Evanescent wave absorbance based U-bent fiber probe for immunobiosensor with gold nanoparticle labels

This study demonstrates a simple evanescent wave absorbance based sensing scheme for plasmonic sandwich immunoassay with the help of U-bent fiber probes as transducers. High absorbance sensitivity of the U-bent probes (200 μm core and 1.5 mm bend diameter) is exploited for sensitive detection of a small number of gold nanoparticles (AuNP) labels bound to the probe for the first time. Using 13 nm AuNP labels conjugated with recognition antibodies, picomolar detection limit (2 pM or 0.3 ng/ml) for human immunoglobulin (HIgG) is achieved. The absorbance sensitivity and dynamic range were 0.019 A530nm/log (ng/ml) and 1-105 ng/ml respectively. Nonspecific adsorption (NSA) of labels is minimized to less than 2% by PEGylation. The ease in U-bent probe fabrication and simple optoelectronic instrumentation consisting of an LED and a fiber optic spectrometer could facilitate extensive use of U-bent probes for several biosensing applications.