Ferroelectric domain breakdown

We observe a stringlike domain penetration from a ferroelectric surface deep into the crystal bulk induced by a high voltage atomic force microscope tip. The domains, which resemble channels of an electrical breakdown, nucleate under an electric field of around 10(7) V/cm at the ferroelectric surface, and grow throughout the crystal bulk where the external electric field is practically zero. A theory explaining the shape of the formed domains is presented. It shows that the driving force for the domain breakdown is the decrease of the total free energy of the system with increasing domain length.     

A fast algorithm for solving systems of linear equations with two variables per equation

We present a fast algorithm for solving m X n systems of linear equations Ax = c with at most two variables per equation. The algorithm makes use of a linear-time algorithm for constructing a spanning forest of an undirected graph, and it requires 5m + 2n – 2 arithmetic operations in the worst case.     

Amplified detection of single-base mismatches in DNA using microgravimetric quartz-crystal-microbalance transduction

Three different methods for the amplified detection of a single-base mismatch in DNA are described using microgravimetric quartz-crystal-microbalance as transduction means. All methods involve the primary incorporation of a biotinylated base complementary to the mutation site in the analyzed double-stranded primer/DNA assembly. The double-stranded assembly is formed between 25 complementary bases of the probe DNA assembled on the Au-quartz crystal and the target DNA. One method of amplification includes the association of avidin- and biotin-labeled liposomes to the sensing interface. The second method of amplified detection of the base mismatch includes the association of an Au-nanoparticle-avidin conjugate to the sensing interface, and the secondary Au-nanoparticle-catalyzed deposition of gold on the particles. The third amplification route includes the binding of the avidin-alkaline phosphatase biocatalytic conjugate to the double-stranded surface followed by the oxidative hydrolysis of 5-bromo-4-chloro-3-indolyl phosphate to the insoluble product indigo derivative that precipitates on the transducer. Comparison of the three amplification routes reveals that the catalytic deposition of gold on the Au-nanoparticle/avidin conjugate is the most sensitive method, and the single-base mismatch in the analyzed DNA is detected with a sensitivity that corresponds to 3x10(-16) M.     

Excited state proton transfer in reverse micelles

The aqueous phase of water/AOT reversed micelles having varying diameters was probed by a single free diffusing proton that was released form a hydrophilic photoacid molecule (2-naphthol-6,8-disulfonate). The fluorescence decay signals were reconstructed through the geminate recombination algorithm, accounting for the reversible nature of the proton-transfer reactions at the surface of the excited molecule and at the water/detergent interface. The radial diffusion of the proton inside the aqueous phase was calculated accounting for both the entropy of dilution and the total electrostatic energy of the ion pair, consisting of the pair-energy and self-energy of the ions. The analysis implied that micellar surface must be modeled with atomic resolution, assuming that the sulfono residue protrudes above the water/hydrocarbon interface by approximately 2 A. The analysis of the fluorescence decay curves implies that the molecule is located in a solvent with physical-chemical properties very similar to bulk water, except for the dielectric constant. For reversed micelles with r(max) > or = 16 A, the dielectric constant of the aqueous phase was approximately 70 and for smaller micelles, where approximately 60% of the water molecule is in contact with the van der Waals surface of the micelle, it is as low as 60. This reduction is a reflection of the increased fraction of water molecule that is in close interaction with the micelle surface.     

Endonuclease-based logic gates and sensors using magnetic force-amplified readout of DNA scission on cantilevers

The endonuclease scission of magnetic particles functionalized with sequence-specific DNAs, which are associated on cantilevers, is followed by the magnetic force-amplified readout of the reactions by the nano-mechanical deflection/retraction of the cantilevers. The systems are employed to develop AND or OR logic gates and to detect single base mismatch specificity of the endonucleases. The two endonucleases EcoRI (E(A)) and AscI (E(B)) are used as inputs. The removal of magnetic particles linked to the cantilever by the duplexes 1/1a and 2/2a via the simultaneous cleavage of the DNAs by E(A) and E(B) leads to the retraction of the magnetically deflected cantilever and to the establishment of the "AND" gate. The removal of the magnetic particles linked to the cantilevers by the duplex 3/3a by either E(A) or E(B) leads to the retraction of the magnetically deflected cantilever and to the establishment of the "OR" gate. The magnetic force-amplified readout of endonuclease activities is also employed to reveal single base mismatch specificity of the biocatalysts.     

