4.7. Raman Spectra Serum

Raman spectra of 8, 18, 28, and 52 weeks of serum samples were thawed, vortexed, and briefly centrifuged. An amount of 5 μL of each previously labeled sample was taken and drop-coated on an aluminum substrate. Raman measurement was performed in a semi-wet drop.

All Raman spectra were recorded using an XPLORA ONE Raman spectrometer system (Horiba Scientific, Piscataway, NJ, USA) and 1800 lines per mm grating and spectral resolution of 0.8 cm⁻¹ per pixel. A 20× objective lens (N.A = 0.4) was used to focus the laser beam on the ring of the drop coating deposited samples. A 532 nm laser wavelength was used, and the power at the sample’s surface was 35 mW. Triplicate measurements with 5 s of integration time were acquired in the “coffee ring” formed for each drop coated.