Methylene blue (MB) is an important photoacoustic contrast agent and its interaction with sodium dodecyl sulfate (SDS) is of interest because it exhibits a characteristic blue shift in the absorbance spectrum. However, the interaction details such as the binding site remained unclear. Here, we study the binding kinetic of MB and SDS using photoacoustic (PA) imaging, nanoparticle tracking analysis (NTA), and spectroscopy. We noted a 492-fold photoacoustic enhancement of 0.05 mM MB upon addition of 3.47 mM SDS and later a 54-fold decrease at a higher concentration above SDS’s critical micelle concentration (CMC) at 8.67 mM (Panel A). The relative quantum yield of MB revealed a trend opposite to the photoacoustic intensity (Panel B). Meanwhile, NTA analysis indicated increasing formation of non-micellar MB-SDS clusters as SDS concentration approaching the CMC whereas the clusters disassociated at SDS concentration above the CMC (Panel C). These trends suggested that the fluorescence quenching and formation of MB-SDS cluster contributed to the photoacoustic enhancement. A comparison study of MB/hexadecyltrimethylammonium bromide (CTAB), MB/sodium octyl sulfate (SOS), and MB/sodium chloride (NaCl) indicated that MB interacted with the sulfate moiety of SDS before and after micellization. We conclude that MB forms aggregates with SDS at premicellar concentrations and MB monomers bound to SDS at micellar concentrations (Panel D).

Switchable photoacoustic effect due to micellization of sodium dodecyl sulfate with methylene blue

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.