Salting-Out-Assisted Liquid-Liquid Extraction Method for the Determination of Nicotine from Oral Traditional and Innovative Tobacco Products Using UPLC-MS/MS

In this study, we developed and validated a novel method that allows for the extraction and quantitation of nicotine from a variety of commercially available oral tobacco products including loose and pouched traditional moist smokeless tobacco products, and oral tobacco-derived nicotine (OTDN) lozenges, gums, and pouches. The method employed an extraction technique consisting of salting-out assisted liquid-liquid extraction using sodium hydroxide and acetonitrile in conjunction with ultra-high pressure liquid chromatography coupled to mass spectrometry. Accurate quantitation was obtained using nicotine methyl-d3 isotopically labeled internal standard. Chromatographic separation of nicotine and nicotine methyl-d3 internal standard was achieved using a Waters Acquity C18 column (50 mm × 2.1 mm i.d., 2.5 μm) with 10 mM ammonium acetate buffer (pH = 10) and acetonitrile as mobile phase A and B, respectively. Using a gradient elution and a flow rate of 0.4 mL/min for 5 min runtime, nicotine eluted at 1.74 min. The method was validated according to ICH guidelines for all the sample types with an accuracy for nicotine within 89-109%. Repeatability and intermediate precision were both estimated to be ≤7% relative standard deviation (% RSD). This method is applicable for a wide range of traditional moist smokeless and OTDN tobacco products.

Small protein sequences can induce cellular uptake of complex nanohybrids

In this letter, we report on the ability of functional fusion proteins presenting a lytic gamma peptide, to promote interactions with HeLa cells and delivery of large hybrid nanostructures.

Accurate Quantitation and Analysis of Nitrofuran Metabolites, Chloramphenicol, and Florfenicol in Seafood by Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry: Method Validation and Regulatory Samples

We developed and validated a method for the extraction, identification, and quantitation of four nitrofuran metabolites, 3-amino-2-oxazolidinone (AOZ), 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), semicarbazide (SC), and 1-aminohydantoin (AHD), as well as chloramphenicol and florfenicol in a variety of seafood commodities. Samples were extracted by liquid-liquid extraction techniques, analyzed by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), and quantitated using commercially sourced, derivatized nitrofuran metabolites, with their isotopically labeled internal standards in-solvent. We obtained recoveries of 90-100% at various fortification levels. The limit of detection (LOD) was set at 0.25 ng/g for AMOZ and AOZ, 1 ng/g for AHD and SC, and 0.1 ng/g for the phenicols. Various extraction methods, standard stability, derivatization efficiency, and improvements to conventional quantitation techniques were also investigated. We successfully applied this method to the identification and quantitation of nitrofuran metabolites and phenicols in 102 imported seafood products. Our results revealed that four of the samples contained residues from banned veterinary drugs.

Gold-doped silver nanoclusters with enhanced photophysical properties

We detail the characterization of atomically precise, luminescent silver and gold bimetallic nanoclusters (Ag and AgAuNCs) grown in the presence of bidentate lipoic acid (LA, the oxidized form) and dihydrolipoic acid (DHLA, the reduced form) ligands.

Self-Assembled Gold Nanoparticle-Fluorescent Protein Conjugates as Platforms for Sensing Thiolate Compounds via Modulation of Energy Transfer Quenching

The ability of Au and other metal nanostructures to strongly quench the fluorescence of proximal fluorophores (dyes and fluorescent proteins) has made AuNP conjugates attractive for use as platforms for sensor development based on energy transfer interactions. In this study, we first characterize the energy transfer quenching of mCherry fluorescent proteins immobilized on AuNPs via metal-histidine coordination, where parameters such as NP size and number of attached proteins are varied. Using steady-state and time-resolved fluorescence measurements, we recorded very high mCherry quenching, with efficiency reaching ∼95-97%, independent of the NP size or number of bound fluorophores (i.e., conjugate valence). We further exploited these findings to develop a solution phase sensing platform targeting thiolate compounds. Energy transfer (ET) was employed as a transduction mechanism to monitor the competitive displacement of mCherry from the Au surface upon the introduction of varying amounts of thiolates with different size and coordination numbers. Our results show that the competitive displacement of mCherry depends on the thiolate concentration, time of reaction, and type of thiol derivatives used. Further analysis of the PL recovery data provides a measure for the equilibrium dissociation constant (Kd-1) for these compounds. These findings combined indicate that the AuNP-fluorescent protein conjugates may offer a potentially useful platform for thiol sensing both in solution and in cell cultures.

