A FRET sensor based on quantum dots-porphyrin assembly for Fe(III) detection with ultra-sensitivity and accuracy

Exploring sensors based on Förster resonance energy transfer (FRET) systems enables the continuous development of biological sensing technologies. Herein, we report the construction of a FRET sensor with dual-emissive quantum dots (QDs) and meso-tetra(4-sulfonatophenyl) porphine (TSPP). The sensor is composed of mesial green-emissive QDs with a thick silica shell (gQD@SiO₂) and circumjacent blue-emissive QDs coated with ultra-thin silica spacer, on which is linked TSPP (bQD@SiO₂-TSPP). The gQD@SiO₂ endows the sensor with a fluorescent background. Due to the ultra-thin silica spacing, coupled with the superior resonance effect of bQD fluorescence and the Soret-band absorption of TSPP, the FRET efficiency is highly sensitive to the chelation state of TSPP. Relying on the absorbance transition of TSPP complexed with Fe(III), the FRET sensor is applied for ultra-sensitive Fe(III) detection. In aqueous solution, the sensor is demonstrated to linearly detect Fe(III) in the range of 0-1 μM, with a limit of detection (LOD) of 40 nM. More importantly, reliable Fe(III) detection can be achieved via the specific complexation of Fe(III) by TSPP and the ratiometric fluorescent response. As such, the inter-/intra-day precisions in standard samples, as well as the recovery rate in biological matrices, are fully validated. The excellent analytical performance, in combination with the excellent biocompatibility of the FRET sensor, allows semi-quantitative Fe(III) imaging in living cells.