High-Sensitivity and High-Speed Single-Particle Inductively Coupled Plasma Spectrometry with the Conical Torch.

Significant advancement has been achieved in single-particle analysis with the new conical ICP torch in terms of sensitivity, precision, and throughput. Monodisperse desolvated particles of eight elements (Na, Al, Ag, Sr, Ca, Mg, Fe, and Be) were injected into the conical torch, and signal peak characteristics, precision, and kinetics of atomization and ionization were investigated with optical spectrometry. A particle introduction system was designed to ensure a smooth and uninterrupted delivery of desolvated particles to the plasma. The important finding is that, compared with the conventional Fassel torch, the conical torch offers a 1.5-8 times higher peak intensity, a 2-4 times higher peak area, a 2 times shorter peak width, and higher precision (i.e., a 1.5 times lower RSD for peak intensity and a 1.8 times lower RSD for peak width on average). Also, mass detection limits were found to be similar or up to 8 times lower (i.e., 2 times lower diameter detection limit) for the conical torch. The results indicate that these features are due to a much higher electron density, excitation temperature, and robustness which, together with an improved particle trajectory, lead to rapid vaporization/atomization/ionization of particles with minimized atom/ion cloud diffusion. Finally, the torch was demonstrated to be capable of analyzing single particles at a rate of at least 2000 particles per second with high sensitivity and precision. On the basis of these results, the conical torch is expected to bring about new possibilities in ICP-based single-particle analysis.

Conical Torch: The Next-Generation Inductively Coupled Plasma Source for Spectrochemical Analysis.

A completely new ICP torch for optical/mass spectrometry is introduced with a conical geometry leading to significant reduction in gas and power consumption. As a new holistic methodology, the torch has been designed on the basis of fluid flow patterns, heat transfer, plasma physics, and analytical performance. Computer simulations, capable of accounting for magneto-hydrodynamic effects, have been used to optimize torch geometry. The result is a "conical" torch with up to 70% reduction in argon flow and more than 4 times power density compared with traditional "cylindrical" torches. Based on experimental measurements, these features lead to a stable plasma with 1000-1700K higher excitation/rotational temperature and a 5-fold increase in electron number density compared to common torches. Interferences from easily ionizable elements (e.g., Na) are also observed to be minimized due to 3 times higher robustness (Mg II/Mg I ratio). Eventually, analytical parameters including detection limits for multielement analysis indicate comparable/better performance of the new torch in comparison with conventional torches.

Investigation of calcium variations in single cells and the impact of Yoda1 on osteocytes by ICP-OES.

BACKGROUND: Detection of elements in individual cells by inductively coupled plasma (ICP) spectrometry has recently attracted significant interest in biological research, due to the unique ability of ICP spectrometry for trace element analysis. However, performing single-cell analysis using ICP optical emission spectrometry (ICP-OES) remains a challenge due to the small size and discrete nature of cells. This is while ICP-OES can serve as a cost-effective and label-free method for this purpose. Therefore, it is necessary to improve the current ICP-OES technique to facilitate the detection of elements in single cells, thereby unlocking novel applications. RESULTS: A new conical ICP torch, which has been illustrated to offer better analytical performance than the conventional ones, was applied to achieve the detection of calcium in single micro-sized cells. A new heated chamber was designed and coupled with a high-efficiency nebulizer as the sample introduction system. For the detection of single SiO2 particles, the number of particle events obtained by the new sample introduction system was found to be up to 9 times higher than that of the conventional system without sacrificing the signal intensity. Subsequently, calcium in human breast cancer cells (MDA-MB-231), mice breast cancer cells (Py8119), and mice osteocytes (MLO-Y4) was successfully detected using the new ICP-OES system. The cell detection efficiency turned out to be around 2%-3% which is much higher than that the reported values in previous single-cell ICP-OES research. Finally, as a new application, the effect of Yoda1, a recently identified activator of Piezo1 calcium channel, on osteocytes was investigated. The calcium content in Yoda1-treated MLO-Y4 cells was seen increase by 36% compared to the control sample. SIGNIFICANCE: This research reveals the capability of ICP-OES in single-cell analysis for micro-sized cells which was made possible by the new conical ICP torch and the new sample introduction system. The ability to detect calcium in single mammalian cells enables the first ever application of this technique to assess the impact of the Yoda1 activator on the calcium level in osteocytes.