We describe here the use of a hybrid ionization approach, matrix-enhanced surface-assisted laser desorption/ionization mass spectrometry (ME-SALDI-MS) in bioimaging. ME-SALDI combines the strengths of traditional matrix-assisted laser desorption/ionization (MALDI) and SALDI and enables successful MS imaging of low-mass species with improved detection sensitivity. Using 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) as the MS standard, MS performances of MALDI, SALDI, and ME-SALDI are systematically compared. The analyte desorption and ionization mechanism in ME-SALDI is qualitatively speculated based on the observation of significantly reduced matrix background and improved survival yields of molecular ions. Improvements in detection sensitivity of low-mass species using ME-SALDI over MALDI in imaging are demonstrated with mouse heart and brain tissues.

Carbon nanotubes (CNTs) have been the focal point of many studies since their discovery two decades ago (Iijima, 1991). They are allotropes of carbon with cylindrical shape and sp 2 hybridization, which are formed by benzene-type hexagonal rings of carbon atoms. CNTs can be classified as either single-walled (SWNTs) or multi-walled carbon nanotubes (MWNTs) depending on their structure. They possess a very high aspect ratio (i.e. length/diameter), with diameters in the range of nanometers and lengths that can reach microns. Additionally, CNTs can be divided according to their conductivity, into metallic or semiconducting tubes. Nanotubes possess outstanding structural, mechanical and electronic properties due to the unique combination of their dimension, structure and topology. For example, CNTs are extremely strong, can be highly conducting, and exhibit high thermal and chemical stability (Mintmire et al., 1993; Mintmire & White, 1998). Also, they are elastic and have many times the tensile strength of steel (Service, 1998). Due to these unique properties, CNTs have been proposed for many applications, ranging from scanning probes (Dai et al., 1996) and hydrogen storage (Dillon et al., 1997), to biosensors (Nguyen et al., 2002). Several methods have been commonly used to synthesize CNTs, including arc discharge, chemical vapor deposition and laser ablation, among others (Ando et al., 2004). After the growth process, CNTs contain impurities such as metal catalyst nanoparticles, amorphous carbon, carbon nanoparticles, and fullerenes, which must be removed. Typical CNTs purification techniques include ultrasonication (Shelimov, et al., 1998), microfiltration (Bandow et al., 1997), chromatographic techniques (Nigoyi et al., 2001), microwave heating (Harutyunyan et al., 2002), gas-phase oxidation (Ebbesen et al., 1994), and acid oxidation (Rinzler et al., 1998). Nevertheless, their purification is not a trivial task, and either improvement on the existing techniques or development of new purification methodologies are required in order to facilitate the use of CNTs and their integration into nanodevices and composite materials. Another main challenge to overcome is the need for the development of new functionalization chemistries that can increase the solubility of CNTs without altering their 35 www.intechopen.com