Laser Ablation-Inductively Coupled Plasma Time-of-Flight Mass Spectrometry Imaging of Trace Elements at the Single-Cell Level for Clinical Practice

Abstract

In this work, a combination of routine clinical practice and state-of-the-art laser ablation-inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) imaging is presented for multielement analysis of single cells on clinical samples. More specifically, routinely drawn blood thin films of a patient undergoing treatment with the anticancer drug cisplatin were studied. The presented label-free approach enabled rapid analysis of hundreds of cells at the single-cell level within a few minutes without additional tailored sample preparation. The employed low-dispersion LA setup is based on the tube-type COBALT ablation cell in combination with the aerosol rapid introduction system (ARIS) providing pixel-resolved imaging at 250–500 Hz for biological sample material. In order to cope with the short transient signals of only a few milliseconds delivered by the laser ablation setup, an icpTOF 2R TOF-based ICP-MS instrument was used for analysis, which has a mass coverage of m/z = 14–256. Leukocytes and erythrocytes, imaged with a laser beam of 4 μm and pixel interspacing of 2 μm, were differentiated on the basis of their intrinsic trace-elemental pattern. Overall, red blood cells displayed high iron intensities, whereas individual white blood cells were characterized by their high phosphorus content and increased sulfur signal. Unsupervised multivariate statistical analysis was applied to the data set. Principal component plots showed a clear clustering of leukocytes versus erythrocytes. The approach allowed studying not only the drug distribution between plasma and cells but also, for the first time, the preferential accumulation of platinum in different blood cell types without the need of cell fixation and labeling. Extracellular hotspots of platinum were observed, whereas only a small fraction of platinum was associated with erythrocytes. The investigation demonstrates the potential of low-dispersion LA-ICP-TOFMS as a rapid and powerful tool for label-free single-cell imaging in the clinical context.

Cisplatin Uptake in Macrophage Subtypes at the Single-Cell Level by LA-ICP-TOFMS Imaging

“…Therefore, method-oriented studies are of paramount importance, focusing on advancement of spatial resolution, 10 , 18 throughput, 17 , 19 and quantification strategies, 28 − 30 as well as on the evaluation of endogenous elemental patterns as cell markers. 11 , 31 , 32 …”

“…Concerning sample types, LA-ICPMS imaging of single cells has covered tissue samples, 33 cell smears (or cell thin films), 11 chambered glass coverslips with cells directly growing on them, 13 cell arrays produced by a piezo-acoustic microarrayer, 34 and cytospins, 14 − 16 where cells are deposited on glass slides through centrifugal forces. In tissue sections, the heterogeneous and very dense cell population poses a challenge for the detection of single-cell boundaries.…”

“… 36 Using blood smear samples of patients undergoing cisplatin chemotherapy, qualitative multielement analysis of several hundred single blood cells enabled differentiation of cell types based on LA-ICP-TOFMS and unsupervised statistical analysis. 11 One study reported on single-cell arraying of THP-1 cells and potential quantitative LA-ICP-TOFMS analysis using microdroplet standards. 34 Recently, multimodal imaging studies have emerged for single-cell analysis.…”

Single-cell Analysis Based on ICP-MS

“…There are two major types of ICP-MS based singlecell analysis (figure shown below), i.e. laser ablation (LA-) ICP-MS for the elemental imaging of single cell, [5][6][7][8][9][10][11][12] and single-cell (sc-) ICP-MS based on the time-resolved analysis of transient elemental signals. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Single quadrupole ICP-MS, i.e.…”

“…The high-resolution scans with a diameter of 2.5 μm and a depth of 800 nm were achieved by Pisonero et al 10 Time-offlight ICP-MS, i.e. ICP-TOFMS, had been applied to single-cell elemental imaging of (Na, Mg, Al, P, S, Ca, Mn, Fe, Cu, Zn, As, Sr, Ba, Ho, Ir) 11 and (Fe, P, Pt), 12 respectively. Lohr et al reported on a high throughput single-cell arraying technique, which permitted over 99% occupancy for LA-ICP-MS analysis.…”