Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging of Tissues via the Formation of Reproducible Matrix Crystals by the Fluorescence-Assisted Spraying Method: A Quantification Approach

Abstract

The application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging to quantitative analyses is restricted by the variability of MS intensity of the analytes in nonreproducible matrix crystals of tissues. To overcome this challenge, a fluorescence-assisted spraying method was developed for a constant matrix amount employing an MSdetectable fluorescent reagent, rhodamine 6G (R6G), which was sprayed with the matrix. To form a homogeneous matrix crystal on the tissue section, a matrix solution, 1,5-diaminonaphthalene (10 mg/mL), containing R6G (40 μg/mL) and O-dinitrobenzene (O-DNB, 10 mg/mL) was sprayed until the desired constant fluorescence intensity was achieved. Compared with that obtained via conventional cycle-number-fixed spraying [relative standard deviation (RSD) = 31.1%], the reproducibility of the relative MS intensity of the analyte [ferulic acid (FA), RSD = 3.1%] to R6G was significantly improved by the fluorescence-assisted matrix spraying. This result indicated that R6G could be employed as an index of the matrix amount and an MS normalizing standard. The proposed matrix spraying successfully quantified nifedipine (0.5−40 pmol/mm 2 in the positive mode, R 2 = 0.965) and FA (0.5−75 pmol/mm 2 in the negative mode, R 2 = 0.9972) in the kidney section of a rat. Employing the quantitative MALDI-MS imaging assay, FA, which accumulated in the kidney of the rat after 50 mg/kg was orally administered, was visually determined to be 3.5, 3.0, and 0.2 μmol/g tissue at 15, 30, and 60 min, respectively.

Current Knowledge on Intestinal Absorption of Anthocyanins

“…Furthermore, in the future, direct evidence of the accumulation of functional anthocyanins on the targeted tissues must be obtained with their quantitative amount to fully understand the mechanism of the physiological functionalities. Thus, further method development, such as a quantitative MS imaging technique, 58 might be essential, which can provide both a spatial distribution and an accumulated amount, as expected. Recently, a novel MS device, namely, trapped ion mobility spectrometry coupled to time-of-flight mass spectrometry (TIMS−TOF/MS) 59 has emerged, which could separate isomers of compounds.…”

Advanced mass spectrometric and spectroscopic methods coupled with machine learning for in vitro diagnosis

“…It is performed on the biological samples from the living body, such as blood plasma, 1 serum, 2 urine, 3 and tissues. 4 IVD accounts for about two-thirds of all clinical diagnoses. 5 The purpose of IVD is to provide information on the current or future status of the patient, often used in tasks such as risk assessment, 6 drug monitoring 7 and prognostic evaluation.…”

“…In vitro diagnosis (IVD) is an important subfield of medical tests. It is performed on the biological samples from the living body, such as blood plasma, 1 serum, 2 urine, 3 and tissues 4 . IVD accounts for about two‐thirds of all clinical diagnoses 5 .…”

Developing a Noncontact Heating Matrix Spraying Apparatus with Controllable Matrix Film Formation for MALDI Mass Spectrometry Imaging

“…21−23 The formation of a uniform matrix film during matrix deposition is one of the challenges for MALDI-MSI, and the heterogeneous matrix crystal or excessive matrix hinders high spatial resolution and reproducibility of MSI. 24 Therefore, matrix deposition plays a vital role in MALDI-MSI. 25 The two most common methods reported in the literature to achieve a high-quality matrix film are matrix sublimation and spraying.…”

“…The formation of a uniform matrix film during matrix deposition is one of the challenges for MALDI-MSI, and the heterogeneous matrix crystal or excessive matrix hinders high spatial resolution and reproducibility of MSI . Therefore, matrix deposition plays a vital role in MALDI-MSI .…”