Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Sensitive optical biosensors for unlabeled targets: a review.

Robotic medical instrument systems and associated methods utilizing an optical fiber sensors such as Bragg sensor optical fibers. In one configuration, an optical fiber is coupled to an elongate instrument body and includes a fiber core having one or more Bragg gratings. A controller is configured to initiate various actions in response thereto. For example, a controller may generate and display a graphical representation of the instrument body and depict one or more position and/or orientation variables thereof, or adjust motors of an instrument driver to reposition the catheter or another instrument. Optical fibers having Bragg gratings may also be utilized with other system components including a plurality of working instruments that are positioned within a sheath lumen, an instrument driver, localization sensors, and/or an image capture device, and may also be coupled to a patient's body or associated structure that stabilizes the body.

Robotic instrument systems and methods utilizing optical fiber sensors

Structural Health Monitoring (SHM) can be understood as the integration of sensing and intelligence to enable the structure loading and damage-provoking conditions to be recorded, analyzed, localized, and predicted in such a way that nondestructive testing becomes an integral part of them. In addition, SHM systems can include actuation devices to take proper reaction or correction actions. SHM sensing requirements are very well suited for the application of optical fiber sensors (OFS), in particular, to provide integrated, quasi-distributed or fully distributed technologies. In this tutorial, after a brief introduction of the basic SHM concepts, the main fiber optic techniques available for this application are reviewed, emphasizing the four most successful ones. Then, several examples of the use of OFS in real structures are also addressed, including those from the renewable energy, transportation, civil engineering and the oil and gas industry sectors. Finally, the most relevant current technical challenges and the key sector markets are identified. This paper provides a tutorial introduction, a comprehensive background on this subject and also a forecast of the future of OFS for SHM. In addition, some of the challenges to be faced in the near future are addressed.

Fiber Optic Sensors in Structural Health Monitoring

Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

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Interferometric Fiber Optic Sensors

An all-fused-silica pressure sensor fabricated directly onto a fiber tip of 125 μm diameter is described. Simple fabrication steps include only cleaving and fusion splicing. Because no chemical processes are involved, the fabrication is easy, safe, and cost effective. Issues in sensor design and loss analysis are discussed. The sensor has been tested for static pressure response, showing a sensitivity of 2.2 nm/psi, a resolution of 0.01 psi (68.9 Pa), a hysteresis of 0.025%, and capability of operation at temperatures up to 600°C. This miniature sensor may be suitable for medical diagnostics, environmental monitoring, and other industrial applications.

All-fused-silica miniature optical fiber tip pressure sensor

We present a miniature diaphragm-based Fabry-Perot (F-P) interferometric fiber optic sensor fabricated by novel techniques for pressure or acoustic wave measurement that is only approximately 032 mm in diameter By choosing different diaphragm thicknesses and effective diameters, we obtain a sensor measurement range from 5 to 10,000 psi (1 psi = 5172 Torr) and a frequency response up to 2 MHz In addition, the sensor's F-P cavity can be set from micrometers to millimeters with a precision of several nanometers With the all-silica structure, the sensor is reliable, biocompatible, and immune to electromagnetic interference and has high-temperature sensing capability

Miniature all-silica fiber optic pressure and acoustic sensors

This paper presents a miniature fiber-optic high-temperature pressure sensor fabricated on the tip of a singlemode (SM) fiber by means of fusion splicing, cleaving, and wet chemical etching. A new approach was developed to simplify the fabrication and greatly improve the sensitivity. The sensor is made entirely of fused silica, whose high-temperature sensing capability is explored in detail for the first time. Two sensors were tested up to 611/spl deg/C and 710/spl deg/C, respectively, showing excellent repeatability better than 0.62% and 1.4%. The maximum operating temperature is limited by the mechanical creep of the fused silica diaphragm.

High-temperature fiber-tip pressure sensor

A fiber-optic sensor is designed based on multicavity Fabry-Perot interferometry for the study of optical thickness in self-assembled thin-film layers. This miniature sensor is applicable not only to the measurement of self-assembled polyelectrolyte layers but also to the immobilization of proteins such as immunoglobulin G (IgG). The binding of IgG and the corresponding antigen is observed, and the nonspecific binding characteristics are investigated. The optical thickness changes are used to evaluate the immobilization of the IgG and the immunological activities of the immobilized layers.

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Miniature fiber-optic multicavity Fabry-Perot interferometric biosensor.

A novel diaphragm-based miniature optical fiber pressure sensor has been shown to work at temperatures up to 700/spl deg/C with a sensitivity of 2.93 nm/psi and a resolution of 0.01 psi (68.9 Pa). A passive temperature compensation scheme was used to reduce the temperature dependence to 0.0076 psi//spl deg/C (52.4 Pa//spl deg/C). The sensor exhibited a linear response in the available testing range from 0 to 200 psi (1.38 MPa), and being composed entirely of fused silica, the sensor's structure is very reliable, corrosion resistant, and immune to electromagnetic interference.

Kristie L. Cooper

Papers

All-fused-silica miniature optical fiber tip pressure sensor

Miniature all-silica fiber optic pressure and acoustic sensors

High-temperature fiber-tip pressure sensor

Miniature fiber-optic multicavity Fabry-Perot interferometric biosensor.

A novel temperature-insensitive optical fiber pressure sensor for harsh environments