UHPLC-MS/MS method for the quantitation of penicillin G and metabolites in citrus fruit using internal standards

Penicillin G has been applied to citrus trees as a potential treatment in the fight against Huanglongbing (HLB). Here, we have developed and validated a method to identify and quantitate penicillin G and two of its metabolites, penillic acid and penilloic acid, in citrus fruit using ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). This method improves upon a previous method by incorporating isotopically labeled internal standards, namely, penillic acid-D₅, and penilloic acid-D₅. These standards greatly enhanced the accuracy and precision of our measurements by compensating for recovery losses, degradation, and matrix effects. When 2g of citrus fruit sample is extracted, the limits of detection (LOD) were determined to be 0.1ng/g for penicillin G and penilloic acid, and 0.25ng/g for penillic acid. At fortification levels of 0.1, 0.25, 1, and 10ng/g, absolute recoveries for penillic and penilloic acids were generally between 50-70%. Recoveries corrected with the isotopically labeled standards were approximately 90-110%. This method will be useful for the identification and quantitation of drug residues and their degradation products using isotopically labeled standards and UHPLC-MS/MS.

LC-MS/MS Validation of a Residue Analysis Method for Penicillin G and Its Metabolites in Commercial Orange Juice

Florida citrus depends on a breakthrough in the fight against citrus greening disease. Of the antibiotics used to treat this disease, penicillin G has been one of the most effective. Because orange fruit grown in the state of Florida are mainly used to produce orange juice, we have validated an ultra-HPLC tandem MS method to screen for penicillin G and its metabolites (penillic and penilloic acids) at the chemical residue level after treatment. In this method, three spike levels (0.25, 1, and 20 ng/g) were tested in triplicate. Absolute recoveries for penillic and penilloic acids were 60-75% depending on the matrix used, whereas corrected recoveries of penicillin G using an isotopically labeled internal standard were ~100%. Two product ion transitions per analyte were required for identification, which contributes to a high degree of selectivity.

Identification of Penicillin G Metabolites under Various Environmental Conditions Using UHPLC-MS/MS

In this work, we investigate the stability of penicillin G in various conditions including acidic, alkaline, natural acidic matrices and after treatment of citrus trees that are infected with citrus greening disease. The identification, confirmation, and quantitation of penicillin G and its various metabolites were evaluated using two UHPLC-MS/MS systems with variable capabilities (i.e., Thermo Q Exactive Orbitrap and Sciex 6500 QTrap). Our data show that under acidic and alkaline conditions, penicillin G at 100 ng/mL degrades quickly, with a determined half-life time of approximately 2 h. Penillic acid, penicilloic acid, and penilloic acid are found to be the most abundant metabolites of penicillin G. These major metabolites, along with isopenillic acid, are found when penicillin G is used for treatment of citrus greening infected trees. The findings of this study will provide insight regarding penicillin G residues in agricultural and biological applications.

Aqueous Growth of Gold Clusters with Tunable Fluorescence Using Photochemically Modified Lipoic Acid-Based Ligands

We report a one-phase aqueous growth of fluorescent gold nanoclusters (AuNCs) with tunable emission in the visible spectrum, using a ligand scaffold that is made of poly(ethylene glycol) segment appended with a metal coordinating lipoic acid at one end and a functional group at the other end. This synthetic scheme exploits the ability of the UV-induced photochemical transformation of LA-based ligands to provide DHLA and other thiol byproducts that exhibit great affinity to metal nanoparticles, obviating the need for chemical reduction of the dithiolane ring using classical reducing agents. The influence of various experimental conditions, including the photoirradiation time, gold precursor-to-ligand molar ratios, time of reaction, temperature, and the medium pH, on the growth of AuNCs has been systematically investigated. The photophysical properties, size, and structural characterization were carried out using UV-vis absorption and fluorescence spectroscopy, TEM, DOSY-NMR, and X-ray photoelectron spectroscopy. The hydrodynamic size (RH) obtained by DOSY-NMR indicates that the size of these clusters follows the trend anticipated from the absorption and PL data, with RH(red) > RH(yellow) > RH(blue). The tunable emission and size of these gold nanoclusters combined with their high biocompatibility would make them greatly promising for potential use in imaging and sensing applications.

