Porphyrin derived dual-emissive carbon quantum dots: Customizable synthesis and application for intracellular Cu2+quantification

Exploring sensory systems from metal ion receptors enables the continuous development of ion sensing technologies. Herein we report the synthesis of carbon quantum dots (CQDs) from 5,10,15,20-tetrakis(4-sulfophenyl) porphyrin (TSPP) and additional carbon source, and its application in Cu2+ imaging and quantifying in living cells. The CQDs are synthesized via a hydrothermal method in a successive polymerization and carbonization process. Due to the surface traps introduced by TSPP residue, the CQDs are featured with dual-emissive property of green (505 nm) and red (682 nm) fluorescence. Moreover, the red-to-green fluorescence ratio is readily customizable by tuning the molar fraction of TSPP. Benefited from Cu2+ complexation induced red fluorescence quenching, the CQDs can be served as the ratiometric fluorescent nanosensor for Cu2+ detection with ultra-high sensitivity and excellent specificity. The nanosensor is demonstrated to linearly detect Cu2+ in the range of 0-50 nM, with an extremely low limit of detection (LOD) of 37 pM. More importantly, interference from other biological compositions, especially Fe3+, is successfully excluded via the site-selective coordination and specific electron transfer path. Based on the excellent analytical performance of the nanosensor, quantifying Cu2+ in living cells is realized according to the linear correlation between fluorescence ratio and intracellular Cu2+ content, which is parallelly detected by inductively coupled plasma mass spectrometry (ICP-MS). To demonstrate its practicality, the nanosensor is challenged to measure Cu2+ uptake kinetics for cell lines derived from different tissues.

Automated summary

The synthesis of carbon quantum dots (CQDs) from 5,10,15,20-tetrakis(4-sulfophenyl) porphyrin (TSPP) and additional carbon source enables Cu2+ imaging and quantifying in living cells with ultra-high sensitivity and excellent specificity. The CQDs exhibit dual-emissive property of green and red fluorescence due to surface traps introduced by TSPP residue, and the red-to-green fluorescence ratio can be customized by tuning the molar fraction of TSPP. The nanosensor shows an extremely low limit of detection (LOD) of 37 pM and successfully excludes interference from other biological compositions, particularly Fe3+, making it a promising tool for quantifying Cu2+ in living cells.