A new technique raises the possibility of a “DNA photocopier” small enough to hold in your hand that could identify the bacteria or virus causing an infection before symptoms appear. Vanderbilt University researchers created the method for controlling a powerful but finicky process called the polymerase chain reaction (PCR). PCR can make billions of identical copies of small segments of DNA so they can be used in molecular and genetic analyses. Biomedical engineers Nicholas Adams and Frederick Haselton came up with an out-of-the-box idea, which they call adaptive PCR, that uses left-handed DNA (L-DNA) to monitor and control the molecular reactions that take place in the PCR process. A small sample in the center of the device is illuminated by an ultraviolet laser on the right and varying levels of fluorescence are detected by the spectrophotometer on the left and are used to control the DNA duplication process.