Targeted surface-enhanced Raman scattering nanosensors for whole-cell pH imagery

In this paper the ability to develop a gold-core, silver-shell surface-enhanced Raman scattering (SERS) nanosensor that has both a targeting component as well as a sensing component is demonstrated. The nanosensor is capable of targeting through the FcepsilonRI receptor-mediated endocytic pathway due to the adsorption of 2,4-epsilon-dinitrophenol-L-lysine (DNP) ligand on the nanoparticle surface. The nanosensor is also sensitive to pH changes in the endocytic vesicle within the pH range of 4.5-7.5 by 4-mercaptopyridine (4-MPy) adsorbed to the particle surface. The targeting and sensing moieties do not significantly interfere with each other's function. The sensing component of the nanosensor is calibrated with in vivo measurements of rat basophil leukemia (RBL-2H3) cells in standard buffer solutions using the ionophore nigericin, which serves to equilibrate the external [H(+)] concentration with that of the cell compartments. The targeting of the nanosensor is verified with a beta-hexosaminidase assay. It is also demonstrated that the targeted nanosensor is capable of making accurate cellular pH measurements in RBL-2H3 cells, out to ninety minutes after targeted nanosensor addition. Whole-cell, time-lapse, hyperspectral image cubes demonstrating endocytic vesicular pH changes during FcepsilonRI receptor mediated endocytosis are demonstrated.