Synthetic Thyroid Hormone Tag Offers Alternative for Labeling ICP-MS Aptamer Assays

Researchers at University Grenoble Alpes, its French National Centre for Scientific Research (CNRS), and Centre Hospitalier Universitaire (CHU) Grenoble Alpes, all in Grenoble, France, and Carleton University in Ottawa, Ontario, Canada have conducted a proof-of-concept study that exploits a simple organic molecule as a tag, in other words a label, for aptamer-based inductively coupled plasma–mass spectrometry (ICP-MS) assays (1).

Dna. | Image Credit: © BillionPhotos.com - stock.adobe.com

The collaborative work of these 10 authors, accepted for publication by the journal Talanta, proposes L-thryoxine, the synthetic form of the thyroid hormone, as a label at one end of a DNA aptamer (an aptamer being a short sequence that binds specific target molecules) used as a reporter agent, with a partially complementary strand called a capture agent immobilized on a microplate (1). The small molecule L-tyrosinamide was selected as the model target for detection in this experiment.

Inductively coupled plasma–mass spectrometry (ICP-MS) was reported by the researchers to be a promising technique for the design of surface-phase aptamer assays because they said it provides very high sensitivity, a large dynamic range, and element specificity (1). Meanwhile, although metallic nanoparticles or nanoclusters and lanthanide chelates have been utilized effectively as tags for reasons including high capability for signal amplification, for the nanoparticles, and low-background and multiplexed analysis, for the chelates, drawbacks such as batch-to-batch reproducibility and multiple labeling steps present ongoing challenges.

Before settling on L-thryoxine, the team said they explored the possibility of using an endogenous, rather than exogenous, non-metallic tag, namely phosphorus, which is a natural heteroelement of the aptamers (1). A similar selection, they said, had previously been made for quantification of nucleic acids. But they found that the analytical signal depended on aptamer length and therefore, would not be able to be fully standardized. By contrast, L-thryoxine contains four iodine atoms that are detectable by ICP-MS.

As stated, the researchers devised a simple, structure-switching format using the L-thryoxine molecule as a tag at one end of a DNA aptamer acting as a reporting agent, juxtaposed with a capture agent strand immobilized on a microplate. After detecting the small molecule L-tyrosinamide, the method and assay were then extended to determine a model protein, α-thrombin (Thb), using a “sandwich” mode or configuration—meaning that two aptamers were capable of binding to different regions of the protein (1). A practical application was then tested, which detected the presence of Thb analyte in human urine.

The success of this assay within the sandwich configuration encouraged the researchers that L-thryoxine might have potential as a tag for aptamer-based assays determined by ICP-MS. As for future research and experimentation, they said other target-aptamer pairs would have to be studied to gauge the feasibility of this labeling strategy. Ultimately, they aim to eventually apply their work to other complex matrices which may have broader impact either biomedically or environmentally.

Reference

(1) Billet, B.; Chovelon, B.; McConnell, E. M.; et al. Iodinated Organic Molecule as Tag for Inductively Coupled Plasma–Mass Spectrometry Aptamer Assays. Talanta 2024, 267, 125107. DOI: 10.1016/j.talanta.2023.125107