A rapid and simple method for ultrasensitive electrochemical immunoassay of protein by an electric field-driven strategy

An impedimetric bioaffinity sensing chip integrated with the long-range DC-biased AC electrokinetic centripetal vortex produced in a high conductivity solution

Immunoreaction of specific antibodies to antigens is widely used in numerous immunoanalysis applications. However, diffusion-dominated transport in stationary solutions limits the rate and binding density of immunoreaction. This research describes the construction of chip-type concentric multi-double ring electrodes and single central disk electrode. A +1 V-biased 6 V_pp voltage was applied to the multi-double ring electrodes to induce a long-range DC-biased AC electrokinetic flow (ACEKF). The immunoreaction was quantified by electrochemical impedance spectrum (EIS). Fluorescence-labeled secondary antibody (FLSA) and protein A were exemplified as an immunoreacting model to demonstrate the effect of ACEKF on immunoreaction efficiency. The results showed that FLSA binding can reach a plateau in 8 min with the DC-biased ACEKF vortex, and the increment of electron transfer resistance is 2.26 times larger than that obtained in the unstirred solution. The sensitivity of the calibration curves obtained by EIS detection with the aid of DC-biased ACEKF vortex is 1.51 times larger than that obtained in an unstirred solution. The label-free EIS-based sensing chip integrated with the long-range DC-biased ACEKF vortex promises to facilitate immunoreaction efficiency, which is beneficial for the development of a miniature and fast-detection in vitro diagnostic device.

Electrochemical Immunoassay Using Open Circuit Potential Detection Labeled by Platinum Nanoparticles

In this work, a simple electrochemical immunoassay based on platinum nanoparticles (PtNPs) using open circuit potential (OCP) detection was developed. The detection of human chorionic gonadotropin hormone (hCG) as a model analyte, was demonstrated by direct electrical detection of PtNPs in hydrazine solution using OCP measurement without any application of either potential or current to the system. Disposable screen-printed carbon electrodes (SPCEs) were utilized for the development of our immunosensor, which required a sample volume as small as 2 μL. After preparation of a sandwich-type immunosystem, hydrazine solution was dropped on the electrode's surface, which was followed immediately by electrical detection using OCP. The change of the OCP signal originated from electrocatalytic oxidation of the hydrazine on PtNPs. Under the optimal conditions of a pH of 6.0 and a hydrazine concentration of 1 mM, a detection limit of 0.28 ng mL^-1 and a linearity of 0-10 ng mL^-1 were obtained. The PtNP-based OCP method is a simpler electrochemical detection procedure than those obtained from other electrochemical methods and has an acceptable sensitivity and reproducibility. The simplicity of the detection procedure and the cost-effectiveness of the disposable SPCE illustrate the attractive benefits of this sensor. Moreover, it could be applied to a simplified and miniaturized diagnostic system with minimal user manipulation.

Microfluidic chips for point-of-care immunodiagnostics

We might be at the turning point where research in microfluidics undertaken in academia and industrial research laboratories, and substantially sponsored by public grants, may provide a range of portable and networked diagnostic devices. In this Progress Report, an overview on microfluidic devices that may become the next generation of point-of-care (POC) diagnostics is provided. First, we describe gaps and opportunities in medical diagnostics and how microfluidics can address these gaps using the example of immunodiagnostics. Next, we conceptualize how different technologies are converging into working microfluidic POC diagnostics devices. Technologies are explained from the perspective of sample interaction with components of a device. Specifically, we detail materials, surface treatment, sample processing, microfluidic elements (such as valves, pumps, and mixers), receptors, and analytes in the light of various biosensing concepts. Finally, we discuss the integration of components into accurate and reliable devices.