Porphyrin-based covalent organic framework as bioplatfrom for detection of vascular endothelial growth factor 165 through fluorescence resonance energy transfer

A fluorescent aptasensor based on porphyrin-based covalent organic framework (p-COF) and carbon dots (CDs) was constructed for detecting vascular endothelial growth factor 165 (VEGF(165)) and for imaging of the breast cancer cell line Michigan cancer foundation-7 (MCF-7). CDs synthesized with strong photoluminescence at lambda similar to 380 nm were used as donors to label the VEGF(165)-targeted aptamers (Apt(VEGF)/CDs). Additionally, the p-COF nanostructure comprised rich functional groups of C-N on the surface and pi-stacking planar nanostructure, resulting in the CDs adsorption via weakly pi-pi stacking, hydrogen bond and the Van der Waals force. Thereby, the fluorescence resonance energy transfer (FRET) occurred due to the close distance between the p-COF network and CDs, leading to the quenching of the fluorescence feature of CDs and p-COF. In the presence of VEGF(165), the G-quadruplex was formed via the specific binding between VEGF(165) and aptamer. It impelled that the release of partial VEGF(165)-AptVEGF/CDs complex, affording the fluorescence recovery of the sensing system to some extent. Consequently, the proposed AptVEGF/CDs/p-COF fluorescence biosensor offered excellent analytical performances for the VEGF(165) detection, displaying a detection limit of 20.9 fg mL(-1) within a wide linear range of the VEGF(165) concentration of 1.0 pg mL 1-100 ng mL(-1). The developed fluorescence biosensor was also used to determine VEGF(165)-overexpressed in MCF-7 cancer cells. Thereby, the present work can greatly widen the application of COFs in the development of aptasensors and cancer diagnosis.