Gold nanorods (GNRs) with different aspect ratios werefabricated through seed-mediated growth and surfaceactivation by alkanethiols for the attachment of antibodiesto yield gold nanorod molecular probes (GNrMPs). Multiplex sensing was demonstrated by the distinct responseof the plasmon spectra of the GNrMPs to binding eventsof three targets (goat anti-human IgG1 Fab, rabbit anti-mouse IgG1 Fab, rabbit anti-sheep IgG (H+L)). Plasmonic sensors are highly specific and sensitive and canbe used to monitor refractive index changes caused bymolecular interactions in their immediate vicinity withpotential to achieve single-particle biosensing. This technique can play a key role in developing novel opticalbiosensors for both in vivo and in vitro detection andsingle-receptor kinetics.