Bifurcated fibers

The design and operation of an NIR probe is similar to that of conventional UV-visible OFCD reported in the literature.(21) These probes consist of a light source, a bifurcated fiber, an NIR dye, a polymer matrix, a detector, and other optical components. 

We are interested in the development of an OFCD using bifurcated fibers.(70) In principle, they operate by first transmitting radiation from the light source through an optical fiber. The radiation exits at the distal end of the fiber where the reaction phase is located and where dye molecules susceptible to the presence of an analyte have been immobilized in a polymer matrix. The dye absorbs some of the incident radiation and, consequently, fluoresces. The fluorescence is collected by a second fiber connected in the same reaction phase, and the intensity exits at the other end and is measured by a detector. 

A fiber optic sensor for the determination of sodium was reported by Burgess.<52) A bifurcated fiber with a reference fiber 5 mm apart from the tip was used to observe the changes of bromothymol blue (Amax = 620 nm) attached to Nafion in the presence of sodium ions. As the tip was saturated, the probe was renewed with fresh reagent. However, the epoxy holding the fibers was prone to damage from high sodium concentrations of around 2.5 M and the sensitivity of analysis was low. 

A reversible, direct fluoroimmunosensor for human serum albumin (HS A) measurement has been described by Bright et al.(m> Antibody Fab fragments are first immobilized on small quartz plates by hinge-region thiols, and then dansylated. The immunosensor is formed by attaching the quartz plates with bound Fab to the distal end of a bifurcated fiber-optic probe, which transmits both the excitation and emission. Binding of ffSA to the immunosensor results in a three- to five-fold enhancement of dansyl fluorescence. The sensor can be reused up to 50 times, with a detection limit of about 1.8 x 10-8 M, and a somewhat limited dynamic range. 

Normal reflection optics have been used to advantage with bulk electrode materials. Examples of this type of spectroelectrochemical cell are shown in Figure 9.11 [67]. Simple bifurcated fiber-optic waveguides are used to direct source light onto reflective bulk electrode surfaces and to collect the reflected light for transmission to a detector. This is a simple means for performing spectroelectrochemical experiments at bulk metal electrodes that cannot be as... 

An example of an optical enzyme sensor (Arnold, 1985) in a bifurcated optical fiber is shown in Fig. 9.32. The bifurcated fiber delivers and collects light to and from the site of the enzymatic reaction. The enzyme, alkaline phosphatase (AP), catalyzes hydrolysis of p-nitrophenyl phosphate to p-nitrophenoxide ion which is being detected (A = 404 nm). 

Figure 2-15 Schematic of FT -Raman instrumentation fitted with a bifurcated fiber optic interface. (Reproduced with permission from Ref. 26.)...

Fig. 1 Accessories for diffuse reflectance spectroscopy (A) Integrating sphere with hemispherical radiation collection (B) Accessory based on ellipsoidal mirrors, used within the sample compartment of the spectrometer (C) Rotational ellipsoidal mirror device with dedicated detector and (D) Bifurcated fiber optic-based accessory (also shown is the random mixture of fibers for illumination and detection compared with devices based on reflection optics the acceptance cone for radiation delivery and collection is limited and depends on the refractive indices of the core and cladding material).

Fig. 6. Types of optoelectronic biosensors based on fiber optics. R — chemically sensitive reagent, (a) Bifurcated fiber optic sensor (b) single fiber optic with a beam splitter for separation of incident and reflected light (c) single fiber optic in which the reagent phase is coated on the optic.

Other types of optode have been designed, often using fluorescent dyes for detecting different analytes. A pH optode was described by Peterson et al [16, 17], who coupled a bifurcated fiber optic cable to a small cavity containing a pH-sensitive dye. Using the Lambert-Beer law, the pH can be related to the concentration of the dye Cjye) and its buffering capacity (pX) by... 

Fiber optics may be used as probes for conventional spectrophotometric and fluorescence measurements. Light must be transmitted from a radiation source to the sample and back to the spectrometer. While there are couplers and designs that allow light to be both transmitted and received by a single fiber, usually a bifurcated fiber cable is used. This consists of two fibers in one casing, split at the end that goes to the radiation source and the spectrometer. Often, the cables consist of a bundle of several dozen small fibers, and half are randomly separated from the other at one end. For absorbance measurements, a small mirror is mounted (attached to the cable) a few millimeters from the end of the fiber. The source radiation penetrates the sample solution and is reflected back to the fiber for collection and transmission to the spectrometer. The radiation path length is twice the distance between the fiber and the mirror. 

Figure 14 14. Biocatalytic optodes based on a bifurcated fiber bundle (top) or a single fiber (bottom). In the recognition part the indicator and an enzyme are immobilized. The reactive layer is permeable to the substrate but protected against light.

