Combined optical and electronic sensing of epithelial cells using planar organic transistors

Abstract

A planar, conducting-polymer-based transistor for combined optical and electronic monitoring of live cells provides a unique platform for monitoring the health of cells in vitro. Monitoring of MDCK-I epithelial cells over several days is shown, along with a demonstration of the device for toxicology studies, of use in future drug discovery or diagnostics applications.

Keywords: MDCK cells; barrier tissue; conducting polymers; poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS); tight junctions.

Figure 1

Simultaneous optical and electronic recording. a,b) Schematic of device which consists of a PEDOT:PSS channel and gate patterned onto a glass slide. Cells and media were contained inside a 3D-printed/PDMS well. Under applied gate voltage, cations from the media penetrate through the cell layer and de-dope the channel. c) Photograph of the optical microscope equipped for long-term live-cell culture. d) 8 OECTs connected via a 3D-printed holder adjusted for the microscope, pictured here on the microscope stage. Connections are made by spring-loaded contacts.

Figure 2

Electrical and optical characterization of MDCK-I cells on the planar OECT. MDCK-I were seeded at 10⁵ cells/cm² and monitored for 4.5 days. a) Micro-optical images of MDCK-I on top of the channel area. The darker horizontal line in the middle of the picture corresponds to the PEDOT:PSS channel. b) Electrical characteristics with a measurement taken every 3 h. c) Immunofluorescence images taken on sub-confluent MDCK-I monolayers show presence of ZO-1 and E-cadherin at the cell periphery very early on. Occludin and Claudin-1 localize in the cytoplasm and just in the cell contacts the first 3 days. At day 5 all the proteins are present at the cell borders.

Figure 3

Electrical signal measured by OECT is related to barrier function of cells. a) Electrical characteristics of various cell lines measured over 8 days: dark round markers for Caco-2 cells, dark-grey diamonds markers for HEK-293 cells, and grey triangle markers for HeLa cells. b) Corresponding micro-optical images of cell coverage over the channel area.

Figure 4

Effect of EGTA and trypsin-EDTA on MDCK-I barrier function. a) Electrical characteristics of MDCK-I barrier tissue measured by an OECT. Normalized τ value of 1 corresponds to an intact cell monolayer and 0 to a disrupted one. At t = 0 min, EGTA was added according to the following concentrations: 1 mM for dark round markers, 5 mM for dark-grey triangle markers, 10 mM for grey diamond markers, and 100 mM for light-grey star markers. b) Corresponding micro-optical images for EGTA = 100 mM and EGTA = 1 mM. c,d) Effect of Trypsin-EDTA on MDCK-I barrier: c) Electrical characteristics of MDCK-I monolayers measured by an OECT. Normalized τ of 1 corresponds to an intact cell monolayer and 0 to a disrupted one. At t = 0 min, Trypsin-EDTA was added according to the following concentrations: 0.25X for dark round markers, 0.5X for dark-grey triangle markers, 0.75X for grey diamond markers, and 1X for light-grey star markers. d) Corresponding micro-optical images for trypsin-EDTA 0.5X and 1X.