PADs were related to the Pd(II) concentrations both when present alone in solution and also in the presence of Cu(II) and Ni(II). Tailored PLS models obtained with matrix-matched standard solutions correctly predicted Pd(II) concentrations in unknown samples and tap water spiked with the metal cation, making the method promising for quick and economical sensing of Pd(II).

A sensitive ratiometric fluorescence probe with a large spectral shift for sensing and imaging of palladium

Palladium (Pd) is an important heavy metal with excellent catalytic properties and widely used in organic chemistry and the pharmaceutical industry. Efficient and convenient analytical techniques for Pd are urgently needed due to the hazardous effects of Pd on the environment and human health. Herein, we have developed five new ratiometric probes for the selective detection of Pd0 based on the Pd-catalyzed Tsuji-Trost reaction. Among them, the F-substituted probe PF-Pd showed the largest spectral shift (148 nm) and the most sensitive response (detection limit 2.11 nM). PF-Pd was employed to determine Pd0 in tap water or lake water samples, which presented satisfactory accuracy and precision. In addition, profiting from its distinct colorimetric response, visual detection of Pd0 was performed on PF-Pd loaded test strips or in field soil samples. Furthermore, fluorescence imaging of living 4T1 cells demonstrated that PF-Pd is suitable for imaging of intracellular Pd0. The good analytical performance of PF-Pd may enable it to be widely used in the convenient, rapid, sensitive and selective detection of Pd0 in environmental or biological analysis.

Dabcyl as a Naked Eye Colorimetric Chemosensor for Palladium Detection in Aqueous Medium

Industrial activity has raised significant concerns regarding the widespread pollution caused by metal ions, contaminating ecosystems and causing adverse effects on human health. Therefore, the development of sensors for selective and sensitive detection of these analytes is extremely important. In this regard, an azo dye, Dabcyl 2, was synthesised and investigated for sensing metal ions with environmental and industrial relevance. The cation binding character of 2 was evaluated by colour changes as seen by the naked eye, UV-Vis and 1H NMR titrations in aqueous mixtures of SDS (0.02 M, pH 6) solution with acetonitrile (99:1, v/v). Out of the several cations tested, chemosensor 2 had a selective response for Pd2+, Sn2+ and Fe3+, showing a remarkable colour change visible to the naked eye and large bathochromic shifts in the UV-Vis spectrum of 2. This compound was very sensitive for Pd2+, Sn2+ and Fe3+, with a detection limit as low as 5.4 × 10-8 M, 1.3 × 10-7 M and 5.2 × 10-8 M, respectively. Moreover, comparative studies revealed that chemosensor 2 had high selectivity towards Pd2+ even in the presence of other metal ions in SDS aqueous mixtures.

Organelle-targeting ratiometric fluorescent probes: design principles, detection mechanisms, bio-applications, and challenges

Biological species, including reactive oxygen species (ROS), reactive sulfur species (RSS), reactive nitrogen species (RNS), F-, Pd2+, Cu2+, Hg2+, and others, are crucial for the healthy functioning of cells in living organisms. However, their aberrant concentration can result in various serious diseases. Therefore, it is essential to monitor biological species in cellular organelles such as the cell membrane, mitochondria, lysosome, endoplasmic reticulum, Golgi apparatus, and nucleus. Among various fluorescent probes for species detection within the organelles, ratiometric fluorescent probes have drawn special attention as a potential way to get beyond the drawbacks of intensity-based probes. This method depends on measuring the intensity change of two emission bands (caused by an analyte), which produces an efficient internal referencing that increases the detection's sensitivity. This review article discusses the literature publications (from 2015 to 2022) on organelle-targeting ratiometric fluorescent probes, the general strategies, the detecting mechanisms, the broad scope, and the challenges currently faced by fluorescent probes.

