Optical measurement of neural activity using surface plasmon resonance

We demonstrate that surface plasmon resonance (SPR) is applicable to the optical detection of neural signals. A low-noise SPR sensor was developed as a label- and artifact-free method for the extracellular recording of neural activity. The optical responses obtained from a rat sciatic nerve were highly correlated with simultaneously recorded electrical responses. Additional studies with stimulation intensity and lidocaine further confirmed that the optically measured signals originated from neural activities.     

Two-dimensional poroelastic acoustical foam shape design for absorption coefficient maximization by topology optimization method

Optimal shape design of a two-dimensional poroelastic acoustical foam is formulated as a topology optimization problem. For a poroelastic acoustical system consisting of an air region and a poroelastic foam region, two different physical regions are continuously changed in an iterative design process. To automatically account for the moving interfaces between two regions, we propose a new unified model to analyze the whole poroelastic acoustical foam system with one set of governing equations; Biot's equations are modified with a material property interpolation from a topology optimization method. With the unified analysis model, we carry out two-dimensional optimal shape design of a poroelastic acoustical foam by a gradient-based topology optimization setting. The specific objective is the maximization of the absorption coefficient in low and middle ranges of frequencies with different amounts of a poroelastic material. The performances of the obtained shapes are compared with those of well-known wedge shapes, and the improvement of absorption is physically interpreted.     

Diagonal quasi-Newton methods via least change updating principle with weighted Frobenius norm

Numerical Algorithms - This paper presents a class of low memory quasi-Newton methods with standard backtracking line search for large-scale unconstrained minimization. The methods are derived by...     

Single Atom Ring Contraction of Peptide Macrocycles Using Cornforth Rearrangement

Site-selective transformations of densely functionalized scaffolds have been a topic of intense interest in chemical synthesis. Herein we have repurposed the rarely used Cornforth rearrangement as a tool to effect a single-atom ring contraction in cyclic peptide backbones. Investigations into the kinetics of the rearrangement were carried out to understand the impact of electronic factors, ring size, and linker type on the reaction efficiency. Conformational analysis was undertaken and showed how subtle differences in the peptide backbone result in substrate-dependent reaction profiles. This methodology can now be used to perform conformation-activity studies. The chemistry also offers an opportunity to install building blocks that are not compatible with traditional C-to-N iterative synthesis of macrocycle precursors.     

Highly Cooperative CO2 Adsorption via a Cation Crowding Mechanism on a Cesium-Exchanged Phillipsite Zeolite

An understanding of the CO₂ adsorption mechanisms on small-pore zeolites is of practical importance in the development of more efficient adsorbents for the separation of CO₂ from N₂ or CH₄. Here we report that the CO₂ isotherms at 25–75 °C on cesium-exchanged phillipsite zeolite with a Si/Al ratio of 2.5 (Cs-PHI-2.5) are characterized by a rectilinear step shape: limited uptake at low CO₂ pressure (P_CO2) is followed by highly cooperative uptake at a critical pressure, above which adsorption rapidly approaches capacity (2.0 mmol g⁻¹). Structural analysis reveals that this isotherm behavior is attributed to the high concentration and large size of Cs⁺ ions in dehydrated Cs-PHI-2.5. This results in Cs⁺ cation crowding and subsequent dispersal at a critical loading of CO₂, which allows the PHI framework to relax to its wide pore form and enables its pores to fill with CO₂ over a very narrow range of P_CO2. Such a highly cooperative phenomenon has not been observed for other zeolites.     

Nanocatalyst-based assay using DNA-conjugated Au nanoparticles for electrochemical DNA detection

Compared to enzymes, Au nanocatalysts show better long-term stability and are more easily prepared. Au nanoparticles (AuNPs) are used as catalytic labels to achieve ultrasensitive DNA detection via fast catalytic reactions. In addition, magnetic beads (MBs) are employed to permit low nonspecific binding of DNA-conjugated AuNPs and to minimize the electrocatalytic current of AuNPs as well as to take advantage of easy magnetic separation. In a sandwich-type electrochemical sensor, capture-probe-conjugated MBs and an indium-tin oxide electrode modified with a partially ferrocene-modified dendrimer act as the target-binding surface and the signal-generating surface, respectively. A thiolated detection-probe-conjugated AuNP exhibits a high level of unblocked active sites and permits the easy access of p-nitrophenol and NaBH 4 to these sites. Electroactive p-aminophenol is generated at these sites and is then electrooxidized to p-quinoneimine at the electrode. The p-aminophenol redox cycling by NaBH 4 offers large signal amplification. The nonspecific binding of detection-probe-conjugated AuNPs is lowered by washing DNA-linked MB-AuNP assemblies with a formamide-containing solution, and the electrocatalytic oxidation of NaBH 4 by AuNPs is minimized because long-range electron transfer between the electrode and the AuNPs bound to MBs is not feasible. The high signal amplification and low background current enable the detection of 1 fM target DNA.     

Temperature effect on nanometer-scale physical properties of mixed phospholipid monolayers

Mixed dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) monolayers have been deposited on mica using Langmuir-Blodgett technique, as a model system for biomembranes. Nanometer-scale surface physical properties were quantitatively characterized with the gradual temperature change using the atomic force microscope. At 25 degrees C, tapping mode imaging revealed the clear phase-separation in the form of microscopic DPPC domain embedded in a DOPC matrix and the obvious step height between the higher DPPC phase and the lower DOPC phase. Surface force measurement made at 25 degrees C in contact mode showed significant contrasts in deformation elasticity, adhesion, and jump-to-surface. These physical property differences were kept below 40 degrees C, while they almost disappeared over 40 degrees C. In addition, the reversibility of the properties for the temperature change was also found.