Great enthusiasm in single-atom catalysts for various catalytic reactions continues to heat up. However, the poor activity of the existing single/dual-metal-atom catalysts does not meet the actual requirement. In this scenario, the precise design of triple-metal-atom catalysts is vital but still challenging. Here, a triple-atom site catalyst of FeCoZn catalyst coordinated with S and N, which is doped in the carbon matrix (named FeCoZn-TAC/SNC), is designed. The FeCoZn catalyst can mimic the activity of oxidase by activating O 2 into • O 2 − radicals by virtue of its atomically dispersed metal active sites. Employing this characteristic, triple-atom catalysts can become a great driving force for the development of novel biosensors featuring adequate sensitivity. First, the property of FeCoZn catalyst as an oxidase-like nanozyme was explored. The obtained FeCoZn-TAC/SNC shows remarkably enhanced catalytic performance than that of FeCoZn-TAC/NC and single/dual-atom site catalysts (FeZn, CoZn, FeCo-DAC/NC and Fe, Zn, Co-SAC/NC) because of trimetallic sites, demonstrating the synergistic effect. Further, the utility of the oxidase-like FeCoZn-TAC/SNC in biosensor field is evaluated by the colorimetric sensing of ascorbic acid. The nanozyme sensor shows a wide concentration range from 0.01 to 90 μM and an excellent detection limit of 6.24 nM. The applicability of the nanozyme sensor in biologically relevant detection was further proved in serum. The implementation of TAC in colorimetric detection holds vast promise for further development of biomedical research and clinical diagnosis.

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Alkaloids, as a natural acetylcholinesterase (AChE) inhibitor, have become a research hotspot in the treatment of Alzheimer's disease (AD) and the most active field in the research and development of AD drugs. Alkaloids can inhibit the activity of AChE in vivo, reduce the decomposition of acetylcholine (ACh), and alleviate the damage of AD to living ability and cognitive ability. In this study, we report a colorimetric sensor array for discrimination of different kinds of alkaloids based on the etching of two kinds of nanomaterials (walnut-like Au@MnO 2 nanoparticles and MnO 2 nanostars) by choline, which is obtained from the catalytic hydrolysis of ACh by AChE. Because different alkaloids have distinguished abilities to inhibit AChE activity, the presence of diverse alkaloids leads to various degrees of reduction etching of MnO 2 , which causes differential variation in colorimetric response signals. Considering this, the use of this underlying mechanism can provide a fingerprint signature for each alkaloid type. Using this strategy, the pattern of colorimetric response of each target alkaloid can be obtained on the sensor array and identified via linear discriminant analysis. The limits of detection of seven alkaloids (5.6 nM for berberine chloride, 3.7 nM for berberine, 11.7 nM for jatrorrhizine, 25.0 nM for palmatine, 5.3 nM for harmane, 7.0 nM for eserine, and 4.8 nM for galanthamine) were obtained using this sensor array in our experiment. The effectiveness of this sensor array is further validated by high accuracy (100%) examination of 28 blinded unknown alkaloid samples. Notably, the sensor array shows the capability to identify alkaloid mixtures and alkaloids in Chinese herbal medicine samples.

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