CoN₄-supported Co₂N metal clusters for developing sensitive chemiluminescent immunochromatographic assays

In view of the optimal catalytic efficiency (∼100%), single-atom site catalysts are being widely exploited in a range of areas including organic synthesis, energy conversion, environmental remediation, biotherapy, etc. However, low loading ratio of the unitary active sites on single-atom site catalysts dramatically hinders the remarkable improvement of their catalytic activity. Hereby, a facile low-temperature reduction protocol was adopted for synthesizing CoN₄-supported Co₂N metal clusters on graphitic carbon nitride, which show the remarkably superior chemiluminescent (CL) catalytic capacity than some reported pure single-atom site catalysts. Nitrogen-encapsulated Co₂N clusters coupled with isolated Co-N₄ moieties (Co₂N@Co-N₄) endowed the synergetic catalysts with high Co content of 53.2 wt%. Through X-ray absorption spectroscopy, the synergetic active sites (Co₂N@Co-N₄) afforded the CoN₄-supported Co₂N clusters with the remarkable catalytic activity for accelerating the decomposition of H₂O₂ to produce extensive superoxide radical anion rather than singlet oxygen or hydroxyl radical. Therefore, the CoN₄-supported Co₂N clusters possessed the superb enhancement effect on luminol-H₂O₂ CL reaction by ∼22829 times. The CoN₄-supported Co₂N clusters were utilized as signal probes to establish a CL immunochromatographic assay (ICA) platform for quantitating mycotoxins. Herein, aflatoxin B1 was employed as a mode analyte and the limit of detection was as low as 0.33 pg mL^-1 (3σ). As a proof-of-principle work, the developed ICA protocol was successfully employed on the detection of aflatoxin B1 spiked in Angelica dahurica and Ganoderma lucidum with acceptable recoveries of 84.0-107.0%. The ideal practicability of the work elucidates that CoN₄-supported Co₂N clusters showed a new perspective for developing the sensitive CL biosensing.