In this study, we fabricated a high-sensitivity “signal-off” electrochemical aptasensing platform for quantifying circulating tumor cells (CTCs) based on target-triggered signal readout of methylene blue (MB). Au nanoparticles (AuNPs) were introduced to enlarge the specific surface area of the gold electrode (GE), which would immobilize homogeneous and more MB-aptamers. MB-modified and stem-loop-like aptamers were assigned as a recognition element with K562 cells. Thiolated complementary strands hybridized with MB-aptamers to form double-stranded DNA (dsDNA) conformation which were further self-assembled on the surface of AuNP-modified GE, leading to a marked current peak of MB signal. In the presence of K562 cells, the MB-aptamers preferred to recognize and bind with the cells, causing the disassembly of MB-aptamers from the GE surface. Therefore, the reduced value of MB signal was related to the number of K562 cells. With the proposed aptasensor, a dynamic linear range from 1 × 10² to 1 × 10⁶ cells mL⁻¹ was obtained with a detection limit of 23 cells mL⁻¹. Moreover, the aptasensor showed good selectivity, stability, and reproducibility as well as potential use in the clinical setting. Meanwhile, characterization techniques such as field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were performed to analyze the evolution of the morphology and each fabricated step of the constructed aptasensor. Our proposed aptasensor could be designed as a universal platform for CTC determination by replacing tumor cell–specific aptamers, which is a promising strategy for basic research and clinical applications.

在这项研究中，我们基于亚甲基蓝（MB）的目标触发信号读数，制造了一个高灵敏度的“信号关闭”电化学适体平台，用于量化循环肿瘤细胞（CTC）。引入金纳米粒子（AuNPs）以扩大金电极（GE）的比表面积，这将固定均匀且更多的MB适体。MB修饰和茎环样适体被分配为K562细胞的识别元件。巯基化的互补链与MB适体杂交形成双链DNA（dsDNA）构象，进一步在AuNP修饰的GE表面自组装，导致MB信号出现明显的电流峰。在存在K562细胞的情况下，MB-适体优选识别并与细胞结合，从而导致MB-适体从GE表面拆卸。因此，MB信号的降低与K562细胞数量有关。使用建议的适体传感器，动态线性范围为1×10^获得2至1×10 ^6个 细胞mL ^-1，检测限为23个细胞mL ^-1。此外，适体传感器显示出良好的选择性，稳定性和可重复性，以及在临床环境中的潜在用途。同时，进行了表征技术，例如场发射扫描电子显微镜，能量色散X射线光谱，原子力显微镜，循环伏安法和电化学阻抗谱，以分析所构造的适体传感器的形态演变和每个制造步骤。通过替代肿瘤细胞特异性的适体，我们提出的适体传感器可以设计为CTC测定的通用平台，这对基础研究和临床应用是一种有前途的策略。