Repeatability is one of the crucial standard for most molecular probes and it is considered generally as the competence of the fluorescence probes designed to display uniform performances and give comparable sensitivity attributes when the molecular probes or mode are repeatedly used. Thus, to qualitatively investigate the reversible sensing process of Al 3+ by NPDM, we add no less than seventeen sorts of physiological and environmental-related anions: F -, Cl -, Br -, I -, AcO -, S2O3 2-, NO3 -, NO2 -, CO3 2-, S 2-, SO4 2-, SO3 2-, H2PO4 -, H2PO2 -, HPO4 2-, PO4 3-, and P2O7 4-(PPi) into NPDM-Al 3+ system (DMSO/H2O, 7/3, v/v, 10 mM, HEPES, pH 7.0), respectively. As shown in Fig. , upon interaction with interfering anions NPDM-Al 3+ adduct showed negligible changes in fluorescence intensity, except that F -(40 μM) caused reliable fluorescence quenching. Additionally, the fluorescence "ON-OFF" switching feature of NPDM-Al ensemble is further verified by fluorescence titration experiments (Fig. ). With the progressive addition of F -(0-40 μM), the emission intensities of NPDM-Al 3+ at 520 nm & 556 nm were gradually declined and reached saturation state when 4 equiv. of F -was added and up to 95% emission intensity of the complex system was quenched. The LOD for F -was estimated to be 34.8 nM, which is not only superior to some previous secondary molecular tweezers for detecting F -, but also well below the recommended dosage (79 μM) by WHO for potable water. Thus, the results suggested that fluorescence tweezers NPDM was reinstated during the sensing procedure of F -. Moreover, to further corroborate the stability and reproducibility of the NPDM-Al 3+ complex, we conduct F --addition experiments. As shown in Fig. , the periodically alternating introduction of given amount of Al 3+ and F -to the solution of NPDM led to a switchable alteration in the fluorescence spectrum. Interestingly enough, such 'off-on-off' fluorescence switching cycles could be repeated at least four times without compromising its sensitivity by modulating the addition of Al 3+ /F -(Fig.