Red fluorescent europium metal-organic framework (Eu-MOF) integrated sensor strip on a 3D-printed device for smartphone-assisted in situ detection of picric acid.

This work focuses on the development of a portable ratiometric luminescent sensor device for the detection of picric acid (PA) in aqueous medium. The present study involves the fabrication of a europium MOF-PMMA polymer film into a 3D-printed device, engineered for red fluorescence emission. The probe (Eu-MOF/PMMA film) was thoroughly characterized using various spectroscopic and microscopic techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The development of an analytical probe to monitor picric acid (PA), a highly mutagenic substance, is of enormous significance for the environment and health. The probe we developed exhibited strong red fluorescence at an excitation wavelength of 294 nm, which was selectively and sensitively quenched by picric acid. Additionally, the Eu-MOF/PMMA fluorescent strip exhibits a hypsochromic shift from red to green upon the addition of picric acid, making it a ratiometric fluorescent sensor for picric acid. The integration of smartphone-based Red-Green-Blue (RGB) analysis enables fast, portable, real-time detection of PA in real samples by quantifying color intensity variations. The PMMA matrix was deliberately chosen for the composite fabrication due to its excellent UV stability and ability to preserve optical transparency under UV irradiation, and the resulting luminescent detection device was found to be reusable, underscoring its potential as a portable, recyclable, and practically viable sensing platform. The device is easy to fabricate and cost-effective for the detection of picric acid in aqueous media, with a detection limit of 31.16 pM.