fig2

Figure 2. Schematic representation of underlying principles in the technologies. A: In SOMAscan^® technology, SOMAmer reagents (single-stranded DNA with modified nucleotides), containing three tags (a fluorophore, a photocleavable linker and biotin), bind to streptavidin beads in the assay wells. Then, the sample (i.e., plasma) is added and SOMAmer-plasma protein complexes are formed. Unbound proteins are washed away, and complexes are tagged with biotin; the addition of polyanionic competitors (negatively charged) breaks up the unspecific complexes. The suspension is then exposed to UV light, which causes the breakdown of photocleavable linkers, releasing all SOMAmer complexes. Streptavidin beads are then used to capture the biotinylated SOMAmer - protein complexes, and SOMAmer reagents are removed from beads with denaturing buffer. SOMAmer reagents are hybridized to complementary sequences on a microarray chip and quantified by florescence. Figure adapted from Rohloff et al.^[21]; B: in SERS label-free technology, the biological sample is loaded on the SERS surface (a surface containing silver or gold nanoparticles). After 25-30 min of sample drying, the SERS spectra are collected during 10 s with a Raman spectrometer (equipped with a laser at 785 nm - the optimal wavelength for blood fraction analysis) connected to optical microscopy; C: in the Glyco Liver Profile technology, protein samples are denatured and treated with buffers containing specific enzymes to reach glycosylation sites. Glycans are release by the enzymatic treatment and labeled for further visualization. Then, the samples are loaded onto the fully automated V8 Nexus machine for separation by capillary electrophoresis (glycans are separated based on the difference in their mass to charge ratio). Data analysis is performed on the electropherograms of four key N-glycans, and liver profile indices are obtained