Optical detection methods

This method is based on optoelectronics, which is the study and application of electronic devices that interact with light and thus is usually considered a subfield of photonics. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet, and infrared. Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers, or instruments that use such devices in their operation. 

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Fig. 3. Schematic of optical detection methods, (a) absorbance or colorimetric (b) turbidimetric and (c) nephelometric.

Hyphenated techniques like combination of optical detection methods based on reflectometry or refractometry and separation techniques are of future interest. The same is valid for the intention to couple SPR or RIfS with mass spectrometry like MALDI33. 

Various optical detection methods have been used to measure pH in vivo. Fluorescence ratio imaging microscopy using an inverted microscope was used to determine intracellular pH in tumor cells [5], NMR spectroscopy was used to continuously monitor temperature-induced pH changes in fish to study the role of intracellular pH in the maintenance of protein function [27], Additionally, NMR spectroscopy was used to map in-vivo extracellular pH in rat brain gliomas [3], Electron spin resonance (ESR), which is operated at a lower resonance, has been adapted for in-vivo pH measurements because it provides a sufficient RF penetration for deep body organs [28], The non-destructive determination of tissue pH using near-infrared diffuse reflectance spectroscopy (NIRS) has been employed for pH measurements in the muscle during... 

Seydack, M., Nanoparticle labels in immunosensing using optical detection methods, Biosen... 

Chitosan films are also transparent in the UV and visible regions of the light spectrum and thus have little effect on most optical detection methods. Also, chitosan s amine groups are more reactive in aqueous environments compared to other polyamines because of the low pKa value possessed by the primary amine (6.3 for chitosan vs. 10.5 for polylysine). Finally, other advantages of chitosan are that it is safe, abundant and inexpensive. 

Optical sensors have the advantage of an easily measured signal that can be seen by the naked eye in some cases. Optical detection methods include fluorescence, surface plasmon resonance spectroscopy, Raman, IR, and chemiluminescence (Fabbrizzi and Poggi 1995 deSilva et al. 1997). However, the fabrication and development of optical MIP sensors requires that a colored, emissive, or fluorescent monomer... 

Postcolumn chemical reactions in LCEC are less common than in optical detection methods, since both the derivatization chemistry and the electrochemis-... 

Another label-free optical detection method—FTIR-ATR—has been applied for detection of thrombin by means of DNA aptamers [73], The antithrombin DNA aptamer previously developed by Tasset et al. [17] was immobilized covalently onto Si surface using UV irradiation method. As a quantitative measure, the area of N-H and CH2 bands was used. This method allowed to detect thrombin with a sensitivity around 10 nmol/L. The specificity of binding of protein to aptamer was also investigated using DNA with no binding site for thrombin. It has been noted that for effective binding study by FTIR-ATR method, the concentration of protein should be kept lower than 100 nmol/L. 

The reduction of sample size calls for an improvement of detection sensitivity. Optical detection methods have been most commonly applied in most cases. However, fluorescence detection will still gain more importance due to the higher sensitivity of this technique. An interesting approach is the combination of reaction vessels and testing cells. One solution is the incorporation of microlenses below the wells which allow a detection on-site . Highly sensitive methods may be also obtained by the use of miniaturized electrochemical detection systems. 

It is from these perspectives that we have reviewed the pulse radiolysis experiments on polymers and polymerization in this article. The examples chosen for discussion have wide spread interest not only in polymer science but also in chemistry in general. This review is presented in six sections. Section 2 interprets the experimental techniques as well as the principle of pulse radiolysis the description is confined to the systems using optical detection methods. However, the purpose of this section is not to survey detail techniques of pulse radiolysis but to outline them concisely. In Sect. 3, the pulse radiolysis studies of radiation-induced polymerizations are discussed with special reference to the initiation mechanisms. Section 4 deals with applications of pulse radiolysis to the polymer reactions in solution including the systems related to biology. In Sect. 5 reaction intermediates produced in irradiated solid and molten polymers are discussed. Most studies are aimed at elucidating the mechanism of radiation-induced degradation, but, in some cases, polymers are used just as a medium for short-lived species of chemical interest We conclude, in Sect. 6, by summarizing the contribution of pulse radiolysis experiments to the field of polymer science. 

In actual experimental setup for the combination of STM with Raman spectroscopy, there are essentially two optical detection methods as shown in... 

In some cases the error limits quoted are based solely on the reproducibility (precision) of the measurements and, in others, an attempt has been made to allow for other sources of error. However, it is clear from the differences in the values of k that in estimating the limits not all errors have been accounted for. The differences do not correlate with the various pressures used, which is sometimes a source of such discrepancies, but appear to be related to errors in the values of the optical absorption coefficient used in measuring the concentration of the CHO radical. In most of the studies optical detection methods were used and, in these cases, very similar experimentally measured values of k/e were obtained, where e is the optical absorption coefficient of CHO at the wavelength used. Differences in the values used for e account for the differences in the quoted values of k [16]. In this case the likely source of error can be identified fairly readily other cases are far less transparent and the reasons for scatter outside the quoted error limits can often not be identified. 

