Cucurbit[7]urils induced bimetallic nanoparticles network for ultra-sensitive detection of Caspase-3 based on surface plasmon resonance

A cucurbit[7]uril-mediated crosslinking-amplified microchannel resistance immunoassay via magnetic interception for point of care testing of insulin

Insulin is the only hormone that lowers blood glucose levels, the abnormal insulin secretion leads to various diseases such as diabetes. Herein, we present a cucurbit[7]uril (CB[7])-mediated crosslinking-amplified microchannel resistance immunoassay (MCRI) via magnetic interception for point of care (POC) testing of insulin in human serum samples. In the developed MCRI, the CB[7] coated gold magnetic nanoparticles (AuMNP@CB[7]) are used for extracting insulin from complex samples by host-guest interaction. The formed AuMNP@CB[7]-insulin plays a role of crosslinker to induce the aggregation of the antibody modified polystyrene microspheres (PS-Ab) through immune recognition. The aggregates are then trapped in a microchannel via magnetic interception, resulting in a decrease in the current intensity, which is quantitatively correlated with the insulin level. Benefiting from the CB[7]-mediated extraction, enrichment, and crosslinking amplification, a satisfactory analytical performance is obtained and the limit of detection (LOD) is as low as 0.35 pg/mL. Thus, the MCRI is appropriate for sensitive detection of insulin and can be extended to POC application by integrating the CB[7]-mediated amplification with the simple MCRI device.

Signal-On Detection of Caspase-3 with Methylene Blue-Loaded Metal-Organic Frameworks as Signal Reporters

In this work, we report on an electrochemical method for the signal-on detection of caspase-3 and the evaluation of apoptosis based on the biotinylation reaction and the signal amplification of methylene blue (MB)-loaded metal-organic frameworks (MOFs). Zr-based UiO-66-NH2 MOFs were used as the nanocarriers to load electroactive MB molecules. Recombinant hexahistidine (His6)-tagged streptavidin (rSA) was attached to the MOFs through the coordination interaction between the His6 tag in rSA and the metal ions on the surface of the MOFs. The acetylated peptide substrate Ac-GDEVDGGGPPPPC was immobilized on the gold electrode. In the presence of caspase-3, the peptide was specifically cleaved, leading to the release of the Ac-GDEVD sequence. A N-terminal amine group was generated and then biotinylated in the presence of biotin-NHS. Based on the strong interaction between rSA and biotin, rSA@MOF@MB was captured by the biotinylated peptide-modified electrode, producing a significantly amplified electrochemical signal. Caspase-3 was sensitively determined with a linear range from 0.1 to 25 pg/mL and a limit of detection down to 0.04 pg/mL. Further, the active caspase-3 in apoptosis inducer-treated HeLa cells was further quantified by this method. The proposed signal-on biosensor is compatible with the complex biological samples and shows great potential for apoptosis-related diagnosis and the screening of caspase-targeting drugs.

Emerging sensing platforms based on Cucurbit[n]uril functionalized gold nanoparticles and electrodes

Cucurbit[n]urils (CB[n]s, n = 5-8, 10, and 14), synthetic macrocycles with unique host-guest properties, have triggered increasing research interest in recent years. Gold nanoparticles (Au NPs) and electrodes stand out as exceptional substrates for sensing due to their remarkable physicochemical characteristics. Coupling the CB[n]s with Au NPs and electrodes has enabled the development of emerging sensing platforms for various promising applications. However, monitoring the behavior of analytes at the single-molecule level is currently one of the most challenging topics in the field of CB[n]-based sensing. Constructing supramolecular junctions in a sensing platform provides an ideal structure for single-molecule analysis, which can provide insights for a fundamental understanding of supramolecular interactions and chemical reactions and guide the design of sensing applications. This feature article outlines the progress in the preparation of the CB[n] functionalized Au NPs and Au electrodes, as well as the construction and application of supramolecular junctions in sensing platforms, based on the methods of recognition tunneling (RT), surface-enhanced Raman spectroscopy (SERS), single-molecule force spectroscopy (SMFS), and electrochemical sensing (ECS). A brief perspective on the future development of and challenges in CB[n] mediated sensing platforms is also covered.