Nanosensors: A smart remedy for early detection of clenbuterol contamination in food

Veterinary drugs which are primarily meant for livestock treatment have now been categorised under potential food contaminant due to its unregulated usage and abuse. Their over usage by animal workers lead to production of contaminated animal-based food products which contain veterinary drug residues. These drugs are also misused as growth promoters to enhance the muscle to fat ratio in human body. This review highlights the misuse of such a veterinary drug; Clenbuterol. In this review, we have comprehensively discussed the usage of nanosensors to detect clenbuterol in food samples. Colorimetric, fluorescent, electrochemical, SERS and electrochemiluminescence are major categories of nanosensors that have been utilized for this purpose. The mechanism through which these nanosensors detect clenbuterol have been discussed in detail. The limit of detection and recovery percentage values of each nanosensor have been compared. This review will impart significant information on various nanosensors for clenbuterol detection in real samples.

Novel Crown Ether Amino Acids as Fluorescent Reporters for Metal Ions

Unnatural amino acids with enhanced properties, such as increased complexing ability and luminescence, are considered to be highly attractive building blocks for bioinspired frameworks, such as probes for biomolecule dynamics, sensitive fluorescent chemosensors, and peptides for molecular imaging, among others. Therefore, a novel series of highly emissive heterocyclic alanines bearing a benzo[d]oxazolyl unit functionalized with different heterocyclic π-spacers and (aza)crown ether moieties was synthesized. The new compounds were completely characterized using the usual spectroscopic techniques and evaluated as fluorimetric chemosensors in acetonitrile and aqueous mixtures in the presence of various alkaline, alkaline-earth, and transition metal ions. The different crown ether binding moieties as well as the electronic nature of the π-bridge allowed for fine tuning of the sensory properties of these unnatural amino acids towards Pd²⁺ and Fe³⁺, as seen by spectrofluorimetric titrations.

Luminescence and Palladium: The Odd Couple

The synthesis, photophysical properties, and applications of highly fluorescent and phosphorescent palladium complexes are reviewed, covering the period 2018–2022. Despite the fact that the Pd atom appears closely related with an efficient quenching of the fluorescence of different molecules, different synthetic strategies have been recently optimized to achieve the preservation and even the amplification of the luminescent properties of several fluorophores after Pd incorporation. Beyond classical methodologies such as orthopalladation or the use of highly emissive ligands as porphyrins and related systems (for instance, biladiene), new concepts such as AIE (Aggregation Induced Emission) in metallacages or in coordination-driven supramolecular compounds (CDS) by restriction of intramolecular motions (RIM), or complexes showing TADF (Thermally Activated Delayed Fluorescence), are here described and analysed. Without pretending to be comprehensive, selected examples of applications in areas such as the fabrication of lighting devices, biological markers, photodynamic therapy, or oxygen sensing are also here reported.

Development of a push-π-pull phenothiazine-vinyl-isophorone fluorophore: a novel solvatochromic and pH indicator

Knoevenagel condensation of phenothiazine-3,7-dicarbaldehyde with an isophorone yielded a new phenothiazine derivative (PTZ-c) fluorophore. The solvatochromic and pH-sensing abilities of PTZ-c, an asymmetric fluorophore with a single isophorone molecule, were shown to be exceptional. PTZ-c produced very delicate absorbance and emission spectra. When the polarity of the solvent was increased, the PTZ-c emission spectra showed greater sensitivity than the absorption spectra. Multiple spectroscopic techniques, including Fourier transform infrared spectroscopy, nuclear magnetic resonance, and mass spectrometry, were used to characterize the manufactured PTZ-c sensor. To demonstrate the beneficial solvatochromic behaviour associated with intramolecular charge transfer, the absorption spectra of the synthesized DA PTZ-c dye were analyzed in different solvents of varying polarity. Band intensity and the wavelength of PTZ-c emission were also found to be highly solvent dependent. It was observed that when solvent polarity was increased to a maximum of 4122 cm^-1 , Stokes' shift also increased. To analyze the Stokes' shift that depended on the solvent, a linear correlation between solvation and energy was used. An investigation of PTZ-c quantum yield (ф) was also conducted. Both the absorbance and fluorescence spectra of the sensor in dimethylformamide as a function of pH were studied. A fluorescence peak was seen at 562 nm, whereas the greatest absorption wavelengths were found at 403 and 317 nm. It was shown that the pH-sensing mechanism depended on protons removed from the PTZ-c chromophore, which caused a colour shift and variation in both emission and colorimetric properties.

