Cell Imaging With The Widefield Surface Plasmon Microscope

Abstract

Imaging interfacial environment has proved challenging using standard imaging systems. This is a problem that may be circumvented using the widefield surface plasmon microscope (WSPR). Surface plasmon microscopy relies on the excitation of electron oscillations at a conductor/dielectric interface by P polarised light striking that interface at a specific surface plasmon resonance (SPR) angle. The SPR angle can be changed by application of a molecular species to the conductor, which modifies the mean refractive index at that interface and thus alters the coupling efficiency between the conductor and the P-polarised light. Commercial SPR microscopes unfortunately have poor lateral resolutions, but the WSPR uses a high numerical aperture lens to excite surface plasmons, and thus not only enables nanometric Z axes imaging of interfacial molecular interactions but also enables SPR imaging at micron to submicron lateral resolutions. Initial work has shown that this system can be used to image cell/surface interactions. This paper focuses on looking at the use of the WSPR microscope in the imaging of a human keratinocyte cell line (HaCat cells), bone cells, neonatal rat intestinal smooth muscle cells and neonatal rat knee joint derived chondrocytes. Of these cell types the HaCat cells couple tightly to the cell culture surface, and this is reflected by clear band like arrangements of focal contacts, in comparison chondrocytes, smooth muscle cells and bone cells couple less strongly to the surface and this is reflected by less clearly defined arrangements of focal contacts. In all cases WSPR microscopy also enabled identification of internal cellular features, specifically the nucleus and in the case of smooth muscle cells contractile filament like structures.