Self-assembly of c-di-GMP, Tb3+, and Ag+ into high-quantum-yield coordination polymer nanoparticles: Mechanism discussion and application as a c-di-GMP sensor

This study disclosed self-assembly of cyclic diguanylate monophosphate (c-di-GMP) and terbium ions (Tb3+) into coordination polymer nanoparticles (CPNPs) at neutral pH based on the electrostatic interaction and coordination-bond formation. The as-synthesized c-di-GMP/Tb3+ CPNPs exhibited weak luminescence due to the coordination of Tb3+ with guanine bases of c-di-GMP that leads to inefficient energy transfer. It was found that the incorporation of Ag+ into the c-di-GMP/Tb3+ CPNPs boosted the luminescence of Tb3+. Since Ag+ can compete with Tb3+ for interacting with guanine bases of c-di-GMP, Tb3+ preferably binds to phosphodioxy groups of c-di-GMP in the presence of Ag+. This electrostatic interaction promotes efficient energy transfer from guanine bases of c-di-GMP to Tb3+. The c-di-GMP/Tb3+/Ag+ CPNPs possessed relatively high quantum yield (30.9 %) and long luminescent lifetime (1.3 ms) as compared to the previously reported nucleotide/Tb3+/Ag+ CPNPs. The CPNP-based sensing system allowed the quantification of c-di-GMP with the linear range of 20-300 nM and the detection limit (signal-to-noise ratio of 3) of 7 nM. The sensing system toward c-di-GMP was created by the combination of the two-step procedure involving the use of polystyrene sulfonic acid-coated magnetite nanoparticles to remove the interfering di- and tri-phosphate nucleotides, followed by the c-di-GMPmediated formation of the CPNPs in the presence of Tb3+ and Ag+. The CPNP-based sensing system was practically utilized to determine the level of c-di-GMP in bacterial lysates.