The authors report a dual signal amplification strategy for improving the sensitivity of an electrochemical immunosensor. Single-walled carbon nanotubes (SCNTs) served as supports for aptamers and alkaline phosphatase (ALP), and then the modified SCNTs were utilized as electrochemical probes. The aptamer contains phosphate groups, while ALP can hydrolyse one molecular pyrophosphate into two molecular phosphate ions. The phosphate can react with molybdate to form a redox-active molybdophosphate precipitate on the surface of the glassy carbon electrode (GCE). With applying a relatively low voltage of 0.21 V (vs. Ag/AgCl), the generated electrochemical current intensity is proportional to the concentration of the analyte. The cancer biomarker platelet-derived growth factor BB (PDGF-BB) was chosen as a model antigen (analyte). The immunosensor was prepared by sequential capturing of the antibodies against PDGF-BB, analyte (PDGF-BB) and modified SCNTs on the GCE to form a sandwich structure. The current signal is linear in the concentration range of 0.1 pg mL⁻¹ to 50 ng mL⁻¹ PDGF-BB, with a detection limit as low as 50 fg mL⁻¹. The immunosensor was finally applied in the determination of PDGF-BB concentration in serum samples. Our perception is that this signal amplification strategy can be adapted to the preparation of other immunosensors and will find wide applications in the detection of different biomarkers and related species.

中文翻译：

---

电化学检测血小板源性生长因子BB的双信号放大策略

作者报告了双重信号放大策略，用于提高电化学免疫传感器的灵敏度。单壁碳纳米管（SCNTs）用作适体和碱性磷酸酶（ALP）的载体，然后将修饰的SCNTs用作电化学探针。适体包含磷酸基团，而ALP可以将一个分子的焦磷酸酯水解为两个分子的磷酸根离子。磷酸盐可以与钼酸盐反应，在玻璃碳电极（GCE）的表面上形成具有氧化还原活性的钼磷酸盐沉淀。施加相对较低的0.21 V电压（vs.（Ag / AgCl），产生的电化学电流强度与分析物的浓度成正比。选择癌症生物标记物血小板衍生的生长因子BB（PDGF-BB）作为模型抗原（分析物）。通过在GCE上依次捕获针对PDGF-BB，分析物（PDGF-BB）和修饰的SCNT的抗体以形成夹心结构来制备免疫传感器。电流信号在0.1 pg mL ^-1至50 ng mL ^-1 PDGF-BB的浓度范围内呈线性，检测限低至50 fg mL ^-1。最终将免疫传感器用于测定血清样品中PDGF-BB的浓度。我们的看法是，这种信号放大策略可以适应于其他免疫传感器的制备，并将在检测不同的生物标志物和相关物种中找到广泛的应用。