Fig. 4
Cell targeting and plasma membrane clustering of biotinylated AuNPs. a Schematic of biotinylated M3-AuNPs and sGFP-AuNPs targeted to avidin fusion proteins at the plasma membrane of cells and their assembly into SERS active clusters. Not to scale. b Bright field (left), single-frame TIRF microscopy image (middle) and maximum intensity projection TIRF image from multiple frames (∑Imax, right) of biotinylated M3-AuNPs bound to GPI-avidin fusion proteins and diffusing at the plasma membrane of live HeLa cells. Scale bar: 7 μm. c Scanning electron microscope images of U2OS cells co-expressing the transmembrane and the GPI-anchored avidin fusion proteins and targeted with biotinylated sGFP-AuNPs alone (top panel), biotinylated M3-AuNPs alone (bottom panel) or both biotinylated sGFP-AuNPs and M3-AuNPs simultaneously (middle panel). White arrows point towards endocytic membrane structures, blue arrowheads point towards AuNPs monomers and red arrowheads point towards some of the AuNP nanoclusters presented in insets. The plus and minus signs identify the avidin-expressing and non-expressing cells, respectively. Scale bars: 2 μm (left panels), 200 nm (insets of left panels), 1 μm (right panels), and 100 nm (insets of right panels). d Cluster size distributions of AuNPs on targeted U2OS cells
