Department of Physics, Arizona State University, Tempe, AZ 85287, USA.
Nanotechnology. 2012 Jun 15;23(23):235101. doi: 10.1088/0957-4484/23/23/235101.
4(5)-(2-mercaptoethyl)-1H-imidazole-2-carboxamide is a molecule that has multiple hydrogen bonding sites and a short flexible linker. When tethered to a pair of electrodes, it traps target molecules in a tunnel junction. Surprisingly large recognition-tunneling signals are generated for all naturally occurring DNA bases A, C, G, T and 5-methyl-cytosine. Tunnel current spikes are stochastic and broadly distributed, but characteristic enough so that individual bases can be identified as a tunneling probe is scanned over DNA oligomers. Each base yields a recognizable burst of signal, the duration of which is controlled entirely by the probe speed, down to speeds of 1 nm s -1, implying a maximum off-rate of 3 s -1 for the recognition complex. The same measurements yield a lower bound on the on-rate of 1 M -1 s -1. Despite the stochastic nature of the signals, an optimized multiparameter fit allows base calling from a single signal peak with an accuracy that can exceed 80% when a single type of nucleotide is present in the junction, meaning that recognition-tunneling is capable of true single-molecule analysis. The accuracy increases to 95% when multiple spikes in a signal cluster are analyzed.
4(5)-(2-巯基乙基)-1H-咪唑-2-甲酰胺是一种具有多个氢键结合位点和短柔性连接体的分子。当它连接到一对电极上时，它会将靶分子捕获在隧道结中。令人惊讶的是，对于所有天然存在的 DNA 碱基 A、C、G、T 和 5-甲基胞嘧啶，都会产生非常大的识别-隧道信号。隧道电流尖峰是随机分布的，但具有足够的特征，以至于可以在 DNA 寡核苷酸上扫描隧道探针时识别出单个碱基。每个碱基都会产生可识别的信号爆发，其持续时间完全由探针速度控制，低至 1nm s-1，这意味着识别复合物的最大离解速率为 3 s-1。同样的测量结果给出了结合速率的下限，为 1M-1 s-1。尽管信号具有随机性，但优化的多参数拟合允许从单个信号峰进行碱基调用，当结中只有一种类型的核苷酸时，准确率可以超过 80%，这意味着识别-隧道能够进行真正的单分子分析。当对信号簇中的多个尖峰进行分析时，准确率提高到 95%。
