Chemical analysis of diesel engine nanoparticles using a nano-DMA/thermal desorption particle beam mass spectrometer.

Diesel engines are known to emit high number concentrations of nanoparticles (diameter < 50 nm), but the physical and chemical mechanisms by which they form are not understood. Information on chemical composition is lacking because the small size, low mass concentration, and potential for contamination of samples obtained by standard techniques make nanoparticles difficult to analyze. A nano-differential mobility analyzer was used to size-select nanoparticles (mass median diameter approximately 25-60 nm) from diesel engine exhaust for subsequent chemical analysis by thermal desorption particle beam mass spectrometry. Mass spectra were used to identify and quantify nanoparticle components, and compound molecular weights and vapor pressures were estimated from calibrated desorption temperatures. Branched alkanes and alkyl-substituted cycloalkanes from unburned fuel and/or lubricating oil appear to contribute most of the diesel nanoparticle mass. The volatility of the organic fraction of the aerosol increases as the engine load decreases and as particle size increases. Sulfuric acid was also detected at estimated concentrations of a few percent of the total nanoparticle mass. The results are consistent with a mechanism of nanoparticle formation involving nucleation of sulfuric acid and water, followed by particle growth by condensation of organic species.

Oral immunization with a recombinant cysteine-rich section of the Entamoeba histolytica galactose-inhibitable lectin elicits an intestinal secretory immunoglobulin A response that has in vitro adherence inhibition activity.

The LC3-encoded 52-kDa recombinant protein includes amino acids 758 to 1134 of the 170-kDa subunit of the galactose-inhibitable lectin. Oral immunization of BALB/c mice with the LC3-encoded protein and cholera holotoxin induced an intestinal secretory immunoglobulin A (IgA) response (P < 0.01 compared with the control). There was a negative correlation (P = 0.001) between intestinal anti-LC3 IgA and serum IgA and IgG antibody responses. Intestinal secretions from immunized mice completely inhibited the galactose-specific adherence of axenic trophozoites ot Chinese hamster ovary cells (P < 0.01).