Rapid and sensitive detection of neuron specific enolase with a polydopamine coated plasmonic chip utilizing a rear-side coupling method.

A rapid and sensitive detection of a cancer marker, neuron specific enolase (NSE), is demonstrated by using a disposable silver plasmonic chip functionalized with a mussel-inspired polydopamine (PDA) coating. A plasmonic chip consisting of a diffraction grating coated with a silver thin film is used for the excitation of propagating surface plasmon resonance through a rear-side grating coupling method. Simple and quick bio-functionalization of the sensor surface is performed by PDA coating which requires 20 min for deposition, and allows direct attachment of the capture antibody without using any coupling agents. A fluorescence based sandwich immunoassay is used for the detection of NSE by utilizing surface plasmon enhanced fluorescence (SPF) spectroscopy. The developed biosensor scheme provides approximately linear sensor responses for the sample containing NSE with the concentration around the clinically important value (12 ng mL-1) in both buffer and diluted human serum (25 vol% to a buffer solution). The detection limit for NSE is 0.5 ng mL-1 (11 pM) and 1.4 ng mL-1 (30 pM) in a buffer solution and diluted human serum, respectively. The presented biosensor scheme requires a small amount of the sample down to 10 μL in human serum and a short incubation time (15 min) of the sample solution containing NSE, enabling less invasive and rapid detection of NSE. This is the first example of the sensitive sandwich immunoassay demonstrated by using a plasmonic chip for the measurement of the sample dissolved in a complex medium with a rear side coupling method, which progresses the universal use of the SPF biosensors with a disposable plasmonic chip.