Mass Spectrometric Identification of Water-Soluble Gold Nanocluster Fractions from Sequential Size-Selective Precipitation

This paper presents a simple and convenient methodology to separate and characterize water-soluble gold nanocluster stabilized with penicillamine ligands (AuNC-SR) in aqueous medium by sequential size-selective precipitation (SSSP) and mass spectrometry (MS). The highly polydisperse crude AuNC-SR product with an average core diameter of 2.1 nm was initially synthesized by a one-phase solution method. AuNCs were then precipitated and separated successively from larger to smaller ones by progressively increasing the concentration of acetone in the aqueous AuNCs solution. The SSSP fractions were analyzed by UV–vis spectroscopy, matrix-assisted laser desorption/ionization time-of-flight-MS, and thermogravimetric analysis (TGA). The MS and TGA data confirmed that the fractions precipitated from 36, 54, 72, and 90% v/v acetone (<i>F</i>_36%, <i>F</i>_54%, <i>F</i>_72%, and <i>F</i>_90%) comprised families of close core size AuNCs with average molecular formulas of Au₃₈(SR)₁₈, Au₂₈(SR)₁₅, Au₁₈(SR)₁₂, and Au₁₁(SR)₈, respectively. In addition, <i>F</i>_36%, <i>F</i>_54%, <i>F</i>_72%, and <i>F</i>_90% contained also the typical magic-sized gold nanoparticles of Au₃₈, Au₂₅, Au₁₈, and Au₁₁, respectively, together with some other AuNCs. This study shed light on the potential use of SSSP for simple and large-scale preliminary separation of polydisperse water-soluble AuNCs into different fractions with a relatively narrower size distribution

Mutual Effects of Dialkyl Phthalate Esters and Humic Acid Sorption on Carbon Nanotubes in Aqueous Environments

Various reaction sequences of mutual sorptions of dimethyl phthalate (DMP) or diethyl phthalate (DEP) and humic acid (HA) on single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) were studied. The results indicate that the sorption of DMP and DEP on CNT decreases owing to its competition effect in the presence of HA. The competition is stronger at lower HA concentration. At higher HA concentration, weaker competition has occurred because there are steric hindrance and pore blockage of HA on CNT. The reaction sequences of DMP (or DEP) and HA sorption could affect their sorption mechanisms. The initial sorbed HA can modify the surface properties of CNT with a concomitant effect on the partial complexation of DMP (or DEP) with the sorbed HA. The Fourier transform infrared (FTIR) spectra indicate that SWCNT and MWCNT contain mainly −COO^– and −COOH moieties, respectively. In addition, the IR spectroscopic and thermogravimetric analyses illustrate that CNTs provide similar sorption capacity regardless of the interaction sequence of DMP (or DEP) and HA. Finally, the fluorescence quenching results indicate that DEP exhibits stronger binding to HA than that of DMP

Phosphorus and Nitrogen Dual-Doped Hollow Carbon Dot as a Nanocarrier for Doxorubicin Delivery and Biological Imaging

Innovative phosphorus and nitrogen dual-doped hollow carbon dots (PNHCDs) have been fabricated for anticancer drug delivery and biological imaging. The functional groups of PNHCDs are introduced by simply mixing glucose, 1,2-ethylenediamine, and concentrated phosphoric acid. This is an automatic method without external heat treatment to rapidly produce large quantities of PNHCDs, which avoid high temperature, complicated operations, and long reaction times. The as-prepared PNHCDs possess small particle size, hollow structure, and abundant phosphate/hydroxyl/pyridinic/pyrrolic-like N groups, endowing PNHCDs with fluorescent properties, improving the accuracy of PNHCDs as an optical monitoring code both in vitro and in vivo. The investigation of PNHCDs as an anticancer drug nanocarrier for doxorubicin (DOX) indicates a better antitumor efficacy than free DOX owing to its enhanced nuclear delivery in vitro and tumor accumulation in vivo, which results in highly effective tumor growth inhibition and improved targeted therapy for cancer in clinical medicine

Probing Histidine-Stabilized Gold Nanoclusters Product by High-Performance Liquid Chromatography and Mass Spectrometry

A major hurdle in assessing the biological, chemical and physical properties of current nanoparticles lies in their complex nature in terms of size, shape, and composition. As such, it is vital to develop a high-resolution analytical separation technique to fractionate these nanomaterials. Herein, we demonstrate an unprecedented chromatographic fractionation of gold nanoclusters stabilized with histidine (His-AuNCs) with core diameter smaller than 1 nm. His-AuNCs product has been successfully separated by reverse-phase high-performance liquid chromatography using a binary mixture of methanol and ammonium acetate in water and an optimal solvent elution program. The separated His-AuNCs are online-characterized by UV–vis absorption spectroscopy, and their spectral features are closely related to the number of gold (Au) atom. The absorption band shifts to the lower energy as the number of Au atom increases. The separated His-AuNCs fractions are further collected and anatomized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, electrospray ionization mass spectrometry, capillary electrophoresis, and fluorescence spectroscopy. The mass spectrometric data unambiguously reveal that the as-synthesized His-AuNCs product is indeed a complex mixture of Au₁₀(His)₉, [Au₁₁(His)₉]⁻, Au₁₁(His)₁₀, Au₁₂(His)₉, Au₁₂(His)₁₁, Au₁₂(His)₁₂, Au₁₃(His)₉, Au₁₃(His)₁₁, and Au₁₄(His)₁₃. All separated His-AuNCs exhibit two emission bands at ca. 410 and 500 nm, demonstrating that the photoluminescence of His-AuNCs is attributed to both the Au core and the surface-attached ligands. The blue-green emission at 500 nm displays a red shift with the increase in ligands (His). This work highlights the virtues of high-resolution chromatography for understanding the identity of individual AuNCs species present in an AuNCs product, which might have been previously hidden

Design of Ratiometric Emission Probe with Visible Light Excitation for Determination of Ca²⁺ in Living Cells

An organic salt as a fluorescent probe based on intramolecular charge transfer for Ca²⁺ determination is developed. Ca²⁺ can be detected by ratiometric emission at 490 and 594 nm with an excitation wavelength of 405 nm. This probe is highly selective for Ca²⁺ over other divalent metal cations and displays a large Stokes shift of 189 nm that can avoid interference of the excitation light beam and autofluorescence of biological samples. The dissociation constant for Ca²⁺ is 2.25 ± 0.47 μM and pertinent to Ca²⁺ detection in cellular resting and dynamic states. The probe demonstrates its application in monitoring Ca²⁺ in living cells under confocal microscopic imaging

Redox Modification of CdSe–ZnS–Polymer Quantum Dots: Photoassisted Fluorescence Quenching and Recovery

Commercial CdSe–ZnS–polymer quantum dots (QDs) were shown to be readily quenched by strong oxidants such as potassium permanganate. When exposed to permanganate solution of millimolar concentration for hours, damage was severe and the QDs would be permanently bleached. When oxidant concentration was micromolar and reaction time was minutes, oxidation would be mild and bleached QDs could recover their fluorescence if the oxidant was removed and the QDs subsequently irradiated. Light was essential in activating the fluorescence recovery. Light could also transform mild oxidations into severe ones if administered with the oxidant simultaneously. A model of the bleaching and recovery was proposed. It was based on the oxidative attack of the Zn–ligand bond and its repair. The model helped explain the critical role that light played and was consistent with all the experimental observations. By means of photocatalyzed oxidation of single QDs, a redox probe of high spatial and temporal resolution was demonstrated