Top-Down Rational Engineering of Heteroatom-Doped Graphene Quantum Dots for Laser Desorption/Ionization Mass Spectrometry Detection and Imaging of Small Biomolecules

Abstract

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) is widely applied in mapping macrobiomolecules in tissues, but it is still limited in profiling low-molecular-weight (MW) compounds (typically metabolites) due to ion interference and suppression by organic matrices. Here, we present a versatile “top-down” strategy for rational engineering of carbon material-based matrices, by which heteroatom-doped graphene quantum dots (HGQDs) were manufactured for LDI MS detection and imaging of small biomolecules. The HGQDs derived from parent materials inherited the π-conjugated networks and doping sites for promoting energy transfer and negative ion generation, while their extremely small size guaranteed the matrix uniformity and signal reproducibility in LDI MSI. Compared to other HGQDs, nitrogen-doped graphene quantum dots (NGQDs) exhibited superior capability of assisting LDI of various small molecules, including amino acids, fatty acids, saccharides, small peptides, nucleobases, anticancer drugs, and bisphenol pollutants. Density functional theory simulations also corroborated that the LDI efficiency was markedly raised by the proton-capturing pyridinic nitrogen species and compromised by the electron-deficient boron dopants. NGQDs-assisted LDI MS further enabled label-free investigation on enzyme kinetics using an ordinary short peptide as the substrate. Moreover, due to the high salt tolerance and signal reproducibility, the proposed negative-ion NGQDs-assisted LDI MSI was able to reveal the abundance and distribution of low-MW species in rat brain tissue and achieved the imaging of low-MW lipids in coronally sectioned rat brains subjected to traumatic brain injury. Our work offers a new route for customizing nanomaterial matrices toward LDI MSI of small biomolecules in biomedical and pathological research.

Host–Guest Self‐Assembled Interfacial Nanoarrays for Precise Metabolic Profiling

“…[ 7 ] Especially, nanomaterials as matrices for LDI‐MS analysis of small molecule metabolites exhibit excellent advantages over traditional organic matrices, [ 8 ] which are suitable and extensively utilized in biomedical analysis of amino acids, lipids, drugs and a variety of analytes. [ 9 ] The current nanomaterial matrices, including metal nanoparticles (NPs) and their oxides, [ 10,11 ] semiconductor quantum dots, [ 12 ] metal/covalent organic frameworks, [ 13,14 ] present specific nanostructures and unique optical, thermal and electromagnetism properties. [ 15 ] They could not only efficiently enhance LDI‐MS performance but also overcome the background interference at low molecular weight region ( m / z < 600).…”

Molecularly Imprinted Heterostructure-Assisted Laser Desorption Ionization Mass Spectrometry Analysis and Imaging of Quinolones

“…15 By leveraging the chemical specificity of MS, MALDI/MSI enables the acquisition of extensive information on the content and spatial distribution of known or unknown compounds. 16 The development of MALDI/MS and MALDI/MSI has opened up new possibilities for the detection and imaging of small molecules in tissue samples. 17 However, complex samples containing low contents of numerous interfering analytes inhibit the analysis of small molecules in real samples.…”

“…Matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS) has attracted great interest in the field of detection since its development because of its advantages of rapid analysis, small sample volume requirement, and high-throughput detection. , MALDI/MS imaging (MALDI/MSI) is a novel molecular visualization technique that allows the in situ ionization of analytes from the sample surface . By leveraging the chemical specificity of MS, MALDI/MSI enables the acquisition of extensive information on the content and spatial distribution of known or unknown compounds . The development of MALDI/MS and MALDI/MSI has opened up new possibilities for the detection and imaging of small molecules in tissue samples .…”