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.