In this paper we adapt to optical wavelengths the principles of operation of trapped dipole antennas, which typically operate in the low MHz frequency range. The proposed nanoantenna consists of a plasmonic nanorod as its baseline element. Along its length the nanorod is loaded with plasmonic core-shell particles also referred to as 'traps'. These function as nanocircuits that create the equivalent response of a parallel LC circuit at resonance. When the traps resonate, open-circuit conditions are established at the two ends of the nanorod section defined in between them. This naturally results in the excitation of the shorter section's λ/2 resonance. In this way trapped dipoles, apart from their original λ/2 resonance (due to their total length), exhibit an additional radiating mode which is excited when the traps resonate. This property enables the dual-mode operation of the dipole antenna. Our analysis clearly demonstrates the tuning capabilities that plasmonic core-shell particles can offer while it further introduces a simple and practical approach to engineer dual-mode optical sensors.