Optical Fiber Quantum Biosensor based on Surface Plasmon Polaritons for the Label-Free Measurement of Protein

•An enhanced taper-based quantum biosensor based on surface plasmon polaritons is demonstrated.•The sensor was with gold coating that operates below the standard quantum limit.•BSA concentration can be measured according to the change of transmitted photons.•Detection limit of the proposed biosensor is 0.971 μg/mL.