Pillararene-based fluorescence indicator displacement assays for the ratiometric and turn-on detection of ATP.

For ATP detection, indicator displacement assays with multicationic macrocyclic hosts and anionic fluorescent dye guests represent an intuitive design strategy. However, such systems typically exhibit turn-off responses. For biological samples with strong background- and autofluorescence, ratiometric or turn-on signaling is preferred, which requires more sophisticated assay architectures. In the present work, the host-guest complexation of fluorescent pH indicator dye trisodium 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) with a cationic ammonium-pillar[6]arene (AP6) was employed in the design of indicator displacement assays featuring two distinct detection modes for the fluorescent sensing of nucleotide ATP. In the first approach, AP6-assisted deprotonation of HPTS enabled the development of a colorimetric and a fluorescent ratiometric assay. In the second strategy, fluorescence turn-on sensing was achieved by exploiting the FRET-type quenching of HPTS fluorescence by AP6-modified reduced graphene oxide (rGO-AP6). Both sensing platforms demonstrated high selectivity toward ATP over structurally similar nucleotides and other biologically relevant anions, a broad dynamic range and a low limit of detection. The performance of the turn-on ATP sensor was validated in the complex biological matrix of human serum, demonstrating its applicability for practical bioanalytical applications.