A self-designed device integrated with a Fermat spiral microfluidic chip for ratiometric and automated point-of-care testing of anthrax biomarker in real samples

A desirable lanthanide-based ratiometric fluorescent probe was designed and integrated into a self-designed Fermat spiral microfluidic chip (FS-MC) for the automated determination of a unique bacterial endospore biomarker, dipicolinic acid (DPA), with high selectivity and sensitivity. Here, a blue emission wavelength at 425 nm was generated in the Fermat spiral structure by mixing the europium (Eu³⁺) and luminol to form the Eu³⁺/Luminol sensing probe. DPA in the reservoir can be used to specifically bind to Eu³⁺ under the negative pressure and transfer energy from DPA to Eu³⁺ sequentially via an antenna effect, thus resulting in a significant increase in the red fluorescence emission peak at 615 nm. According to the fluorescence intensity ratio (F615/F425), a good linearity can be obtained with increasing the concentration of DPA from 0 to 200 μM with a limit of detection as low as 10.11 nM. Interestingly, the designed FS-MC can achieve rapid detection of DPA in only 1 min, reducing detection time and improving sensitivity. Furthermore, a self-designed device integrated with the FS-MC and a smartphone color picker APP was employed for the rapid automatic point-of-care testing (POCT) of DPA in the field, simplifying complex processes and reducing testing times, thus confirming the great promise of this ready-to-use measurement platform for in situ inspection.