Charge‐state‐derivation ion detection using a super‐conducting nanostructure device for mass spectrometry

Abstract

Mass spectrometry (MS) is a method of analyzing ions based on their mass/charge (m/z) ratios. The m/z peak identification requires speculation on the ionic charge states. This problem can be solved by using superconducting junction devices to measure the kinetic energies of single molecules. However, the kinetic energy measurement is followed by the dead time of 1-20 ms, which is fatally slow for modern high-resolution time-of-flight (TOF) analyzers. In this paper, we demonstrate that a superconducting nano-stripline detector (SSLD) composed of a 10-nm-thick and 800-nm-wide NbN strip realizes the charge-state derivation, and furthermore satisfies the ideal MS detector specifications such as a nano-second response, a short recovery time, a wide mass range, and no noise. Copyright # 2010 John Wiley & Sons, Ltd.In mass spectrometry (MS), ionized analytes are accelerated by a static voltage (V ¼ 3-30 kV), acquiring a kinetic energy of zeV, where e is the elementary charge and z is the unit-charge number. The ions are separated either spatially or temporally, and are detected by an ion (particle) detector. The spatial or temporal separation by an electromagnetic force leads to the same result for any ion species having the same mass/charge (m/z) ratio. Therefore, it is impossible to distinguish between different ion species with the same m/z.One type of the modern MS analyzers is based on time-offlight (TOF) spectroscopy, which measures time lags between the acceleration and detection after field-free flight for a certain distance (l). The relationship between TOF and m/z is expressed as TOF ¼ (m/z2eV) 1/2 l. Detectors in the ion counting mode generate an electric pulse, enabling the measurement of each instance of ion arrival. Some specifications for an ideal MS detector are listed in Koppenaal et al., 1 although the charge-state derivation is unlisted because it is essentially impossible by using conventional MS instruments. Satisfying these specifications as well as determining the charge states is a challenging task.Widely used ion detectors such as microchannel plates (MCPs) or secondary electron multipliers (SEMs) have a nano-second ion-counting capability necessary for a resolving power (m/Dm) over 10 000, and a cm size covering the molecular beam. The keV molecular ions induce soft impact and stop on the detector surface.2 Under this soft impact, the ion detection must rely on the emission of one or a few secondary electrons, in contrast to the generation of millions of charge carriers in kinetic-energy-sensitive semiconductor detectors used in nuclear physics. In a mass range over 4000, the quantum efficiency of the secondary electron emission is less than unity when singly charged ions are accelerated at 20 kV, and this efficiency decreases as molecular weight (MW) increases. 3,4 At this low number of secondary electrons, MCPs and SEMs cannot distinguish between every charge state, although rough discrimination between ions with 10þ (e.g., 200 keV) and 50þ (e.g., 1 MeV) is possible by analyzing the pulse he...

Hot-Spot Detection Model in Superconducting Nano-Stripline Detector for keV Ions

“…1(e). This result ensures that the charge-state derivation 4) for singly and doubly charged lysozyme ions accelerated by a higher acceleration voltage of 17.5 kV is practical. The transition width of the detection efficiency ÁI=I c is defined as the relative bias current width for the detection efficiency reduction from 0.1 to 0.001.…”

“…S uperconducting nano-stripline detectors (SSLDs) have been widely investigated because of short response time and high detection efficiency, which are crucial to mass spectrometry (MS) [1][2][3][4][5][6][7] or quantum communication. [8][9][10][11][12][13][14][15][16][17][18][19][20] The SSLDs are expected to realize a high mass resolution and the mass-independent detection sensitivity at the same time, both of which are among the specifications of an ideal mass detector.…”

Superconducting nano-strip particle detectors

“…Suzuki at al. [41] demonstrated that, behind the nanosecond response, the short recovery time, the wide mass range, and low noise, SSPDs also possess the charge-state derivation ability. This was possible by subtracting data at different bias currents that determine detectable lower threshold energies of ions.…”

Demonstration of Individual Readout of Serially-Connected Superconducting Strip Line Detectors

“…The SSLDs have already been applied to detection of a variety of particles such as a single photon [1], a macromolecule [2], a neutron [3], etc. The present phase in the development is to array multiple SSLDs for enhancing a detecting area or for making an imager.…”