Skinning treatment for fixed HeLa cells cultured on an EuTTA nanosheet. Fluorescence image sequences of CellMask Orange (left; i.e., cellular membranes), Calcein (middle), and an EuTTA nanosheet (right). Triton X-100 (final concentration: 0.9%) was added at 90 s. Scale bar, 25 µm. See Fig. S1 H.