Droplet matrix application method

Several methods have been used for the matrix application (1) immersing a tissue section quickly in a matrix solution, (2) spraying matrix solution onto a tissue section with an air brush, (3) putting small droplets of matrix solution onto a tissue section with an automatic pipetting device that can dispense picoliter volumes (lpL = 10 pk) of reagents.4,5,715161819... 

It is clear that matrix application by the dried-droplet method is not the preferred method for (neuro)peptide imaging... 

A number of different sample preparation methods have been described in the literature [37,38], A collection of these protocols is accessible on the Internet [39,40], The original method that is always the most widely used has been called dried-droplet. This method consists of mixing some saturated matrix solution (5-10 pi) with a smaller volume (1-2 pi) of an analyte solution. Then, a droplet (0.5-2 pi) of the resulting mixture is placed on the MALDI probe, which usually consists of a metal plate with a regular array of sites for sample application. The droplet is dried at room temperature and when the liquid has completely evaporated to form crystals, the sample may be loaded into the mass spectrometer. 

Much of the work in this area has been done in emulsions having a droplet size of more than 1 pm, and the application of submicron (nano) emulsions in encapsulation of oils and flavors is relatively new in the literature. Some works have been carried out to determine the influence of submicron emulsions produced by different emulsification methods on encapsulation efficiency and to investigate the encapsulated powder properties after SD for different emulsion droplet sizes and surfactants. The process has been referred to as nanoparticle encapsulation since a core material in nanosize range is encapsulated into a matrix of micron-sized powder particles (Jafari et al., 2008). This area of research is developing. Some patents were filed in the past describing microemulsion formulations applied to flavor protection (Chung et al., 1994 Chmiel et al., 1997) and applications in flavored carbonated beverages (Wolf and Havekotte, 1989). However, there is no clear evidence on how submicron or nanoemulsions can improve the encapsulation efficiency and stability of food flavors and oils into spray-dried powders. 

A more recent study of droplet ejection from small micro-machined nozzles is provided in Meacham et al. [6]. The acoustic droplet ejection method has found applications in photoresist deposition and matrix-assisted laser desorption ionization (MALDI) analysis [3], among others. 

In the UK, researchers at Cambridge University have devised a method of growing vertical carbon nanotubes on a flexible plastic substrate which gives scope for further research into potential applications especially where flexibility is a key element of the product design. At Sheffield University the research project involves the dispersion of nano-sized droplets of PEDOT (or other conducting polymers) into a polyethylene oxide polymer electrolyte matrix. Together with a suitable redox couple, where oxidation and reduction are considered together as complementary processes, it is possible to produce efficient, switchable windows for microwaves. 

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