ISAAC NEWTON has been dead for nearly three centuries, but an idea borrowed from the great man could lead the way to using X-rays to directly image small biological molecules such as proteins. Right now, proteins must be crystallised for their structures to be deduced.
The trick, says Henry Chapman of the Lawrence Livermore National Laboratory in California, is to focus an X-ray laser pulse onto a particle suspended about 100 micrometres in front of a mirror. The particle 鈥� made of polystyrene in Chapman鈥檚 set-up 鈥� absorbs some X-rays and scatters others, some of which are reflected back toward the particle. By the time the reflected X-rays return, the particle has begun to expand as it absorbs laser energy, and rescatters some of those reflected X-rays. The scattered rays produce an interference pattern of concentric rings, which provide information about the particle鈥檚 size and shape ().
Newton saw a similar effect when he lit up a mirror covered in dust particles. When Chapman saw a museum demonstration, he recognised the interference pattern and realised he could use it to measure the size of a particle placed in front of the mirror. His goal is to atoms and proteins.
Advertisement
