Boosting the sensitivity of ICP-TOF-MS for single-cell metallome profiling via overpulsing and isotope summation

Simultaneous determination of endogenous elements in individual cells by single-cell inductively coupled plasma-mass spectrometry (SC-ICP-MS) is challenged by low elemental contents and the intrinsically low sensitivity of time-of-flight ICP-MS (ICP-TOF-MS) in the low-mass range. In this work, overpulsing and isotope summation were evaluated as complementary means to enhance the performance in the low-mass range. Narrowing the mass range monitored from the full elemental mass spectrum to ²³Na-⁷⁵As increased the sensitivity approximately 2-fold and to ³⁰Si-⁷⁵As approximately 5-fold. These gains, combined with isotope summation where possible, translated into significant improvements in limits of detection, typically by a factor of 2-5 across key elements (e.g., ³¹P from 106 to 31 fg/cell; ∑Fe from 0.69 to 0.19 fg/cell; ∑Zn from 2.4 to 1.2 fg/cell). The improved sensitivity directly increased the fraction of detectable cell events. For RBCs, ³¹P was detected in 18% of the cell events (as compared to 0% when monitoring the full mass range) and ³²S detection increased from 46% to 98%. For Jurkat and Raji cells, overpulsing enabled or enhanced the determination of Na, Mg, P, S, K, Ca, Mn, Fe, and Zn, including an increase in Ca detection from 3-4% to 74% and in Mn detection from <1% to 54% of the cells introduced into the ICP. Overall, these improvements extend the capabilities of ICP-TOF-MS for true multi-element single-cell metallomics in biological and biomedical research.