An enzyme-free electrochemical sandwich DNA assay based on the use of hybridization chain reaction and gold nanoparticles: application to the determination of the DNA of Helicobacter pylori

An ultrasensitive enzyme-free electrochemical sandwich DNA biosensor is described for the detection of ssDNA oligonucleotides. A DNA sequence derived from the genom of Helicobacter pylori was selected as a model target DNA. The DNA assay was realized through catching target DNA on capture DNA immobilized gold electrode; then labeling the target DNA with reporter DNA (rpDNA) and initiator DNA (iDNA) co-modified gold nanoparticles (AuNPs). The high density of iDNAs serves as one of the amplification strategies. The iDNA triggers hybridization chain reaction (HCR) between two hairpins. This leads to the formation of a long dsDNA concatamer strand and represents one amplification strategy. The electrochemical probe [Ru(NH₃)₅L]²⁺, where L stands for 3-(2-phenanthren-9-ylvinyl)pyridine, intercalated into dsDNA chain. Multiple probe molecules intercalate into one dsDNA chain, serving as one amplification strategy. The electrode was subjected to differential pulse voltammetry for signal acquisition, and the oxidation peak current at -0.28 V was recorded. On each AuNP, 240 iDNA and 25 rpDNA molecules were immobilized. Successful execution of HCR at the DNA-modified AuNPs was confirmed by gel electrophoresis and hydrodynamic diameter measurements. Introduction of HCR significantly enhances the DNA detection signal intensity. The assay has two linear ranges of different slopes, one from 0.01 fM to 0.5 fM; and one from 1 fM to 100 fM. The detection limit is as low as 0.68 aM. Single mismatch DNA can be differentiated from the fully complementary DNA. Conceivably, this highly sensitive and selective assay provides a general method for detection of various kinds of DNA. Graphical abstractSchematic representation of the detection and the amplification principles of the electrochemical sandwich DNA assay. Purple curl: Captured DNA; Green curl: Reporter DNA; Orange curl: HCR initiator DNA; Yellow solid-circle: Gold nanoparticle; H1 and H2: Two hairpin DNA; [Ru(NH₃)₅L]²⁺: Signal probe.

Microglia M1/M2 polarization contributes to electromagnetic pulse-induced brain injury

The development of electronic technology has attracted attention on the biological effects of electromagnetic fields (EMFs) and electromagnetic pulse (EMP). It remains controversial whether EMP irradiation is neurotoxic or beneficial for recovery from injuryies such as cerebral ischemia. Microglia is innate immune cells in the brain, exhibiting either neurotoxicity or neuroprotection effect during various central nervous system diseases, depending on their activation into a classical (M1) or alternative (M2) phenotype, respectively. The Toll-like receptor-4 (TLR4), myeloid differentiation factor 88 (MyD88) and nuclear factor kappa B (NFκB) pathway is important for microglia activation. In this study, we investigated the effect of EMP on neuronal apoptosis and microglia polarization in vivo and in vitro, using an EMP of 400 kV/m and 1 hertz for 200 pulses. Short EMP irradiation (≤24 h) resulted in microglial conversion from the resting to the M1-type state, activation of the TLR4/MyD88/NFκB pathway, higher levels of inflammatory cytokines including interleukin (IL)-6, IL-1β and tumor necrosis factor-α, as well as neuronal apoptosis induction. In contrast, long EMP irradiation (3 days) resulted in microglial activation into the M2-type, decreased apoptosis and inflammatory mediator production, and increased levels of the neuroprotective effectors IL-10, transforming growth factor beta, and brain-derived neurotrophic factor. EMP induces both neuronal damage and neuronal recovery by influencing the switch of M1/M2 polarization and the TLR4/MyD88/NFκB pathway.