Terminal deoxynucleotidyl transferase-induced DNAzyme nanowire sensor for colorimetric detection of lipopolysaccharides

A new colorimetric DNAzyme nanowire sensor has been developed for the sensitive and selective quantification of lipopolysaccharides (LPS). The sensor was a label-free and isotheral reaction system based on a LPS-binding aptamer and autonomously assembled DNAzyme nanowire. In the sensing system, an aptamer-initiator (AI) was designed to recognize the LPS and initiated the hybridization chain reaction (HCR) of two DNA hairpins (H1 and H2). All the H2 containing sticky ends formed terminal deoxynucleotidyl transferase (TdT) −induced G-quadruplexes. In the presence of LPS, on end of AI, and LPS-aptamer, formed the LPS/aptamer complex with the remaining LPS, the other end of AI, the initiator then started the alternate-opening of H1 and H2 through HCR. Furthermore, TdT-induced hemin/G-quadruplex DNAzymes along DNA nanowires were self-assembled after HCR process. As a result, the solution in light yellow was observed via the addition of H2O2/TMB. After optimization, the time to detect the signal was approximately 40 min, and the reaction temperature was in a broad range from 4 °C to 37 °C. The detection platform showed excellent sensitivity and selectivity for LPS from E. coli O111:B4 in a series of samples. In less than 2 h, a colorimetric response was achieved and the concentrations of LPS detected could be as low as 100 pg/mL. The semi-quantitative observation limit was 20 ng/mL with the naked eye. A drinking water sample was tested, which further demonstrated the feasibility of the proposed method applied for biological samples.