DNA-Redox Cation Interaction Improves the Sensitivity of an Electrochemical Immunosensor for Protein Detection

A simple DNA-redox cation interaction enhancement strategy has been developed to improve the sensitivity of electrochemical immunosensors for protein detection. Instead of labeling with fluorophores or redox-active groups, the detection antibodies were tethered with DNA single strands. Based on the electrostatic interaction between redox cations ([Ru(NH3)6]3+) and negatively charged DNA backbone, enhanced electrochemical signals were obtained. Human chorionic gonadotropin (hCG) detection has been performed as a trial analysis. A linear response range up to the concentration of 25 mIU/mL and a detection limit of 1.25 mIU/mL have been achieved, both are comparable with the ultrasensitive enzyme-linked immunosorbent assay (ELISA) tests. The method also shows great selectivity towards hCG over other hormones such as thyroid stimulating hormone (TSH) and follicle stimulating hormone (FSH). By and large, our approach bears the merits of cost effectiveness and simplicity of instrumentation in comparison with conventional optical detection methods

Adenosine-Triggered Elimination of Methylene Blue Noncovalently Bound to Immobilized Functional dsDNA-Aptamer Constructs

Immobilization and electrochemical characterization of specially designed functional DNA–aptamer constructs are of great importance for the development of versatile biosensors (not limited to gene analysis) and the investigation of molecular interactions between DNA and other molecules. We have constructed a “DNA conformational switch” by incorporating the antiadenosine aptamer sequence in the middle of an otherwise cDNA double helix, as its structural change responds to the presence of small molecule ligands (e.g., adenosine). In particular, methylene blue (MB) was used as a model system to probe the rather complex interaction modes between small redox molecules and the dsDNA–aptamer construct. Besides intercalating with the double-stranded DNA stem, MB can stack with a single guanine base in the relatively unstructured aptamer domain or electrostatically bind to the DNA backbone. The decreased surface density of MB after adenosine binding indicated that the ligand-gated structural change of the dsDNA–aptamer construct can eliminate MB molecules that were originally bound to the aptamer domain but not those in the complementary stem

Blu-ray Technology-Based Quantitative Assays for Cardiac Markers: From Disc Activation to Multiplex Detection

Acute myocardial infarction (AMI) is the leading cause of mortality and morbidity globally. To reduce the number of mortalities, reliable and rapid point-of-care (POC) diagnosis of AMI is extremely critical. We herein present a Blu-ray technology-based assay platform for multiplex cardiac biomarker detection; not only off-the-shelf Blu-ray discs (BDs) were adapted as substrates to prepare standard immunoassays and DNA aptamer/antibody hybrid assays for the three key cardiac marker proteins (myoglobin, troponin I, and C-creative protein) but also an unmodified optical drive was directly employed to read the assay results digitally. In particular, we have shown that all three cardiac markers can be quantitated in their respective physiological ranges of interest, and the detection limits achieved are comparable with conventional enzyme-linked immunosorbent assay (ELISA) kits. The Blu-ray assay platform was further validated by measuring real-world samples and establishing a linear correlation with the simultaneously obtained ELISA data. Without the need to modify either the hardware (Blu-ray discs and optical drives) or the software driver, this assay-on-a-BD technique promises to be a low-cost user-friendly quantitative tool for on-site chemical analysis and POC medical diagnosis