LC-MS/MS Method for the Determination and Quantitation of Penicillin G and Its Metabolites in Citrus Fruits Affected by Huanglongbing

In this study, we developed and validated a method for the extraction, identification, and quantitation of penicillin G and its metabolites (penilloic acid and penillic acid) in a variety of citrus fruits by employing sequential liquid/liquid and solid-phase extraction techniques in conjunction with UHPLC-MS/MS. Two product ion transitions per analyte were required for identification, which contributes to a high degree of selectivity. Corrected recoveries of penicillin G using an isotopically labeled internal standard were 90-100% at fortification levels of 0.1, 0.25, 1, and 10 ng/g. Absolute recoveries for penillic acid and penilloic acid were 50-75% depending on the matrix used. The limit of detection (LOD) of penicillin G and its metabolites was found to be 0.1 ng/g when 2 g of citrus was extracted. This method is useful in determining residue levels of penicillin G and its metabolites in citrus trees infected with huanglongbing bacteria after antibiotic treatment.

Strategies for interfacing inorganic nanocrystals with biological systems based on polymer-coating

A representative set of nanocrystals made of semiconductors, Au and iron oxide, surface-capped with polymer ligands presenting various metal-coordinating groups.

A multifunctional amphiphilic polymer as a platform for surface-functionalizing metallic and other inorganic nanostructures

We designed a new set of polymer ligands that combine multiple metal-coordinating groups and short polyethylene glycol (PEG) moieties in the same structure. The ligand design relies on the controlled grafting of a large number of amine-terminated histamines and PEG short chains onto a poly(isobutylene-alt-maleic anhydride) backbone,viaa one-step nucleophilic addition reaction. This addition reaction is highly efficient, can be carried out in organic media and does not require additional reagents. We show that when imidazole groups are used the resulting polymer ligand can strongly ligate onto metal nanostructures such as nanoparticles (NPs) and nanorods (NRs) made of gold cores. The resulting polymer-coated NPs and NRs exhibit good colloidal stability to pH changes and added electrolytes. This constitutes a departure from the use of thiol-based ligands to coordinate on Au surfaces. The present chemical approach also opens up additional opportunities for designing hydrophilic and reactive platforms where the polymer coating can be adjusted to various metal and metal oxide surfaces by simply modifying or combining the addition reaction with other metal coordinating groups. These could include iron oxide NPs and semiconductor QDs. These polymer-capped NPs and NRs can be used to develop biologically-active platforms with potential use for drug delivery and sensing.

Understanding the self-assembly of proteins onto gold nanoparticles and quantum dots driven by metal-histidine coordination

Coupling of polyhistidine-appended biomolecules to inorganic nanocrystals driven by metal-affinity interactions is a greatly promising strategy to form hybrid bioconjugates. It is simple to implement and can take advantage of the fact that polyhistidine-appended proteins and peptides are routinely prepared using well established molecular engineering techniques. A few groups have shown its effectiveness for coupling proteins onto Zn- or Cd-rich semiconductor quantum dots (QDs). Expanding this conjugation scheme to other metal-rich nanoparticles (NPs) such as AuNPs would be of great interest to researchers actively seeking effective means for interfacing nanostructured materials with biology. In this report, we investigated the metal-affinity driven self-assembly between AuNPs and two engineered proteins, a His7-appended maltose binding protein (MBP-His) and a fluorescent His6-terminated mCherry protein. In particular, we investigated the influence of the capping ligand affinity to the nanoparticle surface, its density, and its lateral extension on the AuNP-protein self-assembly. Affinity gel chromatography was used to test the AuNP-MPB-His7 self-assembly, while NP-to-mCherry-His6 binding was evaluated using fluorescence measurements. We also assessed the kinetics of the self-assembly between AuNPs and proteins in solution, using time-dependent changes in the energy transfer quenching of mCherry fluorescent proteins as they immobilize onto the AuNP surface. This allowed determination of the dissociation rate constant, Kd(-1) ∼ 1-5 nM. Furthermore, a close comparison of the protein self-assembly onto AuNPs or QDs provided additional insights into which parameters control the interactions between imidazoles and metal ions in these systems.

