A fluorometric paper test for chromium(VI) based on the use of N-doped carbon dots.

Water-soluble nitrogen-doped carbon quantum dots (C-dots) were fabricated by microwave-induced decomposition of the precursor materials citric acid and N,N'-bis(2-aminoethyl)-1,2-ethanediamine. The C-dots were placed on portable paper strips with novel origami designs to simplified user operations. The intensity of the blue fluorescence, best measured at excitation/emission wavelengths of 330/420 nm, depends on the pH value in the range from pH 2 to 12. The C-dots on the paper stripe are shown to be a sensitive fluorescent probe for chromium(VI) via an inner filter effect. Response is linear in the 0.08 to 1 mM concentration range, and the detection limit (at S/N = 3) is 0.14 mM. The test was applied to the determination of chromium(VI) in (spiked) environmental water samples. Graphical abstract Schematic presentation of the water-soluble nitrogen-doped carbon dots (C-dots) as a fluorescent probe for Cr6+ based on an inner filter effect. The three-dimensional paper analytical device integrating C-dots was applied to the determination of Cr6+ in (spiked) environmental water samples.

Cell-Based Biosensor with Dual Signal Outputs for Simultaneous Quantification of Phenylacetic Acid and Phenylethylamine.

Despite the importance of 2-phenylacetic acid, a plant hormone in the endogenous auxin family, its biosynthesis pathway has yet to be elucidated. In this study, we developed a novel whole-cell biosensor for the simultaneous quantification of 2-phenylacetic acid (PA) and 2-phenylethylamine (PEA) through the regulation of bacterial catabolism of aromatic compounds. We used the PA regulon to enable the recognition of PA and PEA. Differentiation of PEA from PA involves the incorporation of the FeaR regulon within the same whole-cell biosensor to report the presence of aromatic amines. The proposed system is highly sensitive to PA as well as PEA.