"Giant" multishell CdSe nanocrystal quantum dots with suppressed blinking

Semiconductor nanocrystal quantum dots (NQDs) comprise an important class of inorganic fluorophores for applications from optoelectronics to biology. Unfortunately, to date, NQD optical properties (e.g., their efficient and particle-size-tunable photoluminescence) have been susceptible to instabilities at the bulk and single-particle levels. Specifically, ensemble quantum yields (QYs) in emission are dependent upon NQD surface chemistry and chemical environment, while at the single-particle level, NQDs are characterized by significant fluorescence intermittency (blinking) that hinders applications as single-photon light sources for quantum informatics and biolabels for real-time monitoring of single biomolecules. Furthermore, while NQDs are significantly more photostable than their organic dye counterparts, traditional NQDs photobleach over periods of seconds to many minutes. Here, we demonstrate for the first time that by encapsulating the NQD core in a sufficiently thick inorganic shell, we are able to divorce NQD function from NQD surface chemistry and chemical environment. We show that our "giant" NQDs (g-NQDs) are functionally distinct from standard core-only, core/shell and even core/multishell NQDs. g-NQDs are substantially less sensitive to changes in surface chemistry. They do not photobleach under continuous laser excitation over periods of several hours repeated over several days, and they exhibit markedly different blinking behavior; >20% of the g-NQDs do not blink, while >40% have on-time fractions of >80%. All of these observations are in stark contrast with control samples comprising core-only and standard, thinner core/multishell NQDs.     

Adsorptive and acidic properties, reversible lattice oxygen evolution, and catalytic mechanism of cryptomelane-type manganese oxides as oxidation catalysts

Cryptomelane-type manganese oxides have been synthesized, characterized, and tested in the total oxidation of volatile organic compounds and CO oxidation. The structural, compositional, morphological, acid-base, physisorptive-chemisorptive, and thermal stability properties (especially the reversible evolution of lattice oxygen) have been studied in detail using ICP-AES (inductively coupled plasma-atomic emission spectroscopy), HRSEM (high-resolution scanning electronic microscope), XRD (X-ray diffraction), IR (infrared) and adsorbate-IR, N2 and CO2 physisorption at 77 and 273 K, respectively, TPD-MS (temperature-programmed decomposition-mass spectroscopy), and TGA-DSC (thermogravimetric analysis-differential scanning calorimetry) techniques. Kinetic and mechanistic studies for the catalytic function have been conducted and related to the characterization results. Cryptomelane has shown to be highly microporous, by using CO2 physisorption, and highly hydrophobic, possessing both Br?nsted and Lewis acid sites. A part of the lattice oxygen atoms can be reversibly removed from the framework and recovered at elevated temperature without changing the framework structure. These lattice oxygen atoms can react with CO even at room temperature and are active sites for the oxidation of benzene. The consumed lattice oxygen atoms are replenished by gaseous oxygen to complete a catalytic cycle. The ease of reversible evolution of lattice oxygen, together with the high porosity, hydrophobicity, and acidity, leads to the excellent oxidation properties of OMS-2.     

Hydrogen peroxide biosensor with a supramolecular layer-by-layer design

A new sensor design is reported for the construction of an amperometric enzyme biosensor toward H (2)O(2). It was based in the supramolecular immobilization of alternating layers of horseradish peroxidase (either modified with 1-adamantane or beta-cyclodextrin-branched carboxymethylcellulose residues) on Au electrodes coated with polythiolated beta-cyclodextrin polymer. The analytical response of the electrodes, using 1 mM hydroquinone as an electrochemical mediator, increases when the number of enzyme layers increases. The biosensor having three enzyme layers showed a sensitivity of 720 microA/M cm (2) and a detection limit of 2 microM and retained 96% of its initial activity after 30 days of storage. The host-guest supramolecular nature of the immobilization method was confirmed by cyclic voltammetry.     

Belizeanic acid: a potent protein phosphatase 1 inhibitor belonging to the okadaic acid class, with an unusual skeleton

Belizeanic acid (BA), a novel metabolite belonging to the okadaic acid class of protein phosphatase inhibitors, was isolated from artificial cultures of the dinoflagellate Prorocentrum belizeanum. The structure and conformational behaviour of BA was elucidated by a combination of NMR spectroscopy and conformational analysis. The isolation of this metabolite, which possesses a simplified version of the okadaic acid skeleton, supports the biogenetic pathway previously reported for this class of compounds. BA showed potent inhibitory activity against protein phosphatase 1 (PP1) within the nM range. A plausible model for the interaction of BA with the PP1 binding pocket was derived from computational docking studies.     

Light‐Driven Rotary Molecular Motors on Gold Nanoparticles

We report the synthesis of unidirectional light‐driven rotary molecular motors based on chiral overcrowded alkenes and their immobilisation on the surface of gold nanoparticles through two anchors. Using a combination of ¹H and ¹³C NMR, UV/Vis and CD spectroscopy, we show that these motors preserve their photochemical and thermal behaviour after they have been attached to gold nanoparticles. Furthermore, we describe the synthesis of ²H‐ and ¹³C‐labelled derivatives that were used to verify the unidirectionality of the rotary cycle of these motors both in solution and while grafted to gold nanoparticles. Taken together, these data support the conclusion that these motors maintain their unidirectional rotary cycle when grafted to the surface of small (ca. 2 nm) gold nanoparticles. Thus, continuous irradiation of the system under appropriate conditions leads to unidirectional rotation of the upper half of the molecules relative to the entire nanoparticle.     

