Researchers have developed a two-dimensional cobalt single-atom catalyst with enhanced oxidase-like activity, enabling highly sensitive dual-mode detection of structurally similar bioanalytes.
Taking advantage of the excellent oxidase-like activity of 2D Co-CN(H) catalysts and the good photothermal properties of oxTMB, an innovative dual-mode colorimetric-photothermal sensing platform toward effective discrimination and detection of dihydroxybenzene isomers has been successfully constructed. Image Credit: Nano Research, Tsinghua University Press
Accurately detecting and distinguishing bioanalytes with similar structures remains a key challenge in biological research and environmental monitoring. Enzyme-based colorimetric sensor assays have emerged as a reliable solution, offering high selectivity and sensitivity. These assays, however, depend heavily on the catalytic efficiency of the enzymes involved.
To address limitations in natural enzymes, scientists have turned to single-atom catalysts (SACs), which feature precise geometric and electronic structures that mimic the catalytic centers of enzymes. Cobalt-based SACs anchored on carbon substrates (Co-CN) are especially promising, thanks to their strong oxidase-like activity. By fine-tuning the nitrogen coordination environment—particularly Co-N3(C) configurations—researchers can significantly boost their catalytic performance. Additionally, introducing defects into the carbon support can shift electronic distribution and spin density, further enhancing catalytic behavior.
Despite these advantages, many SACs only utilize surface-level active sites, limiting their effectiveness. This has prompted growing interest in two-dimensional (2D) catalyst designs, which provide larger surface areas, improved exposure of active sites, and better mass transport.
In this context, a team led by Yizhong Lu at the University of Jinan has reported a new class of 2D cobalt single-atom catalysts supported on defect-rich carbon nanosheets (2D Co-CN(H)). Their findings, published in Nano Research, provide valuable insight into how structural defects influence the performance of SACs.
The catalysts were synthesized through high-temperature pyrolysis of Co-ZIF-8 and g-C3N4. As g-C3N4 decomposes, it releases gases that break metal-ligand bonds, etching the precursor and forming porous structures. Milder etching results in low-defect SACs (2D Co-CN(L)), while more aggressive etching produces the highly defective, layered 2D Co-CN(H) catalysts. Increasing the amount of g-C3N4 enhanced this effect, leading to a smoother sheet-like surface with more exposed active sites.
Combined experimental and theoretical analyses reveal that the defects around atomic cobalt sites can rationally regulate the electronic distribution, significantly promoting the cleavage of O-O bonds and thus improving their oxidase-like performance.
Dr. Yizhong Lu, Study Corresponding Author, University of Jinan
The 2D Co-CN(H) catalyst showed strong ability to oxidize 3,3',5,5'-tetramethylbenzidine (TMB), producing a colored product (oxTMB) detectable through a sensitive colorimetric readout. Notably, oxTMB also acts as a photothermal agent, allowing the system to convert optical signals into heat under near-infrared (NIR) light.
“Taking advantage of the excellent oxidase-like activity of 2D Co-CN(H) catalysts and the good photothermal properties of oxTMB, an innovative dual-mode colorimetric-photothermal sensing platform toward effective discrimination and detection of dihydroxybenzene isomers has been successfully constructed,” added Dr. Yizhong Lu.
This study not only advances our understanding of defect-engineered SACs but also highlights their potential in practical applications such as environmental sensing and chemical analysis.
Journal Reference:
Zhang, X., et al. (2025) Single cobalt sites on defective carbon nanosheets as efficient oxidase mimics for visual biosensing. Nano Research . doi.org/10.26599/NR.2025.94907336.