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 mu M. Also, robust and accurate analysis of Pi in various water matrices was demonstrated, indicating our method's great potential in practical applications.