In
this work, a novel zirconium-based metal–organic framework
(MOF) composite material, UiO-(OH)2@RhB, has been solvothermally
prepared with zirconyl chloride octahydrate, 2,5-dihydroxyterephthalic
acid, and rhodamine B (RhB) for ratiometric fluorescence sensing of
Al3+ ions in an aqueous medium. The luminescence measurement
results showed that, at the single excitation wavelength of 420 nm,
the fluorescence intensity of the ligand at 500 nm increased significantly
in the case of Al3+, while that of RhB at 583 nm changed
slightly, together with an apparent color change. Under optimal conditions,
UiO-(OH)2@RhB exhibited an extraordinary sensitivity (10
nM), good selectivity, and a fast response (2 min) for Al3+. As far as we know, the limit of detection is superior to that of
the current reported MOF-based Al3+ fluorescence sensors.
The response mechanism suggested that −OH could capture Al3+ in water through coordination and high electrostatic affinity
and achieved turn-on ratiometric fluorescence through the excited-state
intramolecular proton transfer process and stable fluorescence of
RhB. In addition, this sensor was also applied to actual food samples
(grain beans), with the recoveries ranging from 89.08% to 113.61%.
Such a turn-on ratiometric fluorescence sensor will provide a constructive
strategy for the ultrasensitive detection of Al3+ in practical
applications.
Nanomaterials-based
immunochromatographic assays (ICAs) have gained
great commercial success in real-life point-of-care testing (POCT).
Exploring novel carriers of ICAs with improved signaling and sustained
activity favors the development of sensitive POCT. Herein a potent
signal biotag, colored Staphylococcus aureus (SA),
was created for ICA carriers through a mild self-assembly strategy,
providing high luminance and abundant specific binding sites for immobilization
of monoclonal antibodies (mAbs). The biocompatible SA-dyes (SADs)
retained both an intact surface structure for mAbs labeling (Fc portion)
and the superior bioactivity of immobilized mAbs (affinity constant
was about 109 M–1), thus waiving the
intrinsic limitations of traditional nanomaterials and endowing high
sensitivity. Proof-of-concept was demonstrated by employing Congo
red- or/and fluorescein isothiocyanate-embedded SA (SACR, SAFITC,
and SACR–SAFITC) as ICA carriers to detect zearalenone (ZEN)
through colorimetric or/and fluorimetric signals. Furthermore, the
ICAs satisfied the clinical requirement perfectly, including limit
of detection (0.013 ng/mL, which was at least an 85-fold improvement
over that of traditional gold nanoparticles-based ICA), linearity
(R
2 > 0.98), reproducibility (RSD <
8%), selectivity, and stability. Importantly, the proposed biosensors
could be well-applied in four real samples for ZEN monitoring with
satisfactory recoveries, correlating well with the results from liquid
chromatography–tandem mass spectrometry (LC-MS). This work
also proved a universal design for tailoring coloration bands for
SAD–ICA detection of multiple analytes.
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