α-Synuclein (α-Syn) is an abundant protein in neurons, and changes to a neurotoxic α-helical oligomer in vitro. The goal of our study is to investigate the structure of the α-Syn oligomer in vivo, by delivering 13C-labeled α-Syn into mouse brains and performing a 13C CEST experiment. We report the MRS detection of the 13C signals of the α-Syn monomer in an agarose gel phantom, mimicking a physiological environment. We also report that the in vitro oligomerization rate of α-Syn varies, depending on buffer conditions. We envisage that the CEST effect will be detected by adjusting the oligomerization kinetics of α-Syn.