Bimetal-organic framework nanocomposite based point-of-care visual ratiometric fluorescence pH microsensor for strong acidity

pH is of great importance in understanding physiological and pathologic processes. Abnormal gastric juice pH is an indicator of many gastric diseases such as peptic ulcer and gastric cancer. In this work, a nanocomposite 1-hydroxypyrene@ Co/Tb- dipicolinic acid metal-organic framework (1-OHP@Co/Tb-DPA MOF) was constructed as a ratiometric fluorescent pH sensor for strong acidity. The nanocomposite-based pH sensor was response-rapid (30 s), linearly responsive in the broad pH range of 0.3–7.8 ( r  > 0.95) and ultra-sensitive in the pH range of 0.3–5.0. Importantly, the nanocomposite-loaded fiber paper was prepared as a visual microsensor for point-of-care pH detection via ratiometric chromaticity, coupled with a homemade portable determination device. The paper-based visual microsensor is response-rapid and sensitive, long-term stable (at least 30 days), and suitable for pH assay of microvolume (as little as 5 μL) samples at pH 0.3–5.0. Both the nanocomposite-based ratiometric fluorescent sensor and the paper-based visual microsensor can accurately determine the pH of artificial gastric juices (relative error <5.4%). To our knowledge, this is the first time to report a MOF-based ratiometric fluorescent pH sensor for strong acidity (pH<1) and a paper-based pH microsensor for point-of-care visual assay via ratiometric chromaticity.