Water-Soluble Conjugated Polyelectrolytes for Adenosine Triphosphate (ATP) Detection

Abstract

Facile detection of adenosine triphosphate (ATP) at different concentration levels is important for applications such as assessing physiological status and monitoring bacterial and microbial contamination of food. A series of cationic conjugated polymers, PFPE-TEGx-NMe3+, with poly[fluorenyl-alt-p-phenyleneethynylene] (PFPE) as the backbone and different ratios of side chains consisting of a hexyl quaternary ammonium group and triethylene glycol, were synthesized for ATP sensing. Careful calculations based on the integrals of several specific proton peaks in the NMR spectra suggest that the ratios of different side chains of obtained polymers were consistent with the feeding ratios and the quaternization was close to 100%. Sensing application found that the fluorescence of polymers in aqueous solution was quenched upon adding ATP. The limit of detection (LOD) decreased with the increase in cation density on the polymer, which could be as low as 0.25 μM, and the higher the density of the quaternary ammonium group, the higher the sensitivity of polymer to ATP. The sensing system was selective to ATP over other possible interferents. Dynamic light scattering and zeta potential measurements show that ATP molecules were bound to polymer chains mainly through electrostatic interaction, while other interactions also existed, resulting in the formation of aggregates and the consequent fluorescence quenching. Relating the sensing performance to the chemical structures of analytes and fluorescent polymers revealed that the four negative charges combined with the organic part with a π-structure and some other interaction sites, which makes ATP unique compared with those possible interferents. At relatively low densities, the density of cationic groups had a significant effect on LOD and sensitivity, but at high densities, its effect became smaller; this observation is consistent with a sensing mechanism based on multiple interaction synergies dominated by electrostatic interactions. This study provides a general strategy for the design of sensing systems for biomolecules with relatively complex structures.