Chemiluminescence surface enhancers

Chemiluminescence is a very sensitive and selective technique. Reagent types, analytes, and detection limits have been summarized in a review by Imai.56 Chemiluminescence has been applied to the analysis of compounds that exhibit low UV absorbance, including metal ions, amino acids, fatty acids, and bile acids. Other detectors include detectors for radioactivity, nuclear magnetic resonance (NMR), and surface-enhanced Raman spectroscopy. Radioactivity detection is one of the most selective detectors, as only components that have been radiolabeled will be detected. The interface of NMR with HPLC and has been discussed in detail by Grenier-Loustalot et al.57 Surface-enhanced Raman spectroscopy is another technique that... 

Trace amounts of the nitrite ion (NO ) are indicative of the extent of pollution and eutrophication. The multitude of methods that can measure nitrite ion concentrations, such as colorimetry, chemiluminescence or fluorimetry, are not capable of detecting subnanomole amounts of nitrite. These also suffer from interference problems. A highly sensitive and selective method for the determination of low concentrations of nitrite in aqueous solutions using surface-enhanced resonance Raman (SERRS) has been developed (13) (see Section 3.3). 

Yoshinaga T, Tanaka Y, Ichimura T, Hiratsuka H, Kobayashi M, Hoshi T. Solid surface enhancement effects on chemiluminescence diaryloxalate and polymers as media solids. J Luminescence 1998 78 221-9. 

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. 

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

HTAC cationic micelles also markedly enhance the CL intensity of fluorescein (FL) in the oxidation of hydrogen peroxide catalyzed by horseradish peroxidase (HRP) [39], However, no CL enhancement was observed when anionic micelles of sodium dodecyl sulphate (SDS) or nonionic micelles of polyoxyethylene (23) dodecanol (Brij-35) were used (Fig. 9). CL enhancement is attributed to the electrostatic interaction of the anionic fluorescein with the HTAC micelles. The local concentration of fluorescein on the surface of the micelle increases the efficiency of the energy transferred from the singlet oxygen (which is produced in the peroxidation catalyzed by the HRP) to fluorescein. This chemiluminescent enhancement was applied to the determination of traces of hydrogen peroxide. The detection limit was three times smaller than that obtained in aqueous solution. 

Flow cells may also act as reactors. In BL, enzymes may be immobilized inside the cell either by chemical bonding on the inner surface or by entrapping the enzyme as a heterogeneous system by mechanical ways. This approach has the advantage of low consumption of expensive reagents and enhancement of their stability, which is usually low. Many bioluminescent reactions have utilized the benefit of this process. The flow cell is also used as a reactor in the case of electrogenerated chemiluminescence (ECL) when used with FI manifolds. Some of these applications are included in Table 4. 

Quantum mechanical and classical calculations have been performed [245] for H + Cl2 on a recently optimised extended LEPS surface [204]. The quantum mechanical results were transformed to three dimensions by the information theoretic procedure and are in good agreement with the distributions determined in the chemiluminescence experiments. However, three-dimensional trajectory calculations on the surface consistently underestimate (FR) at thermal energies and it is concluded that the LEPS surface which was optimised using one-dimensional calculations does not possess the angular dependence of the true three-dimensional surface. This appears to result from the lack of flexibility of the LEPS form. Trajectory studies [196] for H + Cl2 on another LEPS surface find a similar disposal of the enhanced reagent energy as was found for H + F2. The effect of vibrational excitation of the Cl2 on the detailed form of the product vibrational and rotational state distributions was described in Sect. 2.3. 

Figure 15.2 Chemiluminescence emission intensity from both the glass and the silvered surface (Ag) (Top). Insert - i tographs of the silvered and glass surfeces, with (insert - Bottom) and without (insert - Top) chemiluminescence material in tiie experimental sandwich. The enhancement factOT was > 20, i.e. intensity on Ag / intensity on glass. Experimental sample sandwich (Bottom). Reproduced frexn AppliedPf sics Letters 88 173104. (2006).

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