Multicolorful ratiometric-fluorescent test paper for determination of fluoride ions in environmental water

Here, a ratiometric fluorescent test paper for the visual and on-site determination of environmental fluoride ions was fabricated by inkjet-printing of the as-prepared “ink” onto a filter paper. The “ink” was prepared by mixing the fluoride-sensitive organic probe (C-TIPS) with red CdTe quantum dots (QDs) in an optimal proportion. The designed fluorescent fluoride probe shows a turn-on effect in the presence of fluoride ions. With the aid of thee red fluorescence of CdTe QDs, the test paper exhibited a distinguishable fluorescence color change from red to purple to blue under a UV lamp. The as-prepared ratiometric-fluorescent test paper displayed a superior sensitivity and visual effectiveness to quantify fluoride ions, with a detection limit of 0.285 μM which is lower than the World Health Organization (WHO) defined limit (79 μM). Moreover, the test paper is highly applicable for the detection of fluoride ions in natural waters in a very simple, cost efficient and on-site way.