Matrix phase fractionation: Investigating the compromise between dynamic range of analyte extraction and spatial resolution in mass spectrometry imaging

Developing CHCA/PPD as a novel matrix for enhanced matrix-assisted laser desorption/ionization-mass spectrometry imaging for analysis of antibiotics in grass carp tissues

Antibiotics have important medical value, but they need to be monitored when used as veterinary drugs. We report α-cyano-4-hydroxycinnamic acid/p-phenylenediamine (CHCA/PPD) hybrid as a novel matrix for enhanced matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) in situ the spatial distribution of antibiotic drugs in grass carp tissues.

METHOD

We have used MALDI-TOF-MSI in positive ion mode for the analysis of quinolones and sulfonamides in grass carps. A novel CHCA/PPD matrix was prepared and applied using a simple method to improve the analysis.

RESULTS

Compared with the traditional matrix, CHCA/PPD significantly improved the detection intensity of quinolones and sulfonamides with better sensitivity (17.20%-94.30%) and reproducibility. For demonstration, this novel matrix was successfully applied to visualize enrofloxacin (ENR) in grass carp tissues, with the entire abundance differences clearly observed based on MALDI-MSI. The concentration levels in different tissues were determined, with a calibration curve of 10-2000 μg/ml (R²  > 0.993).

CONCLUSION

This study was the first to introduce CHCA/PPD as a novel matrix, and the classical acid-base mixing was used to improve the ionization effect of the traditional matrix CHCA in MALDI. Based on CHCA/PPD, MALDI-MSI detected ENR in different grass carp tissues for the first time and realized the spatial distribution and concentration detection.

Viral Biomarker Detection and Validation Using MALDI Mass Spectrometry Imaging (MSI)

(1) Background: MALDI imaging is a technique that still largely depends on time of flight (TOF)-based instrument such as the Bruker UltrafleXtreme. While capable of performing targeted MS/MS, these instruments are unable to perform fragmentation while imaging a tissue section necessitating the reliance of MS1 values for peptide level identifications. With this premise in mind, we have developed a hybrid bioinformatic/image-based method for the identification and validation of viral biomarkers. (2) Methods: Formalin-Fixed Paraffin-Embedded (FFPE) mouse samples were sectioned, mounted and prepared for mass spectrometry imaging using our well-established methods. Peptide identification was achieved by first extracting confident images corresponding to theoretical viral peptides. Next, those masses were used to perform a Peptide Mmass Fingerprint (PMF) searched against known viral FASTA sequences against a background mouse FASTA database. Finally, a correlational analysis was performed with imaging data to confirm pixel-by-pixel colocalization and intensity of viral peptides. (3) Results: 14 viral peptides were successfully identified with significant PMF Scores and a correlational result of >0.79 confirming the presence of the virus and distinguishing it from the background mouse proteins. (4) Conclusions: this novel approach leverages the power of mass spectrometry imaging and provides confident identifications for viral proteins without requiring MS/MS using simple MALDI Time Of Flight/Time Of Flight (TOF/TOF) instrumentation.