Whispering gallery mode resonant microspheres as labels for biological imaging.

Abstract

Optical whispering gallery modes (WGMs) arise from total internal reflection of light from an optical cavity, such as microspheres. Whispering gallery mode phenomena produce resonant frequencies at the reflected wavelengths that appear as peaks in spectrographic data. In microspheres, whispering gallery mode spectra vary by the size and material used. These differences allow for distinct labeling of many targets using only a single fluorescent input and output. In this work we use resonant microspheres that, conjugated to antibodies, label bacterial and mammalian cell populations in vitro. We use 5 µm resonant microspheres of polystyrene and polystyrene-divinylbenzene conjugated with antibodies against biological targets of interest including Epidermal Growth Factor Receptor (EGFR) and Erb-B2 Receptor Tyrosine Kinase 2 (ErbB2) to label human cells and lipopolysaccharide to detect Gram-negative bacterial infection. Beads are distinguished using their whispering gallery mode spectra. This work presents an early step towards labeling and biodetection of many biological targets using a single fluorescent input and output.