A CH₄‐Driven Ion Cloud‐Stretched Approach Enables ICP‐<i>q</i>MS for Multiplex Single‐Cell Analysis

In the last 40 years, inductively coupled plasma quadrupole (q) mass spectrometry (ICP-qMS) has been recognized as one of the best tools for the quantification of multiple elements/isotopes and even the biomolecules they labeled in a homogeneous solution sample. However, it meets a tough challenge when acquiring multi-m/z signals from an intact single-cell dispersed in a cell suspension, since the single-cell ion cloud generated in ICP presents an intermittently transient event with a duration time of hundreds of microseconds while the dwell time plus settling time of the q is at the similar time scale when peak-hopping between different m/z. Herein, we report CH₄ is able to stretch the single-cell ion cloud duration time to more than 7,000 μs in collision-reaction-cell (CRC), allowing multi-m/z signals acquisition by ICP-qMS. Quantification of single-cell's multiple phenotype protein markers can thus be achieved on ICP-(CH₄-CRC)-qMS, not only revealing the heterogeneity between the single cells but also enabling an unambiguous cell-classification of their subtypes. CH₄-driven ion cloud-stretched approach breaks through the long-standing bottleneck limited single-cell multiplex analysis on ICP-qMS, paving a path for more important applications of ICP-qMS in the fields related to single-cell analysis.