Citrate Functionalized Zirconium-Based Metal Organic Framework for the Fluorescent Detection of Ciprofloxacin in Aqueous Media

Ciprofloxacin (CIP) is a commonly used antibiotic for the treatment of infectious diseases in humans and as a prophylactic agent in the livestock industry, leading to the environmental discharge of significant amounts of CIP. CIP is stable in aquatic systems leading to its pseudo-persistence. Constant exposure to these antibiotics results in the generation of antibiotic-resistant pathogens and potential toxicity/hypersensitivity in humans. Therefore, it is necessary to develop a convenient, rapid, and cost-effective method for the monitoring of ciprofloxacin in environmental samples. Rhodamine-based fluorescent receptors have the limitation of aqueous solubility. Therefore, in order to overcome this drawback, we designed a novel fluorescent receptor based on a zirconium-based metal organic framework (MOF-808). The precursor, MOF-808, was synthesized and functionalized by using sodium citrate to obtain a receptor called C-MOF-808. The C-MOF-808 was structurally characterized by XRD and spectroscopic analyses. Thus, this synthesized receptor can be used for the fluorescent detection of CIP in aqueous media with a detection limit of 9.4 µM. The detection phenomena of the receptor were studied by absorption as well as fluorescent spectra. The binding behavior of CIP with the receptor was studied by FT-IR and ¹H-NMR analyses, and a binding mechanism is proposed.

Aryl-Phenanthro[9,10-d]imidazole: A Versatile Scaffold for the Design of Optical-Based Sensors

Fluorescent and colorimetric sensors are important tools for investigating the chemical compositions of different matrices, including foods, environmental samples, and water. The high sensitivity, low interference, and low detection limits of these sensors have inspired scientists to investigate this class of sensing molecules for ion and molecule detection. Several examples of fluorescent and colorimetric sensors have been described in the literature; this Review focuses particularly on phenanthro[9,10-d]imidazoles. Different strategies have been developed for obtaining phenanthro[9,10-d]imidazoles, which enable modification of their optical properties upon interaction with specific analytes. These sensing responses usually involve changes in the fluorescence intensity and/or color arising from processes like photoinduced electron transfer, intramolecular charge transfer, intramolecular proton transfer in the excited state, and Förster resonance energy transfer. In this Review, we categorized these sensors into two different groups: those bearing formyl groups and their derivatives and those based on other molecular groups. The different optical responses of phenanthro[9,10-d]imidazole-based sensors upon interaction with specific analytes are discussed.

Tm3+ Ion Blue Emission Quenching by Pd2+ Ions in Barium Phosphate Glasses: Fundamental Analysis toward Sensing Applications

The quenching effect of Pd²⁺ ions on the blue emission from Tm³⁺ was investigated for the first time using barium phosphate glass as model matrix. Glasses containing fixed Tm₂O₃ at 0.5 mol % and PdO up to 0.3 mol % (added relative to P₂O₅) were prepared by melting and first characterized for basic structural properties by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy. Thermal properties were then evaluated by differential scanning calorimetry (DSC). The focus was thereafter on evaluating the optical properties by absorption and photoluminescence (PL) spectroscopy with decay kinetics assessment. XRD confirmed the amorphous nature of the glasses synthesized. The vibrational spectroscopy assessment consistently exhibited the IR- and Raman-active bands characteristic of phosphate glasses, showing no significant variation with PdO codoping. The DSC analysis revealed all glasses possessed high thermal stability assessed by the differences (ΔT = T_g - T_x ≥ 154 °C) between glass transition temperatures (T_g) and onset of crystallization (T_x). A tendency of the T_g values to increase with PdO contents was however exhibited. In addition, specific enthalpies of crystallization showed magnitudes decreasing with increasing PdO concentration, thus suggesting crystallization suppression by Pd²⁺. Concerning the optical properties, it was observed that codoping the glasses with PdO (0.1-0.3 mol %) led to the development of the visible Pd²⁺ d-d absorption band (peak ≈415-410 nm). In addition, drastic PL quenching of the Tm³⁺ blue emission around 452 nm (¹D₂ → ³F₄ transition) was induced by Pd²⁺. Analyzing PL decay curves obtained by exciting Tm³⁺ ions at 359 nm while monitoring 452 nm emission revealed decreased ¹D₂ state lifetimes. Thus, a potential of Tm³⁺ for analytical sensing of Pd²⁺ in various matrices was suggested. Ultimately determining quenching constants from the PL data and based on the comparison of results from emission intensity and decay rates, likely Tm³⁺ → Pd²⁺ energy transfer processes underlying the PL quenching were proposed.

