A Silicon Nanomembrane Detector for Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) of Large Proteins

Jonghoo Park,Robert Blick

doi:10.3390/s131013708

Abstract

We describe a MALDI-TOF ion detector based on freestanding silicon nanomembrane technology. The detector is tested in a commercial MALDI-TOF mass spectrometer with equimolar mixtures of proteins. The operating principle of the nanomembrane detector is based on phonon-assisted field emission from these silicon nanomembranes, in which impinging ion packets excite electrons in the nanomembrane to higher energy states. Thereby the electrons can overcome the vacuum barrier and escape from the surface of the nanomembrane via field emission. Ion detection is demonstrated of apomyoglobin (16,952 Da), aldolase (39,212 Da), bovine serum albumin (66,430 Da), and their equimolar mixtures. In addition to the three intact ions, a large number of fragment ions are also revealed by the silicon nanomembrane detector, which are not observable with conventional detectors.

Highlights

In time-of-flight (TOF) mass spectrometry (MS) [1], large molecules—the proteins—are desorbed and ionized by the matrix-assisted laser desorption/ionization (MALDI) [2,3] technique before being accelerated in an electric field, and directed into the flight tube where they are separated by their mass-to-charge (m/z) ratio
We speculate that these peaks are fragment ions, which are produced by high laser power
The laser intensity for the spectrum is set to be slightly higher than the threshold laser intensity for BSA in an equimolar mixture of apomyoglobin, aldolase, and BSA, which will be discussed below

Summary

Introduction

In time-of-flight (TOF) mass spectrometry (MS) [1], large molecules—the proteins—are desorbed and ionized by the matrix-assisted laser desorption/ionization (MALDI) [2,3] technique before being accelerated in an electric field, and directed into the flight tube where they are separated by their mass-to-charge (m/z) ratio. The operating principle of the ion detectors used in most TOF mass spectrometers, e.g., the microchannel plates (MCP) and dynodes, are based on secondary electron emission [4]. In these detectors, the incident ion generates secondary electrons, which are multiplied via a sequential cascade process. The secondary electron emission yield decreases as the velocity of the incident ions decreases [5]. This leads to a remarkable decrease in detection sensitivity for larger ions, which drift more slowly down to the detector than lighter ones. MALDI-TOF remains predominantly restricted to the mass analysis of biomolecules with a mass below about 300,000 Daltons [6]

Methods

Results

Conclusion