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1. Mechanistic Elucidation of Nanomaterial-Enhanced First-Generation Biosensors Using Probe Voltammetry of an Enzymatic Reaction

   https://doi.org/10.3390/bios13080798  

   Wemple, Ann H; Kaplan, Jamie S; Leopold, Michael C (August 2023, Biosensors)

   The incorporation of nanomaterials (NMs) into biosensing schemes is a well-established strategy for gaining signal enhancement. With electrochemical biosensors, the enhanced performance achieved from using NMs is often attributed to the specific physical properties of the chosen nanocomponents, such as their high electronic conductivity, size-dependent functionality, and/or higher effective surface-to-volume ratios. First generation amperometric biosensing schemes, typically utilizing NMs in conjunction with immobilized enzyme and semi-permeable membranes, can possess complex sensing mechanisms that are difficult to study and challenging to understand beyond the observable signal enhancement. This study shows the use of an enzymatic reaction between xanthine (XAN) and xanthine oxidase (XOx), involving multiple electroactive species, as an electrochemical redox probe tool for ascertaining mechanistic information at and within the modified electrodes used as biosensors. Redox probing using components of this enzymatic reaction are demonstrated on two oft-employed biosensing approaches and commonly used NMs for modified electrodes: gold nanoparticle doped films and carbon nanotube interfaces. In both situations, the XAN metabolism voltammetry allows for a greater understanding of the functionality of the semipermeable membranes, the role of the NMs, and how the interplay between the two components creates signal enhancement. 

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2. White light emission from co-doped La ₂ Hf ₂ O ₇ nanoparticles with suppressed host → Eu ³⁺ energy transfer via a U ⁶⁺ co-dopant

   https://doi.org/10.1039/D1QI00134E  

   Gupta, Santosh K.; Modak, Brindaban; Modak, Pampa; Mao, Yuanbing (August 2021, Inorganic Chemistry Frontiers)

   null (Ed.)

   Controlled energy transfer has been found to be one of the most effective ways of designing tunable and white photoluminescent phosphors. Utilizing host emission to achieve the same would lead to a new dimension in the design strategy for novel luminescent materials in solid state lighting and display devices. In this work, we have achieved controlled energy transfer by suppressing the host to dopant energy transfer in La 2 Hf 2 O 7 :Eu 3+ nanoparticles (NPs) by co-doping with uranium ions. Uranium acts as a barrier between the oxygen vacancies of the La 2 Hf 2 O 7 host and Eu 3+ doping ions to increase their separation and reduce the non-radiative energy transfer between them. Density functional theory (DFT) calculations of defect formation energy showed that the Eu 3+ dopant occupies the La 3+ site and the uranium ion occupies the Hf 4+ site. Co-doping the La 2 Hf 2 O 7 :Eu 3+ NPs with uranium ions creates negatively charged lanthanum and hafnium vacancies making the system highly electron rich. Formation of cation vacancies is expected to compensate the excess charge in the U and Eu co-doped La 2 Hf 2 O 7 NPs suppressing the formation of oxygen vacancies. This work shows how one can utilize the full color gamut in the La 2 Hf 2 O 7 :Eu 3+ ,U 6+ NPs with blue, green and red emissions from the host, uranium and europium, respectively, to produce near perfect white light emission. 

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3. X-Ray Spectroscopy in the Microcalorimeter Era 4: Optical Depth Effects on the Soft X-Rays Studied with Cloudy

   https://doi.org/10.3847/1538-4357/ac7eb9  

   Chakraborty, Priyanka; Ferland, Gary J.; Chatzikos, Marios; Fabian, Andrew C.; Bianchi, Stefano; Guzmán, Francisco; Su, Yuanyuan (August 2022, The Astrophysical Journal)

   Abstract In this paper, we discuss atomic processes modifying the soft X-ray spectra from optical depth effects like photoelectric absorption and electron scattering suppressing the soft X-ray lines. We also show the enhancement in soft X-ray line intensities in a photoionized environment via continuum pumping. We quantify the suppression/enhancement by introducing a “line modification factor ( f mod ).” If 0 ≤ f mod ≤ 1, the line is suppressed, which could be the case in both collisionally ionized and photoionized systems. If f mod ≥ 1, the line is enhanced, which occurs in photoionized systems. Hybrid astrophysical sources are also very common, where the environment is partly photoionized and partly collisionally ionized. Such a system is V1223 Sgr, an Intermediate Polar binary. We show the application of our theory by fitting the first-order Chandra Medium Energy Grating (MEG) spectrum of V1223 Sgr with a combination of Cloudy -simulated additive cooling-flow and photoionized models. In particular, we account for the excess flux for O vii , O viii , Ne ix , Ne x , and Mg xi lines in the spectrum found in a recent study, which could not be explained with an absorbed cooling-flow model. 

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4. Decoding the compositions of four bright r -process-enhanced stars

   https://doi.org/10.1093/mnras/stad2206  

   Saraf, Pallavi; Prieto, Carlos Allende; Sivarani, Thirupathi; Bandyopadhyay, Avrajit; Beers, Timothy C; Susmitha, A (July 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT There has been a concerted effort in recent years to identify the astrophysical sites of the r-process that can operate early in the galaxy. The discovery of many r-process-enhanced (RPE) stars (especially by the R-process Alliance collaboration) has significantly accelerated this effort. However, only limited data exist on the detailed elemental abundances covering the primary neutron-capture peaks. Subtle differences in the structure of the r-process pattern, such as the relative abundances of elements in the third peak, in particular, are expected to constrain the r-process sites further. Here, we present a detailed elemental-abundance analysis of four bright RPE stars selected from the HESP–GOMPA survey. Observations were carried out with the 10-m class telescope Gran Telescopio Canarias (GTC), Spain. The high spectral signal-to-noise ratios obtained allow us to derive abundances for 20 neutron-capture elements, including the third r-process peak element osmium (Os). We detect thorium (Th) in two stars, which we use to estimate their ages. We discuss the metallicity evolution of Mg, Sr, Ba, Eu, Os, and Th in r-II and r-I stars, based on a compilation of RPE stars from the literature. The strontium (Sr) abundance trend with respect to europium (Eu) suggests the need for an additional production site for Sr (similar to several earlier studies); this requirement could be milder for yttrium (Y) and zirconium (Zr). We also show that there could be some time delay between r-II and r-I star formation, based on the Mg/Th abundance ratios. 

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5. Nanoparticle Diffusion in Crowded Polymer Nanocomposite Melts

   https://doi.org/10.1021/acsmacrolett.4c00438  

   Wang, Kaitlin; Winey, Karen I (September 2024, ACS Macro Letters)

   This study examines nanoparticle diffusion in crowded polymer nanocomposites by diffusing small Al2O3 nanoparticles (NPs) in SiO2-loaded P2VP matrices. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measures Al2O3 NP diffusion coefficients within a homogeneous PNC background of larger, immobile SiO2 NPs. By developing a geometric model for the average interparticle distance in a system with two NP sizes, we quantify nanocomposite confinement relative to the Al2O3 NP size with a bound layer. At low SiO2 concentrations, Al2O3 NP diffusion aligns with the neat polymer results. In more crowded nanocomposites with higher SiO2 concentrations where the interparticle distance approaches the size of the mobile Al2O3 NP, the 6.5 nm Al2O3 NPs diffuse faster than predicted by both core–shell and vehicular diffusion models. Relative to our previous studies of NPs diffusing into polymers, these findings demonstrate that the local environment in crowded systems significantly complicates NP diffusion behavior and the bound layer lifetimes. 

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