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 330/420nm, depends on the pH value in the range from pH2 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 1mM concentration range, and the detection limit (at S/N=3) is 0.14mM. The test was applied to the determination of chromium(VI) in (spiked) environmental water samples.