Portable dual-mode microfluidic sensor for rapid and sensitive detection of DPA on chip

In this work, we developed a dual-mode portable device that integrated a 3D-printed microfluidic chip for detection of dipicolinic acid (DPA) on chip. The system uses a ratiometric fluorescence nanoprobe formed by embedding carbon dots (CDs) into an Eu 3 ⁺ metal–organic framework (Eu-MOF). Upon reaction with DPA in the microchannel, red fluorescence was enhanced and blue fluorescence suppressed, enabling sensitive ratiometric detection of DPA on chip with a detection limit (LOD) of 0.04 µM. Interestingly, the composite Eu MOF /CDs/DPA also exhibits peroxidase-like activity, catalyzing the oxidation of TMB into a blue-colored product (oxTMB), which allows for colorimetric detection with an LOD of 10.14 µM. To improve usability and reduce environmental or instrumental variability, incorporating a microfluidic chip into a semi-portable device and utilizing a smartphone, making the system portable and miniaturized for easy operation. In the smartphone-assisted mode, the LODs were 0.33 µM (ratiometric fluorescence) and 12.27 µM (colorimetry), determined by RGB signal analysis, respectively. Moreover, satisfactory recoveries (85–104.6%) were achieved in the spiked real samples. Overall, this platform offers a straightforward, cost-effective, and versatile approach for DPA detection, with promising applications in food safety, environmental monitoring, and clinical diagnostics.