Based on the key principles of confocal Raman spectroscopy, the focused excitation spot transforms from a convergent point into a convergent line with diffraction-limited width.
The optical setup employs a conjugate imaging design. In the two-dimensional image recorded by the charge-coupled device (CCD), the vertical dimension maps the vertical dimension of the sample along the excitation line, while the spectrum is dispersed along the horizontal dimension.
In this way, a single acquisition provides the spectra for all spatial positions along the excitation line.
The researchers have successfully managed to develop a confocal line-scan Raman micro-spectroscopy system, establish a preprocessing workflow for line-scan Raman spectral data, and apply the factorization into susceptibilities and concentrations (FSC3) to obtain Raman hyperspectral images.
They employed a concave cylindrical lens to generate the excitation line and, using a Powell lens, enhanced the uniformity of energy distribution.
Plastic beads of several sizes were utilized for size and composition identification. The detection of beads with a diameter of 200 nm, which is smaller than the diffraction limit, was identified, thereby illustrating the remarkable sensitivity of the line-scan Raman spectroscopy system.
Moreover, four types of plastic powder samples were utilized for a large-scale area of 40 μm in height and 1.2 mm in length measurement. Impressively, it only took 20 minutes to obtain a 240000-pixel Raman image - which is an extrememly short imaging time.
In comparison with point confocal Raman imaging, the line-scan confocal Raman technology helps increase the imaging speed by around two orders of magnitude.
Line-scan Raman micro-spectroscopy provides non-destructive analysis with high-throughput and high sensitivity. By applying suitable sampling methods like sedimentation or filtration, environmental samples from several sources, such as soil, water, and air, are accessible.
Journal Reference:
Wu, Q., et al. (2023) Rapid identification of micro and nanoplastics by line scan Raman micro-spectroscopy. Talanta. doi.org/10.1016/j.talanta.2023.125067.