5 research outputs found
Pixel Counting of Fluorescence Spots Triggered by DNA Walkers for Ultrasensitive Quantification of Nucleic Acid
A pixel
counting strategy is designed on the basis of DNA walker-triggered
fluorescence spots for ultrasensitive detection of nucleic acid. The
two-dimensional DNA walker was constructed by hybridization of two
types of capture DNAs, which were covalently modified by click chemistry
on a glass slide, and dye-labeled hairpin structure (hDNA) as track
and swing strand (sDNA) as DNAzyme, respectively. Introduction of
target DNA unlocked the sDNA via strand displacement to form the activated
DNAzyme, and the latter cut nearby hDNA with Mn<sup>2+</sup> as cofactor,
resulting in fluorescence recovery of dye-labeled hDNA on the substrate
due to the separation from the quencher. Meanwhile, the DNAzyme sequence
of sDNA was released to cut the next hDNA and, thus, initiated autonomous
walking of sDNA for signal amplification. The enhanced fluorescence
spots were digitalized as pixels on the basis of DNA walker-built
compartments and extracted by a homemade program in MATLAB. The association
between fluorescent pixel numbers and DNA concentrations was further
proved by a mathematical model and led to an ultrasensitive quantification
of nucleic acid with a linear range from 100 fM to 10 pM. The designed
pixel counting strategy shows a more sensitive and accurate comparison
with conventional methods based on fluorescence intensity or spot
counts and provides a new dimension in designing next-type biosensors
Online Monitoring of Intraoperative Exhaled Propofol by Acetone-Assisted Negative Photoionization Ion Mobility Spectrometry Coupled with Time-Resolved Purge Introduction
Online monitoring of exhaled propofol concentration is important for anesthetists to provide adequate anesthesia as propofol concentrations in plasma and breath are correlated reasonably well. Exhaled propofol could be detected by Ni-63 ion mobility spectrometry in negative ion mode; however, the radioactivity of Ni-63 source restricts its clinical application due to safety, environmental, and regulatory concerns. An acetone-assisted negative photoionization ion mobility spectrometer (AANP-IMS) using a side-mounted vacuum ultraviolet (VUV) lamp in the unidirectional (UD) flow mode was developed for sensitive measurement of exhaled propofol by producing a high percentage of O-2(-)(H2O)(n). An adsorption sampling and time-resolved purge introduction system was developed to eliminate the interference of residual inhaled anesthetic sevoflurane based on their different adsorptions between propofol and sevoflurane on the inwall of the fluorinated ethylene propylene (FEP) sample loop. The effects of the inner diameter and the length of the sample loop on the signal intensity of propofol and the time-resolution between propofol and sevoflurane were theoretically and experimentally investigated. A sample loop with 3 mm i.d. and 150 cm length allowed sensitive measurement of exhaled propofol with a response time of 4 s, a linear response range for propofol was achieved to be 0.2 to 14 ppbv with a limit of detection (LOD) of 60 pptv, and the quantification of propofol was not influenced by the change of the sevoflurane concentration. Finally, the performance of monitoring exhaled propofol during surgery was demonstrated on a patient undergoing laparoscopic distal pancreatectomy combined with cholecystectomy
Long-Term Real-Time Monitoring Catalytic Synthesis of Ammonia in a Microreactor by VUV-Lamp-Based Charge-Transfer Ionization Time-of-Flight Mass Spectrometry
With respect to massive consumption of ammonia and rigorous industrial synthesis conditions, many studies have been devoted to investigating more environmentally benign catalysts for ammonia synthesis under moderate conditions. However, traditional methods for analysis of synthesized ammonia (e.g., off-line ion chromatography (IC) and chemical titration) suffer from poor sensitivity, low time resolution, and sample manipulations. In this work, charge-transfer ionization (CTI) with O-2(+) as the reagent ion based on a vacuum ultraviolet (VUV) lamp in a time-of-flight mass spectrometer (CTI-TOFMS) has been applied for real-time monitoring of the ammonia synthesis in a microreactor. For the necessity of long-term stable monitoring, a self-adjustment algorithm for stabilizing O-2(+) ion intensity was developed to automatically compensate the attenuation of the O-2(+) ion yield in the ion source as a result of the oxidation of the photoelectric electrode and contamination on the MgF2 window of the VUV lamp. A wide linear calibration curve in the concentration range of 0.2-1000 ppmv with a correlation coefficient (R-2) of 0.9986 was achieved, and the limit of quantification (LOQ) for NH3 was in ppbv. Microcatalytic synthesis of ammonia with three catalysts prepared by transition-metal/carbon nanotubes was tested, and the rapid changes of NH3 conversion rates with the reaction temperatures were quantitatively measured with a time resolution of 30 s. The high-time-resolution CTI-TOFMS could not only achieve the equilibrium conversion rates of NH3 rapidly but also monitor the activity variations with respect to investigated catalysts during ammonia synthesis reactions
Long-Term Real-Time Monitoring Catalytic Synthesis of Ammonia in a Microreactor by VUV-Lamp-Based Charge-Transfer Ionization Time-of-Flight Mass Spectrometry
With
respect to massive consumption of ammonia and rigorous industrial
synthesis conditions, many studies have been devoted to investigating
more environmentally benign catalysts for ammonia synthesis under
moderate conditions. However, traditional methods for analysis of
synthesized ammonia (e.g., off-line ion chromatography (IC) and chemical
titration) suffer from poor sensitivity, low time resolution, and
sample manipulations. In this work, charge-transfer ionization (CTI)
with O<sub>2</sub><sup>+</sup> as the reagent ion based on a vacuum
ultraviolet (VUV) lamp in a time-of-flight mass spectrometer (CTI-TOFMS)
has been applied for real-time monitoring of the ammonia synthesis
in a microreactor. For the necessity of long-term stable monitoring,
a self-adjustment algorithm for stabilizing O<sub>2</sub><sup>+</sup> ion intensity was developed to automatically compensate the attenuation
of the O<sub>2</sub><sup>+</sup> ion yield in the ion source as a
result of the oxidation of the photoelectric electrode and contamination
on the MgF<sub>2</sub> window of the VUV lamp. A wide linear calibration
curve in the concentration range of 0.2–1000 ppmv with a correlation
coefficient (<i>R</i><sup>2</sup>) of 0.9986 was achieved,
and the limit of quantification (LOQ) for NH<sub>3</sub> was in ppbv.
Microcatalytic synthesis of ammonia with three catalysts prepared
by transition-metal/carbon nanotubes was tested, and the rapid changes
of NH<sub>3</sub> conversion rates with the reaction temperatures
were quantitatively measured with a time resolution of 30 s. The high-time-resolution
CTI-TOFMS could not only achieve the equilibrium conversion rates
of NH<sub>3</sub> rapidly but also monitor the activity variations
with respect to investigated catalysts during ammonia synthesis reactions