Abstract
The development of sensitive and selective assays for protein biomarkers and other biological analytes is important for advancing the fields of clinical diagnostics and bioanalytical chemistry. The potential advantages of using aptamers in electrochemical sandwich assays are being increasingly recognized. These assays may include an aptamer as both capture and detection agent or a combination of an aptamer with a different partner such as an antibody, a lectin or a nanomaterial. The second binding partner in the sandwich structure is typically conjugated to a redox marker, a catalyst or an enzyme that can be used to generate the signal needed for electrochemical detection. Nanoparticles and other nanostructures can be used as the carriers for multiple molecules of the detection partner and thereby increase the signal. Nanostructured surfaces can be used to increase surface area and improve electron transfer. Sensitive electrochemical methods including impedance, differential and square-wave voltammetry and chronocoulometry have been used for electrochemical signal read-out. Impressive results have been achieved using electrochemical sandwich assays in terms of limit of detection and linear range for a growing range of analytes. The recent progress for this type of assay for proteins and other biomarkers is the subject of this review.
Highlights
As a strategy for increasing sensitivity and selectivity, the development of electrochemical assays using aptamers in sandwich structures has become popular
We review electrochemical assays for other analytes that use two aptamers in the sandwich, assays that combine an aptamer and an antibody, and assays that combine an aptamer with a lectin or a nanomaterial as the second partner in the structure
A number of important trends have emerged in the development of electrochemical sandwich assays using aptamers
Summary
As a strategy for increasing sensitivity and selectivity, the development of electrochemical assays using aptamers in sandwich structures has become popular. The affinities achieved for protein targets using aptamers are as high as those achieved by most antibodies, and are in the 1–100 nM range [10] In their use as capture agents on gold electrode surfaces, or for example, as reporter agents on gold nanoparticles, aptamers with thiolated ends can readily be prepared. Methods for immobilization of aptamers onto surfaces are reviewed [23] Given these advantageous properties, significant efforts have been pursued in recent years for the development of biosensors for proteins and some small molecules using aptamers and electrochemical detection strategies have been a prime focus. Aptamer-based systems for these electrochemical assays are steadily emerging and show great potential as described in this review
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