In this report, we demonstrate the use of functionalized gold nanorods as amplification labels for ultra-sensitive surface plasmon resonance biosensing. Drastic sensitivity enhancement, owed to the electromagnetic interaction between the nanotag and the sensing film, was maximized using longitudinal plasmonic resonance of gold nanorods. The detection sensitivity of the nanorod-conjugated antibody is estimated to be approximately 40 pg/ml, which is 25 - 100 times more sensitive than the current reported values in the literature. This work paves the way to a new generation of ultra-sensitive nanoparticles-based biosensor platforms with maximized enhancement of sensitivity for ultra-fast screening and real-time detection of "hard-to-identify" biomolecules.