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Folic acid (FA) is a vitamin essential for human physiology; thus, rapid, accurate, and sensitive methods for its detection and quantification in different biological samples are necessary. A fluorescent ratiometric nanoprobe (the complex composed of quantum dots and carbon dots) based on carboxyl-modified quantum dots (QDs) and amino-modified graphene-based carbon dots (CDs) has been developed for the visual determination of folic acid (FA). The nanoprobe is the composition in which QDs were covalently bonded with CDs. Red and blue fluorescence of nanoprobe can be selectively quenched and enhanced by FA, respectively. Thus, the nanoprobe is capable to generate clearly visible fluorescence color change from pink to blue upon exposure to UV light. Depending on the color change and its intensity, FA can be identified, and their concentrations can be determined. The sensor prepared based on the nanoprobe demonstrated good selectivity and sensitivity toward FA with exceptionally low detection limit equal to 0.039 μM. We also prepared a paper-based sensor to demonstrate convenient and simple approach to visually detect FA. Thus, the nanoprobe demonstrated feasibility of rapid real-time quantitative FA detection; considering its simple, effective, and practicality, expectedly it can be used for practical application. [ABSTRACT FROM AUTHOR]

In this study, a novel fluorescent "turn-on" aptasensor was developed for sensitive and rapid detection of tetracycline (TC) in animal-derived food. It is based on aptamer-functionalized nitrogen-doped graphene quantum dots (N-GQDs-aptamer) coupled with cobalt oxyhydroxide (CoOOH) nanoflakes. The CoOOH nanoflakes are efficient fluorescence quenchers in homogeneous solutions, and this is due to their advantages of excellent optical properties, superior flexibility, and water dispersibility. The proposed method's mechanism is driven by quenching based on the fluorescence resonance energy transfer (FRET) between the donor (N-GQDs) and the acceptor (CoOOH nanoflakes). On the other hand, fluorescence recovery is caused by the structure switching behavior of the aptamer. Compared with previous methods, our developed method exhibits better behavior in terms of being easy to fabricate and being simple in detection procedure and maintains the detection limit low enough in TC determination: a linear range from 1 to 100 ng mL−1 and a detection limit of 0.95 ng mL−1 (S/N = 3). Furthermore, the proposed method was applied to five animal-derived food samples (milk, honey, fish, eggs, and chicken muscle) and demonstrated practical applicability. As well, the method has the advantages of simplicity in pre-treatment and convenience in instruments, saves times, and is cost-effective. Finally, the proposed method demonstrates significant potential for sensitive and rapid detection of specific components in real samples. [ABSTRACT FROM AUTHOR]

Folic acid (FA) is an essential vitamin in humans, and thus, rapid, accurate, and sensitive methods for its quantification in different biological samples are needed. This work describes a novel, simple, and effective dual-emission fluorescence nanoprobe for FA detection and quantification. The probe was covalently linked to amino-modified orange quantum dots (QDs) and carboxyl-modified blue graphene quantum dots (GQDs). The resulting material exhibited two emission peaks at 401 and 605 nm upon excitation at 310 nm. The probe had good selectivity and sensitivity toward FA with an exceptionally low detection limit (LOD = 0.09 nM). This probe was effectively used to quantify FA in animal serum samples. The method has potential utility for FA analysis in different types of biological samples. [ABSTRACT FROM AUTHOR]

The authors describe two kinds of immunochromatographic assays. The first is based on the use of dyed polymer microspheres (MICA), the another on the use of quantum dots (QICA). Both enable visual detection of enrofloxacin (ENR) in animal tissue and milk. Both the MICA and the QICA have visual limits of detection of 1 μg·L when working in buffer, of 5 μg·kg in case of animal tissue, and of 10 μg·L in case of milk. Other quinolones do not interfere. The MICA and QICA described here are convenient and fairly rapid in that the detection process (including sample pretreatment and assay) takes 20 min only which is far less than the commercial enzyme-linked immunosorbent assay (ELISA) test kit which requires 120 min. The MICA and QICA are more sensitive than the immunochromatographic assay using colloidal gold labels and the same polyclonal antibody. The results of analysis of spiked samples via MICA and QICA are in good agreement with those obtained by the commercial ELISA test kit. [ABSTRACT FROM AUTHOR]