Figure 4

Aptamer sensor probing stem cells’ niche environment and signalling. A) Schematic showing the detection of signaling molecules using stem cell-conjugated aptamer probes. B) Aptamers were covalently attached to the cell through a streptavidin-biotin conjugation. C) Structure of PDGF-sensitive aptamer probes used for this study. Upon specific binding with PDGF, the probe conformation is altered and the fluorescent signal of FAM is quenched by Dabcyl. D) Representative fluorescent microscopy images of the sensor-tagged cells before and directly after the addition of 10 nM PDGF in PBS. E) Real-time MDA-MB-231 cells’ PDGF secretion monitoring by apt-tagged MSCs. Left: experimental setup with microwells containing one sensor MSC (red) with different numbers of PDGF-producing MDA-MB-231 cells (green). Here the secreted PDGF has been labeled with a GFP tag, while the apt sensor is labeled with a red dye (Cy5). Right: declining MSCs’ fluorescence was observed during the course of PDGF production. The signal, which is defined as the percentage of MSCs with <50% of their initial fluorescent intensity at any indicated time, correlates with the number of MDA-MB-231 cells. Adapted with permission from ref. [50]. Zhao W, Schafer S, Choi J, Yamanaka YJ, Lombardi ML, Bose S, Carlson AL, Phillips JA, Teo W, Droujinine IA: Cell-surface sensors for real-time probing of cellular environments. Nature nanotechnology 2011, 6:524–531. Copyright 2011 by Nature Publishing Group.