A prototype chip can be used to make cells hop along a magnetic field.

Robert Westervelt and his colleagues at Harvard University, US, have combined microelectronics and microfluidic technologies to develop a hybrid chip that can manipulate individual biological cells.

In Westervelt's chip, cells are contained within microfluidic channels. The microfluidic system is built on top of a custom-designed integrated circuit (IC) that controls microcoils on the chip's surface. By tagging cells with peptide-coated magnetic beads, their motion can be controlled using local magnetic fields generated in the microcoils. 

'The microcoils are matched in size to an individual cell which makes it possible for a microcoil to trap a single cell,' explained Westervelt. Since a single microcoil or a number of microcoils can be activated simultaneously, either single or multiple cells can be held. 

In the single cell case, because only one microcoil is magnetically active at any given moment, applying a current pulse to the hybrid chip forces the cell to hop from one microcoil to another. Time-sharing the current source generates magnetic fields in more than one microcoil, allowing multiple cells to be trapped and moved independently of each other. 'It is this capability to individually control many cells in parallel that allows experiments to be conducted with single-cell level precision,' said Westervelt.

According to Westervelt, these chips offer a powerful tool for biotechnology because they use standard IC technology and can be produced cheaply. They will allow tests, assays and diagnoses to be performed reliably on a scale and at speeds not previously possible, he said.

'Preventing damage to the integrated circuits by the biological fluids is a challenge,' said Westervelt. 'In particular, we need to find coatings that will protect them from salts and organic compounds in biological samples.' 

Janet Crombie