Sensitive Optical Detectors. More sensitive optical techniques that have been used with CE include fluorescence, refractive index, chemiluminescence, Raman spectrophotometry, and circular dichroism. The most sensitive optical detection method used in CE is laser-induced fluorescence (LIE), which is capable of detection limits in the 10 to 10" mol (or better) range. This detection mode is easily accomplished with analytes that are either easily labeled with a fluorescent substrate (e.g., intercalators for double-stranded DNA) or are naturally fluorescent (e.g., proteins or peptides containing tryptophan). CE systems have also been interfaced with mass spectrometers, and electrochemical detection methods have been developed, although such detectors must be isolated electrically from the electrophoretic voltages. 

Gauglitz, G. Optical Detection Methods for Combinatorial Libraries. Curr. Opin. Chem. Biol. 2000,4,351-355... 

Interference with optical detection methods (light absorption,... 

Transient absorption optical detection methods for picosecond and faster resolution are subject to a number of considerations. First, the velocities of high-energy electrons are approximately that ofthe speed of light in vacuum, = c, whereas light itself... 

In comparison to equivalent optical detection methods using whole cell biosensors for water toxicity detection, these results proved to be more sensitive and produce faster response time. Concentrations as low as 1% of ethanol and 1.6 ppm of phenol could be detected in less than 10 min of exposure to the toxic chemical, whilst a recent study [11] which utilized bioluminescent E.coli sensor cells, detected 0.4 M (2.35%) ethanol after 220 min. An additional study [1] based on fluorescent reporter system (GFP), enabled detection of 6% ethanol and 295 ppm phenol after more than one hour. Cha et al [12] used optical detection methods of fluorescent GFP proteins, detected 1 g of phenol per liter (1,000 ppm) and 2% ethanol after 6 hours. Other studies [13] could not be directly compared due to different material used however their time scale for chemicals identification is hours. 

Picosecond spectroscopy enables one to observe ultrafast events in great detail as a reaction evolves. Most picosecond laser systems currently rely on optical multichannel detectors (OMCDs) as a means by which spectra of transient species and states are recorded and their formation and decay kinetics measured. In this paper, we describe some early optical detection methods used to obtain picosecond spectroscopic data. Also we present examples of the application of picosecond absorption and emission spectroscopy to such mechanistic problems as the photodissociation of haloaromatic compounds, the visual transduction process, and inter-molecular photoinitiated electron transfer. 

In the preceding discussion, we have presented several optical detection methods that can be used when one employs picosecond emission or absorption spectroscopy as a means of... 

Cyclohexapeptide monolayers on quartz microbalances are able to discriminate between different analytes in the liquid phase (see Section 10.5.1). On the basis of these results, we also have immobilized cyclopeptides (Fig. 10.14) on glass transducers. In this case, the interaction between cyclopeptides and analytes was monitored by reflectometric interference spectroscopy (RIfS) [98], RIfS is an optical detection method in which the phenomenon of reflection and interference of light at phase boundaries is used to measure changes in optical thickness (refractive index x layer thickness) of transparent films... 

The CPAC group at the University of Washington has developed a refractive index optical detection method that is very sensitive and tailor-made for microchip applications. The advantage of such a technique is that it is a universal detection method, and does not depend on analyte molecules containing chromophores. 

Most optical detection methods for biosensors are based on ultra-violet (UV) absorption spectrometry, emission spectroscopic measurement of fluorescence and luminescence, and Raman spectroscopy. However, surface plasmon resonance (SPR) has quickly been widely adopted as a nonlabeling technique that provides attractive advantages. Fueled by numerous new nanomateiials, their unique, SPR-based or related detection techniques are increasingly being investigated [28-31]. 

Abstract Optical detection continues to dominate detection methods in microfluidics due to its noninvasive nature, easy coupling, rapid response, and high sensitivity. In this review, we summarize two aspects of recent developments in optical detection methods on microfluidic chips. The first aspect is free-space (off-chip) detection on the microchip, in which the conventional absorption, fluorescence, chemiluminescence, surface plasmon resonance, and surface enhanced Raman spectroscopies are involved. The second aspect is the optofluidic (inside-chip) detection. Various miniaturized optical components integrated on the microfluidic chip, such as waveguide, microlens, laser, and detectors are outlined. 

The complete optical setup of induced fluorescence involves an excitation part and an emission part. The intersection point of the two parts is the detection window in the microdevice. The excitation part starts from the light source and ends at the microdevice, while the emission part originates from the microdevice and stops at the detector. In free-space fluorescence detection, the common excitation sources include the laser, light-emitting diode (LED), and mercury or xenon arc lamp, and each light source has its distinctive spectroscopic property and practical benefits. Laser-induced fluorescence (LIE) is a highly sensitive optical detection method and is able to perform even single molecule detection. LIE has been introduced into the... 

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