Figure 6
(a) A fluorescent μPAD assay for detecting caffeine using 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS). (b) Increasing caffeine concentrations in the presence of blue excitation wavelengths (λex = 445 nm) produce a decreasing, or quenched, change in reflected green light intensity (λem, max = 512 nm). (c) Dual-target and negative control solutions were assayed and compared with a (d) HPTS-caffeine standard curve created by single-target μPAD detection of caffeine concentrations using HPTS (n = 4). (e) There was no significant difference in fractional quenching measured between the dual target control solutions and 300 ppm caffeine. However, the UA negative control solution also demonstrated no significant difference in quenching from the caffeine standard (p < 0.05).
