Sandwiched Electrochemiluminescent Peptide Biosensor for the Detection of Prognostic Indicator in Early‐Stage Cancer Based on Hollow, Magnetic, and Self‐Enhanced Nanosheets

Currently, peptide‐based protein‐recognition has been recognized as an effective and promising approach for protein assays. However, sandwiched peptide‐based biosensor with high sensitivity and low background has not been proposed before. Herein, a sandwiched electrochemiluminescence (ECL) peptide‐based biosensor is constructed for Cyclin A 2 (CA2), a prognostic indicator in early stage of multiple cancers, based on nanosheets with hollow, magnetic, and ECL self‐enhanced properties. First, hollow and magnetic manganese oxide nanocrystals (H‐Mn 3 O 4 ) are synthesized using triblock copolymeric micelles with core–shell–corona architecture as templates. Then, polyethyleneimine (PEI) and the composite of platinum nanoparticles and tris (4,4′‐dicarboxylicacid‐2,2′‐bipyridyl) ruthenium (II) (PtNPs–Ru) are immobilized on H‐Mn 3 O 4 to form H‐Mn 3 O 4 –PEI–PtNPs–Ru nanocomposite, in which PEI as coreactant can effectively enhance the luminous efficiency and PtNPs as nanochannels can greatly accelerate the electron transfer. Finally, due to the coordination between Eu 3+ and carboxyl, the obtained H‐Mn 3 O 4 –PEI–PtNPs–Ru aggregates locally to form sheet‐like nanostructures ((H‐Mn 3 O 4 –PEI–PtNPs–Ru) n –Eu 3+ ), by which the luminous efficiency is further increased. Based on the nanosheets and two designed peptides, a sandwiched ECL biosensor, using palladium nanocages synthesized through galvanic replacement reaction as substrate, is proposed for CA2 with a linear range from 0.001 to 100 ng mL −1 and a detection limit of 0.3 pg mL −1 .