A common goal for astrobiology is to detect organic materials that may indicate the presence of life. However, organic materials alone may not be representative of currently living systems. Thus, it would be valuable to have a method with which to determine the health of living materials. Here, we present progress toward this goal by reporting on the application of laser-induced breakdown spectroscopy (LIBS) to study characteristics of live and dead cells using Escherichia coli (E. coli) strain K12 cells as a model organism since its growth and death in the laboratory are well understood. Our goal is to determine whether LIBS, in its femto-and/or nanosecond forms, could ascertain the state of a living organism. E. coli strain K12 cells were grown, collected, and exposed to one of two types of inactivation treatments: autoclaving and sonication. Cells were also kept alive as a control. We found that LIBS yields key information that allows for the discrimination of live and dead E. coli bacteria based on ionic shifts reflective of cell membrane integrity. Key Words: E. coli-Trace elements-Live and dead cells-Laser-induced breakdown spectroscopy-Atomic force microscopy. Astrobiology 15, 144-153.
The impact of altering laser focusing conditions on laser-induced breakdown spectroscopy experiments is investigated under ambient Earth laboratory and simulated Martian atmospheres. Experiments were performed in which the focal spot size was varied on a sample by altering the lens to sample distance with respect to targets of interest. Samples investigated include aluminum, copper, and steel. Specific neutral and ionic transitions of each sample were monitored. Atomic and ionic emissions show different intensity peak distributions along the varying lens to sample distance. Ionic species have peak emissions when laser plasma is initiated with a focused spot within the sample in ambient Earth laboratory air, while atomic emissions have peak intensities several millimeters deeper into a sample. In simulated Martian atmospheres, atomic emissions are observed to peak when the laser is focused within the sample, while ionic emissions have peak intensities when the laser is focused near the surface of a sample.
The physical properties of amorphous biomolecules play a critical role in stability of food, pharmaceutical, and biotechnological products. Consequently, they have an impact on formulation design and quality control of amorphous products. Molecular mobility, heterogeneity, and air permeability have been monitored in amorphous materials using Generally Recognized as Safe (GRAS) luminescent probes, i.e., tryptophan and erythrosine B. Given its GRAS status and widespread availability, we hypothesize that riboflavin can be used as a convenient and safe intrinsic luminescent probe to study the physical properties of amorphous films. Riboflavin phosphorescence has only been reported at temperatures below 77K and in solid matrices. The objectives of this study were: 1)to investigate riboflavin phosphorescence sensitivity towards molecular mobility in a disaccharide model system, 2)to characterize the temperature dependence of riboflavin phosphorescence in amorphous films. Sucrose was used as a model system to assess riboflavin's applicability as a phosphorescent probe of the physical state of edible films. Steady-state and time-resolved phosphorescence of riboflavin in amorphous sucrose films were collected over the temperature range from À30 C to 60 C. Emission spectra were fitted with a log-normal function. The performance of a stretched exponential and a multi-exponential function were evaluated to characterize riboflavin lifetimes. The rate constant of non-radiative decay (kTS0), a measure of molecular mobility, was calculated from riboflavin's average lifetime. Measures of the distribution of energetically distinct environments were obtained from bandwidth (G), stretching exponential factor (b), and fractional amplitudes (ai) parameters. The analysis of fitted parameters as a function of temperature revealed two temperature regimes below Tg in sucrose films with a transition at 10 C. Implications of these findings on riboflavin's potential applications as a luminescent probe of physical properties of amorphous biomolecules and edible films are discussed.
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