Smartphone-integrated colorimetric sensor for rapid detection of phenolic compounds based on the peroxidase-mimicking activity of copper/cerium-aspartic acid metal-organic framework

Abstract

A smartphone-integrated colorimetric sensor is introduced for the rapid detection of phenolic compounds, including 8-hydroquinone (HQ), p-nitrophenol (NP), and catechol (CC). This sensor relies on the peroxidase-mimicking activity of aspartate-based metal-organic frameworks (MOFs) such as Cu-Asp, Ce-Asp, and Cu/Ce-Asp. These MOFs facilitate the oxidation of a colorless substrate, 3,3',5,5'-tetramethylbenzidine (TMB), by reactive oxygen species (ROS) derived from hydrogen peroxide (H₂O₂), resulting in the formation of blue-colored oxidized TMB (ox-TMB). Among the synthesized MOFs, Cu/Ce-Asp nanorods had the highest activity, probably due to the synergistic effect of aspartate and copper coordination, as well as their large surface area, which allows for improved electron transport. Consequently, Cu/Ce-Asp nanorods were utilized for the detection of phenolic compounds under optimized conditions. In the presence of phenolic compounds, the interaction between TMB and H₂O₂ is inhibited, resulting in various colorimetric responses. This method accurately determined HQ, NP, and CC in a linear range of up to 5 μM, with detection limits of 0.30 μM, 0.76 μM, and 0.50 μM, respectively. To facilitate real-time and portable analysis, smartphone technology was integrated for color detection, eliminating the need for expensive and bulky laboratory-based optical instruments. In addition, the sensor was effectively employed for real water sample analysis, yielding satisfactory recovery outcomes. The proposed sensor offers a rapid, user-friendly, and portable method for detecting phenolic compounds, even at low concentrations. This study not only advances the application of MOF-based nanozymes in environmental monitoring but also expands their potential use in other fields.

Keywords: Colorimetry; Metal–organic frameworks; Nanozyme; Peroxidase mimic; Phenolic compounds; RGB color space.