We report a versatile approach for the colorimetric assay of alkaline phosphatase (ALP) activity based on the distinctive metal-to-ligand charge-transfer (MLCT) absorption properties of Fe(II)-phenanthroline reporter. In the presence of ALP, the applied substrate ascorbic acid 2-phosphate is enzymatically hydrolyzed to produce ascorbic acid, which then reduces Fe 3+ to Fe 2+ . The complexation of Fe 2+ with the bathophenanthroline disulfonate (BPS) ligand generates a blood-red Fe(BPS) 3 4− reporter, which is characterized by an intense MLCT absorption band at 535 nm in the visible range. Under optimal conditions, the spectral output exhibits a good quantitative relationship with ALP activity over the range of 0–220 mU mL −1 with a detection limit of 0.94 mU mL −1 . Moreover, the activity of ALP can also be conveniently judged through naked-eye observations. Results indicate that it is highly selective and can be applied to the screening of ALP inhibitors. In addition, it has been successfully employed to detect the endogenous ALP level of undiluted human serum samples, with a detection limit of 1.05 mU mL −1 being achieved. This approach avoids any elaborately designed substrates and holds considerable simplicity and flexibility for reporter design. This study broadens the horizon of the applications of phenanthroline-based transition metal complexes. Furthermore, an efficient and practical method like this has the potential to be widely used in clinical applications and in the point-of-care testing.
Yang Chunlei,Xu Guiju,Hou Chenghao,Peng Lizeng,Wang Weiting,Zhang Hongwei,Zhang Xiaoling
A fluorometric and colorimetric dual-modal nanoprobe (denoted as Fe 2+ -Phen/SiNPs) has been developed for selective and sensitive determination of nitrite (NO 2 − ). The mechanism is based on fluorescence quenching between silicon nanoparticles (SiNPs) and Fe(II)-phenanthroline complex (Fe 2+ -Phen) via inner filter effect and redox. With the addition of increasing NO 2 − , Fe 2+ is oxidized to Fe 3+ , recovering the fluorescence of SiNPs. Meanwhile, the color of the system gradually changes from orange-red to colorless, which enables colorimetric measurement. The NO 2 − concentration shows a wide linear relationship with fluorescence intensity from 0.1 to 1.0 mM ( R 2 = 0.9955) with a detection limit of 2.4 μM in the fluorometric method (excitation wavelength: 380 nm). By contrast, the linear range of the colorimetric method ranges from 0.01 to 0.35 mM ( R 2 = 0.9953) with a limit of detection of 6.8 μM (proposed selective absorbance: 510 nm). The probe has been successfully applied to nitrite determination in water, salted vegetables, and hams demonstrating broad application prospects for the determination of nitrite in complicated matrices. Graphical Abstract
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