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Two water-soluble colorimetric and turn-on fluorescent probes STP1–2 were rationally designed and synthesized for selective recognition of GSH. Both probes are colorless 4-thioether-1,8-naphthalimide derivatives, which are almost non-fluorescent due to the photoinduced electron transfer from the fluorophore to the 4-nitrobenzene. Upon addition of GSH to STP1/STP2–CTAB solution, obvious spectral responses were observed: the absorption peak shifted from 345 nm to 390 nm companied with ∼90-fold fluorescence enhancement at 487 nm. A good linear relationship between the fluorescence intensity and GSH concentration was obtained, and the detection limit of GSH was estimated to be 8.40 × 10−8 mol L−1. The experimental results imply that both probes could be applied in fluorescent imaging of GSH within living cells and in the detection of mercapto-containing proteins as well.

Two biotinylated coumarin-based fluorescent probes SPS3 and RC3 were designed for differentiating between structurally similar proteins streptavidin (SA) and avidin (AV). A substituted phenyl group is introduced onto SPS3, which may quench the fluorescence through twist intramolecular charge transfer (TICT). The fluorescence of SPS3 is turned on, by restraining the TICT process, when the fluorophore is buried at the surface of SA. RC3 is constructed by incorporating a biotin molecule to a coumarin fluorophore through a 4-atom spacer. The fluorescence intensity of RC3 is enhanced significantly when its fluorophore enters into the less polar binding pocket of AV. SPS3 and RC3 could be applied in distinguishing between SA and AV as well as in fluorescence imaging of biotin receptor over-expressed Hela cells.

Fluorescent probes 1 – 3 with coumarin as the fluorophore were designed and synthesized for the determination of bovine serum albumin (BSA). All three probes exhibited evidently solvatochromic UV–vis and fluorescence spectra. Compound 3 was the most effective towards the solvent's polarity: 155 nm (vs. 60 nm for 1 and 100 nm for 2 ) red shift in the emission maximum was found as the solvent changing from cyclohexane to phosphate buffer solution. These compounds were applied to detect BSA based on the hypothesis that the polarity of the microenvironment surrounding the probe will undergo significant change when the probe moves from the bulk solution to the hydrophobic domains of BSA. 3 was the most sensitive towards BSA and the detection limit of BSA was 0.6 μg/mL with 3 as the probe, which ensured the detection of BSA content in fetal bovine serum with good recovery.

Two fluorescent probes, m-PSP and p-PSP, for sulfite and/or sulfide were constructed by connecting a pyridinium ion to a coumarin fluorophore through an alpha,beta-unsaturated ketone. The presence of the pyridinium salt promoted the nucleophilic addition of sulfite and sulfide to the alpha,beta-unsaturated ketone, which could be visualized by dramatic changes in the solution's color and fluorescence intensity. Both probes exhibit good selectivity (the selectivity coefficients toward major interferences are less than 0.07) and high sensitivity for sulfite and sulfide over biothiols and other potential analytes. The detection limits of m-PSP for the analysis of sulfite and sulfide are calculated to 8.5 x 10(-7) M and 2.7 x 10(-7) M, respectively. Living cell imaging results indicate that both probes can be applied in biological systems.

A single boronic acid-based fluorescent probe (compound CSP) for saccharides was designed and synthesized. The probe, with an α,β-unsaturated ketone conjugated into the coumarin fluorophore, was synthesized by 4 steps from the commercial material 4-diethylamino salicylaldehyde. The electron push-pull effect is enhanced with the N,N-diethyl amino as the electron donor and the carbonyl as the electron acceptor. Both the absorption (463 nm) and emission (616 nm) maxima of CSP are in the visible wavelength region with a Stokes shift of about 150 nm, which ensures CSP a potential probe for biological application. Under near physiological conditions, significant fluorescence enhancement of CSP was observed upon the addition of some saccharides, namely, D-sorbitol, D-fructose, D-glucose, D-mannose and D-galactose. The probe showed relatively high sensitivity towards D-fructose and D-sorbitol, and their detection limits were 0.05 mmol/L and 0.1 mmol/L, respectively.

In this paper, two colorimetric and turn-on fluorescent probes N-[2-(2-hydroxy)-ethoxy] ethyl-4-azido-1,8-naphthalimide ( SS1 ) and N-butyl-4-azido-1,8-naphthalimide ( SS2 ) for selective recognition of H 2 S were designed and synthesized. The probes were constructed by incorporating an azido group into the naphthalimide fluorophore as a specifical reaction group for sulfide utilizing its reducing property. Once treated with H 2 S, the azido groups of the probes were converted to amino groups and the solutions’ color changed from colorless to yellow companied with a strong yellow-green fluorescence. Rapid and sensitive responses of the probes towards H 2 S were achieved in the presence of cationic surfactant cetyltrimethyl ammonium bromide (CTAB): the reaction was completed within 10 min in CTAB compared to more than 4 h in buffer solution, and the detection limit decreased from 0.5 μM to 20 nM. High selectivity and good competition of both probes towards H 2 S over other 11 ions and 2 reducing agents were realized in CTAB micelle. An overall linear concentration range of 0.05 μM to 1 mM was achieved with the assistance of differently charged surfactants CTAB and sodium dodecyl sulfate (SDS). The probes were applied to rapidly and sensitively detect H 2 S levels in fetal bovine serum without any pretreatment of the sample.

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 TSSP-N3 was developed, in which para-azidobenzenyl ketone was covalently incorporated to a coumarin fluorophore linked by a CC double bond. Sulfite and sulfide can respectively react with the CC 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 TSSP-N3 is a good candidate for the detection of sulfide and sulfite. The bioimaging experiment demonstrates the potential of the TSSP-N3 probe for the differential imaging of sulfide and sulfite in living cells.

Three fluorescent probes were constructed by incorporating an α,β-unsaturated ketone to a coumarin fluorophore. The selective addition of sulfite to the alkene of TSP assisted by cetyltrimethyl ammonium bromide (CTAB) micelle can be visualized by dramatic color and ratiometric fluorescence changes. In CTAB–PBS system, the fluorescence intensity ratio at 465 nm and 592 nm (I465/I592) and the absorbance ratio at 390 nm and 470 nm (A390/A470) were linearly proportional to sulfite concentration in the range of 0.5–150 μM, and the detection limit was 0.2 μM. Good selectivity and competition of TSP1 towards sulfite over several anions and biological thiols were acquired. Probe TSP1 was used to detect sulfite in three realistic samples (mineral water, sugar and white wine) with good recovery.

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.

Two fluorescent probes SPS1 and SPS2 were designed by connecting biotin to an environment-sensitive coumarin fluorophore. Streptavidin and avidin induced dramatical fluorescence changes in both probes. SPS2 has potential in fluorescent imaging of biotin receptor-enriched tumor cells.