Multifunctional fluorescent sensing of chemical and physical stimuli using smart riboflavin-5′-phosphate/Eu³⁺ coordination polymers

A novel type of stimuli-responsive fluorescent polymers has been developed via the self-assembly of riboflavin-5′-phosphate (RiP) as ligand and europium (III) (Eu³⁺) as central metal ion coordinated with the ligand. The as-prepared RiP/Eu³⁺ coordination polymers (RiP/Eu³⁺ CPs) are smart and multifunctional for respectively responding to chemical and physical stimuli, in which RiP acts as the stimuli-responsive fluorescent signal indicator. For sensing chemical stimuli, 2,6-pyridinedicarboxylic acid (DPA, an anthrax biomarker) having higher bonding force towards Eu³⁺ can grab it from smart RiP/Eu³⁺ CPs through competition reaction, resulting in the release of RiP for highly sensitive and selective DPA monitoring in a mix-and-read fluorescent enhancement format, and the detection limit is as low as 41.5 nM. Density functional theory (DFT) calculations has been also performed to verify the DPA sensing principle. For sensing physical stimuli, the smart RiP/Eu³⁺ CPs can be acting as a novel sensory probe for the determination of temperature from 10 °C to 40 °C based on the thermal-induced disruption of the binding between Eu³⁺ and RiP and the disassembly of the smart RiP/Eu³⁺ CPs accompanying with the recovery of the fluorescence of RiP. This work establishes an effective platform for multifunctional sensing of chemical and physical stimuli utilizing both smart lanthanide nanoscale coordination polymers (LNCPs) and novel sensing strategies.