Photoelectrochemical immunoassay of lipoprotein-associated phospholipase A2 via plasmon-enhanced energy transfer between gold nanoparticles and CdS QDs/g-C3N4

A miniprotein receptor electrochemical biosensor chip based on quantum dots

Recently protein binders have emerged as a promising substitute for antibodies due to their high specificity and low cost. Herein, we demonstrate an electrochemical biosensor chip through the electronic labelling strategy using lead sulfide (PbS) colloidal quantum dots (CQDs) and the unnatural SARS-CoV-2 spike miniprotein receptor LCB. The unnatural receptor can be utilized as a molecular probe for the construction of CQD-based electrochemical biosensor chips, through which the specific binding of LCB and the spike protein is transduced to sensor electrical signals. The biosensor exhibits a good linear response in the concentration range of 10 pg mL-1 to 1 μg mL-1 (13.94 fM to 1.394 nM) with the limit of detection (LOD) being 3.31 pg mL-1 (4.607 fM for the three-electrode system) and 9.58 fg mL-1 (0.013 fM for the HEMT device). Due to the high sensitivity of the electrochemical biosensor, it was also used to study the binding kinetics between the unnatural receptor LCB and spike protein, which has achieved comparable results as those obtained with commercial equipment. To the best of our knowledge, this is the first example of using a computationally designed miniprotein receptor based on electrochemical methods, and it is the first kinetic assay performed with an electrochemical assay alone. The miniprotein receptor electrochemical biosensor based on QDs is desirable for fabricating high-throughput, large-area, wafer-scale biochips.

Novel Electrochemiluminescent Immunosensor Using Dual Amplified Signals from a CoFe Prussian Blue Analogue and Au Nanoparticle for the Detection of Lp-PLA2

Coronary heart disease (CHD) poses an important threat to human health, and its pathogenesis is the formation of atheromatous plaques in coronary ventricles. Compared to other biomarkers, lipoprotein-associated phospholipase A2 (Lp-PLA2), which is involved in multiple processes of atherosclerosis, is a noticeable inflammatory biomarker related to CHD. Herein, using a multifunctional nanocomposite containing a CoFe Prussian blue analogue (PBA) and Au nanoparticles (AuNPs) (AuNPs@CoFe PBA) as a sensing substrate, an electrochemiluminescent (ECL) immunosensor was developed for the highly sensitive detection of Lp-PLA2. Benefiting from the synergistic effect of the PBA and AuNPs, the nanocomposite exhibits excellent peroxidase-like activity and can catalyze the luminol-ECL reaction, amplifying the ECL signal by ∼29-fold. Meanwhile, the enlarged specific surface area of the nanocomposite and the presence of abundant AuNPs allow the immobilization of more antibody proteins, thereby improving the sensing response of the immunosensor. When the target Lp-PLA2 is captured by the antibody on the sensor surface, the sensor emits a reduced ECL signal because of the increased mass and electron transfer resistance due to the formation of the immune complex. Under optimized conditions, the constructed ECL immunosensor exhibits a broad linear range from 1 to 2200 ng/mL and a low detection limit of 0.21 ng/mL. Additionally, the ECL immunosensor exhibits high specificity, stability, and reproducibility. This work provides a new approach to diagnose CHD and broadened the application of the PBA in the field of ECL sensors.

DNAzyme concatemer-catalyzed precipitation on an interdigitated micro-comb electrode for capacitance immunosensing of interleukin-6 with rolling circle amplification

A novel capacitance immunosensor based on DNAzyme concatemer-amplified signal-generation tags was developed for the sensitive detection of interleukin-6 (IL-6) on an interdigitated micro-comb electrode.

Au-coated Fe3O4 core-shell nanohybrids with photothermal activity for point-of-care immunoassay for lipoprotein-associated phospholipase A2 on a digital near-infrared thermometer

A portable photothermal immunoassay based on Au-coated magnetic Fe₃O₄ core-shell nanohybrids (Au-Fe₃O₄) was developed for point-of-care (POC) testing of lipoprotein-associated phospholipase A₂ (Lp-PLA₂) on a digital near-infrared (NIR) thermometer. Au-Fe₃O₄ photothermal materials were first synthesized through reverse micelle method, and then functionalized with polyclonal rabbit anti-human Lp-PLA₂ antibody. A sandwiched immunoreaction was carried out in polyclonal mouse anti-human Lp-PLA₂ antibody-coated microplate using Au-Fe₃O₄-labeled antibody as the detection antibody. With formation of sandwich-type immunocomplex, the captured Au-Fe₃O₄ on the plate converted the light into heat under an 808-nm laser irradiation (1.5 W cm^-2), thereby resulting in the increasing temperature of the detection solution. The temperature variations relative to surrounding temperature was determined on a portable NIR thermometer. Several labeling protocols with gold nanoparticle, Fe₃O₄ nanoparticle, or Au-Fe₃O₄ nanohybrids were investigated for determination of Lp-PLA₂ and improved analytical features were achieved with the core-shell Au-Fe₃O₄ nanohybrids. Under optimum conditions, Au-Fe₃O₄-based immunoassay exhibited good photothermal responses for the detection of Lp-PLA₂ with a dynamic linear range of 0.01-100 ng mL^-1 at a low detection limit of 8.6 pg mL^-1. Good reproducibility and intermediate precision were less than 9.7%. Other biomarkers or proteins did not interfere with responses of this system. An acceptable accuracy was acquired for analysis of human serum sample between Au-Fe₃O₄-based photothermal immunoassay and commercialized human Lp-PLA₂ ELISA kit.