Counting single proteins with a superconducting nanowire 

The detection, identification, and analysis of macromolecules is needed in many areas of life sciences, including protein research, diagnostics, and analytics. Mass spectrometry is often used as a detection system for proteins – a method that typically separates charged particles (ions) according to their mass-to-charge-ratio and measures the intensity of the signals generated by a detector. This provides information about the relative abundance of the different types of ions and therefore the composition of the sample. However, conventional detectors have only been able to achieve high detection efficiency and spatial resolution for particles with high impact energy.

Now, a team of researchers demonstrates ¹ for the first time the use of superconducting nanowires as excellent detectors for protein beams in so-called quadrupole mass spectrometry. Ions from the sample to be analyzed are fed into a quadrupole mass spectrometer where even particles that hit the detector with low kinetic energy can be identified thanks to the nanowires being superconductors.

High detection efficiency and spatial resolution for proteins

The key is that nanowires enter a superconducting state at very low temperatures, in which they lose their electrical resistance and allow lossless current flow. Excitation of the superconducting nanowires by incoming ions causes a return to the normal conducting state. The change in the electrical properties of the nanowires during this transition is interpreted as a detection signal, outperforming conventional ion detectors by up to three orders of magnitude.

This new nanowire detector have a remarkable quantum yield at exceptionally low impact energies – and redefine the possibilities of conventional detectors. Thus, a mass spectrometer adapted with such a quantum sensor can not only distinguish molecules according to their mass to charge state, but also classify them according to their kinetic energy. This improves the detection and enhances the spatial resolution.

Nanowire detectors can find new applications in mass spectrometry, molecular spectroscopy, molecular deflectometry, or quantum interferometry of molecules, where high efficiency and good resolution are required, especially at low impact energy.