Vortex-assisted restricted access-based supramolecular solvent microextraction of trace Pb(II) ions with 4-(benzimidazolisonitrosoacetyl)biphenyl as a complexing agent before microsampling flame AAS analysis

A new oxime compound, 4-(benzimidazolisonitrosoacetyl)biphenyl (BIBP) was synthesized and used as a complexing agent in this study to preconcentrate trace amounts of Pb(II) ions with vortex-assisted restricted access-based supramolecular solvent microextraction (RA/SUPRAS-LPME) method. The new complexing agent was characterized by a combination of elemental analyses, Proton Nuclear Magnetic Resonance (¹H- NMR), Carbon-13 Nuclear Magnetic Resonance (¹³C NMR) and Fourier Transform Infrared spectroscopy (FT-IR) and techniques. Extraction of the complex which was formed at pH 8.0 was done by using a supramolecular solvent phase of tetrahydrofuran (THF) and 1-decanol. A microsampling flame atomic absorption spectrophotometer was used to measure the lead ion concentrations of the extract. The method optimized and the optimum experimental conditions were found as; pH = 8, amount of the ligand 2,25 mg, supramolecular solvent volume 50 μL, sample volume 20 mL and vortex time 3 min. The limit of detection (LOD), limit of quantification (LOQ) were calculated as 0.69 μg L^-1 and 2.29 μg L^-1, respectively. Linear range was found between 15.1 μg L^-1 and 606 μg L^-1. The developed method was applied to Pb(II) determination in real samples after evaluating the accuracy by using the TMDA-53.3 fortified environmental water sample as certified reference material.

Fluorescent-based nanosensors for selective detection of a wide range of biological macromolecules: A comprehensive review

Thanks to their unique attributes, such as good sensitivity, selectivity, high surface-to-volume ratio, and versatile optical and electronic properties, fluorescent-based bioprobes have been used to create highly sensitive nanobiosensors to detect various biological and chemical agents. These sensors are superior to other analytical instrumentation techniques like gas chromatography, high-performance liquid chromatography, and capillary electrophoresis for being biodegradable, eco-friendly, and more economical, operational, and cost-effective. Moreover, several reports have also highlighted their application in the early detection of biomarkers associated with drug-induced organ damage such as liver, kidney, or lungs. In the present work, we comprehensively overviewed the electrochemical sensors that employ nanomaterials (nanoparticles/colloids or quantum dots, carbon dots, or nanoscaled metal-organic frameworks, etc.) to detect a variety of biological macromolecules based on fluorescent emission spectra. In addition, the most important mechanisms and methods to sense amino acids, protein, peptides, enzymes, carbohydrates, neurotransmitters, nucleic acids, vitamins, ions, metals, and electrolytes, blood gases, drugs (i.e., anti-inflammatory agents and antibiotics), toxins, alkaloids, antioxidants, cancer biomarkers, urinary metabolites (i.e., urea, uric acid, and creatinine), and pathogenic microorganisms were outlined and compared in terms of their selectivity and sensitivity. Altogether, the small dimensions and capability of these nanosensors for sensitive, label-free, real-time sensing of chemical, biological, and pharmaceutical agents could be used in array-based screening and in-vitro or in-vivo diagnostics. Although fluorescent nanoprobes are widely applied in determining biological macromolecules, unfortunately, they present many challenges and limitations. Efforts must be made to minimize such limitations in utilizing such nanobiosensors with an emphasis on their commercial developments. We believe that the current review can foster the wider incorporation of nanomedicine and will be of particular interest to researchers working on fluorescence technology, material chemistry, coordination polymers, and related research areas.

