Immunoassays based on inductively coupled plasma mass spectrometry detection: So far so good, so what?

Iodinated organic molecule as tag for inductively coupled Plasma-mass spectrometry aptamer assays

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) aptamer-based assays using metallic nanostructures or chelates as exogenous tags have gained growing attention in the last decade. We describe here a proof-of-concept study based on the exploitation of a simple organic molecule as a tag, i.e.l-thyroxine carrying four iodine atoms detectable by ICP-MS. A solid-phase assay involving the structure-switching format was deployed for the detection of the small molecule l-tyrosinamide as model target. The overall design involved (i) a reporter agent consisting of a DNA aptamer incorporating a single l-thyroxine label at its end and (ii) a capture agent, which is a partially complementary strand, immobilized on a microplate. Limit of detection in the nanomolar range was reported. The present labeling approach was further developed for the detection of a model protein (α-thrombin), using a sandwich mode, and proved effective in a biological matrix. We believe that the l-thyroxine tagging method could become a simple and robust alternative to commonly used labeling methods for ICP-MS aptamer-based assays.

Ultrasensitive determination of β-conglutin food allergen by means an aptamer assay based on inductively coupled plasma mass spectrometry detection

The overall objective of this work is the evaluation of different competitive aptamer assays based on inductively coupled plasma mass spectrometry (ICP-MS) detection for the determination of β-conglutin (food protein allergen from lupin) in flour samples. To this end, two competitive aptamer assay schemes were developed using either thiolated aptamers chemisorbed onto gold nanoparticles (AuNPs) or biotinylated aptamers linked to streptavidin-AuNPs. The influence of ICP-MS detection mode (i.e., conventional vs single particle) on assay performance was explored. In the case of the thiolated aptamer, the limit of detection (LoD) obtained using the single particle mode was improved 2-fold as compared to the LoD provided by the conventional mode. With regards to the biotinylated aptamer, the use of the conventional mode provided a 5-fold improvement of LoD as compared to that obtained for the single particle one. Using the optimized conditions, the best LoD of 2 pM was obtained with the biotinylated aptamer operating with conventional ICP-MS detection. When compared to previous reports using the same aptamer in a competitive assay, the developed method significantly improved the LoD by at least an order of magnitude. Different flour samples containing lupin were successfully analyzed according to European Conformity guidelines for the analysis of food contaminants.

A renewable platform based on the entropy-driven catalytic amplification and element labeling inductively coupled plasma mass spectrometry for microRNA analysis

The element labeling inductively coupled plasma mass spectrometry (ICP-MS) strategy has been increasingly applied to the bioanalysis for various bio-targets. Herein, a renewable analysis platform with element labeling ICP-MS was firstly proposed for microRNA (miRNA) analysis. The analysis platform was established on the magnetic bead (MB) with entropy-driven catalytic (EDC) amplification. When the EDC reaction was initiated by target miRNA, numerous strands labeled with Ho element were released from MBs, and ¹⁶⁵Ho in the supernatant detected by ICP-MS could reflect the amount of target miRNA. After detection, the platform was easily regenerated by adding strands to reassemble EDC complex on MBs. This MB platform could be used four times, and the limit of detection for miRNA-155 was 8.4 pmol L^-1. Moreover, the developed regeneration strategy based on EDC reaction can be easily expanded to other renewable analysis platforms, such as, the renewable platform involving EDC and rolling circle amplification technology. Overall, this work proposed a novel regenerated bioanalysis strategy to reduce the consumption of reagent and time for probe preparation, profiting the development of bioassay based on element labeling ICP-MS strategy.

Highly sensitive and multiplexed mass spectrometric immunoassay techniques and clinical applications

Immunoassay is one of the most important clinical techniques for disease/pathological diagnosis. Mass spectrometry (MS) has been a popular and powerful readout technique for immunoassays, generating the mass spectrometric immunoassays (MSIAs) with unbeatable channels for multiplexed detection. The sensitivity of MSIAs has been greatly improved with the development of mass labels from element labels to small-molecular labels. MSIAs are also expended from the representative element MS-based methods to the laser-based organic MS and latest ambient MS, improving in both technology and methodology. Various MSIAs present high potential for clinical applications, including the biomarker screening, the immunohistochemistry, and the advanced single-cell analysis. Here, we give an overall review of the development of MSIAs in recent years, highlighting the latest improvement of mass labels and MS techniques for clinical immunoassays.

Diamond-Based Electrodes for Detection of Metal Ions and Anions

Diamond electrodes have long been a well-known candidate in electrochemical analyte detection. Nano- and micro-level modifications on the diamond electrodes can lead to diverse analytical applications. Doping of crystalline diamond allows the fabrication of suitable electrodes towards specific analyte monitoring. In particular, boron-doped diamond (BDD) electrodes have been reported for metal ions, anions, biomolecules, drugs, beverage hazards, pesticides, organic molecules, dyes, growth stimulant, etc., with exceptional performance in discriminations. Therefore, numerous reviews on the diamond electrode-based sensory utilities towards the specified analyte quantifications were published by many researchers. However, reviews on the nanodiamond-based electrodes for metal ions and anions are still not readily available nowadays. To advance the development of diamond electrodes towards the detection of diverse metal ions and anions, it is essential to provide clear and focused information on the diamond electrode synthesis, structure, and electrical properties. This review provides indispensable information on the diamond-based electrodes towards the determination of metal ions and anions.