Chemists from the National Institute of Standards and Technology (NIST) and Arizona State University have proposed an elegantly simple technique for cleaving proteins into convenient pieces for analysis. The prototype sample preparation method, detailed recently in Analytical Chemistry,* uses ultraviolet light and titanium dioxide and could be ideal for new microfluidic lab-on-a-chip devices designed to rapidly analyze minute amount of biological samples.
Because most proteins are very large, complex molecules made up of hundreds or thousands of amino acids, they usually must be cut up into more manageable pieces for analysis. Today, this most commonly is done by using special enzymes called proteases that sever the chains at well-known locations. The protease trypsin, for example, cuts proteins at the locations of the amino acids lysine and arginine. Analyzing the residual fragments can identify the original protein. But enzymes are notoriously fussy, demanding fairly tight control of temperature and acidity, and the enzymatic cutting process can be time-consuming, from a matter of hours to days.
For a radically different approach, the NIST group turned to a semiconductor material, titanium dioxide. Titanium dioxide is a photocatalystwhen exposed to ultraviolet light its surface becomes highly oxidizing, converting nearby water molecules into hydroxyl radicals, a short-lived, highly reactive chemical species.** In the NIST experiments, titanium dioxide coatings were applied to a variety of typical microanalysis devices, including microfluidic channels and silica beads in a microflow reactor. Shining a strong UV light on the area, in the presence of a protein solution, creates a small cleavage zone of hydroxyl radicals that rapidly cut nearby proteins at the locations of the amino acid proline.
Although development work remains to be done, according to the researchers, the NIST photocatalysis technique offers several advantages over
Contact: Michael Baum
National Institute of Standards and Technology (NIST)