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Understanding the early stages of interactions between oxygen and material surfaces—especially at very high spatial resolutions—is highly beneficial for fields ranging from materials degradation, corrosion, geological sciences, forensics, and catalysis. The ability of in situ atom probe tomography (APT) is demonstrated to track the diffusion of oxygen and metal ions at nanoscale spatial resolution during the early stages of oxidation of a model Fe–Cr–Ni alloy. Using 18O isotope tracers in these in situ APT experiments and complementary ex situ multimodal microscopy, spectroscopy, and computational simulations allows to precisely analyze the kinetics of oxidation and determine that outward cation diffusion to oxide/air interface is the primary mechanism for intragranular oxide growth in this alloy at 300 °C. This unique in situ isotopic tracer APT approach and the insights gained can be highly beneficial for studying early stages of gas–surface reactions in a broad array of materials.

Nitrogen-doped carbon nanodots (CNDs) were synthesized and utilized as sensing probes to detect different anions and metallic ions within aqueous solutions. The pristine CNDs were developed through a one-pot hydrothermal synthesis. o-Phenylenediamine was used as the precursor. A similar hydrothermal synthesis technique in the presence of polyethylene glycol (PEG) was adopted to form the PEG-coated CND clusters (CND-100k). Through photoluminescence (PL) quenching, both CND and PEG-coated CND suspensions display ultra-high sensitivity and selectivity towards HSO4− anions (Stern–Volmer quenching constant (KSV) value: 0.021 ppm−1 for CND and 0.062 ppm−1 for CND-100k) with an ultra-low detection limit (LOD value: 0.57 ppm for the CND and 0.19 ppm for CND-100k) in the liquid phase. The quenching mechanism of N-doped CNDs towards HSO4− ions involves forming the bidentate as well as the monodentate hydrogen bonding with the sulfate anionic moieties. The detection mechanism of metallic ions analyzed through the Stern–Volmer formulation reveals that the CND suspension is well suited for the detection of Fe3+ (KSV value: 0.043 ppm−1) and Fe2+ (KSV value: 0.0191 ppm−1) ions, whereas Hg2+ (KSV value: 0.078 ppm−1) sensing can be precisely performed by the PEG-coated CND clusters. Accordingly, the CND suspensions developed in this work can be employed as high-performance PL probes for detecting various anions and metallic ions in the liquid phase. [ABSTRACT FROM AUTHOR]

This paper reports notable observations regarding the ion charge states of thermally stable cytochrome c, generated using an alternating current (AC) electrospray ionization (ESI) device. An AC ESI sprayer entrains low‐mobility ions to accumulate at the meniscus cone tip prior to the ejection of detached aerosols to produce analyte ions. Therefore, as the solvent acidity varies, protein ions entrained in the AC cone tip are found to change conformation less significantly compared with those in the direct current (DC) cone. We acquired the AC ESI mass spectra of cytochrome c at pH range from 2 to 4. Unlike the DC ESI mass spectra showing clear conformation changes due to denaturing, the AC spectra indicated that only partial denaturing occurs even at extremely acidic pH 2. More native cytochrome c in lower charge states therefore remained. Moreover, with a solvent mixture of aqueous buffer and acetonitrile (70:30), partially denatured cytochrome c was still preserved at pH 2 by using AC ESI. Completely denatured proteins are observed at pH 2 by using DC ESI. [ABSTRACT FROM AUTHOR]