Developing efficient strategies for the simultaneous discrimination and detection of bioanalytes with similar structures holds great importance for biological research and environmental protection. Recently, enzyme-based colorimetric sensor assays have been extensively used as an effective approach to detect structurally similar bioanalytes with high selectivity and sensitivity. Generally, the analytical performance of an enzyme-based colorimetric assay is closely related to the catalytic efficiency of the enzymes. Single-atom catalysts with well-defined geometric and electronic structures have been regarded as promising alternatives to natural enzymes through mimicking their metallic catalytic centers. Among various single-atom nanozymes, cobalt single-atom catalysts incorporated in carbon substrates (Co-CN) have proven to exhibit excellent enzyme-like activity. The oxidase-like performance of single-atom Co nanozymes could be effectively tuned by regulating the nitrogen coordination environment. Specifically, the Co-N3(C) species with three-coordinated nitrogen atoms exhibited the highest activity. Moreover, recent studies have shown that the defects in the carbon substrate can disrupt the charge symmetry of single-atom catalysts, redistributing spin density and thus affecting their catalytic properties. However, most of these single-atom Co nanozymes utilize only a small fraction of the active sites located on their surface, and as a result, their catalytic potentials may not be fully realized. Owing to their high surface area to host exposed active sites, two-dimensional catalysts, which can maximize the availability of active sites and provide enhanced mass transport, have garnered great attention in catalytic applications.
A team of material scientists led by Yizhong Lu from University of Jinan recently report that two-dimensional defect carbon nanosheets supported single-atom cobalt catalysts (2D Co-CN(H)) with enhanced oxidase-like performance.
This study offers an in-depth investigation into how defects influence the catalytic activity of single-atom nanozymes and develops a colorimetric-photothermal dual-mode sensing platform for the analysis and detection of dihydroxybenzene isomers.
The team published their research in Nano Research on April 29, 2025.
Two-dimensional Co single-atom catalysts anchored on defective carbon nanosheets (2D Co-CN(H)) were synthesized via high-temperature pyrolysis of Co-ZIF-8 and g-C₃N₄ mixtures. The g-C₃N₄ decomposes into corrosive gases at high temperatures, disrupting metal-ligand bonds, leading to progressive thermal etching and disintegration of the precursor. Minor etching produces a low-defect cobalt SACs (2D Co-CN(L)), while higher-intensity etching yields a layered, porous, and highly defective cobalt SACs (2D Co-CN(H). With the increase of g-C3N4, the thermal etching effect became more pronounced, transforming the outer surface from a progressively recessed appearance to a perfect sheet structure, indicating an increase in 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," said Dr. Yizhong Lu, the corresponding auther of the paper.
The oxidase-like activity of 2D Co-CN(H) catalysts can effectively catalyze the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) into oxidized TMB (oxTMB) with sensitive colorimetric readout. And the oxTMB generated can also serve as a photothermal agent to convert the colorimetric readout into heat under near-infrared (NIR) irradiation. "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," said Dr. Yizhong Lu.
This study not only highlights the important role of defects on the oxidase-like activity of single-atom nanozymes, but also broadens their potential applications in environmental conservation.
Other contributors include Yuanyuan Jiang, Wendong Liu, Xueli Zhang, Chenyu Tao, Shushu Chu and Mingyuan Xia from School of Materials Science and Engineering, Jinan University.
This work was supported by the National Natural Science Foundation of China (22172063), the Young Taishan Scholar Program (tsqn201812080) and the Independent Cultivation Program of Innovation Team of Ji'nan City (2021GXRC052).
About the Authors
Yizhong Lu is a full professor and doctoral supervisor at the School of Materials Science and Engineering, University of Jinan. He received his Ph.D. from the State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, in 2015. Following his doctoral studies, he conducted postdoctoral research at Nanyang Technological University, Singapore. In April 2017, he joined the University of Jinan as an academic leader. Prof. Lu has been recognized with several prestigious honors, including the Taishan Scholar Young Expert, Shandong Outstanding Young Scholar, First Prize of Jilin Provincial Science and Technology Award (Second Place), and Elsevier Highly Cited Chinese Researcher (2020-2023). His research focuses on photo/electrocatalysis and bioanalysis. He has published over 100 SCI papers as the first or corresponding author in Chem. Soc. Rev., J. Am. Chem. Soc. (2 papers), Adv. Mater., Nano Lett., Adv. Energy Mater. (2 papers), Anal. Chem. (6 papers), among others, with more than 8,000 citations. Additionally, he holds over 10 invention patents.
Yuanyuan Jiang is an associate professor and master's supervisor at the School of Materials Science and Engineering, University of Jinan. Her research interests include (1) the design and synthesis of metal nanomaterials, carbon nanomaterials, and nanocomposites for applications in electrochemistry, energy conversion, and storage; (2) analytical detection and biosensing. Dr. Jiang has led and participated in multiple research projects funded by the National Natural Science Foundation of China, the Shandong Provincial Natural Science Foundation, and the University of Jinan Ph.D. Fund. She has published several SCI papers as the first or corresponding author in Adv. Energy Mater., ACS Catal., Small Methods, Science China Mater., Chem. Eng. J., Anal. Chem., Sensor. Actuat. B, Food Chem., J. Colloid Interf. Sci., and other journals.
Wendong Liu is a faculty postdoctoral researcher at the School of Materials Science and Engineering, University of Jinan. His research focuses on the precise design and synthesis of single-atom catalysts, as well as their applications in antibacterial and anticancer therapy. Dr. Liu has led or participated in multiple research projects, including the Shandong Provincial Postdoctoral Innovation Talent Support Program and the National Natural Science Foundation of China. He has published several SCI papers as the first or corresponding author in Adv. Funct. Mater., Chem. Eng. J., ACS Sustainable Chem. Eng., and other high-impact journals.
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.
