We report a label-free universal biosensing platform for highly selective detection of long nucleic acid strands. The sensor consists of an electrode-immobilized universal stem-loop (USL) probe and two adaptor strands that form a 4J structure in the presence of a specific DNA/RNA analyte. The sensor was characterized by electrochemical impedance spectroscopy (EIS) using K₃[Fe(CN)₆]/K₄[Fe(CN)₆] redox couple in solution. An increase in charge transfer resistance (R_CT) was observed upon 4J structure formation, the value of which depends on the analyte length. Cyclic voltammetry (CV) was used to further characterize the sensor and monitor the electrochemical reaction in conjunction with thickness measurements of the mixed DNA monolayer obtained using spectroscopic ellipsometry. In addition, the electron transfer was calculated at the electrode/electrolyte interface using a rotating disk electrode. Limits of detection in the femtomolar range were achieved for nucleic acid targets of different lengths (22 nt, 60 nt, 200 nt). The sensor produced only a background signal in the presence of single base mismatched analytes, even in hundred times excess in concentration. This label-free and highly selective biosensing platform is versatile and can be used for universal detection of nucleic acids of varied lengths which could revolutionize point of care diagnostics for applications such as bacterial or cancer screening.

我们报告了无标签的通用生物传感平台，可高度选择性地检测长核酸链。该传感器由固定有电极的通用茎环（USL）探针和两条衔接子链组成，在存在特定DNA / RNA分析物的情况下，两条衔接子链形成4J结构。使用溶液中的K ₃ [Fe（CN）₆ ] / K ₄ [Fe（CN）₆ ]氧化还原对通过电化学阻抗谱（EIS）对传感器进行表征。电荷转移电阻（R _CT）是在4J结构形成时观察到的，其值取决于分析物的长度。循环伏安法（CV）用于进一步表征传感器并监测电化学反应，并结合使用光谱椭圆偏光法获得的混合DNA单层的厚度测量结果。另外，使用转盘电极在电极/电解质界面处计算电子转移。对于不同长度的核酸靶标（22 nt，60 nt，200 nt），达到了飞摩尔范围内的检测限。在存在单个碱基不匹配的分析物的情况下，传感器甚至仅产生背景信号，即使浓度超出数百倍。