Gold Nanoparticles as a Matrix for Visible-Wavelength Single-Particle Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry of Small Biomolecules

Abstract

Gold nanoparticles (GNPs) are used as the matrix for visible-wavelength matrix-assisted laser desorption/ionization (VIS-MALDI) of individual aerosol particles containing ∼50 attomole of a small peptide. A dual polarity time-of-flight mass spectrometer was used to obtain both positive and negative ion mass spectra simultaneously from individual particles using a tunable wavelength desorption/ionization laser. The wavelength of the laser was changed from λ = 440 to 680 nm to observe the wavelength dependence of analyte ion formation. Detection of the positive sodiated molecular ions and negative deprotonated molecular ion of a small peptide was only possible using 5-nm GNPs and not with larger sized (19- and 44-nm) GNPs. While the masses of gold within the sample particles were similar, surface areas were about 10 times more in the 5-nm GNPs, suggesting the total surface area of GNPs within the sample particles may play a role in the formation of molecular ions. At wavelengths near the peak plasmon resonance of the GNPs (λ = 500−540 nm), negative molecular ion signals from a small peptide was higher than with desorption/ionization at λ = 440 nm, with increased fragmentation observed at λ = 440 nm. At wavelengths longer than the peak plasmon absorption, the ability to generate a detectable ion signal decreased rapidly, which is consistent with the steep decrease in the absorbance of GNPs by surface plasmon resonance at these wavelengths. Silver nanoparticles, which also exhibit a surface plasmon resonance, were tested and under our conditions did not appear to work as well. The presented results demonstrate that noble metal nanoparticle matrices can be used for on-line VIS-MALDI analysis of small molecular weight species such as peptides or sugars.

Mass spectrometry of nanodiamonds

“…Because gold nano‐particles (GNPs) can also serve as a matrix42 we have examined whether GNPs can be used as a matrix for NDs. When GNPs were used, a similar mass distribution of carbon clusters was observed (Fig.…”

UV-Vis-NIR Laser Desorption/Ionization of Synthetic Polymers Assisted by Gold Nanospheres, Nanorods and Nanostars

“…Nevertheless, the substrate produces good quality LDI mass spectra at 1064 nm (see below). The only previous systematic wavelength dependence study of the LDI response of gold nanospheres was performed under quite different experimental conditions [11]. It employed an aerosol suspension of the nanoparticles, and involved laser energies two orders of magnitude higher than the present ones.…”

“…Plasmon absorbance in the gold nanospheres leads to a characteristic band centered in the range 500-600 nm (e.g., see ref. [11]). The broader spectra of the nanorods and the nanostars are qualitatively similar to each other.…”

“…Even though the concept was demonstrated more than two decades ago [1][2][3][4], it has been within the last few years that the consolidation of nanoparticle synthesis techniques has catalyzed systematic studies in this field [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. There is a growing interest in the application of plasmonic LDI, in particular, to organic and biochemical analysis and in the development of novel molecular sensors [19][20][21][22][23].…”

“…They concluded that the plasmonic resonant 532 nm wavelength was most efficient. Spencer and coworkers employed a tunable dye laser to scan the visible plasmonic band of gold nanospheres suspended in aerosols, and found negligible LDI signal in the region of weak absorbance (wavelengths longer than 600 nm) [11]. In contrast, Schürenberg and coworkers reported a weak dependence on laser wavelength in LDI processes assisted by different conducting nanoparticles dispersed in glycerol [4].…”