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Development of novel near-infrared (NIR) fluorescent probes for the monitoring of active substances in living organism is desirable in biological studies. Herein, we designed a novel NIR MTR fluorophore which has a longer emission wavelength, greater Stokes shift and higher quantum yield than the classic hemicyanine NIR fluorophore. The synthesized MTR-derived NIR probe (MTR-P) is highly selective and sensitive to alkaline phosphatase (ALP) activity. In the presence of ALP, MTR-P exhibited increased fluorescence signal by up to 56 fold at 723 nm, and it was determined to be 0.042 U L -1 . In addition, the mechanism of the MTR-P probe was further examined by HPLC, mass spectrometry and DFT/TDDFT calculations. The NIR probe MTR-P was successfully applied to measure the levels of alkaline phosphatase in different types of cells by fluorescence imaging.

In this work, two novel fluorescence probes, named as RBQ1 and RBQ2, were designed and synthesized based on rhodamine B lactam. RBQ1 was employed for sensitive fluorometric sensing of H + in the pH range of 2–4. Since RBQ1 exhibits color responses toward Cu 2+ , it was also employed for sensitive detection of Cu 2+ by photoelectric colorimetry. By using RBQ1 as the fluorescence probe, the detection limit of Cu 2+ obtained was 0.0365 μmol L −1 . RBQ2, with a similar chemical structure to RBQ1, also shows obvious fluorescence responses to H + , but no response to any metal ions. By using H + and Cu 2+ ions as chemical inputs and fluorescence or absorbance as outputs, a novel dual-mode molecular logic gate was constructed with RBQ1. [ABSTRACT FROM AUTHOR]

• Development of a novel red-emitting fluorescent probe (HSA) for the detection of Cys. • The probe can high sensitivity detect Cys with a low LOD. • Successfully verified the experimental results by the theoretical calculation study. • The probe can be used for exogenous Cys monitoring and endogenous Cys cell imaging experiments. Herein, we synthesized a red-emitting fluorescence turn-on probe (HSA) for specific detection of cysteine (Cys) over other biothiols (glutathione (GSH) and homocysteine (Hcy)). The acrylate group was chosen as the recognition site for specific discrimination of Cys. Absorption and emission spectra display a high selectivity towards Cys over GSH/Hcy, organic small-molecule interfering substances and anions, with a high sensitivity towards Cys (0.12 μM) in 1% ethanol-containing PBS buffer solution (25 mM, pH = 7.4). Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were conducted to clarify the luminescence mechanism of the probe. Furthermore, the probe was successfully applied to the determination of free Cys in human serum and the fluorescence imaging of endogenous Cys in living cells. [ABSTRACT FROM AUTHOR]

Abstract A novel fluorescence detection method based on competitive immunoassay and magnetic bioseparation technique was developed and applied to the determination of pig immunoglobulin G (IgG) in serum samples. Core-shell structured Fe 3 O 4 @SiO 2 nanoparticles were synthesized by chemical coprecipitation, followed by functionalization with amino groups and immobilization of pig IgG antibodies. The synthesized Fe 3 O 4 @SiO 2 -antibody nanoparticles were employed as the probe for the competitive immune recognition of the target antigens in samples and the antigens labeled with fluorescein isothiocyanate (FITC). After the magnetic separation of probes binding with these two types of antigens, fluorescence of the free FITC-labeled antigens was measured for the quantification of the target antigens, since the ratio of the FITC-labeled antigens in supernatant before and after the competitive immune recognition depends on the amount of the target antigens in sample, due to the competitive nature of the binding of the antibody for these two types of antigens. Under the optimal conditions, a linear relationship was obtained between the change of fluorescence intensity and the concentration of pig IgG in a range from 0.75 to 23.50 µg L−1, with a detection limit (LOD) of 0.031 µg L−1. With the facile-prepared probes, this fluorescence competitive method can provide a rapid, specific and highly sensitive immunoassay protocol for the determination of target proteins in complex matrix samples. Graphical abstract fx1 Highlights • The analysis was simplified through competitive immunoreactions and magnetic bioseparation. • Good sensitivity and selectivity were obtained by taking advantage of fluorescence immunoassay. • The results of analyzing serum samples indicate its promising potential in clinical diagnosis. [ABSTRACT FROM AUTHOR]