Xtra 2

As previously described, briefly, confocal Raman spectral acquisition was performed on a custom-built laser trapping Raman spectroscopy system.^{[32 (link)]} The light source used was a 785 nm laser (Toptica XTRA II) with a 63× 1.0 numerical aperture (NA) water immersion microscope objective lens (W Plan-Apochromat, Zeiss, Oberkochen, Germany). The epicollected scattered light was focused into a 100 μm fibre with a 600 groove mm⁻¹ grating spectrograph (UHTS 300, WITec, Ulm, Germany) and spectra were acquired using a thermoelectrically cooled back-illuminated CCD camera (iDus DU401-DD, Andor, Belfast, UK) with a spectral resolution of 3 cm⁻¹ and 85 mW laser power at the sample. Laser control and measurement evaluation for automated trapping were remotely controlled via a serial connection and custom MATLAB (2018b, The Mathworks, Natick, MA, USA) scripts.

Confocal Raman spectral acquisition was performed on a Raman micro-spectroscope (alpha300R + , WITec, Ulm, Germany). The light source used was a 785 nm laser (Toptica XTRA II) with a 63 × /1.0 NA water immersion microscope objective lens (W Plan-Apochromat, Zeiss, Oberkochen, Germany). The scattered light was collected via a 100 μm fibre with a 600 groove mm⁻¹ grating spectrograph (UHTS 300, WITec, Ulm, Germany) and spectra were acquired using a thermoelectrically cooled back-illuminated CCD camera (iDus DU401-DD, Andor, Belfast, UK) with a spectral resolution of 3 cm⁻¹ and 85 mW laser power at the sample. Laser control was performed remotely via a serial connection and custom MATLAB (2016b, The Mathworks, MA, USA) scripts.

The DMD-based SORS instrument was equipped with a 785 nm wavelength laser (Xtra II, Toptica). A 100 mm focal length 2-inch diameter lens was used to focus the laser beam on the sample (120 mW power, spot size ~0.5 mm) and to collect the backscattered Raman photons. After passing through a dichroic filter that blocked the elastically scattered photons, the Raman photons were focused with a lens on a software-controlled DMD (size 14.4 mm x 8.8 mm, resolution 1920 x 1080 pixels, DLP6500 Texas Instrument). As the DMD was located in a plane conjugate to the sample, it allowed the selection of multiple spatially offset collection points (0.22 mm size) distributed in a semi-circle around the point conjugated to the laser excitation, equivalent to spatial offset values in the range of 0-4 mm. The Raman photons reflected by the DMD collection points were analyzed by a spectrometer (Holospec, Andor) equipped with a deep-depletion back-illuminated CCD (iDus 420, Oxford Instruments). For a selected spatial offset, the SORS spectrum was calculated as the sum of the spectra corresponding to all DMD collection points on the corresponding semi-circle, after aligning and calibrating them along the wavenumber axis. For each spatial offset, 18 repeat spectra were measured at an acquisition time of 10 s per spectrum.