Electrochemiluminescent/colorimetric biosensors for ultrasensitive detection of Aβ based on CdS quantum dot-modulated HOFs-Cu2+-g-C₃N₄.

In this work, we presented an electrochemiluminescent (ECL)/colorimetric biosensors for ultrasensitive detection of β-amyloid peptide (Aβ) based on hydrogen-bonded organic framework (HOFs)-Cu2+-graphitic carbon nitride (g-C3N4) nanocomposites. HOFs-Cu2+-g-C3N4 could be used both as an ECL luminescent substrate and as a nanozyme to catalyze the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB). Specifically, in the ECL mode, HOFs-Cu2+-g-C3N4 were firstly loaded on the surface of the electrode. The target analyte Aβ could simultaneously bind both Cu2+ and the peptide fragment KLVFF, thereby capturing the CdS quantum dots (QDs)-KLVFF on the electrode. The CdS QDs could perform ECL resonance energy transfer with HOFs-Cu2+-g-C3N4, resulting the increase in the ECL intensity. Meanwhile, in the colorimetric mode, the aptamer loaded on the magnetic beads could specifically capture the target Aβ. HOFs-Cu2+-g-C3N4 used as the nanozyme in the TMB-H2O2 chromogenic system could be sequentially bound with the target Aβ. The convenient colorimetric detection of Aβ was achieved after magnetically separating using the functionalized magnetic beads. The concentration range of Aβ detected by ECL mode was 0.1 pM ∼ 0.1 μM with a detection limit of 0.07 pM, while the concentration range of Aβ detected by colorimetric assay was 0.1 pM ∼ 0.1 μM with a detection limit of 0.032 pM. These two different assay modes enhanced the sensitivity and reliability of the detection of Aβ and demonstrated potential applicability in the early diagnosis of Alzheimer's disease.