Cu2+ triggered fluorescence sensor based on fluorescein derivative for Pd2+ detection

Recent advances in dual-target-activated fluorescent probes for biosensing and bioimaging

Fluorescent probes have been powerful tools for visualizing and quantifying multiple dynamic processes in living cells. However, the currently developed probes are often constructed by conjugation a fluorophore with a recognition moiety and given signal-output after triggering with one singly target interest. Compared with the single-target-activated fluorescent probes mentioned above, the dual-target-activated ones, triggering with one target under stimulus (such as photoirradiation, microenvironment) or another targets, have the advantages of advoiding nonspecific activation and "false positive" results in complicated environments. In recent years, many dual-target-activated fluorescent probes have been developed to detect various biologically relevant species. In view of the importance of a comprehensive understanding of dual-target- activated fluorescent probes, a thorough summary of this topic is urgently needed. However, no comprehensive and critical review on dual target activated fluorescent probes has been published recently. In this review, we focus on the dual-target-activated fluorescent probes and briefly outline their types and current state of development. In each type, the chemical structure, proposed responsive mechanism and application of probes are highlighted. At last, the challenges and prospective opportunities of every type were proposed.

Fluorescein Based Fluorescence Sensors for the Selective Sensing of Various Analytes

Fluorescein molecules are extensively used to develop fluorescent probes for various analytes due to their excellent photophysical properties and the spirocyclic structure. The main structural modification of fluorescein occurs at the carboxyl group where different groups can be easily introduced to produce the spirolactam structure which is non-fluorescent. The spirolactam ring opening accounts for the fluorescence and the dual sensing of analytes using fluorescent sensors is still a topic of high interest. There is an increase in the number of dual sensors developed in the past five years and quite a good number of fluorescein derivatives were also reported based on reversible mechanisms. This review analyses environmentally and biologically important cations such as Cu2+, Hg2+, Fe3+, Pd2+, Zn2+, Cd2+, and Mg2+; anions (F-, OCl-) and small molecules (thiols, CO and H2S). Structural modifications, binding mechanisms, different strategies and a comparative study for selected cations, anions and molecules are outlined in the article.

Rhodamine-Appended Benzophenone Probe for Trace Quantity Detection of Pd2+ in Living Cells

Designing a fluorogenic probe for the determination of Pd²⁺ is a challenging analytical task. Pd²⁺ is a potentially toxic and harmful substance even at a very low level of contamination in the end product. Herein, a promising spirolactam-functionalized chemosensor, rhodamine-appended benzophenone (HBR), is designed and characterized by spectroscopic (¹H NMR, ¹³C NMR, ESI-MS, and FT-IR) data along with the single-crystal X-ray diffraction technique. It acts as a highly sensitive and selective fluorogenic chemosensor for Pd²⁺ ions over other environmentally relevant cations in aqueous ethanol (1:1, v/v) at pH 7.4. The limit of detection (LOD) is 34 nM that is far below the WHO recommended Pd uptake (47 μM). The plausible mechanism involves the specific binding of HBR with Pd²⁺ and the formation of 1:1 stoichiometry of the complex, which has been supported by ESI-MS, FT-IR data, Job plot, and association constant data (Benesi-Hildebrand plot). The computation study has been attempted to explain the ring cleavage fluorescence enhancement scheme of HBR upon binding with Pd²⁺. Furthermore, this "turn-on" probe has successfully applied to image the Pd²⁺ ion in cultured MDA-MB-231 cells.

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).

Green and Red Fluorescent Dyes for Translational Applications in Imaging and Sensing Analytes: A Dual-Color Flag

Red and green are two of the most-preferred colors from the entire chromatic spectrum, and red and green dyes are widely used in biochemistry, immunohistochemistry, immune-staining, and nanochemistry applications. Selective dyes with green and red excitable chromophores can be used in biological environments, such as tissues and cells, and can be irradiated with visible light without cell damage. This critical review, covering a period of five years, provides an overview of the most-relevant results on the use of red and green fluorescent dyes in the fields of bio-, chemo- and nanoscience. The review focuses on fluorescent dyes containing chromophores such as fluorescein, rhodamine, cyanine, boron-dipyrromethene (BODIPY), 7-nitobenz-2-oxa-1,3-diazole-4-yl, naphthalimide, acridine orange, perylene diimides, coumarins, rosamine, Nile red, naphthalene diimide, distyrylpyridinium, benzophosphole P-oxide, benzoresorufins, and tetrapyrrolic macrocycles. Metal complexes and nanomaterials with these dyes are also discussed.

