Optical probe

The quickest path to the fabrication of an optical sensor is to make a film that can be used in one of the commercially available film holders such as the one from Ocean Optics. Since absorbance-based probes require a differential measurement, they employ three fibres with source, signal and reference legs. The need for two spectroscopic channels is usually avoided by storing a reference spectrum. For luminescence measurements, the reference leg can be ignored or used to correct the spectra for variations in source intensity. A similar commercial probe was employed by Kriz and Mosbach [33]. 

Luminescence probes can be made by employing the polymer as a coating for an optical fibre. The polymer coating can be directly applied to the fibre as with the PMP sensor above, it can be bonded to a vinyl-silanised fibre surface or it can be implanted as a fine powder in a sol-gel coating. The fibre sensor can be addressed in a variety of ways [34], of which the simplest is to use a bifurcated fibre. In this configuration the sensor is attached to the common leg and the detector and source are attached to the bifurcated legs. This configuration is illustrated in Fig. 19.12. 

A common method for on-line monitoring of chemical compositions is the use of FIA. This approach is in essence a miniaturised wet chemical laboratory analysis. The approach was developed in the 1970s to adapt existing measurement methods to the task of rapid measurements. Typically, small pumps, tubes and mixing chambers combine to produce a flowing solution that is subjected to analysis by optical or electrochemical means using essentially the same reagents as in a normal-scale analytical determination. The key to sensitivity with these systems is to prevent dispersion in the stream. There are opportunities for imprinted polymers in both the sample purification and the detection of analytes. 

Ionic sensors based on molecularly imprinted polymers 

The most developed areas for imprinted polymers are for sequestration and separation. Several reported imprinted polymer sensors have in actuality been pretreatments by separation to allow a selective determination using a general detection method. The adaptation of this to an FIA system would be relatively simple. For example, Kriz et al. [31] report a sensor for morphine (see Chapter 18). The method of morphine detection involved two steps. The first step was to immobilise the morphine by loading it on the imprinted polymer. In the detection step, the morphine was released from the column by elution of an electro-inactive competitor (codeine) and the released morphine was detected by an amperometric method. The polymer was tested after exposure to extremes of heat and chemicals and proved resilient. This method would probably be suitable for automation as a flow injection technique. 

---

Optical Probe for Steam Generator Tube Dent Measurement , EPRI NP-2863, Project SI81-1, February, 1983. 

Tsai D P, Othonos A, Moskovits M and Uttamchandani D 1994 Raman spectroscopy using a fibre optic probe with subwavelength aperture Appl. Phys. Lett. 64 1768... 

Smith D A, Webster S, Ayad M, Evans S D, Fogherty D and Batchelder D 1995 Development of a scanning near-field optical probe for localised Raman spectroscopy Ultramicroscopy 61 247... 

Every property of an interface that can be optically probed can, in prmciple, be measured with the SEA. This may include infonnation obtainable from absorption spectroscopy [M], fluorescence, dicln-oism, birefringence, or nonlinear optics [43], some of which have already been realized. 

Moerner W E, Piakhotnik T, Irngartinger T, Croci M, Palm V and Wild U P 1994 Optical probing of single molecules of terryiene in a Shpol skii matrix a two-state single-molecule switch J. Chem. Phys. 98 7382-9... 

Other solubilization and partitioning phenomena are important, both within the context of microemulsions and in the absence of added immiscible solvent. In regular micellar solutions, micelles promote the solubility of many compounds otherwise insoluble in water. The amount of chemical component solubilized in a micellar solution will, typically, be much smaller than can be accommodated in microemulsion fonnation, such as when only a few molecules per micelle are solubilized. Such limited solubilization is nevertheless quite useful. The incoriDoration of minor quantities of pyrene and related optical probes into micelles are a key to the use of fluorescence depolarization in quantifying micellar aggregation numbers and micellar microviscosities [48]. Micellar solubilization makes it possible to measure acid-base or electrochemical properties of compounds otherwise insoluble in aqueous solution. Micellar solubilization facilitates micellar catalysis (see section C2.3.10) and emulsion polymerization (see section C2.3.12). On the other hand, there are untoward effects of micellar solubilization in practical applications of surfactants. Wlren one has a multiphase... 

The path length is set by the experimental configuration while a is known for each transition (such as OO O J—> OO l, J 1 or OO l J—> 00 2, J 1). Thus, a measurement of zi///provides the partial pressure P of molecules produced in probed states such as OO O Jor 00 1 J. (Strictly, optical probing measures the difference in the partial pressures between the upper and lower states of the probed transition however, in practice, the lower state population is always much larger than the upper state population so that the probe senses only the lower state population in the experiment.)... 

The sample cells for molecular fluorescence are similar to those for optical molecular absorption. Remote sensing with fiber-optic probes (see Figure 10.30) also can be adapted for use with either a fluorometer or spectrofluorometer. An analyte that is fluorescent can be monitored directly. For analytes that are not fluorescent, a suitable fluorescent probe molecule can be incorporated into the tip of the fiber-optic probe. The analyte s reaction with the probe molecule leads to an increase or decrease in fluorescence. 

