A highly sensitive self-enhanced aptasensor based on a stable ultrathin 2D metal–organic layer with outstanding electrochemiluminescence property

3D bulk metal-organic frameworks (MOFs) have received growing interest in electrochemiluminescence (ECL) assays because they can provide a high specific surface for loading a large quantity of ECL luminophores, but the ECL efficiency of bulk MOFs is still low since some interior luminophores are difficult to be excited. Herein, an ultrathin 2D metal-organic layer (MOL) for grafting self-enhanced ruthenium complexes (Ru-l-Lys) was first synthesized to greatly increase the utilization ratio of luminophores. Compared with 3D bulk MOFs, ultrathin 2D MOL could provide more accessible postmodification sites for grafting the Ru-l-Lys complexes; the self-enhanced Ru-l-Lys complexes on MOL were easily excited by electrons due to the shortened ion/electron-transport distance and the removal of diffusion barriers. Furthermore, the electron transfer path between the Ru(ii) luminophore and coreactant (l-Lys) was shortened and the energy loss of the luminophores decreased, which significantly improved the ECL efficiency. As expected, our work manifested that the Zr-MOL's loading amount of Ru-l-Lys was about 1.23-fold higher than that of a 3D bulk Zr-MOF, and the ECL intensity and efficiency of Ru-l-Lys-Zr-MOL were around 93.45-fold and 1.64-fold higher than those of control Ru-l-Lys-Zr-MOF, respectively. Considering all of these merits, in this work, we utilized the prepared Ru-l-Lys-Zr-MOL as a highly efficient ECL indicator for the first time to fabricate a highly sensitive self-enhanced aptasensor for mucin 1 (MUC1) determination. The proposed aptasensor showed high sensitivity with a linear range from 1 fg mL-1 to 100 pg mL-1 with a detection limit of 0.72 fg mL-1; it also exhibited excellent specificity and stability. It is noteworthy that this work not only provides a new strategy to design and synthesize high-performance ECL materials, but also opens a new way to develop ultrasensitive ECL sensors for bioanalysis.