Mass spectrometry has proven to be a useful technique for rapid identification of bacterial cells. Among various ionization techniques in mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) has been commonly used for the identification of bacterial cells. Recently, MALDI mass spectrometry has also been utilized to distinguish cellular responses. Ambient ionization techniques do support whole bacterial cell analysis, which include desorption electrospray ionization (DESI). Nanospray DESI (nDESI) is a new variant of DESI, and its application to whole-cell mass spectrometry is limited. In this project, the use of nDESI mass spectrometry to measure probiotic Lactobacillus reuteri (LR) cells is explored. A unique and reproducible mass spectral pattern of untreated LR cells was obtained by using 50% methanol/water as nDESI solvent. The use of nDESI mass spectrometry is further extended to distinguish untreated LR cells from treated LR cells that have been exposed to low pH. These findings demonstrate the feasibility of using nDESI in whole-cell mass spectrometry.

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质谱已被证明是快速鉴定细菌细胞的有用技术。在质谱法中的各种电离技术中，基质辅助激光解吸/电离（MALDI）已普遍用于鉴定细菌细胞。最近，MALDI质谱也已用于区分细胞反应。环境电离技术确实支持整个细菌细胞分析，包括解吸电喷雾电离（DESI）。纳米喷雾DESI（nDESI）是DESI的新变体，其在全细胞质谱分析中的应用受到限制。在该项目中，使用nDESI质谱法测量益生菌路透氏乳杆菌（LR）细胞被探索。通过使用50％甲醇/水作为nDESI溶剂，可以得到未经处理的LR细胞的独特且可重现的质谱图。nDESI质谱的使用进一步扩展，以区分未处理的LR细胞和已暴露于低pH值的已处理LR细胞。这些发现证明了在全细胞质谱中使用nDESI的可行性。

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