Ratiometric responses of AIE/ACQ co-guests functionalized ZIF-8 nano-vehicles: Color-oriented ATP detection and intracellular imaging

In this work, two guests with opposite emission characteristics in aggregated states were rationally selected and delicately incorporated into zeolitic imidazolate framework-8 (ZIF-8) host. The simultaneous presentation aggregation-induced emission (AIE) of 1,1,2,2-Tetra (4-carboxyphenyl) ethylene (H₄TCPE) and aggregation-caused quenching (ACQ) of 5-carboxytetramethylrhodamine (5-TAMRA) endowed the as-formed H₄TCPE/5-TAMRA@ZIF-8 with dual responsive properties. Upon stimulation with ATP, the coordination environment of H₄TCPE/5-TAMRA@ZIF-8 was interrupted, leading to the collapse of ZIF-8 host and the release of guests into their free states. The corresponding quenched blue AIE at 453 nm and recovered red ACQ at 586 nm, as well as the appearance of slight monomer emission (ME) at 409 nm possibly due to weak interaction between H₄TCPE and 2-methylimidazole (Hmim), constituted a double-ratiometric sensing strategy for ATP. By plotting the fluorescence intensity ratio of (F₄₀₉ + F₅₈₆)/F₄₅₃ to the concentration of ATP ranging from 0.02-9 mM, a linear relationship was found with the limit of detection as low as 6.09 μM. This along with the good sensitivity and robust reliability of H₄TCPE/5-TAMRA@ZIF-8 probe enabled ATP detection in complex biofluids such as artificial serum and cell lysates (2.927 ± 0.565 mM) directly. Moreover, as the unique color-oriented sensing feature is inherited on the test paper, the scarcely reported H₄TCPE/5-TAMRA@ZIF-8 test strip was developed. Via the values of R/B, ATP in cell lysates can also be reported (3.1 ± 0.590 mM) easily, which may be even feasible for point-of-care diagnosis of ATP-related diseases in remote areas lacking resources. Meanwhile, as a nano-sized vehicle, H₄TCPE/5-TAMRA@ZIF-8 can easily enter cells and report intracellular ATP fluctuations by color-oriented imaging, which offers a more comprehensive and precise insight into cellular metabolism, holds significant potential for applications in bioanalytical research and environmental monitoring.