Bimodal determination of immunoglobulin E by fluorometry and ICP-MS by using platinum nanoclusters as a label in an immunoassay

Palladium nanoclusters as a label to determine GFAP in human serum from donors with stroke by bimodal detection: inductively coupled plasma-mass spectrometry and linear sweep voltammetry

Water-soluble, stable, and monodisperse palladium nanoclusters (PdNCs) were synthesized using NaBH4 as a reductant and lipoic acid as a ligand. PdNCs, measured by high-resolution transmission electron microscopy, showed a round shape and a diameter of 2.49 ± 0.02 nm. It was found that each PdNC contains 550 Pd atoms on average. These PdNCs offer high amplification as a label of biochemical reactions when inductively coupled plasma-mass spectrometry (ICP-MS) is used as a detector. In addition, PdNCs have catalytic activity on electrochemical reactions, allowing detection by linear sweep voltammetry (LSV). As a proof of applicability, a competitive immunoassay based on PdNC labels was developed for the determination of glial fibrillary acidic protein (GFAP) in human serum, comparing ICP-MS and LSV detection. GFAP is a biomarker for differentiating between patients with ischemic stroke (IS) and hemorrhagic stroke (HS). The limit of detection (LoD), corresponding to IC10 (4-parameter logistic curve), was 0.03 pM of GFAP, both by ICP-MS and LSV, being lower than the 0.31 pM LoD provided by the ELISA commercial kit. Using the error profile method, 0.03 pM and 0.11 pM LoDs were obtained respectively by ICP-MS and LSV: LoD is lower by ICP-MS due to the better precision of the measurements. The analyses of human serum samples from IS, HS, and control (CT) donors using PdNC labels and detection by ICP-MS and LSV were validated with a commercial ELISA kit (for CT donors only ICP-MS provided enough sensitivity). Results point out toward the future use of PdNCs as a label in other immunoprobes for the determination of specific proteins requiring very low LoDs as well as the development of electrochemical decentralized methodologies.

Fluorescent enzyme-linked immunosorbent assay based on alkaline phosphatase-responsive coordination polymer composite

The fabrication of alkaline phosphatase (ALP)-responsive coordination polymer (CP) composite is demonstrated for establishing a fluorescent immunoassay. The CP composite (ThT@GMP/Eu) was synthesized by encapsulating thioflavin T (ThT) into the CP host that was composed of europium ion (Eu³⁺) and guanine monophosphate (GMP). The ThT@GMP/Eu composite shows a strong fluorescence in aqueous solution due to the confinement effect of GMP/Eu CPs, which restricts the conformational rotation of ThT. However, upon the addition of ALP, the structure of GMP/Eu CPs was disrupted to release ThT into solution. This results in the quenching of the fluorescence of ThT@GMP/Eu. The fluorescence of ThT@GMP/Eu has a linear response that covers 0.8 to 120 mU/mL ALP with a detection limit of 0.26 mU/mL and exhibits excellent specificity towards ALP against other enzymes. On this basis, inspired by the wide application of ALP as an enzyme label in enzyme-linked immunosorbent assay (ELISA), an ALP-based fluorescent immunoassay was further developed for the detection of mouse immunoglobulin G (mIgG). The developed immunoassay displays a linear fluorescent response towards mIgG from 0.8 to 100 ng/mL, and the detection limit is 0.16 ng/mL. The fluorescent immunoassay was successfully applied to the determination of mIgG in serum samples. Schematic of the responsivity of ThT@GMP/Eu to ALP that hydrolyzes GMP to release ThT, which leads to fluorescent quenching, and its application in the construction of a fluorescent immunoassay for mIgG determination.

Multiplex bioimaging of proteins-related to neurodegenerative diseases in eye sections by laser ablation - Inductively coupled plasma - Mass spectrometry using metal nanoclusters as labels

Simultaneous determination of proteins with micrometric resolution is a significant challenge. In this study, laser ablation (LA) inductively coupled plasma - mass spectrometry (ICP-MS) was employed to quantify the distribution of proteins associated to the eye disease age-related macular degeneration (AMD) using antibodies labelled with three different metal nanoclusters (MNCs). PtNCs, AuNCs and AgNCs contain hundreds of metal atoms and were used to detect metallothionein 1/2 (MT1/2), complement factor H (CFH) and amyloid precursor protein (APP) in retina, ciliary body, retinal pigment epithelium (RPE), choroid and sclera from human cadaveric eye sections. First, the labelling of MNCs bioconjugated primary antibodies (Ab) was optimised following an immunolabelling protocol to avoid the non-specific interaction of MNCs with the tissue. Then, the LA and ICP-MS conditions were studied to obtain high-resolution images for the simultaneous detection of the three labels at the same tissue section. A significant signal amplification was found when using AuNCs, AgNCs and PtNCs labelled Ab of 310, 723 and 1194 respectively. After the characterisation of MNCs labelled immunoprobes, the Ab labelling was used for determination of MT1/2, CFH and APP in the RPE-choroid-sclera, where accumulation of extracellular deposits related to AMD was observed. Experimental results suggest that this method is fully suitable for the simultaneous detection of at least three different proteins.