Classical Monte Carlo simulations have been carried out for liquid water in the NPT ensemble at 25 °C and 1 atm using six of the simpler intermolecular potential functions for the water dimer: Bernal–Fowler (BF), SPC, ST2, TIPS2, TIP3P, and TIP4P. Comparisons are made with experimental thermodynamic and structural data including the recent neutron diffraction results of Thiessen and Narten. The computed densities and potential energies are in reasonable accord with experiment except for the original BF model, which yields an 18% overestimate of the density and poor structural results. The TIPS2 and TIP4P potentials yield oxygen–oxygen partial structure functions in good agreement with the neutron diffraction results. The accord with the experimental OH and HH partial structure functions is poorer; however, the computed results for these functions are similar for all the potential functions. Consequently, the discrepancy may be due to the correction terms needed in processing the neutron data or to an effect uniformly neglected in the computations. Comparisons are also made for self‐diffusion coefficients obtained from molecular dynamics simulations. Overall, the SPC, ST2, TIPS2, and TIP4P models give reasonable structural and thermodynamic descriptions of liquid water and they should be useful in simulations of aqueous solutions. The simplicity of the SPC, TIPS2, and TIP4P functions is also attractive from a computational standpoint.

Comparison of simple potential functions for simulating liquid water

Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO 2 or NH 3 , the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated.

https://science.sciencemag.org/content/sci/287/5453/622.full.pdf

Nanotube molecular wires as chemical sensors

This paper describes a procedure that makes it possible to design and fabricate (including sealing) microfluidic systems in an elastomeric materialpoly(dimethylsiloxane) (PDMS)in less than 24 h. A network of microfluidic channels (with width >20 μm) is designed in a CAD program. This design is converted into a transparency by a high-resolution printer; this transparency is used as a mask in photolithography to create a master in positive relief photoresist. PDMS cast against the master yields a polymeric replica containing a network of channels. The surface of this replica, and that of a flat slab of PDMS, are oxidized in an oxygen plasma. These oxidized surfaces seal tightly and irreversibly when brought into conformal contact. Oxidized PDMS also seals irreversibly to other materials used in microfluidic systems, such as glass, silicon, silicon oxide, and oxidized polystyrene; a number of substrates for devices are, therefore, practical options. Oxidation of the PDMS has the additional advantage that it ...

Rapid prototyping of microfluidic systems in poly(dimethylsiloxane)

Scientific and practical applications of supported lipid-protein bilayers are described. Membranes can be covalently coupled to or separated from solids by ultrathin layers of water or soft polymer cushions. The latter systems maintain the structural and dynamic properties of free bilayers, forming a class of models of biomembranes that allow the application of a manifold of surface-sensitive techniques. They form versatile models of low-dimensionality complex fluids, which can be used to study interfacial forces and wetting phenomena, and enable the design of phantom cells to explore the interplay of lock-and-key forces (such as receptor-ligand binding) and universal forces for cell adhesion. Practical applications are the design of (highly selective) receptor surfaces of biosensors on electrooptical devices or the biofunctionalization of inorganic solids.

https://science.sciencemag.org/content/sci/271/5245/43.full.pdf

Supported Membranes: Scientific and Practical Applications

Isolation and characterization of a novel endogenous peptide ligand for the human APJ receptor.

A silicon-based device, dubbed a microphysiometer, can be used to detect and monitor the response of cells to a variety of chemical substances, especially ligands for specific plasma membrane receptors. The microphysiometer measures the rate of proton excretion from 10(4) to 10(6) cells. This article gives an overview of experiments currently being carried out with this instrument with emphasis on receptors with seven transmembrane helices and tyrosine kinase receptors. As a scientific instrument, the microphysiometer can be thought of as serving two distinct functions. In terms of detecting specific molecules, selected biological cells in this instrument serve as detectors and amplifiers. The microphysiometer can also investigate cell function and biochemistry. A major application of this instrument may prove to be screening for new receptor ligands. In this respect, the microphysiometer appears to offer significant advantages over other techniques.

https://science.sciencemag.org/content/sci/257/5078/1906.full.pdf

The cytosensor microphysiometer: biological applications of silicon technology

Cellular metabolism is affected by many factors in a cell's environment. Given a sufficiently sensitive method for measuring cellular metabolic rates, it should be possible to detect a wide variety of chemical and physical stimuli. A biosensor has been constructed in which living cells are confined to a flow chamber in which a potentiometric sensor continually measures the rate of production of acidic metabolites. Exploratory studies demonstrate several applications of the device in basic science and technology.

https://science.sciencemag.org/content/sci/246/4927/243.full.pdf

Detection of cell-affecting agents with a silicon biosensor

Fluorescence polarization and anisotropy are two nearly equivalent techniques that have together, over the past 5 years, achieved wide use in high throughput screening in drug discovery. These are single-label methods that can be used to construct homogeneous assays that are fast, sensitive, and resistant to some significant interferences. Moreover, the assays are relatively inexpensive. This review surveys the peer-reviewed literature on the subject and explores some of the fundamental issues that bear on assay performance.

Fluorescence Polarization and Anisotropy in High Throughput Screening: Perspectives and Primer

PRINCIPLES OF THE LIGHT-ADDRESSABLE POTENTIOMETRIC SENSOR 88 Measurement of pH 89 The Photoeffect 90 Light Addressability 93 Measurement of Other Chemical Species 93 THE LAPS AS A SENSOR IN AN ANALYTICAL SYSTEM 94 Electrical Measurement of Phospholipid Membranes 94 Discrete Sensor Arrays 94 LAPS as an Imaging Sensor 94 Microvolume Systems 95 The Sensor as a Structural Element of Analytical Systems 96 Data Analysis in LAPS Systems 96 APPLICATIONS FOR BIOCHEMICAL ASSAYS 98 Measurement of Enzyme Substrates and lnhibitors 98 Enzyme-Linked lmmunoassays 98 APPLICATIONS FOR CELL-BASED BIOASSAYS: THE MICROPHYSIOMETER 102 Biological Basis 102 Instrumental Characteristics 102 Applications of Microphysiometry 105 Prospects 108 CONCLUDING PERSPECTIVE 109

John C. Owicki

Papers

The cytosensor microphysiometer: biological applications of silicon technology

Detection of cell-affecting agents with a silicon biosensor

Fluorescence Polarization and Anisotropy in High Throughput Screening: Perspectives and Primer

The Light-Addressable Potentiometric Sensor: Principles and Biological Applications

Biosensors based on the energy metabolism of living cells: The physical chemistry and cell biology of extracellular acidification