Magnetoimpedance (MI) has been proposed as a sensible detection method for quantifying the concentration of magnetic microparticle and nanoparticle. The use of samples with severe surface roughness, induced by acid treatments, seems to enhance the detection power. Here, we clarify the role of surface modification in the detection of magnetic particles and ferrofluids. Experimentally, lithography is used to produce a regular pattern of pits in an amorphous ribbon. The influence of the patterning on the MI of the sample, in the presence of magnetic nanoparticles, is analyzed. Contrary to what has been published previously, the patterning seems to worsen the particle detection capability. To clarify the situation, a thorough study is performed with numerical simulations using a finite-element analysis resembling the experimental conditions in a 2-D geometry. The presence of magnetic particles is simulated as a continuum medium with a given permeability, which is a realistic assumption for the case for ferrofluids. The conclusion is that the effect of the magnetic particles on MI depends strongly on the characteristics of the patterning and on the concentration of particles. The simulation results not only qualitatively explain ours experimental results, but also help interpreting previous reports and hints the optimal conditions for the surface patterning in order to maximize the sensibility of the sample to the presence of magnetic particles.