Optical Sensor Array for the Early Diagnosis of Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder and has complicated pathobiology, leading to irreversible memory loss and severe cognitive dysfunction. For patients with AD, the advent of the disease usually occurs after years of pathological changes. The early diagnosis and monitoring of AD are of great significance as the early-stage intervention and treatment may be the most effective. Biomarkers, such as beta-amyloid and tau levels in cerebrospinal fluid (CSF) and brain, offer one of the most promising paths and are combined with neuroimaging and immunological detection for AD diagnosis. However, high expense and radiation of neuroimaging and low sensitivity of immunosorbent assay limited their applications. Meanwhile, the relevance of Aβ peptides and tau proteins to the development of AD remains highly debatable, meaning that detecting one specific biomarker holds limited prospects in achieving early and accurate detection of AD. Optical sensor arrays based on pattern recognition enable the discrimination of multiple analytes in complicated environments and are thus highly advantageous for the detection of AD with multi-biomarkers. In this review, we survey the recent advances of optical sensor arrays for the diagnosis of AD, as well as the remaining challenges.

Fluorescent “OFF–ON” Sensors for the Detection of Sn2+ Ions Based on Amine-Functionalized Rhodamine 6G

These structurally isomeric rhodamine 6G-based amino derivatives are designed to detect Sn2+ ions. The receptors exhibit rapid fluorescent “turn-on” responses towards Sn2+. The absorption (530 nm) and fluorescent intensity (551 nm) of the receptors increase when increasing the concentration of Sn2+. The hydrazine derivative exhibits more rapid sensitivity towards Sn2+ than the ethylene diamine derivative, indicating that the presence of an alkyl chain in the diamine decreases the sensitivity of the receptors towards Sn2+. The presence of carbonyl groups and terminal amino groups strongly influences the sensitivity of the chemosensors toward Sn2+ by a spirolactam ring-opening mechanism. The receptors exhibit 1:1 complexation with Sn2+ as evidenced by Job plot, and the corresponding limit of detection was found to be 1.62 × 10−7 M. The fluorescence images of the receptors and their complexes reveal their potential applications for imaging of Sn2+ in real/online samples.

Multicolour lanthanide(III) porous 1D coordination polymers: tunable wide spectrum emission and efficient CuII sensing

Five isostructural 1D porous coordination polymers (PCPs) with a general formula of {[M(L)(DMF)(H₂O)]·1.5H₂O}_n [M = Tb^III (1), Eu^III (2), Yb^III (3), Nd^III (4) and Er^III (5)] have been synthesized using a flexible tripodal organic linker (L) and characterized. Tb^III (1) and Eu^III (2) PCPs exhibit metal-based green and red emission, respectively, whereas Yb^III (3), Nd^III (4) and Er^III (5) PCPs show near-infrared (NIR) emission. Doping Eu^III in 1 in a precisely controlled stoichiometric amount leads to different mixed lanthanide PCPs, {[Tb_1-xEu_x(L)(DMF)(H₂O)]·1.5H₂O}_n (1a-1f) that show tunable emission including that of bright white light. The PCPs decorated with Lewis basic -O- binding sites make them potential candidates for the binding and selective sensing of traces of Cu^II ions, and this is illustrated for PCP 2 (limit of detection = 0.69 ± 0.02 ppm). The photoluminescence of 2 can be recovered by the introduction of a chelating ligand ethylenediaminetetraacetic acid (EDTA) without any structural disintegration, indicating the potential of the lanthanide PCPs for future sensing applications.

Aggregation Induced Emissive Luminogens for Sensing of Toxic Elements

The major findings in the growing field of aggregation induced emissive (AIE) active materials for the detection of environmental toxic pollutants have been summarized and discussed in this Review article. Owing to the underlying photophysical phenomenon, fluorescent AIE active molecules show more impact on sensing applications. The major focus in current research efforts is on the development of AIE active materials such as TPE based organic fluorescent molecules, metal organic framework, and polymers that can be employed for the detection of toxic pollutants such as CN- , NO2- , Hg2+ , Cd2+ , As3+ , As5+ , F- , Pb2+ , Sb3+ ions.

