Direct analysis of lateral flow immunoassays for deoxynivalenol using electrospray ionization mass spectrometry

Abstract

Lateral flow immunoassays (LFIAs) are widely used for rapid food safety screening analysis. Thanks to simplified protocols and smartphone readouts, LFIAs are expected to be increasingly used on-site, even by non-experts. As a typical follow-up in EU regulatory settings, suspect samples are sent to laboratories for confirmatory analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). However, re-analysis by LC-MS/MS is laborious and time-consuming. In this work, an identification LFIA (ID-LFIA) approach followed by quadrupole-orbitrap MS or triple quadrupole MS/MS analysis is presented. As a proof of concept, a dedicated ID-LFIA strip was developed for the mycotoxin deoxynivalenol (DON) following its initial screening by a commercial smartphone LFIA. The ID-LFIA strip can be simply immersed in the same sample extract used for the smartphone LFIA screening, and next, DON is retrieved from the monoclonal antibody with a dissociation solution consisting of methanol/ammonia. The solution thus obtained was analyzed directly in MS in order to rapidly confirm the presence of DON and any cross-reacting species. The protocol developed is capable of coping with severe ion suppression caused by LFIA buffers and nitrocellulose substrate residues. Initial analysis of blank, spiked, and incurred samples showed that the newly developed ID-LFIA-MS method was able to confirm the presence or absence of mycotoxins in the samples previously analyzed by LFIA and also differentiate between DON and DON 3-glucoside yielding the positive screening result. The concept and technique developed are envisaged to complement on-site screening and confirmation of any low molecular weight contaminant in future food control frameworks.

From Smartphone Lateral Flow Immunoassay Screening to Direct MS Analysis: Development and Validation of a Semi-Quantitative Direct Analysis in Real-Time Mass Spectrometric (DART-MS) Approach to the Analysis of Deoxynivalenol

“…As described in our previously published work [ 17 ], we envisage a future of smartphone-based on-site screening of food quality and safety parameters that will unavoidably increase confirmatory analysis requirements. Several smartphone-based screening methods have been developed, some of which demonstrate great citizen science potential [ 20 , 21 , 22 ].…”

“…Furthermore, mouse monoclonal antibodies (mAb) for DON, clone 2, were purchased from Aokin AG (Berlin, Germany) and diluted with 1× Phosphate Buffer Saline (PBS) to a concentration of 0.3 mg/mL. The diluted mAb were used to construct the ID-LFIA as described in the previous publication [ 17 ]. In short, 15 identical lines of the diluted mAb, forming a bioaffinity trapping zone, are sprayed on top of the center of a nitrocellulose membrane (HiFlow Plus HF13502, Millipore, Carrigtwohill, Ireland) secured on a plastic backing (G & L, San Jose, CA, USA), using an XYZ3060 BioJet and AirJet instrument (Biodot Inc., Irvine, CA, USA).…”

“…The protocol developed for direct MS analysis of the ID-LFIA [ 17 ] was further improved to achieve a more time-efficient procedure of retrieving the final solution from the ID-LFIA for subsequent MS analysis. First, the part of the ID-LFIA with the rectangular mAb trapping zone was cut and washed with 500 μL of MilliQ water in an Eppendorf tube under slight manual agitation for 30 s. The rectangular mAb trapping zone was then placed in an Eppendorf with 200 μL of MeOH/NH 3 2% v / v dissociation solution, followed by vigorous manual agitation for 1 min only.…”

“…In our recently published work [ 17 ], we developed an approach for the direct MS analysis of screening LFIAs for DON with smartphone readout. At first, mycotoxins are extracted from the sample, a screening assay is performed with a smartphone readout, and the same sample extract is used to develop an identification LFIA (ID-LFIA); the latter acts as a bioaffinity trapping device.…”

“…The ID-LFIA/ESI-MS approach is to be used as a moderator for increased use in screening assays with smartphone readout, which will inevitably increase the number of samples that need to undergo confirmatory analysis to an overload of work in the food control laboratories. With the ID-LFIA/ESI-MS approach, we offered an intermediate rapid confirmatory analysis technique [ 17 ]. However, the ID-LFIA/ESI-MS approach was restricted to the negative ion (−) mode due to ion suppression caused by residues from the LFIA assay buffer residues.…”