Supramolecular aptamer-thrombin linear and branched nanostructures

Alpha and beta conjugated bis-aptamers against thrombin act as bidentate "glue" for the self-assembly of thrombin nanowires; mixing the bidentate aptamer with a tripodal tridentate alpha aptamer construct yields branched thrombin nanowire structures.     

Discrete angle rotations of Bi nanoparticles embedded in a Ga matrix

Spontaneous instabilities of nanoparticles are known to be influenced by the temperature, and strongly depend on the particle size. However, it is not clear what is the role of the surrounding material that is in contact with the particle. Here we report on the difference between spontaneous rotations of Bi nanoparticles embedded in amorphous SiO and those embedded in liquid Ga. The phenomenon was studied quantitatively by time resolved transmission electron microscopy using Fourier Transform analysis of highresolution electron microscopy images. While rotations of Bi nanoparticles embedded in amorphous SiO occur by all angles, the rotations of Bi nanoparticles embedded in liquid Ga occur by discrete angles. Our results point quantitatively, for the first time, to the role and importance of the contacting surrounding surface during the rotation of nanoparticles.     

Application of Fluorescent Nanocrystals (q-dots) for the Detection of Pathogenic Bacteria by Flow-Cytometry

Fluorescent semiconductor nanocrystals (q-dots) benefit from practical features such as high fluorescence intensity, broad excitation band and emission diameter dependency. These unique spectroscopic characterizations make q-dots excellent candidates for new fluorescent labels in multi-chromatic analysis, such as Flow-Cytometry (FCM). In this work we shall present new possibilities of multi-labeling and multiplex analysis of pathogenic bacteria, by Flow-Cytometry (FCM) analysis and new specific IgG—q-dots conjugates. We have prepared specific conjugates against B. anthracis spores (q-dots585-IgGαB. anthracis and q-dots655-IgGαB.anthracis). These conjugates enabled us to achieve double staining of B. anthracis spores which improve the FCM analysis specificity versus control Bacillus spores. Moreover, multiplexed analysis of B. anthracis spores and Y. pestis bacteria was achieved by using specific antibodies labeled with different q-dots to obtain: q-dots585-IgGαB. anthracis and q-dots655-IgGαY.pestis, each characterized by its own emission peak as a marker. Specific and sensitive multiplex analysis for both pathogens has been achieved, down to 10³ bacteria per ml in the sample.     

Temperature-Dependent and pH-Responsive Pillar[5]arene-Based Complexes and Hydrogen-Bond-Based Supramolecular Pentagonal Boxes in Water

Supramolecular systems in water are of paramount importance and those based on hydrogen bonds are both intriguing and scarce. Here, after studying the peculiar host–guest complexes formed between per-dimethylamino-pillar[5]arene ( 1 ) and the bis-sulfonates 2 a – c , we describe the formation of the first hydrogen-bond-based supramolecular pentagonal boxes (SPBs), which are stable in water. These pH-responsive SPBs are constructed from 1 as a body, benzene polycarboxylic acids 3 a , b as lid compounds, and 2 a – c as guests. We demonstrate that encapsulation of 2 a – c in pillar[5]arene 1 and in the highly stable water-soluble SPBs, that is, 1(3 a) ₂ and 1(3 b) ₂, is both temperature and pH dependent and, quite interestingly, depends, on the nature of the lid compounds used for capping the boxes even at high pH. We also highlight the difference in the ¹H NMR characteristics of 2 b and 2 c in the cavity of 1 and the SPBs.