Aggregation-Induced Emission-Active Fluorescent Polymer: Multi-Targeted Sensor and ROS Scavenger

A multi-functional polymer with aggregation-induced emission (AIE)-active salicylaldehyde azine (SA) functionality and reactive oxygen species (ROS)-responsive thioether groups is readily prepared via thiol-ene click polymerization of SA derivative diacrylate monomer, poly(ethylene glycol) diacrylate, and 3,6-dioxa-1,8-octanedithiol. The obtained AIE-active polymer exhibited an unexpected strong emission in amide solvents compared to that in other common organic solvents that was dramatically decreased by adding a trace amount of water, suggesting that the polymer could be utilized as a water trace indicator in amide solvents. In the backbone, the PEG segments make the polymer well dispersed in water and the ROS-responsive thioether groups enable this polymer as a promising ROS scavenger, with embedded SA moieties as a fluorescent indicator for the hemolysis determination. Due to the ability of SA moieties to complex with Cu²⁺, this AIE polymer can also be utilized as a fluorescent sensor for selective Cu²⁺ detection in real-world water samples. Thus, this multi-functional polymer is anticipated to be well applied in biological and environmental applications.

Name reactions: strategies in the design of chemodosimeters for analyte detection

The design and synthesis of suitable chemodosimeters for the detection of toxic analytes has become challenging for new researchers nowadays in the molecular recognition field.

Ratiometric fluorescent determination of palladium based on the C–N bond cleavage of allyl quaternary ammonium

Allylpyridinium conjugated phenanthroimidazole is encapsulated into CTAC micelles, which can ratiometrically detect Pd⁰ with a LOD of 11.5 nM.

A Boron Dipyrromethene-Based Fluorescence 'OFF-ON' Probe for Sensitive and Selective Detection of Palladium(II) Ions and Its Application in Live Cell Imaging

A novel boron dipyrromethene (BODIPY)-based fluorescent probe BDP-Pd was designed and synthesized. Upon coordination with Pd²⁺ , the emission of the probe at 508 nm significantly increased, showing an 'OFF-ON' fluorescence response. The complexation of BDP-Pd with Pd²⁺ in both acetonitrile and aqueous solution were then studied by absorption and fluorescence spectra. The binding stoichiometry between the probe and Pd²⁺ was found to be 1 : 2, and the binding constant was determined to be 8.5×10¹⁰  M^-2 and 8.2×10¹⁰  M^-2 in acetonitrile and aqueous solution, respectively. The probe exhibited a detection limit as low as 0.72 ppb toward Pd²⁺ with no obvious interference from up to 21 species of common metal ions, suggesting BDP-Pd as a sensitive and selective fluorescent probe for Pd²⁺ detection. The fast fluorescence 'OFF-ON' phenomenon of the probe upon coordination with Pd²⁺ ions could be easily observed by a hand-hold UV lamp under naked eye in solution as well as on homemade test trips. Density functional theory (DFT) calculations were carried out to give the optimized structure of complex BDP-Pd : 2Pd²⁺ and rationalize the detection mechanism through a prohibited intramolecular photoinduced electron transfer (PET) process. The bio-imaging application of the probe was investigated and it showed excellent cell permeability for fluorescent imaging of Pd²⁺ ions in A549 human non-small cell lung cancer cells.

Novel pyrene-pyridine oligomer nanorods for super-sensitive fluorescent detection of Pd2

Conjugated polymers (CPs) can be fabricated into conjugated polymer nanoparticles of various shapes, thus tuning the hydrophobicity and sensing performances of the parent polymers. Herein, two new hydrophobic oligomeric CPs containing pyrene-pyridyl moieties, P1 and P2, were directly prepared and conveniently converted into hydrophilic nanorods, i.e. P1NRs and P2NRs (about 4-21 and 6-20 nm in diameter), by a modified microemulsion method. Notably, separated P1NRs exhibit excellent stability while P2NRs tend to stack on each other perhaps due to their different rigidity of π-delocalized backbones, which may have a profound effect on their fluorescence properties. In addition, Pd²⁺ can coordinate with the pyridyl N atoms, thereby causing ultrasensitive fluorescence quenching of P1NRs and P2NRs owing to the aggregation of oligomeric CP nanorods. These two simple nanosensors can help to determine Pd²⁺ with detection limits as low as 1 and 70 nM, respectively. It is worth noting that biocompatible P1NRs with bright blue fluorescence can be employed for efficient imaging of trace level Pd²⁺ ions in live cells.