Fig. 2. (A) Raman spectra of the Ag–Fe NP dispersion in a solution of 8.3 nM MG before (“H off”, black line) and after (“H on”, red line) magnetic focusing. The reference spectrum collected from a MG solution with the same concentration is also shown (grey line). (B) Magnetic amplification of the SERS signal as a function of thiolated PEG concentration added during the Ag–Fe NP coating procedure. (C) Magnetic amplification of the SERS signal as a function of the PEG molecular weight and the corresponding estimated chain length according to ref. 65 and 66.