Enhanced flow cytometry-based bead immunoassays using metal nanostructures

While the principle of fluorescence enhancement of metal nanostructures is well-known, the utility of this effect in practical methodologies used in analytical laboratories remains to be established. In this work, we explore the advantage of fluorescence enhancement for flow cytometry. We report the observation of metal-enhanced fluorescence emission of fluorophores located on the surface of silica beads coated with nanostructured silver, suitable for flow cytometry detection. The fluorescence enhancement was investigated using a model AlexaFluor 430 IgG immunoassay and AlexaFluor 430 labeling. Approximately 8.5-fold and 10.1-fold higher fluorescence intensities at 430 nm excitation were, respectively, observed from silvered ∼400 nm and 5 μm silica beads deposited on glass as compared to the control sample. The 400 nm and 5 μm beads were compatible with the flow cytometry readout, although lower enhancement factors of 3.0 and 3.7 were obtained. We show that such values are consistent with less favorable overlap of the plasmon resonance in silver nanostructures with 488 nm excitation wavelength used in the flow cytometry experiment. We, thus, demonstrated that the silvered silica beads are able to provide intensified fluorescence signals in flow cytometry which can improve the sensitivity of flow cytometry-based bioassay systems.