Surface Enhanced Raman Scattering of a Lysosomal Fluorescent Dye

Knowledge about the molecular structure and interactions of intracellular dyes is important to understand their function and possible effects in the biological environment. Here we discuss vibrational spectra of LysoSensor (LSG), a fluorescent marker for the acidic lysosomal compartment in cells. Raman spectra of the molecule at concentrations typically applied in experiments with cell cultures were obtained by surface‐enhanced Raman scattering (SERS) experiments at varying pH values, using biocompatible gold nanoprobes also used in live cell SERS. The signals in the SERS spectrum of LSG were assigned based on spectra collected from its aromatic constituents benzimidazole and naphthalimide under the same conditions. The data indicate a strong pH dependence of the spectra of benzimidazole that is less pronounced in the vibrational signature of the LSG molecule. Despite excitation of the SERS off‐resonance with the dye molecule, spectra obtained with the biocompatible wavelength of 785 nm have better sensitivity towards pH‐dependent structural changes, due to favorable electromagnetic enhancement of vibrational modes, than when using excitation at 633 nm. The characterization based on SERS will help to understand the interactions of LSG with the cellular environment and with other probes, which will be useful for the design of efficient labels for bioanalysis.