Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093, USA.
Analyst. 2018 Jun 11;143(12):2765-2774. doi: 10.1039/c8an00171e.
New developments in nanoscale analytical techniques have paved the way for detailed spectroscopic and microscopic measurements of substrate-deposited aerosol particles on a single particle basis. Atomic force microscopy based photothermal infrared (AFM-PTIR) spectroscopy is a technique that combines the nanometer spatial resolution of AFM with the chemical analysis capabilities of vibrational IR spectroscopy. Herein we demonstrate the capability of AFM-PTIR to investigate single and multi-component systems comprised of inorganic salts and organic compounds relevant to the atmosphere. Chemical and microscopic characterization of individual particles as small as 50 nm in diameter is shown. Moreover, single particle spectro-microscopic characterization as a function of relative humidity using this technique is shown for the first time. These new measurements as a function of relative humidity allow for the simultaneous and independent acquisition of photothermal IR spectra, contact resonance frequency shifts, and water uptake growth factors, providing insight on changes in the composition, stiffness, and size of the particles, respectively. These results lay the foundation for more detailed AFM-PTIR studies of multicomponent aerosol particles under a range of environmental conditions.
纳米分析技术的新进展为在单颗粒基础上对基底沉积气溶胶颗粒进行详细的光谱和微观测量铺平了道路。基于原子力显微镜的光热红外（AFM-PTIR）光谱是一种将 AFM 的纳米空间分辨率与振动红外光谱的化学分析能力相结合的技术。本文展示了 AFM-PTIR 研究由与大气有关的无机盐和有机化合物组成的单组分和多组分系统的能力。证明了直径小至 50nm 的单个颗粒的化学和微观特征。此外，首次展示了使用该技术的单颗粒光谱微观特征随相对湿度的变化。这些新的相对湿度测量值可同时且独立地获取光热红外光谱、接触共振频率位移和水吸收生长因子，分别提供有关颗粒组成、刚性和大小变化的信息。这些结果为在一系列环境条件下对多组分气溶胶颗粒进行更详细的 AFM-PTIR 研究奠定了基础。
