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The unique quality of Pu-erh tea is due to the process of pile fermentation that the tea leaves undergo, but this process can lead to the risk of producing aflatoxin B1 (AFB1), the most toxic of aflatoxins. The commonly used methods for the determination of AFB1 in foods are complex and time-consuming. In this paper, an accurate and rapid method for the determination of aflatoxin B1 in Pu-erh tea was developed by isotope dilution mass spectrometry. After extraction of AFB1 in Pu-erh tea using acidified acetonitrile (1% formic acid), a purification step was performed by the QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method with primary secondary amine (PSA) and octadecylsilyl silica (C18) as the absorbents. The quantification of AFB1 was performed by liquid chromatography tandem mass spectrometry (LC-MS/MS) in positive mode (ESI+) and selective reaction monitoring (SRM) with 13C-labeled aflatoxin B1 (13C17-AFB1) as the internal standard in less than 5 min. A complete validation study was carried out after method optimization to ensure adequate performance of the developed method. The results showed good linear correlation in the range from 0.10 to 10.00 μg L−1with a correlation coefficient (R2) > 0.99. The average recoveries of AFB1 from blank samples fortified at three levels (0.50, 5.00, and 20.00 μg kg−1) ranged from 81.4 to 100.8% with the relative standard deviations (RSDs, n= 6) between 1.7 and 4.8%. The limit of detection (LOD) was 0.50 μg kg−1. The validation method was applied to an analysis of AFB1 in 50 raw Pu-erh teas and 50 ripened teas. None of the investigated Pu-erh samples showed an AFB1 content above the LOD. The results indicate that people who are keen on drinking Pu-erh tea are not at risk from AFB1 exposure. The proposed method was demonstrably simple, rapid, highly sensitive and accurate, and was effective in the rapid qualitative and quantitative analysis of AFB1 in Pu-erh tea.

Secreted proteins are critical mediators in various biological systems, including the immune system, nervous system, and tumor microenvironment. Understanding profound cellular functional heterogeneity in secretion requires multiplexed secreted protein analysis at the single‐cell level. However, most single‐cell protein secretion analysis technologies rely on bulky, expensive instruments, preventing widespread use. Herein, we proposed using a portable and low‐cost desktop scanner to detect multiplexed proteins secreted from single cells. Gold nanoparticle‐enhanced silver staining and tyramide signal amplification are combined to construct a two‐step amplification for single‐cell secretion assay detection. We used this approach to investigate the heterogeneous immune response of macrophages at the single‐cell level, which revealed that only a minority of cells could secrete 10‐fold more MCP‐1 and TNF‐α than the averaged secretion. The reported platform eliminates bulky equipment for single‐cell secretion analysis, making it affordable for basic and clinical research. Currently, evaluating cellular functional heterogeneity with multiplexed secreted protein analysis at the single‐cell level relies on bulky, expensive instruments, preventing widespread use. This article aims to develop a point‐of‐care multiplexed single‐cell protein secretion analysis platform with a home‐use desktop scanner, eliminating bulky equipment requirements for single‐cell secretion assay detection and making it affordable for basic and clinical research.