Fluorescent detection of an anthrax biomarker based on PVA film

Due to the dangerous nature of anthrax, the development of a cost-effective, sensitive and field-portable sensor for the anthrax biomarker--calcium dipicolinate (CaDPA)--is of exceptional significance for both military and civilian use. Herein, a flexible polymer-film-based ratiometric sensor for detecting CaDPA was demonstrated. A reference dye and a probe ligand were covalently immobilized onto the film surface through a highly selective and efficient "click chemistry" reaction. The reference dye, whose fluorescence intensity does not change with varying amounts of CaDPA, offers a non-interfering internal calibration. The ethylenediaminetetraacetic acid (EDTA)-based ligand binds with Eu(III) and serves as the probe. In the absence of CaDPA, the film sensor exhibited almost no red fluorescence because the Eu(III) ions themselves give no emission without sensitization by CaDPA owing to the small molar absorption coefficients of Eu(III) ions. The presence of CaDPA induces a significantly enhanced emission intensity of the sensor, and thereby enables the film as a ratiometric sensor for CaDPA. This sensor can selectively detect CaDPA in water with a detection limit of 100 nM. Moreover, this sensor exhibited strong anti-interfering capability, it can not only be used in milieus that contain various amino acids and some biologically-abundant cations, but can also be usable in some biological fluids such as urine and serum. This test-paper-like film sensor is suitable for portable field analysis and needs no extra protective measures during transport due to its flexibility, and it can easily be separated from the analyte solution after the detection.