New Insight into the Formation Mechanism of PCDD/Fs from 2‑Chlorophenol Precursor

Chlorophenols are known as precursors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). The widely accepted formation mechanism of PCDD/Fs always assumes chlorophenoxy radicals as key and important intermediates. Based on the results of density functional theory calculations, the present work reports new insight into the formation mechanism of PCDD/Fs from chlorophenol precursors. Using 2-chlorophenol as a model compound of chlorophenols, we find that apart from the chlorinated phenoxy radical, the chlorinated phenyl radical and the chlorinated α-ketocarbene also have great potential for PCDD/F formation, which has scarcely been considered in previous literature. The calculations on the self- and cross-coupling reactions of the chlorophenoxy radical, the chlorinated phenyl radical and the chlorinated α-ketocarbene show that the formations of 1-MCDD, 1,6-DCDD, 4,6-DCDF, and 4-MCDF are both thermodynamically and kinetically favorable. In particular, some pathways involving the chlorinated phenyl radicals and the chlorinated α-ketocarbene are even energetically more favorable than those involving the chlorophenoxy radical. The calculated results may improve our understanding for the formation mechanism of PCDD/Fs from chlorophenol precursors and be informative to environmental scientists

Cysteamine-Modified Silver Nanoparticle Aggregates for Quantitative SERS Sensing of Pentachlorophenol with a Portable Raman Spectrometer

Cysteamine-modified silver nanoparticle aggregates has been fabricated for pentachlorophenol (PCP) sensing by surface-enhanced Raman spectroscopy (SERS) using a portable Raman spectrometer. The cysteamine monolayers could preconcentrate PCP close to the substrate surface through the electrostatic interaction, which makes the SERS detection of PCP possible. Moreover, the Raman bands of cysteamine could be used as the internal spectral reference in the quantitative analysis. Qualitative detection of PCP was carried out by SERS without any sample pretreatment. Quantitative analysis of PCP was further realized based on the prepared substrate, as the log–log plot of normalized SERS intensity of PCP versus its concentrations exhibits a good linear relationship. The SERS signals collected on 20 randomly selected points show that the relative standard deviation of the normalized Raman intensity is 5.8%, which indicates the substrate had good uniformity. The PCP sensor also shows good long-term stability in the analyte solution. The substrate was cyclic immersed into PCP and methanol solution; after several cycles, the sensor still had good adsorption to PCP, which revealed the sensor has good reusability. Coupling with a portable Raman spectrometer, the cysteamine-modified silver nanoparticle aggregates have the potential to be used for in situ and routine SERS analysis of PCP in environmental samples

Electric Field Promoted Click Surface-Enhanced Raman Spectroscopy for Rapid and Specific Detection of DNA 2‑Deoxyribose 5′-Aldehyde Oxidation Products in Plasma

Rapid identification of DNA oxidative damage sites is of great significance for disease diagnosis. In this work, electric field-regulated click reaction surface-enhanced Raman spectroscopy (e-Click-SERS) was developed aiming at the rapid and specific analysis of furfural, the biomarker of oxidative damage to the 5-carbon site of DNA deoxyribose. In e-Click-SERS, cysteamine-modified porous Ag filaments (cys@p-Ag) were prepared and used as electrodes, amine-aldehyde click reaction sites, and SERS substrates. Cysteamine was controlled as an “end-on” conformation by setting the voltage of cys@p-Ag at −0.1 V, which ensures its activity in participating in the amine-aldehyde click reaction during the detection of furfural. Benefiting from this, the proposed e-Click-SERS method was found to be sensitive, rapid-responding, and interference-resistant in analyzing furfural from plasma. The method detection limits of furfural were 5 ng mL–1 in plasma, and the whole “extraction and detection” procedure was completed within 30 min with satisfactory recovery. Interference from 13 kinds of common plasma metabolites was investigated and found to not interfere with the analysis, according to the exclusive adaptation of the amine-aldehyde click reaction. Notably, the e-Click-SERS technique allows in situ analysis of biological samples, which offers great potential to be a point-of-care testing tool for detecting DNA oxidative damage