During the progression of Parkinson's disease (PD), aggregated α-synuclein (aSyn) species appear early, making them crucial biomarkers for early diagnosis. However, their detection remains challenging. Building on our previous research showing that certain tetracycline derivatives selectively bind to aggregated aSyn but not to its monomeric form, we evaluated two modified doxycycline derivatives using an immunoassay and developing a biosensor. The immunoassay successfully distinguished between aggregated and monomeric aSyn in PBS (phosphate-buffered saline), and we further tested it in cerebrospinal fluid (CSF) to assess potential interferents. We identified NaHCO₃ as the main interferent and evaluated strategies to mitigate its effect, such as dialysis and pH adjustment, which restored the signal attenuated by the interferent in CSF samples spiked with aggregated aSyn. In the biosensor approach, a thiolated doxycycline derivative was used to form a monolayer on the gold electrode and characterized by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). We evaluated its binding to aggregated aSyn at increasing concentrations by measuring changes in the oxidation peak with CV. Both approaches enable sensitive detection of aggregated aSyn, providing cost-effective and scalable alternatives for PD diagnostics. These strategies hold promise for clinical translation, including point-of-care applications that could support earlier diagnosis and intervention.