Liquid biopsy assays for tumour biomarkers circulating in blood are perspective non-invasive tools for cancer diagnosis and treatment monitoring. Here, we suggest a simple, 1 h long electrochemical DNAzyme-linked aptamer- and immuno-sandwich magnetic assay for analysis of serum HER-2/neu protein overexpressed in several aggressive cancers. In the assay, we used a covalent hemin-guanine quadruplex (G4) complex as a novel O₂-dependent electrocatalytic label that allowed 10 fM (aptamer-aptamer) and 1 fM (aptamer-antibody) detection of HER-2/neu in human serum. The O₂ reactivity of the aptamer-conjugated label was detected at high-surface-area graphite electrodes displaying a high efficiency of O₂ reduction electro-catalyzed by this DNAzyme. In contrast to the recognised H₂O₂ reactivity, the O₂ reactivity of the covalent hemin/G4 complex depended only on ambient O₂ present in solutions, and did not require adding such traditional reagents as hemin and H₂O₂, and solution de-aeration. Human serum albumin, urokinase plasminogen activator and thrombin did not interfere, and the assay was used for analysis of basal serum levels of HER-2/neu. Due to the simplicity and low cost, sandwich assays exploiting O₂-linked electrocatalysis by the covalent hemin-G4 complexes represent a more advanced electrochemical ELISA platform for ultrasensitive and fast detection of low concentrations of proteins in complex biological matrices.

血液中循环肿瘤生物标志物的液体活检分析是癌症诊断和治疗监测的前瞻性非侵入性工具。在这里，我们建议使用一种简单的、1 小时长的电化学脱氧核糖核酸酶连接适体和免疫夹心磁试验来分析在几种侵袭性癌症中过表达的血清 HER-2/ neu蛋白。在该测定中，我们使用共价血红素-鸟嘌呤四链体 (G4) 复合物作为新型 O ₂依赖性电催化标记，允许 10 fM（适体-适体）和 1 fM（适体-抗体）检测 HER-2 / neu人血清。在高表面积石墨电极上检测到适体共轭标记的 O _{2反应性，显示出高效率的 O 2}由这种脱氧核糖核酸酶电催化的还原。与公认的 H ₂ O ₂反应性相反，共价 hemin/G4 复合物的 O ₂反应性仅取决于溶液中存在的环境 O ₂，​​并且不需要添加诸如 hemin 和 H ₂ O ₂等传统试剂和溶液脱气。人血清白蛋白、尿激酶纤溶酶原激活剂和凝血酶没有干扰，该测定法用于分析基础血清HER-2/ neu水平。由于简单和低成本，夹心测定利用 O ₂共价血红素-G4复合物的-连接电催化代表了更先进的电化学ELISA平台，用于超灵敏和快速检测复杂生物基质中的低浓度蛋白质。