Glucose oxidase as a blocking agent-based signal amplification strategy for the fabrication of label-free amperometric immunosensors

An effective electrochemical signal amplification strategy based on enzyme membrane modification and redox probe immobilization was proposed to construct an amperometric immunosensor.L-cysteine@ferrocene functionalized chitosan,which possessed not only efficient redox-activity but also excellent film-forming ability,was coated on the bare glass carbon electrode. Moreover,the thiol groups(SH)in the ferrocenyl compound were used for gold nanoparticles immobilization via the strong bonding interaction,which co...     

Two-dimensional self-assembly of esters with different configurations at the liquid-solid interface

Self-assembled monolayers of hexadecyl palmitate (HP) and 3,3′-thiodipropionic acid di-n-octadecyl ester (TADE) physisorbed on highly oriented pyrolytic graphite (HOPG) are investigated using scanning tunneling microscope (STM) and computer simulation. Both molecules form alkane-like linear shapes to maximize the interactions with substrate when they adsorb on HOPG surface. The HP molecules self-assemble into lamellae with the chain-trough angle of 48°, which is the result of a shifting 3/2 units from the adjacent molecule in a lamella. Based on the simulation insights combined with STM images, we confirm that a perpendicular orientation appears in which the HP molecular backbone is rotated 90° with respect to the substrate such that the carbonyl points away from the HOPG surface. TADE molecules form three kinds of configurations with chain-trough angles of 90°, 72° and 60° by shifting 0, 1/2 and 1 units from their adjacent molecules, respectively. The bright stripes in STM images reveal the electron density distribution of the part between two ester groups. The energy differences of three TADE adsorption configurations by molecular mechanics (MM) simulation are used to explain the structural coexistence phenomenon. It is also shown that lattice match between alkyl chain of molecules and HOPG substrate could change molecular conformation upon self-assembly.     

Interrelation of intrinsic and extrinsic defects – congruent, stoichiometric, and regularly ordered lithium niobate

A new approach to the intrinsic and extrinsic defect subsystems, considering them as one integrated functional system, is developed for complex oxides. The strong interrelation of these subsystems becomes especially apparent when concentrations of both defect classes are comparable. A new parameter, reflecting the total intrinsic defect concentration, is introduced to determine the degree of crystal imperfection. The necessity of at least two calibrated samples – congruent and regularly ordered crystals – is substantiated. The accuracy by which the parameter can be determined can serve as a criterion in comparison of different methods of crystal characterisation. A procedure for crystal calibration by several physical characteristics is illustrated. Such a heuristic generalisation of the concept of mutual correlation of the whole defect system and the material only became possible on the basis of experimental and theoretical study of large numbers of LiNbO₃ crystals. The spectra of EPR, NMR, ENDOR, and other properties of crystals with different compositions, diverse modifiers (K, Mg,...), and various probe impurities have been analysed. It is found that crystals with vanishingly small concentration of intrinsic defects offer extraordinary informative opportunities. Their micro- and macroscopic properties are discussed. The developed ideas have a general character; therefore they should also be valid for other non-stoichiometric complex oxides. Received: 3 December 1998 / Revised version: 15 February 1999 / Published online: 12 April 1999     

Laser mode manipulation by intracavity dynamic holography: Application to mode selection

Intra-cavity dynamic holography is proposed as a self-adaptive, easy to set up technique for efficient laser mode manipulation. A first implementation is presented here as a longitudinal mode selector providing a spectacular spectral narrowing in linear laser cavities operating both in the pulsed and the cw regimes. Received: 12 April 1999 / Published online: 24 June 1999     

Combined electric field and near-field scanning optical microscopy: modification of silicon surfaces

Received: 3 July 1998     

Contrast enhancement on crystalline silicon in polarized reflection mode tip-enhanced Raman spectroscopy

Tip-enhanced Raman spectroscopy in reflection mode makes possible the nanoscale characterization of non-transparent samples, such as silicon, inaccessible in transmission mode. However, a particular feature of this technique is the superposition of the far-field Raman signal with the near-field one generated in the tip vicinity sometimes resulting in a low near-field-to-far-field contrast. By using a polarized configuration and orientation optimization of a (0 0 1) crystalline Si sample we were able to enhance significantly the contrast through reducing the far-field contribution, reaching a value of about 40. This contrast enhancement method can be applied in principle to any crystalline sample.     

Intensity resonances in a double-mode HeNe/CH4 laser with synchronized modes

4 gas laser with an intracavity absorbing cell is studied experimentally and theoretically at a modulation frequency approximately equal to the intermode beat frequency. It is revealed that in the vicinity of the absorption-line centre the intensity of every mode for certain system parameters displays resonance structures narrower than the homogeneous line width of the absorption line. This occurs when the range of mode synchronization is near the absorption-line centre and its size is less than the homogeneous width of the absorption line. Received: 29 February 1996/Revised version: 4 February 1997     

Delineation of a p–n junction using dC/dX imagery produced by shear-mode scanning capacitance microscopy

Using a laterally oscillating all-metallic probe, a scanning capacitance microscope (SCM) has been used to yield an image of the spatial derivative of the local capacitance, dC/dX, where C and X are the local capacitance and the axis of the probe tip locus on the sample surface, respectively. Bias fields, except for the ultra-high-frequency fields used for sensing the capacitance, are not necessary to detect the dC/dX signal, which yields an image delineating clearly the depletion region due to the p–n junction. Simultaneously with the dC/dX image, the new SCM can give images of topography and dC/dV if an alternating field V is applied between the probe and sample. Received: 19 March 2001 / Accepted: 22 March 2001 / Published online: 27 June 2001     

Dynamic and static contributions to the zero-field splitting term of divalent nickel in fluosilicate crystals

Previously published electron paramagnetic resonance (EPR) data for Ni²⁺(3d⁷) in hydrated and deuterated crystals of zinc and nickel fluosilicate have been re-analyzed to separate the static and dynamic contributions to the fine-structure (or axial zero-field-splitting) term D in the spin-Hamiltonian. While the Debye parameters of ZnSiF₆·6H₂O and ZnSiF₆·6D₂O were determined in an earlier low-temperature study¹, those of the undiluted nickel crystals, for which good data between 4 and 77 K is lacking, have been estimated here by comparison of the data above 60 K with those for the corresponding zinc compounds. The numerical results indicate that the measured values of D are composed of a negative dynamical contribution produced by the rotational motions of the water ligands, together with both negative and positive static contributions produced by the water ligands, and the more distant [SiF₆]²⁻ and [Ni.6H₂O]²⁺ complexes, respectively. A point-charge calculation shows the contribution of the latter to be roughly +2.5 cm⁻¹ in NiSiF₆·6H₂O. The exceptionally large temperature variations of D in these crystals is attributed to the near-cancellation of the positive and negative static contributions, leaving the effect of the dynamical contribution dominant.     

Acousto-optic mode-locker for Nd:Lasers using paratellurite

The design of an acousto-optic modulator using paratellurite requiring only low driving power is described. Because of the high figure of merit a high modulation index can be achieved. To avoid an intermediate transmission peak the modulator should not be operated in the Bragg-regime but rather in the transition regime. The time dependent transmission for this regime is calculated as a function of the material parameters. Experimentally, modulation indices up to 10 are obtained. Using such a TeO₂ mode-locker a pulsed Nd:Cr:GSGG laser delivered pulses down to 70 ps.