Fiber-Optic Probes. Fiber-optic probes provide remote sampling capabilities to Raman instmmentation, are stable, and give reproducible signals. Their historical niche has been in environmental monitoring. More recently these probes have been used in chemical process control and related areas such as incoming materials inspection. 

Direct photography of drops in done with the use of fiber optic probes using either direct or reflected light. StiU or video pictures can be obtained for detailed analysis. The light transmittance method uses three components a light source to provide a uniform collimated beam, a sensitive light detector, and an electronic circuit to measure the amplified output of the detector. The ratio of incident light intensity to transmitted intensity is related to interfacial area per unit volume. 

Radiometry. Radiometry is the measurement of radiant electromagnetic energy (17,18,134), considered herein to be the direct detection and spectroscopic analysis of ambient thermal emission, as distinguished from techniques in which the sample is actively probed. At any temperature above absolute zero, some molecules are in thermally populated excited levels, and transitions from these to the ground state radiate energy at characteristic frequencies. Erom Wien s displacement law, T = 2898 //m-K, the emission maximum at 300 K is near 10 fim in the mid-ir. This radiation occurs at just the energies of molecular rovibrational transitions, so thermal emission carries much the same information as an ir absorption spectmm. Detection of the emissions of remote thermal sources is the ultimate passive and noninvasive technique, requiring not even an optical probe of the sampled volume. 

Sample preparation is straightforward for a scattering process such as Raman spectroscopy. Sample containers can be of glass or quartz, which are weak Raman scatterers, and aqueous solutions pose no problems. Raman microprobes have a spatial resolution of - 1 //m, much better than the diffraction limit imposed on ir microscopes (213). Eiber-optic probes can be used in process monitoring (214). 

Fig. 5. (a) Antibody 2 is added to test solution where some or all of becomes complexed with target, T. (b) A fiber-optic probe containing covalently attached target is insetted into the solution. Unbound binds to probe, (c) The probe is inserted into solution containing en2yme-modified detector antibody which binds to probe if any is attached, (d) The probe is inserted into a solution producing a fluorescent compound, which is then... 

Not a solid-state measurement device but an optical probe of high-intensity laser light is introduced into the fluid under investigation, avoiding disturbance on the flow field. 

With the use of appropriate transmission optics, high focusing of the laser light is carried out and the extension of the optical probe is considerably reduced. Accordingly, laser-based techniques offer the possibility of measurements of high spatial resolution. 

Depending on the structure of the optical probe, components of vector quantities (velocity field, displacement field) and their signs can be distinguished in measurements, ensuring directional sensitivity. 

In certain cases, the optical probe can be used at a large distance from the experimental equipment. Hence, spatial zones can be probed that are normally accessible with difficulty or inaccessible for traditional measurement devices. This arrangement provides a means for remote measurements. 

In the intersection space (optical probe) of two coherent laser beams, planar interference fringes are formed. These are normal to the plane of beams, parallel to the beam bisector, and of a known uniform distance. 

Some general quantitative characteristics (orders of magnitudes) of LDA systems are velocity measurement range 1 mm s -100 m s relative measurement uncertainty 0.1-1% rate of accepted data 0.1-10 kHz size of the optical probe 10 p.m-1 mm for each dimension measuring distance 0.1-1 m. 

Another approach to the estimation of the surface potential is to incorporate the moiety of an optical probe into the polyelectrolyte through covalent bonding. 

A merocyanine dye, l-ethyl-4-(2-(4-hydroxyphenyl)ethenyl)pyridinium bromide (M-Mc, 2), exhibits a large spectral change according to the acid-base equilibrium [40, 41]. The equilibrium is affected by the local electrostatic potential and the polarity of the microenvironment around the dye. Hence, this dye is useful as a sensitive optical probe for the interfacial potential and polarity when it is covalently attached to the polyelectrolyte backbone. 

The biberty (Fig. 10), a monomode microwave reactor for automated SPPS, was recently introduced by the CEM Corporation [153]. Although this instrument was originally developed for SPPS, it also allows for a broader scale of solid-phase applications. The solid-phase vial is equipped with a polypropylene frit and cap at one end (the entire assembly fitting into the standard 10 mb CEM reaction vessel) to allow the processing of 0.1 to 1.0 mmol quantities of resin attached substrates. An integrated fiber optic probe provides... 

Variation of the individual velocities (U ,fd, U pf, Undr and Umb) with opening fraction of the distributor in the conical fluidized beds with the uniform distributor is shown in Fig. 6. With increasing Ug, Umb determined by the optical probe method is well agrees with Umu. However, with decreasing Ug, there is some discrepancy between Umb and Umfd since the optical probe in the lowest part is located 0.05 m above the distributor. 

Figure 2.2 Optical probe of surface-enhanced microscopy proposed byj. Wessel. A metallic nanoparticle attached to a glass substrate confines and enhances the light field.

---