On-line monitoring of gas-phase bioreactors for biogas treatment: hydrogen sulfide and sulfide analysis by automated flow systems

Biogas is produced by biological processes under anaerobic conditions and may contain up to 20,000 ppm_v hydrogen sulfide (H₂S), a corrosive substance that attacks power engines and can affect the health of the industrial staff. H₂S must be removed from the biogas, especially in co-generation facilities where the biogas is burnt for energy production. Nowadays, biofiltration is being studied and considered as an interesting alternative for removing H₂S from the biogas besides classical chemical processes. The novelty of this work is the design and construction of an automated H₂S on-line analyser to assess the composition of the liquid and gas phases of gas-phase bioreactors. The analyser is made of two parallel flow configurations which share the same detection device. The first configuration is a single-channel flow injection analyser (FIA) to detect S²⁻ in the liquid phase. The second configuration is a continuous flow analyser (CFA) with a gaseous diffusion step (GD–CFA) for detecting H₂S in the gas phase. The diffusion step enables separation of the H₂S_(g) from the sample and its conversion into a detectable chemical species (S²⁻). S²⁻ detection was performed with an Ag₂S ion-selective electrode (ISE) selective to . The main response parameters of the FIA system are a linear range between 3 × 10⁻⁵ and 1 × 10⁻¹ mol L⁻¹ S²⁻ (0.61–3,200 mg L⁻¹), with a sensitivity of 27.9 mV decade⁻¹ and a detection limit of 1.93 × 10⁻⁵ mol L⁻¹ S²⁻. The GD–CFA configuration presents a linear range between 400 and 10,000 ppm_v H₂S_(g) with a sensitivity of 26.1 mV decade⁻¹ and a detection limit of 245 ppm_v H₂S. The proposed analyser was used by analysing real gas and liquid samples with optimal results at a full-scale biotrickling filter for biogas treatment at a municipal wastewater treatment plant. Figure The novelty of this work is the design and construction of an automated H₂S on-line analyzer to assess the composition of the liquid and gas phases of gas-phase bioreactors. The analyser is made of two parallel flow configurations which share the same detection device. The first configuration is a single-channel flow injection analyser (FIA) to detect S^2- in the liquid phase. The second configuration is a continuous flow analyser (CFA) with a gaseous diffusion step (GD-CFA) for detecting H₂S in the gas phase.     

Analytical prospect of compact disk technology in immunosensing

A sensitive and versatile methodology involving recordable compact disks as molecular screening surfaces and a standard optical CD/DVD drive as detector, is reported. Quantitative immunoanalysis, in microarray format, of a cancer marker (alpha-fetoprotein, AFP) and a selective herbicide (atrazine) on four types of audio-video disc was conducted. Enzyme or gold nanoparticle-labeled antibodies were used as tracers, forming a precipitate on the sensing disk surface. The principle of disk reading is based on capture of analog signals with the disk drive that were proportional to the darkness of the immunoreaction product. Detection limits for AFP (8.0 μg L⁻¹) and for atrazine (0.04 μg L⁻¹) were under the threshold needed to detect nonseminomatous testicular cancer, and below the maximum E.U. residue limit for drinking water, respectively. The described methodology improves the previous developments using CDs and highlights the enormous potential of immunoassay methods using standard audio–video disk surfaces in combination with the CD/DVD drive for clinical analysis, drug discovery, or high-throughput multiresidue screening applications. Figure  Eye-catching image The analytical potential of commercial audio–video discs as molecular screening surfaces in combination with use of a standard CD/DVD drive as detector for quantitative immunoanalysis of a cancer marker and agrochemical residues is demonstrated.     

Preparation of antibodies and development of a sensitive immunoassay with fluorescence detection for triazine herbicides

Specific polyclonal antibodies against s-triazine herbicides were obtained by preparing immunogens coupling home-synthesized haptens derivatives of simazine (6-chloro-N-ethyl-N′-ethyl-1,3,5-triazine-2,4-diamine) to lysine groups of hemocyanin from keyhole limpets and bovine serum albumin carrier proteins. Three highly sensitive rabbit antisera were obtained and evaluated with a battery of six enzyme tracers derived from triazine structures in an optimized ELISA format. The antiserum As8 and the HRP-2f tracer, which yield the best assay sensitivity for simazine (detection limit 0.11 ± 0.02 μg L⁻¹, IC₅₀ 0.88 ± 0.04 μg L⁻¹), were applied to the development of a sensitive flow-through immunoassay for the analysis of this herbicide. The automated assay was based on a direct competitive immunosorbent assay and fluorescence detection. The optimized method presents an IC₅₀ value of 0.35 ± 0.04 μg L⁻¹ with a detection limit of 1.3 ± 0.9 ng L⁻¹ and a dynamic range from 0.010 to 7.5 μg L⁻¹ simazine. The generic nature of the antiserum was shown by good relative cross-reactivities with other triazines such as atrazine (420%) or propazine (130%) and a lower response to terbutylazine (6.4%) and desethyl-atrazine (2.2%). No cross-reactivity was obtained for nonrelated pesticides such as 2,4-dichlorophenoxyacetic acid or linuron and the assay could be applied as a screening method for triazine herbicides. The total analysis time was 30 min per determination and the immunosensor could be reused for more than 150 cycles without significant loss of activity. The immunosensor has been successfully applied to the direct analysis of simazine in surface water samples at the nanogram per liter level. The results obtained by comparative analysis of the immunosensor with a chromatographic procedure for triazines showed a close correspondence.     

A Critique of Armstrong’s Truthmaking Account of Possibility

In this paper I argue against Armstrong’s recent truthmaking account of possibility. I show that the truthmaking account presupposes modality in a number of different ways, and consequently that it is incapable of underwriting a genuine reduction of modality. I also argue that Armstrong’s account faces serious difficulties irrespective of the question of reduction; in particular, I argue that his Entailment and Possibility Principles are both false.