Material-enhanced laser

Figure 3.10 Material-enhanced laser desorption/ionization (MELDI)-based biomarker discovery. (Courtesy of C. Huck and M. Rainer.)...

Another novel approach to utilizing affinity surfaces is referred to as the material-enhanced laser desorption/ionization (MELDI) technique [95] (Figure 3.10). This method was developed with the use of specially derivatized chromatographic materials (cellulose, silica, poly [glycidyl methacrylate/divinylbenzene] particles, and diamond powder) for fast and direct protein profiling to evaluate normal and pathological human serum samples. 

A new technique, known as material-enhanced laser desorption/ionization (MELDI), has become available for profiling proteins in complex mixtures [67], It uses derivatized carrier materials, such as cellulose, silica, poly(glycidyl methylacrylate/divinylbenzene), or diamond powder, to bind proteins from the sample. The carrier particles are derivatized with iminodiacetic acid (IDA) and loaded with ions to form [carrier-IDA-Cu +] complex, which is then added to the protein sample. The protein-bound carrier materials are spotted on the MALDI target, mixed with a MALDI matrix and analyzed by MALDI-TOF-MS. 

I. Feuerstein, et al.. Material-enhanced laser desorptionAonization (MELDI)—A new protein profiling tool utilizing specific carrier matoials for time-of-flight mass spec-trometric analysis, J. Am. Soc. Mass Spectrom. 17, 1203-1208 (2006). 

MELDI material-enhanced laser desorption/ionization... 

Qureshi, M.N., Stecher, G., Huck, C., and Bonn, G.K. 2010. Online coupling of thin layer chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry Synthesis and application of a new material for the identification of carbohydrates by thin layer chromatography/matrix free material enhanced laser desorption/ ionization mass spectrometry. Rapid Commun. Mass Spectrom., 24 2759-2764. 

Recently it was shown that matrix-free material enhanced laser desorption/ion-ization mass spectrometry (mf-MELDI-MS) is a powerful method to study the carbohydrate compositions of medicinal plants [23]. Using this approach, common silica gel is converted into 4,4 -azodianiline modified silica, which helps to generate a significant quantity of carbohydrate ions. 

Silica gel can be derivatized in multiple ways, e.g., by covalently binding ligands via Si-O bonds to its surface. Both surface-enhanced laser desorption/ionization (SELDI) and material-enhanced laser desorption/ionization (MELDI) make use of the presence of metal complexes on a silica gel surface to selectively adsorb target compounds via conplex formation ftom solution to a target surface [197]. Besides silica gel, also cellulose or glyddyl methacrylate particles, and even diamond powder have been enployed as carriers for the metal conplex-fiinctionalized groups [198,199]. 

Hashir, M.A. Stecher, G. Bakry, R. Kasemsook, S. Blassnig, B. Fenerstein, I. Abel, G. Popp, M. Bobleter, O. Boim, G.K. Identification of Carbohydrates by Matrix-Free Material-Enhanced Laser Desorption/Ionisation Mass Spectrometry. Rapid Commuru Mass Spectrom. 2007,21,2759-2769. 

IR absorbers and reflectors are used to limit the heat development in rooms (e.g., in greenhouses) and are incorporated in agricultural films or in glazing. Typical materials range from kaolin (aluminum silicate) or other silicates and hydrotalcites [68] in agricultural films to dyes (e.g., phthalocyanines or anthraquinones). Furthermore, dyes with near-IR absorption are added to enhance laser welding of polymers. 

Many modern semiconductor devices comprise alternating layers of different materials forming superlattices and multiple quantum wells. One well-known example of such structures is the diode laser, a mass-produced device. This device depends on confinement of charges in the two-dimensional structures for enhanced laser output at lowered current thresholds. Such alternating semiconductor layers are usually manufactured either by chemical vapor deposition or by molecular beam epitaxy. The thickness of the layers can be closely controlled in both techniques. As mentioned earlier, electrodeposition also allows good control of thickness. 

Firebrake 500 is recommended for use in engineering plasties proeessed at above 300 °C, which is the upper limit of Firebrake ZB. It is reported to be an effeetive smoke suppressant in fluoropolymers for certain cable applications. This anhydrous material ean replace antimony oxide completely in high temperature nylon applications. For aircraft applications Firebrake 500 is also reported to be effective in reducing the rate of heat release in polyether ketones and polysulfones. It is also claimed to enhance laser-marking quality of flame-retardant engineering plastics. 

Much of the energy deposited in a sample by a laser pulse or beam ablates as neutral material and not ions. Ordinarily, the neutral substances are simply pumped away, and the ions are analyzed by the mass spectrometer. To increase the number of ions formed, there is often a second ion source to produce ions from the neutral materials, thereby enhancing the total ion yield. This secondary or additional mode of ionization can be effected by electrons (electron ionization, El), reagent gases (chemical ionization. Cl), a plasma torch, or even a second laser pulse. The additional ionization is often organized as a pulse (electrons, reagent gas, or laser) that follows very shortly after the... 

The intrinsic drawback of LIBS is a short duration (less than a few hundreds microseconds) and strongly non-stationary conditions of a laser plume. Much higher sensitivity has been realized by transport of the ablated material into secondary atomic reservoirs such as a microwave-induced plasma (MIP) or an inductively coupled plasma (ICP). Owing to the much longer residence time of ablated atoms and ions in a stationary MIP (typically several ms compared with at most a hundred microseconds in a laser plume) and because of additional excitation of the radiating upper levels in the low pressure plasma, the line intensities of atoms and ions are greatly enhanced. Because of these factors the DLs of LA-MIP have been improved by one to two orders of magnitude compared with LIBS. 

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

Interestingly, it has been argued that nanoparticulate formation might be considered as a possibility for obtaining new silicon films [379]. The nanoparticles can be crystalline, and this fact prompted a new line of research [380-383], If the particles that are suspended in the plasma are irradiated with, e.g., an Ar laser (488 nm), photoluminescence is observed when they are crystalline [384]. The broad spectrum shifts to the red, due to quantum confinement. Quantum confinement enhances the bandgap of material when the size of the material becomes smaller than the radius of the Bohr exciton [385, 386]. The broad PL spectrum shows that a size distribution of nanocrystals exists, with sizes lower than 10 nm. 

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