Direct structural observation of liquid molecules in single picoliter microdroplets using near-infrared Raman microprobe spectroscopy combined with laser trapping and chemical-tomographic imaging techniques

Abstract

Two near-infrared (NIR) Raman microprobe spectroscopic techniques were developed for the direct structural observation of liquid molecules in single picoliter microdroplets. The use of NIR laser light as the excitation light source instead of visible laser light provides Raman spectra with lower fluorescence interference, which makes it easier to determine the structure of liquid molecules. Combining an NIR Raman microprobe with a laser trapping technique makes it possible to classify molecular species in a single picoliter microdroplet during laser trapping in solution. An NIR Raman microprobe chemical-tomographic (RMCT) imaging technique provides the three-dimensional distribution of molecular species in a picoliter microdroplet with a spatial resolution of several femtoliters in volume. Both techniques show sufficient sensitivity to obtain Raman spectra of liquid molecules in single picoliter microdroplets.