Single cells can now be manipulated in physiological buffers without damage or interruption to cell functions thanks to a new device developed by US scientists.

When light is projected onto the phototransistor, it switches the phototransistor on and generates an electric field locally in the media. The electric field then exerts a force on the particles or cells.

Optoelectronic tweezers (OETs) use silicon photoconductors to capture light and induce an electric field that can move cells by attracting or repelling them. But because amorphous silicon's photoconductivity is low, the OETs only work in media with low conductivities. Cell culture media and physiological buffers have high conductivities so can only be used with OETs if their salts are replaced with non-conducting molecules. However, this causes cells to lose their normal functions.

Now Hsian-yin Hsu, at the University of California, Berkeley, and colleagues have adapted the technology by replacing the silicon photoconductors with crystalline silicon wafer phototransistors doped with boron and arsenic. This enhances photoconductivity by two orders of magnitude, says Hsu. 'With optical illumination, the photosensitive layer has higher conductivity than the media and becomes electrode-like. This allows it to operate with highly conductive media,' he explains.

'The approach is compelling as it yields a cell-handling platform that could readily be implemented, enabling studies of fundamental properties of cells,' comments Jody Vykoukal, an expert in microfluidics and cell separation at the University of Texas, Houston, US.

Hsu expects that the device will have a broad impact in cell-based biology research. 'Equipped with this new tool, we are pursuing the sorting of differentiated neural cells for cell replacement therapy and developing a smart petri dish in which cells can be tested, sorted and collected while they are being cultured,' he says.

Keith Farrington

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