A label-free electrochemical miRNA biosensor was developed based on a pyrrolidinyl peptide nucleic acid (acpcPNA)/polypyrrole (PPy)/silver nanofoam (AgNF) modified electrode. The AgNF was electrodeposited as redox indicator on a gold electrode, which was then functionalized with an electropolymerized layer of PPy, a conducting polymer, to immobilize the PNA probes. The fabrication process was investigated by electrochemical impedance spectroscopy. The biosensor was used to detect miRNA-21, a biomarker abnormally expressed in most cancers. The signal was monitored by the change in current of the AgNF redox reaction before and after hybridization using cyclic voltammetry. Two PNA probe lengths were investigated and the longer probe exhibited a better performance. Nucleotide overhangs on the electrode side affected the signal more than overhangs on the solution side due to the greater insulation of the sensing surface. Under optimal conditions, the electrochemical signal was proportional to miRNA-21 concentrations between 0.20 fM and 1.0 nM, with a very low detection limit of 0.20 fM. The biosensor showed a high specificity which could discriminate between complementary, single-, doubled-base mismatched, and non-complementary targets. Three out of the seven tested plasma samples provided detectable concentrations (63 ± 4, 111 ± 4 and 164 ± 7 fM). The sensor also showed good recoveries (81–119%). The results indicated the possibilities of this biosensor for analysis without RNA extraction and/or amplification, making the sensor potentially useful for both the prognosis and diagnosis of cancer in clinical application.

基于吡咯烷基肽核酸（acpcPNA）/聚吡咯（PPy）/银纳米泡沫（AgNF）修饰电极开发了无标记的电化学miRNA生物传感器。将AgNF作为氧化还原指示剂电沉积在金电极上，然后用导电聚合物PPy的电聚合层进行功能化以固定PNA探针。通过电化学阻抗谱研究了制备过程。该生物传感器用于检测miRNA-21，miRNA-21是在大多数癌症中异常表达的生物标志物。通过使用循环伏安法在杂交之前和之后，通过AgNF氧化还原反应的电流变化来监测信号。研究了两种PNA探针的长度，较长的探针表现出更好的性能。电极侧的核苷酸突出端比溶液侧的突出端对信号的影响更大，这是由于传感表面的绝缘性更好。在最佳条件下，电化学信号与miRNA-21的浓度成正比，介于0.20 fM和1.0 nM之间，检测限非常低，仅为0.20 fM。该生物传感器显示出高特异性，可以区分互补，单碱基，双碱基错配和非互补靶标。在七个测试血浆样本中，有三个样本提供了可检测的浓度（63±4、111±4和164±7 fM）。传感器还显示出良好的回收率（81–119％）。结果表明该生物传感器无需进行RNA提取和/或扩增即可进行分析的可能性，