Exploring the photophysical interaction of xanthene dyes with gold nanorods by optical spectroscopic techniques and in-vitro cytotoxicity studies of dye-nano conjugates

The current study investigates the photophysical interactions of xanthene dyes such as fluorescein (FL) and rose bengal (RB) dyes with cetyltrimethylammonium bromide stabilized gold nanorods (CTAB-AuNRs) using optical spectral techniques, and computational interaction analyses. When xanthene dyes are conjugated with CTABAuNRs, significant modifications in their optical spectroscopic characteristics are found. In the absorption spectrum analyses of dye-AuNRs systems, the appearance of longitudinal plasmon resonance bands and the hypochromic behavior of xanthene dyes were observed in response to the interaction of CTAB-AuNRs. The gathered extinction spectral results indicated that there were significant electrostatic interactions between the positively charged CTAB-AuNRs and the negatively charged xanthene dye molecules. At the same time, the substantial quenching with a reduced quantum yield of the dye molecules is shown in the emission spectra of xanthene dyes with CTAB-AuNRs. The strong electrostatic interactions and ground state complex between xanthene dyes and CTAB-AuNRs have been suggested as the mechanism of emission quenching. The results of the emission quenching are supported by the calculated high binding constant values. Additionally, the results of computational interaction investigations also demonstrate the near closeness of xanthene dye molecules and CTAB-AuNRs. Finally, the cytotoxicity of free dyes and dye-nanoconjugates was next tested against breast (MCF7) and lung (A-549) cancer cells. All the tested samples exhibit significant antiproliferative activity against MCF7 and A-549 cancer cells. These cytotoxic study results showed that cells treated with xanthene dyes were less sensitive than FL-AuNRs and RB-AuNRs dye nanoconjugates.

Automated summary

The current study investigates the photophysical interactions between xanthene dyes and CTAB-AuNRs. Significant modifications in the optical spectroscopic characteristics of the dyes were observed when they are conjugated with CTAB-AuNRs. Extinction spectral results indicate strong electrostatic interactions and ground state complex between the dyes and CTAB-AuNRs, which lead to the emission quenching of the dyes. The computational interaction analyses also support the near closeness of the dye molecules and CTAB-AuNRs. Additionally, the cytotoxicity study shows that the dye-nanoconjugates exhibit higher toxicity against cancer cells compared to the free dyes.