Metal-enhanced fluorescence of the trimethine cyanine dyes complexed with amyloid fibrils

In this work, we present the investigation of metal enhancement effect of silver island films (SIF) on the fluorescence intensity and correspondingly reporting properties of amyloid- sensitive trimethine cyanine dyes. The benzothiazole dyes zwitterionic D-51 and multiply positively charged D-151 as well as their complexes with amyloid fibrils of proteins insulin and lysozyme were examined. The obtained data revealed that the presence of SIF causes aggregation of the positively charged dye D-151 and the destruction of the dye-fibril complex. That could be explained by electrostatic interactions between multiply charged molecules and electrically polarized silver islands. For the zwitterionic dye D-51, the presence of SIF caused metal enhancement of fluorescence emission intensity in 5.2, 6 and 3.4 times for the free dye and its complexes with fibrils of insulin and lysozyme respectively. Thus metal enhancement as emission intensity enhancement method offers a potential platform to increase the sensitivity of probes detecting protein amyloid fibrils.