Switch-on fluorescence scheme for antibiotics based on a magnetic composite probe with aptamer and hemin/G-quadruplex coimmobilized nano-Pt–luminol as signal tracer

• A fluorescence switch-on assay was fabricated.
• This probe can be fabricated through the immunoreaction between ds-Apt and dsDNA antibody.
• The nanotracer could double catalyze luminol–H2O2 system to amplify fluorescent signal.
• The LOD was 0.500 pg mL−1 of CAP which is lower than ELISA by 2 orders of magnitude.

A selective and facile fluorescence “switch-on” scheme is developed to detect antibiotics residues in food, using chloramphenicol (CAP) as model, based on a novel magnetic aptamer probe (aptamer–Pt–luminol nanocomposite labeled with hemin/G-quadruplex). Firstly, the composite probe is prepared through the immuno-reactions between the capture beads (anti-dsDNA antibody labeled on magnetic Dynabeads) and the nanotracer (nano-Pt–luminol labeled with double-strand aptamer, as ds-Apt, and hemin/G-quadruplex). When the composite probe is mixed with CAP, the aptamer preferentially reacted with CAP to decompose the double-strand aptamer to ssDNA, which cannot be recognized by the anti-dsDNA antibody on the capture probes. Thus, after magnetic separation, the nanotracer can be released into the supernatant. Because the hemin/G-quadruplex and PtNPs in nanotracer can catalyze luminol–H2O2 system to emit fluorescence. Thus a dual-amplified “switch-on” signal appeared, of which intensity is proportional to the concentration of CAP between 0.001 and 100 ng mL−1 with detection limit of 0.0005 ng mL−1 (S/N=3). Besides, our method has good selectivity and was employed for CAP detection in real milk samples. The results agree well with those from conventional gas chromatograph–mass spectrometer (GC–MS). The switch-on signal is produced by one-step substitution reaction between aptamer in nanotracer and target. When the analyte is changed, the probe can be refabricated only by changing the corresponding aptamer. Thus, all features above prove our strategy to be a facile, feasible and selective method in antibiotics screening for food safety.

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