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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]

A fluorometric aptamer-based method is described for the determination of aflatoxin B1 (AFB1). The fluorescent dye thioflavin T (ThT) forms a complex with the aptamer against AFB1 (aptamer/ThT), and the fluorescence of the complex is strongly enhanced. On addition of AFB1, it will bind to the aptamer and release ThT. The fluorescence of free ThT is much weaker. The fluorescence of the system, best measured at excitation/emission wavelengths of 440/487 nm, drops gradually in the AFB1 concentration range from 0.2 to 200 ng·mL−1, exhibiting good linearity. The detection limits are 0.2 ng·mL−1 in buffer solution, and 1 ng·mL−1 when applied to plant-derived food. The recovery of AFB1 from spiked foodstuff ranges from 74.7% to 121%. The assay can be performed within 20 min. Graphical abstract Schematic presentation of label-free thioflavin T (ThT)-based fluorescence aptasensor using aflatoxin B1(AFB1) aptamer/ThT G-quadruplex complex and the AFB1 aptamer/AFB1 complex fluorescent signal system for the rapid and sensitive detection of AFB1 in soy sauce, spirits, rice, corn and peanuts. [ABSTRACT FROM AUTHOR]