Ratiometric Luminescent Detection of Bacterial Spores with Terbium Chelated Semiconducting Polymer Dots

We report a ratiometric fluorescent sensor based on semiconducting polymer dots chelated with terbium ions to detect bacterial spores in aqueous solution. Fluorescent polyfluorene (PFO) dots serve as a scaffold to coordinate with lanthanide ions that can be sensitized by calcium dipicolinate (CaDPA), an important biomarker of bacterial spores. The absorption band of PFO dots extends to deep UV region, allowing both the reference and the sensitizer can be excited with a single wavelength (similar to 275 nm). The fluorescence of PFO remains constant as a reference, while the Tb3+ ions exhibit enhanced luminescence upon binding with DPA. The sharp fluorescence peaks of beta-phase PFO dots and the narrow-band emissions of Tb3+ ions enable ratiometric and sensitive CaDPA detection with a linear response over nanomolar concentration and a detection limit of similar to 0.2 nM. The Pdots based sensor also show excellent selectivity to CaDPA over other aromatic ligands. Our results indicate that the Tb3+ chelated Pdots sensor is promising for sensitive and rapid detection of bacterial spores.