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 novel ratiometric two-photon fluorescent probe for imaging of Pd(2+) ions in living cells and tissues

Ratiometric two-photon fluorescent probes can not only eliminate interferences from environmental factors but also achieve deep-tissue imaging with improved spatial localization. To quantitatively track Pd(2+) in biosystems, herein, we reported a ratiometric two-photon fluorescent probe, termed as Np-Pd, which based on a D-π-A-structure two-photon fluorophore of the naphthalimide derivative and deprotection of aryl propargyl ethers by palladium species. The probe Np-Pd displayed a more than 25-fold enhancement towards palladium species with high sensitivity and selectivity. Additionally, the probe Np-Pd was further used for fluorescence imaging of Pd(2+) ions in living cells and tissues under two-photon excitation (820nm), which showed large tissue-imaging depth (19.6-184.6μm), and a high resolution for ratiometric imaging.

A fluorescent and colorimetric probe containing oxime-ether for Pd(2+) in pure water and living cells

Palladium contamination causes potential danger to the environment, and a study of its biological safety is still on the way. Here, a fluorescent and colorimetric probe (compound 1) containing oxime-ether for Pd(2+) has been developed. 1 can detect Pd(2+) in aqueous samples with high selectivity and sensitivity. 1 can also work well in biological samples, which gives access to detect Pd(2+) in an organism.

Through-bond energy transfer-based ratiometric two-photon probe for fluorescent imaging of Pd(2+) ions in living cells and tissues

Palladium can cause severe skin and eye irritation once it enters the human body. Ratiometric two-photon fluorescent probes can both eliminate interference from environmental factors and realize deep-tissue imaging with improved spatial localization. To quantitatively track Pd(2+) in biosystems, we report here a colorimetric and two-photon ratiometric fluorescent probe, termed Np-Rh-Pd, which consists of a two-photon fluorophore (naphthalene derivative with a D-π-A structure) and a rhodamine B dye. The two fluorophores are directly linked to form a two-photon ratiometric fluorescent probe for Pd(2+) based on a through-bond energy transfer (TBET) strategy. It exhibits highly efficient energy transfer (90%) with two well-resolved emission peaks (wavelength difference of 100 nm), which could efficiently diminish the cross talk between channels and is especially favorable for ratiometric bioimaging applications. A signal-to-background ratio of 31.2 was observed for the probe, which affords a high sensitivity for Pd(2+) with a detection limit of 2.3 × 10(-7) M. It was also found that acidity does not affect the fluorescent response of the probe to Pd(2+), which is favorable for its applications in practical samples. The probe was further used for fluorescence imaging of Pd(2+) ions in live cells and tissue slices under two-photon excitation, which showed significant tissue-imaging depths (90-270 μm) and a high resolution for ratiometric imaging.

Fluorescence sensors for Zn(2+) based on conjugated indole Schiff base

Two novel fluorescence probes based on conjugated Schiff base for the detection of Zn(2+) were developed. Corresponding molecular geometries, orbital energies, electron contributions and absorption properties of the fluorescence probes were calculated at B3LYP/6-31G(∗) by density functional theory. The fluorescence properties of the probes were investigated by UV-vis and fluorescence spectrometer. Results indicate that the probes exhibit excellent sensitivity and selectivity for Zn(2+) compared with metal ions examined. For example, the enhancement efficiency of the compound 2 for Zn(2+) is up to 846%. The detection limit of the sensor toward Zn(2+) could low to 1.0×10(-7)M. Moreover, mechanisms for the high selectivity and sensitivity of the probes to Zn(2+) were studied.

A colorimetric and fluorescent turn on chemodosimeter for Pd(2+) detection

A novel rhodamine derivative L had been successfully developed and well characterized by NMR, and Mass spectroscopy. Chemodosimeter L is a naked-eye fluorescent chemodosimeter for Pd(2+) in aqueous solution. More over the detection limit of Chemodosimeter L is in 10(-7)M level. The Ligand to L ratio was determined to be 1:2 according to the job's plot.

Highly selective and reversible chemosensor for Pd(2+) detected by fluorescence, colorimetry, and test paper

A "turn-on" fluorescent and colorimetric chemosensor (RBS) for Pd(2+) has been designed and synthesized through introduction of sulfur as a ligand atom to Rhodamine B. RBS exhibits high selectivity (freedom from the interference of Hg(2+ )in particular) and sensitivity toward Pd(2+) with a detection limit as low as 2.4 nM. RBS is also a reversible sensor, and it can be made into test paper to detect Pd(2+) in pure water. Compared to the chemosensors that introduced phosphorus to Rhodamine to detect Pd(2+), RBS can be synthesized more simply and economically.

A sensitive and selective chemiluminogenic probe for palladium

Palladium triggered removal of a propargyl group leads to the cleavage of the 1,2-dioxetane ring, leading to bright chemiluminescence.

Colourimetric and fluorescent probes for the optical detection of palladium ions

In recent years, the development of optical probes to analyse trace palladium ions (Pd(2+)) has attracted great attention because of the residual palladium released by catalytic converters or from various Pd-catalysed reactions. These residual palladium ions may cause potential health hazards. This review provides a brief introduction to the new methods used to determine trace amounts of Pd(2+), which then mainly focuses on the different reporting systems and unique mechanisms of the colourimetric and fluorescent probes used to detect Pd(2+), including Pd(2+) complex formation or Pd-catalysed reactions.