A resorufin-based highly sensitive and selective fluorescence off–on probe with a new recognition moiety for tyrosinase is developed, and applied to detect and image endogenous tyrosinase activity in different living cells.

A simple and stable fluorescent off–on probe for discrimination of cysteine (Cys) from glutathione (GSH) has been developed by combining resorufin with 7-nitrobenzofurazan. The probe, displaying distinct emission patterns for Cys and GSH at just one excitation wavelength, can be used for simultaneous determination of Cys and GSH in human plasma.

A new upconversion luminescence nanoprobe for the detection of hyaluronidase has been developed by coupling the hyaluronic acid-bearing upconversion fluorescence nanoparticles (HA-UCNPs) with poly(m-phenylenediamine) (PMPD) nanospheres via covalent linkage. The nanoprobe alone exhibits an extremely low background signal owing to the effective fluorescence quenching by electron-rich PMPD and the near-infrared excitation characteristic (λex = 980 nm) of HA-UCNPs; upon reaction with hyaluronidase, however, a more than 31-fold fluorescence enhancement is produced. Compared with the corresponding nanosystem assembled via physical adsorption, the prepared nanoprobe shows a largely increased stability and a much higher signal-to-background ratio, which offers an ultrasensitive assay for hyaluronidase, with a detection limit of 0.6 ng/mL. The nanoprobe has been successfully used to determine hyaluronidase in human serum samples from both colorectal cancer patients and healthy people, disclosing that the serum hyaluronidase level in colorectal cancer patients is roughly 3 times higher than that in healthy people. Furthermore, the nanoprobe has also been employed to study the activity change of hyaluronidase affected by different concentrations of arsenate (a potential carcinogen), and the results show that even a low dosage of arsenate (50 μg/L) can raise the activity of hyaluronidase by about one-third, revealing the relationship between arsenate and the enzyme. The proposed method is not only simple but also highly sensitive, making it useful to assay hyaluronidase in relevant clinical samples.

A novel fluorescence nanoprobe for the detection of matrix metalloproteinase 2 (MMP2) has been developed by engineering the fluorescein isothiocyanate-labeled peptide onto the surface of poly(m-phenylenediamine) (PMPD) nanoparticles through covalent linkage. The nanoprobe itself displays a low background signal due to the effective fluorescence quenching by electron-rich PMPD, but its reaction with MMP2 causes 11-fold fluorescence enhancement. Compared with similar fluorescence nanosystems for MMP2 assembled through physical adsorption, the as-prepared nanoprobe is significantly more stable and displays a strikingly higher signal-to-background ratio, which leads to a high sensitivity for MMP2 assay, with a detection limit of 32 pM. Most notably, the nanoprobe has been successfully applied to determine MMP2 in human serum samples, demonstrating that the MMP2 level in serum from colorectal cancer (CRC) patients is 2 times higher than that from healthy people. Moreover, the nanoprobe has also been used to monitor MMP2 secreted by CRC cells that were grown under normoxic and hypoxic conditions, respectively, and the results show that the cells under hypoxic conditions produce higher level of MMP2 than those under normoxic conditions. Our method is simple and can offer a highly sensitive detection of MMP2 in relevant clinical samples.

A highly selective and sensitive fluorescence probe, 7-[(5-nitrofuran-2-yl)methoxy]-3H-phenoxazin-3-one (1), is developed for imaging the hypoxic status of tumor cells via the indirect detection of nitroreductase. The detection mechanism is based on the fact that nitroreductase can selectively catalyze the reduction of the nitro group in 1 to a hydroxylamine or amino group in the presence of reduced nicotinamide adenine dinucleotide as an electron donor that is indispensable, followed by the 1,6-rearrangement–elimination and the release of resorufin. As a result, the reaction produces a distinct color and fluorescence change from almost colorless and nonfluorescent to pink and strong red fluorescence. The fluorescence increase of probe 1 at λ550/585 nm is directly proportional to the concentration of nitroreductase in the range of 15–300 ng/mL, with a detection limit of 0.27 ng/mL. The ready reduction of the nitro group in 1 under hypoxic conditions leads to the establishment of a sensitive and selective fluorescence method for imaging the hypoxic status of tumor cells, and with this method Hela and A549 cells under normoxic and hypoxic conditions (even for different extents of hypoxia) can be differentiated successfully. This method is simple and may be useful for the imaging of disease-relevant hypoxia.

This paper presents a novel sensor to detect proteolytically active prostate-specific antigen (PSA) by assembling a purpose-designed FITC-labeled peptide with graphene oxide (GO). The fluorescence of the dye-labeled peptide was quenched in the presence of GO. Reaction of the sensor with PSA cleaves the peptide, leading to the release of the dye moiety and a great increase in fluorescence intensity in a dose- and time-dependent manner, and PSA can be quantified accordingly. This approach is simple compared to existing methods since the GO-peptide-based sensor is easily assembled and detection can be achieved without the involvement of complicated procedures. Moreover, the applicability of the method has been demonstrated by detecting PSA in spiked urine samples.

A novel fluorescent probe is designed and synthesized for the determination of cysteine in biological samples by incorporating 2,4-dinitrobenzenesulfonyl (DBS) group as a quencher into the BODIPY skeleton. The BODIPY-based probe itself shows weak fluorescence due to the strong intramolecular charge transfer process. Upon reaction with cysteine, however, the probe produces a rapid and large fluorescence enhancement through the removal of the DBS unit by nucleophilic aromatic substitution. This valuable property leads to the development of a new and simple method for cysteine assay. Under the optimized conditions, the fluorescence enhancement value is directly proportional to the concentration of cysteine in the range 2–12 μM, with a detection limit of 30 nM (S/N = 3). The applicability of the developed method has been successfully demonstrated on the determination of non-protein cysteine in human serum. Compared to most of the existing fluorescent probes proposed for cysteine, the BODIPY-based one exhibits an excellent overall performance in terms of selectivity, sensitivity and simplicity.

A new cyanine-based near-infrared fluorescent probe has been developed for monitoring tyrosinase activity.

A resorufin-based highly sensitive and selective fluorescence off–on probe with a new recognition moiety for tyrosinase is developed, and applied to detect and image endogenous tyrosinase activity in different living cells.

A new cyanine-based near-infrared fluorescent probe has been developed for monitoring tyrosinase activity.

A simple and stable fluorescent off–on probe for discrimination of cysteine (Cys) from glutathione (GSH) has been developed by combining resorufin with 7-nitrobenzofurazan. The probe, displaying distinct emission patterns for Cys and GSH at just one excitation wavelength, can be used for simultaneous determination of Cys and GSH in human plasma.