Surface Modified Nano-Electrospray Needles Improve Sensitivity for Native Mass Spectrometry

Native mass spectrometry (MS) and charge detection-mass spectrometry (CD-MS) have become versatile tools for characterizing a wide range of proteins and macromolecular complexes. Both commonly use nanoelectrospray ionization (nESI) from pulled borosilicate needles, but some analytes are known to nonspecifically adsorb to the glass, which may lower sensitivity and limit the quality of the data. To improve the sensitivity of native MS and CD-MS, we modified the surface of nESI needles with inert surface modifiers, including polyethylene-glycol. We found that the surface modification improved the signal intensity for native MS of proteins and for CD-MS of adeno-associated viral capsids. Based on mechanistic comparisons, we hypothesize that the improvement is more likely due to an increased flow rate with coated ESI needles rather than less nonspecific adsorption. In any case, these surface-modified needles provide a simple and inexpensive method for improving the sensitivity of challenging analytes.