Lingling Zhang,Shuangru Yang,Yuge Liu,Yongmei Jia,Zhiguo Li
Understanding the electron transfer performance of DNA self-assembled monolayers (SAMs) on a transducer substrate was important for constructing DNA electrochemical sensors with high sensitivity. Here we immersed the gold electrodes in mixed solutions comprising thiol-modified stem-loop DNA (SL-DNA) or linear DNA (L-DNA) terminally bound with methylene blue (MB), and aliphatic thiols (HOC6SH, C6SH, HOOCC5SH, H2NC6SH, HOC11SH, C12SH, or HOOCC10SH) to obtain DNA/thiols mixed self-assembled monolayers (SAMs). MB electron transfer performances through SL-DNA/thiols and L-DNA/thiols mixed SAMs were investigated by cyclic voltammetry (CV). Our results showed that the mixed assembly of thiols with DNA was conducive to MB electron transfer. The electron transfer rate (ks) values of MB through L-DNA SAMs were bigger than those through SL-DNA SAMs, indicating that the flexibility of DNA chains was important to MB electron transfer. Thiols chain length or terminal groups influenced ks of MB significantly, that increasing NaCl or MgCl2 concentrations in solution around DNA availed MB electron transfer, and Mg2+ advanced MB electron transfer more than Na+, and that the stability of L-DNA/thiols SAMs was much better than SL-DNA/thiols SAMs. These conclusions might provide a reference for studying DNA electron transfer mechanisms or designing DNA or RNA electrochemical sensors with optimal performance.
Fan Yang,JinBo Gong,Ming Li,Xiangyang Jiang,Jiawen Zhang,Meiyan Liao,Hanfei Zhang,Pier-Luc Tremblay,Tian Zhang
PCR-based techniques routinely employed for the detection of mutated linear DNA molecules, including circulating tumor DNA (ctDNA), require large nucleotide sections on both sides of the mutation for primer annealing. This means that DNA fragments with a mutation positioned closer to the extremities are unlikely to be detected. Thus, sensors capable of recognizing linear DNA with characteristic mutations closer to the ends would be advantageous over the state-of-the-art approaches. Here, an electrochemiluminescence-resonance energy transfer (ECL-RET) biosensor comprising capped CdS quantum dots and hairpin DNA probes labeled with Au nanoparticles was developed for the detection of epidermal growth factor receptor (EGFR) ctDNA carrying the critical T790M lung cancer mutation. The ECL-RET system detected different DNA molecules including single-stranded 18-nucleotides (nt) and 40-nt as well as double-stranded 100-nt with the single nucleotide polymorphism (SNP) coding for T790M located either in the middle or only 7 nt from one end. For all target DNA, the sensor’s limits of detection (LODs) were in the aM range, with excellent selectivity. It was the case of 100-nt target linear ctDNA fragments with LODs of 8.1 and 3.4 aM when the EGFR T790M SNP was either in the middle or at the end, respectively. These results show that ECL-RET systems can sense mutations in DNA fragments that would remain undetected by standard techniques.
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