A fluorosensor for monitoring blood gases and pH in an extracorporal loop is commercially available [125]. Arterial or venous oxygen and carbon dioxide pressure, pH, and temperature can be determined continuously during cardiopulmonary bypass surgery. The system consists of a microprocessor-based instrument, bifurcated fiber-optic cables, and a disposable sensor head with fluorescent spots sensitive to the respective analytes. 

Figure I3-I6b is a schematic representation of a double-beam photometer used to measure the absorbance of a sample in a flowing stream. Here, the light beam is split by a iwo-branched (bifurcated) fiber optic, which transmits about 50% of the radiation striking it in the upper arm and about. 50% imho lower arm. One beam passes through the sample, and the other passes through the reference cell. Filters are placed after the cells before the photodiode transducers. Note that this is the double-bcam-in-spacc design, which requires photodiodes with nearly identical response. The electrical outputs from the two photodiodes arc converted...

A model 6500 On-Line Vis-NIR spectrophotometer (NIR Systems, Inc., Silver Spring, MD) equipped with single bundle bifurcated fiber optics was used for data acquisition. An Interactance Reflectance probe was used along with a novel extruder/monitor interface design to obtain diffuse reflectance spectra of the plastic melt near the die. The visible region of the spectrum (400-700 nm) was used for analysis. Figure 2 shows a schematic of the experimental setup. 

Apparatus. The fiber optic photometer is similar to the instrument used in earlier work (2). It includes a tungsten-halogen source, a photomultiplier detector, interference filters for wavelength selection and a bifurcated fiber optic bundle 3 mm in diameter at the common end. In this study, excitation filters had peak transmittances at 420 and 480 nm and the emission filter had peak transmittance at 520 nm. The bandwiths at half-maximum transmittance were 9.4, 8.2 and 8.6 nm for the 420, 480 and 520 nm filters, respectively. An automated filter wheel allowed for rapid switching from one filter to another. 

The first step in preparing a sensor is to dissolve 100 mg of PVOH/indicator conjugate in 2.0 mL of water. Five minutes in a water bath at 30°C is required to get the PVOH to dissolve. After cooling to room temperature, 0.5 mL of PVOH/indicator solution is combined with 0.050 mLs each of 2% aqueous glutaraldehyde and 4 M HCl. This mixture can be manipulated as a liquid for about five, minutes until sufficient crnsslinking takes place to cause the solution to gel. During this interval a micropipet is used to precisely transfer 3 microliters to the common end of the bifurcated fiber optic bundle so that the gel forms in situ. 

This reaction produces p-nitrophenoxide which strongly absorbs 404 nm radiation. The sensor tip is constructed with alkaline phosphatase covalently immobilized on a nylon membrane. This membrane is positioned at the common end of a bifurcated fiber-optic bundle. One arm of this bundle is connected to the source optics and the other is connected to the detector optics. Incident radiation is transported from a 100 watt tungsten-halogen lamp source to the sensor tip. A fraction of this incident radiation is back scattered off the nylon mesh and a fraction of this back scattered radiation is collected by the fiber-optic bundle and directed to a 404.7 nm interference filter and then to a photomultiplier tube detector. 

A reflective (also called bifurcated ) fiber is a fiber-optic assembly with the fibers from the emitter and receiver combined into a single unit. Reflective fibers can be used for direct reflective sensing in which the target object reflects the emitted light back to the fiber, or they can be equipped with a lens and reflector for use in the retroreflective mode. In the retroreflective mode, the emitted light bounces off a reflector and back to the receiver. The part breaks the beam to actuate the sensor. 

A bifurcated fiber optic light source to transilluminate the uterine swellings (see Note ). 

If reflection occurs at not just one interface but at least two adjacent boundaries, the regularly reflected beams can superimpose and interfere. Interference occurs in certain preferred directions, at certain wavelengths, and with certain substrate and superstrate materials (see Fig. 33 A). If the partial beams extinguish each other, it is called destructive interference if they reinforce each other, constructive interference [11]. If white light is used, well-resolved interference spectra are obtained with film thicknesses of 1-5 pm [146]. Bifurcated fibers are used for incident radiation and its collection after reflection at the phase boundaries. 

One of the attractions of working with a laser is the fact that its beam can be split for multiple use within one station or even shared between two or more stations. The split can be accomplished by the use of bifurcated fibers or beam splitting mirrors. The beam of a single laser cavity can be duplexed to solder two sides of a surface-mount component simultaneously. It is entirely possible to share a common beam between two or more laser soldering stations either simultaneously or in a time-shared manner. 

FIGURE 5 Design principle of fiber-optic chemical sensors, (a) Two single fibers, (b) Two fiber bundles, (c) Bifurcated fiber. 

The fiberoptic spectrophotometer was composed of a bifurcated fiber optic (common leg bundle diameter 4.5 mm, individual leg bundle diameter 2.5 mm) and a fluoropho-tometer with a data recorder. Two arms of the bifurcated fiberoptic bundle were fixed between the excitation monochromator and the emission monochromator. 

---