miRNAs (miRs) are short, noncoding RNA sequences that are present in biofluids such as blood, plasma, and serum. Their disrupted levels of expression correlate with different stages of various diseases, making them suitable as potential biomarkers. In this study, we present magnetic nanoprobes (MNPs) designed to capture specific target miRs (TmiRs) in biofluids like serum. The nanoprobes were formulated starting from PEGylated SPIONs using streptavidin−biotin interactions. The PEG chains were functionalized with complementary DNA sequence (cDNA-484) able to bind to TmiR-484, which is known to be overexpressed in serum of patients with colorectal cancer. The two-step formulation of the MNPs was monitored by SE-HPLC, following a previously established protocol. The colloidal stability of the MNPs and their ability to capture TmiR-484 were first determined in model solutions and then in human serum enriched with the commercially purchased TmiR-484. After magnetic sorting, the TmiR was released from the MNPs (dehybridization step) and quantified using qRT-PCR