Colorimetric Sensors for Alkaloids Based on the Etching of Au@MnO₂ Nanoparticles and MnO₂ Nanostars

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@MnO2 nanoparticles and MnO2 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 MnO2, 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.