Growth of highly fluorescent polyethylene glycol- and zwitterion-functionalized gold nanoclusters

We have prepared and characterized a new set of highly fluorescent gold nanoclusters (AuNCs) using one-step aqueous reduction of a gold precursor in the presence of bidentate ligands made of lipoic acid anchoring groups, appended with either a poly(ethylene glycol) short chain or a zwitterion group. The AuNCs fluoresce in the red to near-infrared region of the optical spectrum with emission centered at ∼750 nm and a quantum yield of ∼10-14%, and they exhibit long fluorescence lifetimes (up to ∼300 ns). Dispersions of these AuNCs exhibit great long-term colloidal stability, over a wide range of pHs (2-13) and in the presence of high electrolyte concentrations, and a strong resistance to reducing agents such as glutathione. The growth strategy further permitted the controlled, in situ functionalization of the NCs with reactive groups (e.g., carboxylic acid or amine), making these nanoclusters compatible with common and simple-to-implement coupling strategies, such as carbodiimide chemistry. These properties combined make these fluorescent NCs greatly promising for use in various imaging and sensing applications where NIR and long-lived excitations are desired.

Growth of in situ functionalized luminescent silver nanoclusters by direct reduction and size focusing

We have used one phase growth reaction to prepare a series of silver nanoparticles (NPs) and luminescent nanoclusters (NCs) using sodium borohydride (NaBH(4)) reduction of silver nitrate in the presence of molecular scale ligands made of polyethylene glycol (PEG) appended with lipoic acid (LA) groups at one end and reactive (-COOH/-NH(2)) or inert (-OCH(3)) functional groups at the other end. The PEG segment in the ligand promotes solubility in a variety of solvents including water, while LAs provide multidentate coordinating groups that promote Ag-ligand complex formation and strong anchoring onto the NP/NC surface. The particle size and properties were primarily controlled by varying the Ag-to-ligand (Ag:L) molar ratios and the molar amount of NaBH(4) used. We found that while higher Ag:L ratios produced NPs, luminescent NCs were formed at lower ratios. We also found that nonluminescent NPs can be converted into luminescent clusters, via a process referred to as "size focusing", in the presence of added excess ligands and reducing agent. The nanoclusters emit in the far red region of the optical spectrum with a quantum yield of ~12%. They can be redispersed in a number of solvents with varying polarity while maintaining their optical and spectroscopic properties. Our synthetic protocol also allowed control over the number and type of reactive functional groups per nanocluster.

Glycosylated quantum dots for the selective labelling of Kluyveromyces bulgaricus and Saccharomyces cerevisiae yeast strains

Highly fluorescent CdTe quantum dots (QDs) stabilized by thioglycolic acid (TGA) were prepared by an aqueous solution approach and used as fluorescent labels in detecting yeast cells. Sugars (mannose, galactose or glucose) were adsorbed on CdTe@TGA QDs and the interaction of these nanoparticles with yeast cells was studied by fluorescence microscopy. Results obtained demonstrate that galactose and mannose functionalized QDs associate respectively with Kluyveromyces bulgaricus and Saccharomyces cerevisiae yeast strains due to saccharide/lectin specific recognition. Glucose-functionalized CdTe QDs, which are not recognized by cell lectins, preferentially localize in the bud scars of S. cerevisiae.

The influence of capping thioalkyl acid on the growth and photoluminescence efficiency of CdTe and CdSe quantum dots

The influence of thioalkyl acid ligand was evaluated during aqueous synthesis at 100 °C and under hydrothermal conditions (150 °C) of CdTe and CdSe quantum dots (QDs). Experiments performed with 3-mercaptopropionic acid (MPA), 6-mercaptohexanoic acid (MHA) and 11-mercaptoundecanoic acid (MUA) demonstrated that the use of MHA and MUA allowed for the preparation of very small nanoparticles (0.6-2.5 nm) in carrying out the reaction under atmospheric pressure or in an autoclave and that the photophysical properties of QDs were dependent on the ligand and on the synthesis conditions. The influence of various experimental conditions, including the Te-to-Cd ratio, temperature, and precursor concentration, on the growth rate of CdTe or CdSe QDs has been systematically investigated. The fluorescence intensities of CdTe QDs capped with MPA, MHA, or MUA versus pH were also found to be related to the surface coverage of the nanoparticles.