Figure 3.

Cell culture and lysis on mixed monolayers. Cells were cultured on patterned monolayers as described in Figure 2a. Individual cells attached to each 10 × 10 fibronectin nanoarray and remained confined to these regions of the substrate (b). The media was then removed from the entire plate and a lysis buffer was added to each spot of the 384 spot array to allow phosphatase enzymes in the lysate to act on peptides immobilized on the monolayer. The scale bar is 500 μm. SAMDI spectra of the surface after removal of the lysate showed a peak corresponding to generation of the dephosphorylated product (c, top). Addition of the phosphatase inhibitor PTPI-I to the lysis buffer resulted in a loss of phosphatase activity (middle) as did proteolytic removal of the cells without lysis (bottom). Separately, populations of HeLa cells were treated with PTPI-I in concentrations ranging from 0 to 200 μM and then lysed and analyzed with SAMDI-MS. A dose–response curve shows half-maximum inhibition at concentration of approximately 22 μM. Standard errors were determined from three independent experiments with at least five spots per condition.