Characterization of Mega-Dalton-Sized Nanoparticles by Superconducting Tunnel Junction Cryodetection Mass Spectrometry

Abstract

The characterization of nanomaterials is critical to understand the size/structure-dependent properties of these particles. In this report, a form of heavy ion mass spectrometry, namely, superconducting tunnel junction (STJ) cryodetection mass spectrometry (MS) is used to characterize quantum dot semiconductor nanocrystals and gold nanoparticles. The nanoparticles studied ranged in mass from 200 kDa to >1.5 MDa and included lead sulfide quantum dots, various cadmium selenide and/or telluride-based core-shell quantum dots coated with different ligands, and gold nanoparticles. Nanoparticles were ionized by both matrix-assisted laser desorption ionization (MALDI) and laser desorption ionization (LDI), shot with an aimed ion gun into a flight tube, mass separated by time-of-flight (TOF), and detected by an energy-sensitive STJ cryodetector. STJ cryodetection MS can be used to analyze intact heterogeneous nanoparticles, allowing determination of average particle mass, dispersity, and ligand loading. Some nanoparticles, however, do undergo fragmentation during the MALDI or LDI-TOF mass analyses. The measurement of the energy deposited into the detector was found to be different for different types of particles. Metastable fragments from these nanoparticles were observed at lower energies. The lower energies deposited for metastable fragments can provide insight into the stability and surface compositions of these materials. Cadmium selenide core-shell quantum dots (655 nm emission) conjugated to biomacromolecules, such as cholera toxin B and human serum transferrin, were also analyzed. When compared to unconjugated particles by mass, it was determined that ∼96 cholera toxin B and ∼14 transferrin proteins were attached to the surface of these nanoparticles.

Multiplexed Charge Detection Mass Spectrometry for High-Throughput Single Ion Analysis of Large Molecules

“…By doing so, the presence of other ions cannot interfere with the mass measurement of another. Single molecule and ion mass measurements have been demonstrated using ion nanoelectromechanical systems and with Fourier-transform ion cyclotron resonance (FTICR), , ion trap, − cryodetector time-of-flight, , orbitrap, , and charge detection mass spectrometry (CDMS). − These methods can provide accurate masses of individual ions but often at the expense of analysis time. The number of individual ion measurements necessary to characterize a sample depends on sample complexity.…”

Recent Advances in Instrumental Approaches to Time‐of‐flight Mass Spectrometry

“…Recently, the high‐mass detection efficiency of STJs was used to measure the iron content and dispersity of intact ferritin (Plath et al, 2015), a common ion storage protein complex, as well as kDa sized ZnO nanoparticles (Plath et al, 2017). The same group also characterized MDa sized nanoparticles and lead selenide quantum dots using STJs (Sipe et al, 2018).…”

Resolving heterogeneous high-mass macromolecular machineries by Orbitrap-based single particle charge detection mass spectrometry

“…An attractive alternative may come from measuring one particle (or ion) at a time, thereby avoiding the problematic convolution of signals that stem from insufficient resolving power [17][18][19][20][21][22][23][24][25][26][27] . When such single-particle detection approaches can be combined with an independent measure of the charge of ions, or when masses can be estimated using entirely different physical principles that circumvent the need to work with multiply charged ions, this opens up the door to bona fide single-particle mass spectrometry measurements.…”