Configuration of super-fast Cu2+-responsive chemosensor by attaching diaminomaleonitrile to BODIPY scaffold for high-contrast fluorescence imaging of living cells

A highly fluorescent Cu2+-responsive sensor, 2-amino-3-(BODIPYmethyleneamino)maleonitrile (BD) was constructed by attaching diaminomaleonitrile to a BODIPY scaffold. Cu2+ can be selectively recognized on a 2-s time-scale by way of fluorescence emission. When Cu2+ and BD coexist in solution, typical BODIPY emission was observed and the emission intensity could be increased to 334 times that of the blank dye solution. The mechanism of fluorescence increase is based on the generation of highly fluorescent species by Cu2+-triggered oxidative cyclization of the attached diaminomaleonitrile. The absolute fluorescence quantum yield (AFQY) of the cyclization product is 98% determined by integrating sphere. The highly emissive character can be attributed to the imidazole ring and dicarbonitrile on the BODIPY scaffold. It surpasses the meso-phenyl substituted analogue in AFQY and detection limits (DL). The specific Cu2+ recognition behavior was also validated in Hela cells with high-contrast fluorescence images.

Optical Imaging Opportunities to Inspect the Nature of Cytosolic Iron Pools

The chemical nature of intracellular labile iron pools (LIPs) is described. By virtue of the kinetic lability of these pools, it is suggested that the isolation of such species by chromatography methods will not be possible, but rather mass spectrometric techniques should be adopted. Iron-sensitive fluorescent probes, which have been developed for the detection and quantification of LIP, are described, including those specifically designed to monitor cytosolic, mitochondrial, and lysosomal LIPs. The potential of near-infrared (NIR) probes for in vivo monitoring of LIP is discussed.

A Phenalenone-based Fluorescent Probe for the Detection of Fe3+ ions

A phenalenone based "turn on" probe was developed for selective and sensitive detection of Fe³⁺ ions in aqueous solutions. The thiophene-2-carboxaldehyde (receptor unit) was integrated into the 6-amino-1-phenalenone (6-AP) (signal reporter unit) through the C = N bond formation. The probe, 6-APT, operated through subsequent hydrolysis of the C = N bond induced by the coordination of Fe³⁺ ions to the heteroatoms to form highly fluorescent 6-AP. The probe displayed remarkable characteristics such as rapid response time (< 1 min), high analyte selectivity, and low limit of detection (1.3 µM). The sensing approach offered an accurate method for the detection of Fe³⁺ ions in real water samples (tap water and drinking water). In addition to the fluorometric response, the presence of Fe³⁺ ions can be monitored under daylight by the change in the color of the solution. Importantly, this study is the first example of a phenalenone-based sensor developed for metal ion sensing in literature.

A Fluorescent Turn-On Sensor Toward Multiple Heavy Metal Ions Based on Meso-anisole Modified BODIPY Scaffold

A fluorescent turn-on sensor (BOPA) was configured by anchoring bis(pyridin-2-ylmethyl)-amine (DPA) unit to the BODIPY scaffold. It exhibits highly sensitivity and selectivity towards Pb²⁺, Ba²⁺, Cr³⁺, Cd²⁺, Hg²⁺, Zn²⁺ against the competent metal ions. Job's plot analysis supports the 1:1 stoichiometry of BOPA and metal ions. And linear relationship between fluorescence intensity and concentration of Zn²⁺ (representative metal ion) was observed over the range 0 ~ 20 μM Zn²⁺. The limit detection of BOPA in recognition of Pb²⁺, Ba²⁺, Cr³⁺, Cd²⁺, Hg²⁺, Zn²⁺ was ranged from 15.99 to 43.57 nM. Photo induced transfer (PET) in the excited state of BOPA determines the emission "off/on". Coordination of metal ions by DPA significantly weakened the electron-donating ability of nitrogen atom and inhibits the PET, recovering emission of BODIPY. In addition, the attachment of anisole at meso-position of BODIPY finely modulated the recognition of metal ions category.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.

