Gibbons Angel M, Ohno Paul E
Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States.
Anal Chem. 2025 Jun 17;97(23):12180-12188. doi: 10.1021/acs.analchem.5c00717. Epub 2025 Jun 5.
Phase transitions in respiratory and environmental aerosols impact critical processes ranging from virus transmission to atmospheric light scattering. Yet, small particle sizes and low mass densities in air make experimental measurements of aerosol phase state challenging. Fluorescence probe spectroscopy is one of the only analytical techniques capable of determining aerosol phase state in situ at the submicron sizes that are implicated in long-range virus transmission and that dominate the size distribution in the atmosphere. However, previous fluorescent probe-based measurements of aerosol phase state have relied on solvatochromic probe molecules and their associated relatively small shifts in emission wavelength, necessitating relatively high-resolution spectral measurements and greatly limiting optical throughput and therefore sensitivity. Here, measurements of aerosol phase state are demonstrated using a different class of molecules, excited-state intramolecular proton transfer (ESIPT) probes, that exhibit two emission peaks with an intensity ratio that is highly dependent on the surrounding chemical environment. The ESIPT probe 2-(2-benzofuranyl)-3-hydroxychromone is shown to be sensitive to phase state, including both solid-liquid and liquid-liquid phase transitions, in mixed organic/inorganic aerosols. The origin of the sensitivity was investigated by varying the chemical identity of the aerosol constituents and the results indicate that the probe is particularly sensitive to the presence of Na and Cl ions, which are involved in key phase transitions in respiratory particles as well as sea-spray aerosols. These findings highlight the potential of ESIPT-based fluorescent sensing as a powerful technique for real time analysis of aerosol phase state in submicron particles combining unprecedented sensitivity and experimental simplicity.
呼吸道和环境气溶胶中的相变影响着从病毒传播到大气光散射等关键过程。然而，空气中的小粒径和低质量密度使得气溶胶相态的实验测量具有挑战性。荧光探针光谱法是仅有的能够在亚微米尺寸下原位测定气溶胶相态的分析技术之一，这种尺寸与远距离病毒传播有关，并且在大气中占主导地位。然而，以前基于荧光探针的气溶胶相态测量依赖于溶剂化显色探针分子及其发射波长相对较小的变化，这需要相对高分辨率的光谱测量，从而极大地限制了光通量，进而限制了灵敏度。在此，使用另一类分子，即激发态分子内质子转移（ESIPT）探针，来演示气溶胶相态的测量，这类探针表现出两个发射峰，其强度比高度依赖于周围的化学环境。结果表明，ESIPT探针2-(2-苯并呋喃基)-3-羟基色酮对混合有机/无机气溶胶中的相态敏感，包括固-液相转变和液-液相转变。通过改变气溶胶成分的化学特性来研究这种敏感性的来源，结果表明该探针对Na和Cl离子的存在特别敏感，它们参与了呼吸道颗粒以及海喷雾气溶胶中的关键相变。这些发现突出了基于ESIPT的荧光传感作为一种强大技术的潜力，可用于实时分析亚微米颗粒中的气溶胶相态，兼具前所未有的灵敏度和实验简便性。
