Tracking Bulk and Interfacial Diffusion Using Multiplex Coherent Anti-Stokes Raman Scattering Correlation Spectroscopy

Multiplex coherent anti-Stokes Raman
scattering correlation spectroscopy
(CARS-CS) is shown as a label-free, chemically specific approach for
monitoring the molecular mobility of particles in solution and at
interfaces on the millisecond time scale. The CARS spectral range
afforded by broadband excitation facilitates a quantitative measurement
for the number of particles in the focal volume, whereas the autocorrelation
of spectral data elucidates dynamic events, such as diffusion. The
measured diffusion coefficients for polymer beads ranging from 100
nm to 1.1 μm in diameter are on the order of 10–8–10–9 cm2/s, in good agreement
with predicted Stokes–Einstein values. Diffusion at different
interfaces shows particles are fastest in bulk medium, marginally
slower at the liquid/glass interface, and 1.5–2 times slower
rate at the air/liquid interface. Multivariate curve resolution analysis
of distinct spectral features in multiplex CARS measurement distinguishes
different composition lipid vesicles in a mixture diffusing through
the focal volume. The observed diffusion is consistent with results
obtained from single particle tracking experiments. This work demonstrates
the utility of multiplex CARS correlation spectroscopy for monitoring
particle diffusion from different chemical species across diverse
interfaces.

多路相干反斯托克斯拉曼散射关联光谱（CARS-CS）是一种无需标记、具有化学特异性的分析手段，可在毫秒时间尺度上监测溶液及界面处粒子的分子运动行为。宽带激发所覆盖的相干反斯托克斯拉曼散射（Coherent Anti-Stokes Raman Scattering, CARS）光谱范围，可实现对聚焦体积内粒子数量的定量检测；而光谱数据的自相关分析则能阐明扩散等动态过程。对直径介于100 nm至1.1 μm的聚合物微球测得的扩散系数约为10⁻⁸~10⁻⁹ cm²/s，与斯托克斯-爱因斯坦（Stokes-Einstein）模型的预测值吻合良好。不同界面处的扩散行为表明，粒子在本体介质中扩散最快，在液/玻璃界面扩散速度略慢，而在气/液界面的扩散速率则降低1.5~2倍。对多路CARS检测中不同光谱特征开展多元曲线分辨分析（Multivariate Curve Resolution Analysis），可区分混合体系中通过聚焦体积的不同组成脂质囊泡。实验观测到的扩散行为与单粒子追踪（single particle tracking）实验所得结果一致。本研究证实了多路CARS关联光谱可用于监测不同化学种类粒子在多种界面间的扩散行为。