Development of MALDI MS peptide array for thrombin inhibitor screening

MALDI Mass Spectrometry on High-Density Droplet Arrays: Matrix Deposition, Selective Removal, and Recrystallization

High-density droplet arrays are emerging as a powerful tool for high-throughput bioanalytical applications. These arrays are formed of thousands of nanoliter droplets, which can be analyzed by various optical and spectroscopic methods as well as label-free matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). However, special precautions are required for the massive number of small droplets, particularly in the deposition of matrix compounds. Here, we introduce a new workflow for the analytical preparation of an array comprising 6048 droplets, which significantly improves the intensity of the MALDI-MS signals. We deposited matrix compounds in a custom-made sublimation chamber followed by a recrystallization step to achieve significant signal intensity increases for three model proteins with low, medium, and large masses, respectively. Furthermore, selective removal of the matrix before recrystallization enhanced the spatial resolution and increased the signal intensity by an average of 57%. This method can be easily standardized and upscaled for the preparation of an even larger number of droplets per array for MS analysis.

Carbon dots doped with nitrogen as an ultrasensitive fluorescent probe for thrombin activity monitoring and inhibitor screening

A simple and sensitive fluorometric assay based on nitrogen-doped carbon dots (N-CDs) was developed for the determination of thrombin (TB) activity in human serum samples and living cells. The novel N-CDs were prepared by a facile one-pot hydrothermal method using 1,2-ethylenediamine and levodopa as precursors. Such N-CDs exhibited green fluorescence with excitation/emission peaks at 390/520 nm and a high fluorescence quantum yield of approximately 39.2%. H-D-Phenylalanyl-L-pipecolyl-Larginine-p-nitroaniline-dihydrochloride (S-2238) was hydrolyzed by TB to produce p-nitroaniline which was capable of quenching the fluorescence of N-CDs due to an inner filter effect. This assay was used to detect TB activity with a low detection limit of 11.3 fM. The proposed sensing method was then expanded to the TB inhibitor screening and exhibited excellent applicability. As a typical TB inhibitor, argatroban was determined in a concentration as low as 1.43 nM. The method has also been successfully employed for the determination of TB activity in living HeLa cells. This work showed significant potential for TB activity assay in clinical and biomedicine applications.

Image to insight: exploring natural products through mass spectrometry imaging

Covering: 2017 to 2022Mass spectrometry imaging (MSI) has become a mature molecular imaging technique that is well-matched for natural product (NP) discovery. Here we present a brief overview of MSI, followed by a thorough discussion of different MSI applications in NP research. This review will mainly focus on the recent progress of MSI in plants and microorganisms as they are the main producers of NPs. Specifically, the opportunity and potential of combining MSI with other imaging modalities and stable isotope labeling are discussed. Throughout, we focus on both the strengths and weaknesses of MSI, with an eye on future improvements that are necessary for the progression of MSI toward routine NP studies. Finally, we discuss new areas of research, future perspectives, and the overall direction that the field may take in the years to come.