Sonication-Assisted Metal-Enhanced Fluorescence-Based Bioassays

A new bioassay technique, sonication-assisted metal-enhanced fluorescence, which is based on the combined use of ultrasound waves and metal-enhanced fluorescence (MEF), is reported. In this technique, low-intensity ultrasound waves significantly reduce the bioassay time by creating a temperature gradient between the bulk and the surface, which is thought to result in a mass transport of biomolecules from the bulk to the surface. After the assay is completed in 1 min, fluorescence emission is enhanced due to the MEF phenomenon. For proof-of-concept, a model bioassay based on the interactions of biotin and fluorophore-labeled avidin was constructed on SIFs and was subsequently completed in < 1 min using low-intensity ultrasound at 40 kHz. The end-point values for fluorescence emission from sonicated assays were compared to those measured from assays carried out at room temperature without sonication to confirm to accuracy of the new technique. The effect of sonication on the assay components were studied using optical absorption spectroscopy, atomic force microscopy, and fluorescence spectroscopy techniques. Real-time thermal imaging was used to measure the changes in temperature of the bioassay components during the sonication process. Fluorescence resonance energy transfer (FRET) was also employed to investigate the effect of sonication on potential surface protein denaturation and conformational changes.