Novel Fluorescent Probe toward Fe3+ Based on Rhodamine 6G Derivatives and Its Bioimaging in Adult Mice, Caenorhabditis elegans, and Plant Tissues

A new fluorescent probe LXY based on the rhodamine 6G platforms has been designed, synthesized, and characterized, which could recognize Fe³⁺ effectively in HEPES buffer (10 mM, pH = 7.4)/CH₃CN (2:3, v/v). And the distinct color change and the rapid emergence of fluorescence emission at 550 nm achieved "naked eye" detection of Fe³⁺. The interaction mode between them was achieved by Job's plot, MS, SEM, and X-ray single-crystal diffraction. Importantly, the crystal structures proved that Fe³⁺ could induce the rhodamine moiety transform the closed-cycle form to the open-cycle form. But it is interesting that Fe³⁺ did not appear in the crystal structures. Meanwhile, the limit of detection (LOD) of LXY to Fe³⁺ was calculated to be 3.47 × 10^-9. In addition, the RGB experiment, test papers, and silica gel plates all indicated that the probe LXY could be used to distinguish Fe³⁺ quantitatively and qualitatively on-site. Moreover, the probe LXY has also been successfully applied to Fe³⁺ image in Caenorhabditis elegans, adult mice, and plant tissues. Thus, LXY was considered to have some potential for application in bioimaging.

A diaminomaleonitrile-appended BODIPY chemosensor for the selective detection of Cu2+ via oxidative cyclization and imaging in SiHa cells and zebrafish

A specific Cu²⁺ sensor, 2-amino-3-(BODIPYmethyleneamino)maleonitrile (BDM), was established by a simple dehydration between BODIPY and diaminomaleonitrile. Cu²⁺ could be recognized by BDM over other competing metal ions in acetonitrile with distinct fluorescence emission signal response. Upon the addition of Cu²⁺ to BDM in acetonitrile, the maximum absorption at approximately 530 nm on the longer wavelength side was quenched, and the emission at 530 nm was ignited simultaneously. The fluorescence intensity enhancement could reach a maximum of 204 times the intensity of the BDM blank solution. The fluorescence "off-on" effect is established according to the Cu²⁺-induced fast intramolecular oxidative cyclization reaction, which could be deduced from the formation of an imidazole ring appended to the cyclization product (2-BODIPY-1H-imidazole-4,5-dicarbonitrile, BMC). Single-crystal structure analysis of the sensor BDM and cyclization product BMC further demonstrated this oxidative cyclization. Finally, the Cu²⁺ recognition property of BDM was validated in SiHa cells and living zebrafish. Additionally, the blood-brain barrier of the zebrafish can be penetrated by the BDM dye and the neuron cells in the brain were stained.

A stimuli responsive triplet-triplet annihilation upconversion system and its application as a ratiometric sensor for Fe3+ ions

A ratiometric fluorescent sensor for the detection of Fe3+ ions is achieved based on triplet-triplet annihilation upconversion (TTA-UC) luminescence. A new anthracene derivative (named as DHTPA) is designed and synthesized and reveals similar optical properties to 9,10-diphenylanthracene (DPA) and is used as a stimuli responsive annihilator in a TTA-UC system due to its complexation ability. As a result, the UC emission can be significantly quenched by Fe3+ ions, while the phosphorescence (PL) emission of sensitizer palladium(ii) octaetylporphyrin (PdOEP) remains nearly constant, which makes the PL signal an appropriate internal reference for the UC signal. The UC and ratio signals (I UC/I PL) both reveal a good linear relationship with Fe3+ ion concentration, which for the first time makes the TTA-UC system a perfect ratiometric sensor for Fe3+ ion detection. This sensing method will open a novel avenue to achieve ratiometric sensors in chemical and biological fields.

A dual target chemosensor for the fluorometric detection of In3+ and colorimetric detection of Fe3

A new dual target chemosensor 1, 1,1'‑((1E,1'E)‑((thiobis(ethane‑2,1‑diyl))bis(azanylylidene))bis(methanylylidene))bis(naphthalen‑2‑ol), was prepared by the reaction of a hydroxy-naphthaldehyde and a thiobis(ethylamine). Sensor 1 detected In³⁺ with turn-on fluorescence and Fe³⁺ via the change of color from colorless to pale violet. The sensing behaviors of 1 toward In³⁺ and Fe³⁺ were studied through photophysical experiments, ESI-mass, NMR titration, and theoretical calculations. In particular, 1 can discriminate In³⁺ from Al³⁺ and Fe³⁺ from Fe²⁺. Limits of detection for the analysis of In³⁺ and Fe³⁺ ions turned out to be 5.89 μM and 0.30 μM, respectively. In addition, sensor 1 functioned practically as a naked-eye test strip for Fe³⁺ and could be recycled by using EDTA for In³⁺ and DFO for Fe³⁺.

Sequential detection of Fe3+/2+ and pyrophosphate by a colorimetric chemosensor in a near-perfect aqueous solution

A colorimetric chemosensor was developed for Fe^3+/2+ and pyrophosphate with low detection limit and practical application for Fe³⁺ in water samples.

The photoprocess effects of an amino group located at different positions along the polymethine chain in indodicarbocyanine dyes

The amino group is a-ICT in the even position but is the ICT in the odd position.