Xuan Zhao,Dandan Qi,Kaixuan Yang,Chen Chen,Lei Xu,Yaoyao Ying,Tianjiao Li,Dong Liu
This work focused on effects of n- butanol addition on sooting transition process in iso -octane counterflow diffusion flames using optical and chemical diagnostics. Three iso -octane flames were studied with pure iso -octane, a 20% n- butanol addition mixture and a 40% n- butanol addition mixture as fuels. Optical diagnostics was carried out to determine effects of n -butanol addition on the sooting transition process using a high-resolution digital camera based on image processing and transition point extraction methods. Online gas chromatograph was used to investigate the flame chemistry in the sooting transition process. The results showed that the sooting transition point was delayed with the increase of n -butanol addition, which indicated that the addition of n -butanol could suppress the soot formation. To reveal the mechanism for effects of n -butanol on sooting transition process, kinetic simulations were further performed. The experimental results of flame chemistry were compared with the predictions from two mechanisms for iso -octane and n -butanol mixture. Both mechanisms were found to be capable of well capturing the main variations of most species in flames. After n -butanol addition, the changes of fuel-specific primary decomposition products were more obvious. It was noted that the decreased concentration of carbon which was available for benzene formation was the main reason for the delay of sooting transition point with n -butanol additions. Moreover, the inhibition of PAHs growth from n -butanol addition also could contribute to this kind of delayed effects.
A label-free fluorescence method based on self-assembled DNA nanopompom has been developed for miRNA-21 detection. In the presence of miRNA-21, three DNA hairpin probes with split G-quadruplex assemble the DNA nanopompom. Based on the isothermal toehold-mediated DNA strand displacement reaction, the target miRNA can be catalytically recycled and trigger three DNA hairpin probes to self-assemble the DNA nanopompom and release the G-quadruplex. The formation of the G-quadruplex increases the fluorescence emission intensity of thioflavin. For thioflavin-based miRNA-21 detection, the excitation and emission wavelengths are set to 425 nm and 490 nm, respectively. The limit of detection for miRNA-21 is 0.8 pM according to F / F 0 = 0.0031 × C miRNA-21 + 1.0382 ( R 2 = 0.9978). This sensing system provides a low-cost, effective, and convenient method for miRNA detection, which holds great potential in biochemical diagnosis and clinical practice.
Label-free and self-assembled fluorescent DNA nanopompom for miRNA detection
Herein, we describe a micro-nuclear magnetic resonance (μNMR) relaxometer miniaturized to palm-size and electronically automated for multi-step and multi-sample chemical/biological diagnosis. The co-integration of microfluidic and microelectronic technologies enables an association between the droplet managements and μNMR assays inside a portable sub-Tesla magnet (1.2 kg, 0.46 Tesla). Targets in unprocessed biological samples, captured by specific probe-decorated magnetic nanoparticles (NPs), can be sequentially quantified by their spin–spin relaxation time (T2) via multiplexed μNMR screening. Distinct droplet samples are operated by a digital microfluidic device that electronically manages the electrowetting-on-dielectric effects over an electrode array. Each electrode (3.5 × 3.5 mm2) is scanned with capacitive sensing to locate the distinct droplet samples in real time. A cross-domain-optimized butterfly-coil-input semiconductor transceiver transduces between magnetic and electrical signals to/from a sub-10 μL droplet sample for high-sensitivity μNMR screening. A temperature logger senses the ambient temperature (0 to 40 °C) and a backend processor calibrates the working frequency for the transmitter to precisely excite the protons. In our experiments, the μNMR relaxometer quantifies avidin using biotinylated Iron NPs (Φ: 30 nm, [Fe]: 0.5 mM) with a sensitivity of 0.2 μM. Auto-handling and identification of two targets (avidin and water) are demonstrated and completed within 2.2 min. This μNMR relaxometer holds promise for combinatorial chemical/biological diagnostic protocols using closed-loop electronic automation.
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