Darmawan Y Albert, Yanagishima Taiki, Fuji Takao, Kudo Tetsuhiro
Laser Science Laboratory, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku-ku, Nagoya 468-8511, Japan.
Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan.
Anal Chem. 2025 Jul 15;97(27):14658-14665. doi: 10.1021/acs.analchem.5c02185. Epub 2025 Jul 4.
Separation and spectroscopy are essential and complementary techniques in molecular analysis, including gas/liquid chromatography, electrophoresis, flow cytometry, and vibrational spectroscopies, where independent modalities are required for separation and spectral characterization. In many cases, separated materials require spectroscopic analysis, whereas characterized components in a mixture may need further separation. Here, we present a mid-infrared optical force technique in which spectroscopic differences alone can be directly utilized to separate materials based on their molecular species and structures without labeling. In particular, we demonstrate an optical manipulation of micro- and nanospheres via a tunable mid-infrared laser, where their velocity, induced by optical force, at different wavenumbers closely match the Fourier-transform infrared spectra of the constituent material. The mid-infrared laser covers the spectral range of the vibrational mode of carbonyl bonds in the particles: we successfully demonstrate the selective manipulation of PMMA (poly(methyl methacrylate)) and TPM (3-(trimethoxysilyl)propyl methacrylate), which contain the same carbonyl bonds but in different surrounding environments. The experimental results agree with optical force calculations based on the finite-difference time-domain simulation. This constitutes the first direct evidence that the velocity is proportional to infrared absorbance at different wavenumbers, enabling precise reconstruction of infrared absorbance spectra from measured velocities. We believe that the proposed method enables a versatile particle separation and characterization across a wide range of materials, e.g., cells, nucleic acids, viruses, proteins, and potentially down to molecules, as the mid-infrared region is home to the molecular vibrational modes in a vast array of compounds.
分离和光谱学是分子分析中必不可少的互补技术，包括气相/液相色谱、电泳、流式细胞术和振动光谱学，这些技术中分离和光谱表征需要独立的模式。在许多情况下，分离后的材料需要进行光谱分析，而混合物中已表征的成分可能需要进一步分离。在此，我们提出一种中红外光力技术，其中仅光谱差异就可直接用于基于分子种类和结构分离材料，无需标记。特别地，我们展示了通过可调谐中红外激光对微米和纳米球的光学操控，其中它们在不同波数下由光力诱导的速度与组成材料的傅里叶变换红外光谱紧密匹配。中红外激光覆盖了颗粒中羰基键振动模式的光谱范围：我们成功展示了对聚甲基丙烯酸甲酯（PMMA）和甲基丙烯酸3-(三甲氧基硅基)丙酯（TPM）的选择性操控，它们含有相同的羰基键，但周围环境不同。实验结果与基于时域有限差分模拟的光力计算结果一致。这首次直接证明了速度与不同波数下的红外吸光度成正比，从而能够根据测量的速度精确重建红外吸收光谱。我们相信，由于中红外区域是大量化合物分子振动模式的所在，所提出的方法能够对广泛的材料，如细胞、核酸、病毒、蛋白质，甚至可能低至分子进行通用的颗粒分离和表征。
