Two-dimensional graphene as a matrix for MALDI imaging mass spectrometry

Abstract

Here, a matrix using two-dimensional (2D) graphene is demonstrated for the first time in the context of MALDI IMS using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Although graphene flakes have been used previously in MALDI, it is described here how a single 2D layer of graphene is applied directly on top of rat brain sections and soybean leaves. Several classes of molecules are desorbed and ionized off of the surface of the tissues examined using 2D graphene, with minimal background interference from the matrix. Moreover, no solvents are employed in application of 2D graphene, eliminating the potential for analyte diffusion in liquid droplets during matrix application. Because 2D graphene is an elemental form of carbon, an additional advantage is its high compatibility with the long duration needed for many IMS experiments. Graphical Abstract ᅟ.

Keywords: Brain; Fourier transform ion cyclotron resonance; Graphene; Imaging mass spectrometry; MALDI; Soybean.

Figure 1

3D AFM image of graphene on ITO slide after laser ablation. A: Laser focus setting small, B: Laser focus setting minimum. Ablated area marked with dashed line and dimensions of ablated regions are noted in projection. All dimensions shown are provided in micrometers.

Figure 2

MALDI IMS FT-ICR using a 2D graphene layer matrix on a soybean leaf section. The lightened area represents the area examined. Bright white represents high ion intensity, using summed ion abundance of only four m/z at 868.9, 873.1, 887.4, and 1109.2.

Figure 3

MALDI IMS FT-ICR using a 2D graphene layer matrix for a pixel located on a soybean leaf vein.

Figure 4

MALDI IMS using a 2D graphene layer matrix on a mouse hemisphere section. Images represent selected ion current as a function of position for ions at m/z A) 429.1, B) 494.7, C) 612.6, D) 828.5, E) 844.4, and F) 868.4. White represents high intensity ion signals while black represents low intensity ion signals.