Dopamine (DA) plays a central role in regulating neural function, and its reliable detection is essential for both fundamental neuroscience research and bioanalytical applications. Capacitive biosensors combined with aptamer recognition offer a label-free sensing strategy; however, constructing reproducible and well-defined aptamer-functionalized interfaces remains a significant challenge. Here, we report a vapor-phase approach for engineering aptamer-based capacitive DA sensors using a poly(2-hydroxyethyl methacrylate-co-pentafluorophenyl methacrylate) (p(HEMA-co-PFMA)) copolymer film deposited by photo-initiated chemical vapor deposition (piCVD). The solvent-free deposition process enables the conformal and site-selective formation of nanoscale polymer films with precisely controlled chemical compositions. Pentafluorophenyl (PFP) ester moieties provide reactive sites for covalent conjugation of amine-modified DA aptamers, while the HEMA component tunes surface wettability and interfacial ionic behavior. The optimized pH1P4 copolymer film (HEMA:PFMA = 1:4) exhibited superior conjugation efficiency, and the resulting biofunctional electrodes achieved a limit of detection of 0.23 µM with excellent selectivity against structurally similar interferents. This vapor-phase interface engineering strategy offers a generalizable framework for constructing aptamer-functionalized capacitive biosensors applicable to diverse small-molecule targets and electrode configurations.