A new detector could improve the sensitivity of time-of-flight mass spectrometry (TOF MS) for large ions such as proteins, according to a report in Nano Letters (DOI: 10.1021/nl201645u). TOF MS has no theoretical limit to its mass range, but the detectors currently used are less sensitive to large, slow-moving ions than to fast, light ones. Robert H. Blick and coworkers at the University of Wisconsin, Madison, report a new type of detector based on the mechanical deformation and vibration of a nanometer-thin membrane. The three-layer nanomembrane consists of silicon nitride sandwiched between aluminum. The two metal layers act as an absorber of incident ions and as a cathode that emits electrons, which are amplified by a microchannel plate and collected by an anode. Ions striking the membrane cause vibrations that increase the electron emission and modulate the current. The researchers used the nanomembrane to detect a mixture containing the proteins insulin, bovine serum albumin, and immunoglobulin G that were separated by TOF MS. There is minimal drop-off in signal intensity as the mass of the ions increases.