Paper-Based Microfluidic Sensors Utilizing Metal–Organic Framework Materials Modified with Europium and Carbon Quantum Dots for Anthrax Spore Biomarker Detection

The germination of bacterial spores presents a considerable challenge to health and safety due to the current scarcity of cost-effective and efficient tools for their prompt identification. Addressing this critical need, our study introduces a novel paper-based ratiometric fluorescence sensor platform utilizing a composite of Eu3+-doped carbon quantum dots (CQDs) within ZIF-8 (Eu3+-CQDs@ZIF-8). This platform facilitates the rapid detection of 2, 6-pyridinedicarboxylic acid (DPA), a biomarker of bacterial spore germination. To fabricate this sensor, CQDs and Eu3+ ions were synergistically integrated into the ZIF-8 framework. The resultant composite was then applied to filter paper via screen printing technology, creating a paper-based microfluidic analytical device (μPAD). During the process of detecting DPA, strong coordination between DPA and Eu3+ ions is established, resulting in an enhanced red emission due to energy transfer through the antenna effect. Concurrently, the interaction between DPA and CQDs leads to a quenching of the CQDs' green fluorescence, enabling a ratiometric detection of DPA. The efficacy of this composite material was validated through the visualization of DPA release during spore germination. Further enhancing the platform's utility, integration with a smartphone enabled the quantification of DPA concentrations in real samples by analyzing the red-to-green (R/G) value in the detection area. Demonstrating rapid, sensitive, and precise DPA detection, the platform confirms its suitability for practical applications. Conclusively, with its compact design, straightforward preparation, and comprehensive integration, this sensor platform emerges as a promising solution for on-site spore detection, highlighting its potential for widespread testing applications.