A ratiometric fluorescent probe for iron(III) and its application for detection of iron(III) in human blood serum.

A simple and versatile ratiometric fluorescent Fe(3+) detecting system, probe 1, was rationally developed based on the Fe(3+)-mediated deprotection of acetal reaction. Notably, this reaction was firstly employed to design fluorescent Fe(3+) probe. Upon treatment with Fe(3+), probe 1 showed ratiometric response, with the fluorescence spectra displaying significant red shift (up to 132 nm) and the emission ratio value (I522/I390) exhibiting approximately 2362-fold enhancement. In addition, the probe is highly sensitive (with the detection limit of 0.12 μM) and highly selective to Fe(3+) over other biologically relevant metal ions. The sensing reaction product of the probe with Fe(3+) was confirmed by NMR spectra and mass spectrometry. TD-DFT calculation has demonstrated that the ratiometric response of probe 1 to Fe(3+) is due to the regulation of intramolecular charge transfer (ICT) efficiency. Moreover, the practical utility in fluorescence detection of Fe(3+) in human blood serum was also conducted, and probe 1 represents the first ratiometric fluorescent probe that can be used to monitor Fe(3+) level in human blood serum. Finally, probe 1 was further employed in living cell imaging with pancreatic cancer cells, in which it displayed low cytotoxicity, satisfactory cell permeability, and selective ratiometric response to Fe(3+).