Fluorescent Polymer Carbon Dots for the Sensitive–Selective Sensing of Fe³⁺ Metal Ions and Cellular Imaging

Poly(ether amine) (PEA)-based fluorescent polymer carbon dots (FPCDs) have been synthesized via a simple Schiff base reaction between poly(ether amine) (PEA) and formaldehyde followed by its hydrothermal treatment. The resulting water-soluble FPCDs are 2 nm in size and show excitation-dependent emission properties. Blue-emissive FPCDs exhibit the maximum intensity of fluorescence at 440 nm under 360 nm excitation and show a high quantum yield of ∼18%. FPCDs are used for selective Fe³⁺ metal ion sensing in aqueous media through the fluorescence quenching of FPCDs with a limit of detection of ∼162 nM. Nontoxic FPCDs have been used for cancer cell imaging and also for intracellular Fe³⁺ metal ion sensing in cancer cells. FPCDs have been used for Fe³⁺ ion sensing in industrial effluents, and they serve as sensors even in the presence of other competing metal ions. To determine the real application potential of FPCDs as a sensor, FPCDs are used to establish the Fe³⁺ metal ion content in samples of spiked blood serum with remarkable specificity, sensitivity, and accuracy. Moreover, we proposed a possible sensing mechanism wherein Fe³⁺ metal ions interacted with the functional groups present on the surface of FPCDs, and fluorescence quenching occurred via a static quenching mechanism along with an inner filter effect (IFE).