High-performance dual-channel ratiometric colorimetric sensing of phosphate ion based on target-induced differential oxidase-like activity changes of Ce-Zr bimetal-organic frameworks

Phosphate ion (Pi) is an inorganic anion widely distributed and commonly regarded as a significant indicator of water eutrophication, and thus it is urgent to develop convenient, cost-effective and reliable analytical approaches for the monitoring of Pi for water quality control. In this work, we propose the high-performance dual-channel ratiometric colorimetric sensing of Pi based on the analyte-triggered differential oxidase-mimicking activity changes of oxidized Ce-Zr bimetal-organic frameworks (oxidized UiO-66(Ce/Zr)). By integrating two types of metal nodes with different functions into one framework structure, the proposed oxidized UiO-66(Ce/Zr) not only exhibits excellent activity to catalyze the chromogenic oxidation of both 3,3′,5,5′-tetramethylbenzidine (TMB) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) due to oxidase-like active Ce4+/Ce3+ sites but also provides main Zr4+ sites to specifically recognize Pi. When Pi is in presence, it is rapidly adsorbed onto oxidized UiO-66(Ce/Zr) and changes the surface chemistry of the latter, leading to differential enzyme-like activity changes towards the two chromogenic substrates TMB and ABTS. Based on this finding, a dual-channel ratiometric colorimetric method was established for the sensitive determination of Pi. Compared to conventional single-signal colorimetric sensors, our method offered a widened linear detection scope from 3.3 to 666.7 μM. Also, robust and accurate analysis of Pi in various water matrices was demonstrated, indicating our method’s great potential in practical applications.