Iron(III) Sensors Based on the Fluorescence Quenching of Poly(phenylene ethynylene)s and Iron-Detecting PDMS Pads

The detection of Fe ions is critical to environmental monitoring and disease diagnosis. We herein report fluorescent conjugated polymers that exhibit fluorescence quenching upon the addition of Fe (III) ions with the total concentration of 2 ppm. The polymer backbone consists of poly(phenylene ethynylene) (PPE) with side-chains bearing triethylene glycols or alkyl groups. The quenching phenomenon was analyzed by the Stern-Volmer equation, and the resulting Stern-Volmer constants show that the alkyl functional PPE presents higher sensitivity than the triethylene glycol functional PPE, which was unexpected. The polymer sensors showed the selectivity in that the Stern-Volmer constants for Fe3+ are 2-3 times higher than those for Na+, K+, and Ca2+. Time-resolved photoluminescence spectroscopy revealed that the quenching is static, indicating that there may be coordination between Fe (III) and alkyne/phenyl groups in the PPE backbone. For practical applications, we produced a PPE-containing, fluorescent polydimethylsiloxane (PDMS) pad. Dropping Fe solution like an ink on the pad exhibits a dark stain, demonstrating the scheme of producing Fe-detecting flexible pads for future applications in wearable sensor technology.