In a demonstration reminiscent to the one performed by IBM in 1990 that showed the ability of a STM (scanning tunnelling microscope) to move atoms to 'write' the letters IBM on a surface the researchers have used an optical trap 'tractor beam' to write the letters MIT on a microchip using 16 living E. coli (Escherichia coli) cells.
While optical traps have already been used successfully for studying colloid phase transitions, measurement of biological motor motility and the control of microfluidic flows in glass systems, integrating the technique with the materials used in microchip design and manufacturing has proven troublesome.
The new research, published as an early access article in the journal Lab on a Chip by Dr Matthew Lang and David Appleyard of MIT (Massachusetts Institute of Technology), managed to overcome the inherent problems of using light trapping techniques through silicon-based microchips that poorly transmit light.
Current methods for manipulating cells on surfaces involve dielectrophoresis or magnetic beads and these methods play a key role in microfluidic devices for many cellular applications.
The key advantage of using light trapping techniques is that the cells and surfaces do not need modification, ensuring that measurement of cellular interactions are not hindered or influenced by those modifications.
Optical traps use a beam of laser light to control the objects and this means that working with silicon systems that are opaque and do not efficiently transmit light is problematic.
However, silicon is transparent to infrared light and the researchers used infrared lasers to control the cells rather than visible light.
One possible drawback of infrared light is its warming properties, but the researchers showed that the temperature rise at a spot 1mm from the focal point of the laser was 4ºC over the ambient 21ºC room temperature at an input power of 1W.
According to Dr Lang this system represents "one of the world's smallest microtools," and that his group was now "applying it to building on a chip."
One application for the technology muted by Appleyard was to enable researchers to study how neurons communicate more easily.
"[Currently] they randomly put cells down on a surface, and hope one lands on [or near] a [sensor] so its activity can be measured. With [our technology], you can put the cell right down next to the sensors," said Appleyard.
"We've shown that you could merge everything people are doing with optical trapping with all the exciting things you can do on a silicon wafer…There could be lots of uses at the biology-and-electronics interface."
