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Amino groups terminated luminescent SiNPs have been designed for ratiometric visual detection of OTC in vitro and milk samples.

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A novel ratiometric fluorescence strategy is developed for specific detection of folic acid (FA) by using 11-mercaptoundecanoic acid protected gold nanoclusters (AuNCs@MUA). In this design, the fluorescence color of the probe can be switched among red, pink, violet and blue by varying the concentration of FA.AuNCs@MUA possesses strong fluorescence peaking at 612 nm (R-signal) and FA exhibits blue emissive auto-fluorescence at 446 nm (B-signal), showing a large emission shift of $170 nm. When AuNCs@MUA approaches FA through electrostatic binding, the R-signal decreases while the B-signal increases with titration of FA. Based on the above phenomenon, a radiometric analysis platform is constructed for FA target detection, with a wide linear response range from 0 to 20 mM, and an excellent detection limit of 26 nM. This new ratiometric strategy exhibits low background, and wide signal changes in a low concentration range, which presents obvious advantages over most previous FA detections based on single-responsive fluorescence methods. Furthermore, the proposed method is successfully applied to determine FA in human serum samples.

BSA-protected gold nanoclusters (AuNCs@BSA), as near infrared fluorescence probes, are synthesized to detect metronidazole (MTZ) and nitroimidazole derivatives, based on a photon-induced electron transfer (PET) process.

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A magnetic molecularly imprinted polymer-based fluorescent (MIP-FL) probe has been synthesized by embedding glutathione-stabilized gold nanoclusters (GSH-AuNCs) and Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs) into silica composites. The Fe 3 O 4 NPs/AuNCs@MIPs are characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and UV-Vis absorption spectroscopy. The results show that the spherical Fe 3 O 4 NPs/AuNCs@MIPs contain a core-shell structure with GSH-AuNCs anchored on the surface of silica-protected Fe 3 O 4 NPs. As a fluorescence probe (excitation: 360 nm, emission: 615 nm), Fe 3 O 4 NPs/AuNCs@MIPs can selectively detect metronidazole (MNZ) among other nitroimidazoles (ronidazole, ornidazole, and tinidazole). During the detection, the fluorescence intensity of the MIP-FL probe drops gradually with increasing MNZ concentration. The sensitive linear range of the fluorescence probe is from 0 to 5 μM, and the limit of detection is 4.2 nM. After the recognition sites interact with the template, the occurrence of charge transfer from the GSH-AuNCs to MNZ results in fluorescence quenching. Finally, a real sample test has been performed in spiked milk. Satisfactory recoveries spanning from 96% to 102% indicate that Fe 3 O 4 NPs/AuNCs@MIPs enable highly sensitive detection of MNZ based on fluorescence signal output, while the MIPs also have enrichment potential for the target from complex samples due to the magnetic properties.

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