Facile fabrication of the immuno-MALDI-MS chip for the enrichment of abused drug in human urine integrated with MALDI-MS analysis

Abstract

Background: Drug abuse can result in both physical and mental health issues for individuals, and can also contribute to broader societal problems. The number of drug abuse cases rose to 296 million in 2021. The sample pretreatment methods commonly employed typically require longer processing times and occasionally necessitate derivatization. Furthermore, with the increase in sample sizes, traditional chromatography-mass spectrometry methods for analyzing abused drugs were no longer sufficient to handle such numerous samples. In this study, immuno-MALDI-MS chip were fabricated for specific enrichment of illicit drugs, integrating with the rapid and accurate capabilities of MALDI-MS for high-throughput analysis of drug abuse.

Results: The immuno-MALDI-MS chip was successfully prepared by coating an aluminum chip with antibody-conjugated boronic acid-modified gold nanoparticles. Ketamine, a frequently abused illicit drug, served as the proof of concept for this study. The immuno-MALDI-MS chip was employed to selectively enrich ketamine in human urine samples, facilitating direct MALDI-MS analysis with the addition of α-CHCA matrix solution. The challenge of detecting abused drugs, exacerbated by interfering peaks in the low m/z region from salts and small molecules in human urine samples, was successfully overcome. The developed method exhibited a wide linear range of 10-5000 ng/mL with a limit of detection of 3.3 ng/mL for ketamine. Notably, the proposed method enabled high-throughput screening and accurate confirmation of ketamine concentrations in suspects' urine samples within few minutes, requiring a minimal sample volume of 1 μL. The obtained data were in complete agreement with the previous GC/MS analysis.

Significance: A straightforward, cost-effective and sensitive method for the selective enrichment and absolute quantification of abused drugs was developed using a homemade immuno-MALDI-MS chip integrated with MALDI-MS analysis. This method combines the advantages of immunoassay and mass spectrometry, offering both speed and accuracy. The reported method for the quantification of ketamine in human urine offers a practical approach and has the potential to analyze emerging new psychoactive substances in the future.

Keywords: Abused drug; Immuno-MALDI-MS chip; Ketamine; Matrix-assisted laser desorption ionization mass spectrometer; Single drop analysis.