Optical trapping-Raman spectroscopy (OT-RS) with embedded microscopy imaging for concurrent characterization and monitoring of physical and chemical properties of single particles

Abstract

The study of physical and chemical properties of a microscopic object, such as a single particle, is made possible using optical trapping (OT) technology combined with other measuring techniques. Here we show a universal optical trap combined with Raman spectroscopy (RS) and microscopy imaging for single-particle studies. The universal optical trap is constructed using two counter-propagating hollow beams and is able to stably levitate single particles of a wide range of properties, such as transparent or absorbing materials, organic (polymers, bioaerosols, etc.) or inorganic constituents (carbon, silica, glass, etc.), and spherical or irregularly shaped morphologies. Both physical and chemical properties and their temporal evolution of the trapped particle can be characterized simultaneously using the integrated OT-RS and imaging system. We created three sample cases to demonstrate the analytical merits of the system: (I) a single particle with no change, (II) partially degraded over the measuring period, and (III) one part from the fragmentized single particle. The particles' chemical compositions, crystalline states, etc. are inferred from their Raman spectra, while their physical properties (sizes, shapes, morphologies, etc.) are revealed by images. This integrated OT-RS system provides a new approach to concurrently characterize and monitor physical and chemical properties of single micrometer-sized objects optically trapped in air.