Immunogold-silver staining (IGSS) based U-bent fiberoptic sandwich biosensor

An evanescent wave absorbance (EWA) based U-bent fiberoptic sandwich immunobiosensor with human IgG detection limits of 6.67 fM (1 pg/ml of human IgG) and 66.7 aM (10 fg/ml of HIgG) is demonstrated by exploiting immunogold labels and subsequently silver enhancement respectively. Such very low detection limits were achieved with the help of enhanced evanescent filed at the bend region of U-bent optical fiber probe that allows efficient interaction of light with 40 nm immunogold labels on the probe surface resulting in measurable optical absorbance changes. The other significant advantages of the demonstrated sensing scheme are low cost optoelectronic instrumentation consisting of an commercial green LED and a photodetector (S150C, Thorlabs Inc.), small volumes of sample and immunogold reagent each of 25 μl and rapid detection in 20 min. These results from the plasmonic fiberoptic biosensor demonstrate its huge potential for development of point-of-care diagnostic devices for sensitive and rapid detection of analytes.