Online analysis of single cyanobacteria and algae cells under nitrogen-limited conditions using aerosol time-of-flight mass spectrometry.

Metabolomics studies typically perform measurements on populations of whole cells which provide the average representation of a collection of many cells. However, key mechanistic information can be lost using this approach. Investigating chemistry at the single cell level yields a more accurate representation of the diversity of populations within a cell sample; however, this approach has many analytical challenges. In this study, an aerosol time-of-flight mass spectrometer (ATOFMS) was used for rapid analysis of single algae and cyanobacteria cells with diameters ranging from 1 to 8 µm. Cells were aerosolized by nebulization and directly transmitted into the ATOFMS. Whole cells were determined to remain intact inside the instrument through a combination of particle sizing and imaging measurements. Differences in cell populations were observed after perturbing Chlamydomonas reinhardtii cells via nitrogen deprivation. Thousands of single cells were measured over a period of 4 days for nitrogen-replete and nitrogen-limited conditions. A comparison of the single cell mass spectra of the cells sampled under the two conditions revealed an increase in the dipalmitic acid sulfolipid sulfoquinovosyldiacylglycerol (SQDG), a chloroplast membrane lipid, under nitrogen-limited conditions. Single cell peak intensity distributions demonstrate the ability of the ATOFMS to measure metabolic differences of single cells. The ATOFMS provides an unprecedented maximum throughput of 50 Hz, enabling the rapid online measurement of thousands of single cell mass spectra.

Nanoparticle characteristics affecting environmental fate and transport through soil.

Nanoparticles are being used in broad range of applications; therefore, these materials probably will enter the environment during their life cycle. The objective of the present study is to identify changes in properties of nanoparticles released into the environment with a case study on aluminum nanoparticles. Aluminum nanoparticles commonly are used in energetic formulations and may be released into the environment during their handling and use. To evaluate the transport of aluminum nanoparticles, it is necessary not only to understand the properties of the aluminum in its initial state but also to determine how the nanoparticle properties will change when exposed to relevant environmental conditions. Transport measurements were conducted with a soil-column system that delivers a constant upflow of a suspension of nanoparticles to a soil column and monitors the concentration, size, agglomeration state, and charge of the particles in the eluent. The type of solution and surface functionalization had a marked effect on the charge, stability, and agglomeration state of the nanoparticles, which in turn impacted transport through the receiving matrix. Transport also is dependent on the size of the nanoparticles, although it is the agglomerate size, not the primary size, that is correlated with transportability. Electrostatically induced binding events of positively charged aluminum nanoparticles to the soil matrix were greater than those for negatively charged aluminum nanoparticles. Many factors influence the transport of nanoparticles in the environment, but size, charge, and agglomeration rate of nanoparticles in the transport medium are predictive of nanoparticle mobility in soil.