We have developed a rapid and homogeneous method for the highly selective detection of Hg(2+) and Ag(+) using Tween 20-modified gold nanoparticles (AuNPs). Citrate ions were found to still be adsorbed on the Au surface when citrate-capped AuNPs were modified with Tween 20, which stabilizes the citrate-capped AuNPs against conditions of high ionic strength. When citrate ions had reduced Hg(2+) and Ag(+) to form Hg-Au alloys and Ag on the surface of the AuNPs, Tween 20 was removed from the NP surface. As a result, the AuNPs were unstable under a high-ionic-strength solution, resulting in NP aggregation. The formation of Hg-Au alloys or Ag on the surface of the AuNPs was demonstrated by means of inductively coupled plasma mass spectroscopy and energy-dispersive X-ray spectroscopy. Tween 20-AuNPs could selectively detect Hg(2+) and Ag(+) at concentrations as low as 0.1 and 0.1 microM in the presence of NaCl and EDTA, respectively. Moreover, the probe enables the analysis of AgNPs with a minimum detectable concentration that corresponds to 1 pM. This probe was successfully applied to detect Hg(2+) in drinking water and seawater, Ag(+) in drinking water, and AgNPs in drinking water.

This study presents a one-step approach to prepare lysozyme type VI-stabilized gold nanoclusters (Lys VI-AuNCs) for the ultrasensitive detection of Hg(2+) and CH(3)Hg(+) based on fluorescence quenching. The optical properties and size of Lys VI-AuNCs are highly dependent on the concentration of Lys VI, which acts as both a reducing and a stabilizing agent. With an increase in the concentration of Lys VI, we observed a systematic blue shift in the fluorescence maxima, an increase in the quantum yields, and a reduction in the particle size. When using 25 mg/mL Lys VI as a reducing agent, the formed Lys VI-AuNCs (denoted as Au-631) were found to be highly stable in a high-concentration glutathione or NaCl. Additionally, the Au-631 were capable of sensing Hg(2+) and CH(3)Hg(+) through the interaction between Hg(2+)/CH(3)Hg(+) and Au(+) on the Au surface; the limits of detection (LODs) for Hg(2+) and CH(3)Hg(+) were 3 pM and 4 nM, respectively. The selectivity of this probe is more than 500-fold for Hg(2+) over any metal ions. As compared to bovine serum albumin-stabilized AuNCs, Au-631 provided an approximately 330-fold improvement in the detection of Hg(2+). To the best of our knowledge, Au-631 not only provide the first example for detecting CH(3)Hg(+) but also have the lowest LOD value for Hg(2+) when compared to other AuNC-based Hg(2+) sensors. Importantly, this probe was successfully applied to the determination of Hg(2+) and CH(3)Hg(+) in seawater.

Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester, J. Chem. Phys. 149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only the syn-conformers are observed; anti-conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction of syn-MVK-oxide with SO2 and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO3 and identifying organic hydroperoxide formation from reaction with SO2 and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model.