High-sensitivity miniature dual-resonance photoacoustic sensor based on silicon cantilever beam for trace gas sensing.

We report a miniature dual-resonance photoacoustic (PA) sensor, mainly consisting of a small resonant T-type PA cell and an integrated sensor probe based on a silicon cantilever beam. The resonance frequency of the miniature T-type PA cell is matched with the first-order natural frequency of the cantilever beam to achieve double resonance of the acoustic signal. The volume of the designed T-type PA cell is only about 2.26 cubic centimeters. A PA spectroscopy (PAS) system, employing the dual-resonance photoacoustic (PA) sensor as the prober and a high-speed spectrometer as the demodulator, has been implemented for high-sensitivity methane sensing. The sensitivity and the minimum detection limit can reach up to 2.0 pm/ppm and 35.6 parts-per-billion, respectively, with an averaging time of 100 s. The promising performance demonstrated a great potential of employing the reported sensor for high-sensitivity gas sensing in sub cubic centimeter-level spaces.

Ultra-High-Sensitivity, Miniaturized Fabry-Perot Interferometric Fiber-Optic Microphone for Weak Acoustic Signals Detection.

An ultra-high-sensitivity, miniaturized Fabry-Perot interferometric (FPI) fiber-optic microphone (FOM) has been developed, utilizing a silicon cantilever as an acoustic transducer. The volumes of the cavity and the FOM are determined to be 60 microliters and 102 cubic millimeters, respectively. The FOM has acoustic pressure sensitivities of 1506 nm/Pa at 2500 Hz and 26,773 nm/Pa at 3233 Hz. The minimum detectable pressure (MDP) and signal-to-noise ratio (SNR) of the designed FOM are 0.93 µPa/Hz1/2 and 70.14 dB, respectively, at an acoustic pressure of 0.003 Pa. The designed FOM has the characteristics of ultra-high sensitivity, low MDP, and small size, which makes it suitable for the detection of weak acoustic signals, especially in the field of miniaturized all-optical photoacoustic spectroscopy.

High-Sensitivity Multitrace Gas Simultaneous Detection Based on an All-Optical Miniaturized Photoacoustic Sensor.

We propose an all-optical miniaturized multigas simultaneous detection photoacoustic (PA) sensor, which is primarily composed of a copper tube, a silica cantilever, and four single-mode fibers. Three single-mode fibers are used as excitation fibers to transmit lasers of different wavelengths, and the remaining one is used as a probe fiber. The volumes of the PA cell (PAC) and the sensor are 36 µL and 71 cubic millimeters, respectively. A laser photoacoustic spectroscopy (PAS) system, using the all-optical miniaturized PA sensor as a detector, 1532.8, 1576.3, and 1653.7 nm distributed feedback (DFB) lasers as the excitation sources for acetylene (C2H2), hydrogen sulfide (H2S), and methane (CH4) gases, and a high-speed spectrometer as a demodulator, has been developed for multigas simultaneous measurements. The minimum detection limits of 4.8, 162, and 16.6 parts per billion (ppb) have been achieved for C2H2, H2S, and CH4, respectively, with an integration time of 100 s. The reported sensor shows a potential for high-sensitivity multigas simultaneous measurements in cubic millimeter-scale space.

All-optical high-sensitivity resonant photoacoustic sensor for remote CH4 gas detection.

This paper presents an all-optical high-sensitivity resonant photoacoustic (PA) sensor to realize remote, long-distance and space-limited trace gas detection. The sensor is an integration of a T-type resonant PA cell and a particular cantilever-based fiber-optic acoustic sensor. The finite element simulations about the cantilever vibration mode and the PA field distributions are carried out based on COMSOL. The all-optical high-sensitivity resonant PA sensor, together with a high-speed spectrometer and a DFB laser source, makes up of a photoacoustic spectroscopy (PAS) system which is employed for CH4 detection. The measured sensitivity is 0.6 pm/ppm in the case of 1000 s average time, and the minimum detection limit (MDL) reaches 15.9 parts per billion (ppb). The detective light source and the excitation light source are all transmitted by optical fibers, therefore remote and long-distance measurement of trace gas can be realized. Furthermore, the excitation light source and the acoustic sensor are designed at the same side of the PA cell, the sensor may be used for space-limited trace gas detection.

A novel method to rescue and culture duck Astrovirus type 1 in vitro.

BACKGROUND: Reverse genetics systems enable the manipulation of viral genomes and therefore serve as robust reverse genetic tools to study RNA viruses. A DNA-launched rescue system initiates the transcription of viral genomic cDNA from eukaryotic promoter in transfected cells, generating homogenous RNA transcripts in vitro and thus enhancing virus rescue efficiency. As one of the hazardous pathogens to ducklings, the current knowledge of the pathogenesis of duck astrovirus type 1 (DAstV-1) is limited. The construction of a DNA-launched rescue system can help to accelerate the study of the virus pathogenesis. However, there is no report of such a system for DAstV-1. METHODS: In this study, a DNA-launched infectious clone of DAstV-1 was constructed from a cDNA plasmid, which contains a viral cDNA sequence flanked by hammerhead ribozyme (HamRz) and a hepatitis delta virus ribozyme (HdvRz) sequence at both terminals of the viral genome. A silent nucleotide mutation creating a Bgl II site in the ORF2 gene was made to distinguish the rescued virus (rDAstV-1) from the parental virus (pDAstV-1). Immunofluorescence assay (IFA) and western blot were conducted for rescued virus identification in duck embryo fibroblast (DEF) cells pre-treated with trypsin. The growth characteristics of rDAstV-1 and pDAstV-1 in DEF cells and the tissue tropism in 2-day-old ducklings of rDAstV-1 and pDAstV-1 were determined. RESULTS: The infectious DAstV-1 was successfully rescued from baby hamster kidney (BHK-21) cells and could propagate in DEF cells pre-treated with 1 µg/ml trypsin. Upon infection of DEF cells pre-treated with trypsin, DAstV-1 mRNA copies were identified after serial passaging, and the result showed that rDAstV-1 and pDAstV-1 shared similar replication kinetics. Animal experiment showed that the rDAstV-1 had an extensive tissue tropism, and the virus was capable of invading both the central and the peripheral immune organs in infected ducklings. CONCLUSIONS: An improved DNA-launched reverse genetics system for DAstV-1 was firstly constructed. Infectious virus recovered from BHK-21 cells could propagate in DEF cells pre-treated with trypsin. This is the first report of the successful in vitro cultivation of DAstV-1. We believe this valuable experimental system will contribute to the further study of DAstV-1 genome function and pathogenesis.