In this feature article, we report our recent progresses in fluorescent sensors of biological dyes from the viewpoint of supramolecular and bioorganic chemistry. For signalling fluorophores, we extended or created naphthalene-based ICT systems, e.g. amino-1,8-naphthalimides, amino-1,8-dicyanonaphthalenes and acenaphthopyrrol-9-carbonitriles. We also developed BODIPY derivatives with large Stokes shifts and high fluorescence quantum yields in polar solvents, and a rhodamine analogue working in strong competitive aqueous solution as well as its silaanthracene analogue with a bathochromic shift as large as 90 nm. For sensing mechanisms, we extended or developed the following methods to improve sensing: e.g. PET in a photogenerated electronic field, TICT promoted PET derived from aminoalkyl or piperazino aminonaphthalimides, and the translation/amplification effect of surfactant micelles or aggregation on fluorescent sensing. We also successfully designed deprotonation strengthened ICT, FRET-chemodosimeter sensing systems. For non-cyclic recognition receptors, naphthalimides with two or more side chains at their 4,5- or 3,4-positions, as a convenient and simple platform for ratiometric sensors, were created for the recognition of heavy and transition metallic cations; multi-armed polyamides with more side chains were innovated as a versatile platform for the sensing of metal ions with high affinity, selectivity and positive homotropic allosteric effects. We designed V-shape sensors of the bis(aminomethyl)pyridine receptor with two fluorophores to show high performance. Finally, the intracellular applications of the above sensors and dyes, e.g. imaging heavy and transition metal ions in cells, fluorescent marking of hypoxia of tumour cells, are also reviewed.

In regard to the phosphoproteome, highly specific and efficient capture of heteroideous kinds of phosphopeptides from intricate biological sample attaches great significance to comprehensive and in-depth phosphorylated proteomics research. However, until now, it has been a challenge. In this study, a new-fashioned porous immobilized metal ion affinity chromatography (IMAC) material was designed and fabricated to promote the selectivity and detection limit for phosphopeptides by covering a metal-organic frameworks (MOFs) shell onto Fe3O4 nanoparticles, taking advantage of layer-by-layer method (the synthesized nanoparticle denoted as Fe3O4@MIL-100 (Fe)). The thick layer renders the nanoparticles with perfect hydrophilic character, super large surface area, large immobilization of the Fe(3+) ions and the special porous structure. Specifically, the as-synthesized MOF-decorated magnetic nanoparticles own an ultra large surface area which is up to 168.66 m(2) g(-1) as well as two appropriate pore sizes of 1.93 and 3.91 nm with a narrow grain-size distribution and rapid separation under the magnetic circumstance. The unique features vested the synthesized nanoparticles an excellent ability for phosphopeptides enrichment with high selectivity for β-casein (molar ratio of β-casein/BSA, 1:500), large enrichment capacity (60 mg g(-1)), low detection limit (0.5 fmol), excellent phosphopeptides recovery (above 84.47%), fine size-exclusion of high molecular weight proteins, good reusability, and desirable batch-to-batch repeatability. Furthermore, encouraged by the experimental results, we successfully performed the as-prepared porous IMAC nanoparticle in the specific capture of phosphopeptides from the human serum (both the healthy and unhealthy) and nonfat milk, which proves itself to be a good candidate for the enrichment and detection of the low-abundant phosphopeptides from complicated biological samples.

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Sulfite and sulfide share several similarities in terms of chemical properties, such as nucleophilic and reducing reactivities. Therefore, they may disturb the detection of each other. In order to discriminate between these two kinds of sulfur-containing species, a new probe -N3 was developed, in which para-azidobenzenyl ketone was covalently incorporated to a coumarin fluorophore linked by a C=C double bond. Sulfite and sulfide can respectively react with the C=C double bond and the azido group to give different products, consequently, they can be differentially identified by UV-vis and fluorescence spectroscopy as well as by the naked eye. Selectivity and competition results reveal that -N3 is a good candidate for the detection of sulfide and sulfite. The bioimaging experiment demonstrates the potential of the -N3 probe for the differential imaging of sulfide and sulfite in living cells.

4-Nitro-1,8-naphthalic anhydride (NNA) was used to distinguish cysteine from homocysteine and other potentially interfering thiols through a novel sequential substitution mechanism. The discrimination involves a blue-fluorescent thioether formation via nucleophilic aromatic substitution of the nitro group by thiol, followed by a second intramolecular nucleophilic aromatic substitution of alkylthio with the amino group to give the green-fluorescent 4-amino derivative. NNA is highly selective towards Cys, and the detection limit of Cys by this method is 0.3 μM.