On-chip non-invasive and label-free cell discrimination by impedance spectroscopy

OBJECTIVES: Many flow-cytometric cell characterization methods require costly markers and colour reagents. We present here a novel device for cell discrimination based on impedance measurement of electrical cell properties in a microfluidic chip, without the need of extensive sample preparation steps and the requirement of labelling dyes. MATERIALS AND METHODS, RESULTS: We demonstrate that in-flow single cell measurements in our microchip allow for discrimination of various cell line types, such as undifferentiated mouse fibroblasts 3T3-L1 and adipocytes on the one hand, or human monocytes and in vitro differentiated dendritic cells and macrophages on the other hand. In addition, viability and apoptosis analyses were carried out successfully for Jurkat cell models. Studies on several species, including bacteria or fungi, demonstrate not only the capability to enumerate these cells, but also show that even other microbiological life cycle phases can be visualized. CONCLUSIONS: These results underline the potential of impedance spectroscopy flow cytometry as a valuable complement to other known cytometers and cell detection systems.

Energetic neutral atom imaging of the lunar surface

Since the Moon is not shielded by a global magnetic field or by an atmosphere, solar wind plasma impinges onto the lunar surface almost unhindered. Until recently, it was assumed that almost all of the impinging solar wind ions are absorbed by the surface. However, recent Interstellar Boundary Explorer, Chandrayaan-1, and Kaguya observations showed that the interaction process between the solar wind ions and the lunar surface is more complex than previously assumed. In contrast to previous assumptions, a large fraction of the impinging solar wind ions is backscattered as energetic neutral atoms. Using the complete Chandrayaan-1 Energetic Neutral Analyzer data set, we compute a global solar wind reflection ratio of 0.16 ± 0.05 from the lunar surface. Since these backscattered neutral particles are not affected by any electric or magnetic fields, each particle's point of origin on the lunar surface can be determined in a straight-forward manner allowing us to create energetic neutral atom maps of the lunar surface. The energetic neutral atom measurements recorded by the Chandrayaan-1 Energetic Neutral Analyzer cover ˜89% of the lunar surface, whereby the lunar farside is almost completely covered. We analyzed all available energetic neutral atom measurements recorded by the Chandrayaan-1 Energetic Neutral Analyzer to create the first global energetic neutral hydrogen maps of the lunar surface.

Lunar energetic neutral atom (ENA) spectra measured by the interstellar boundary explorer (IBEX)

The solar wind continuously flows out from the Sun, filling interplanetary space and directly interacting with the surfaces of small planetary bodies and other objects throughout the solar system. A significant fraction of these ions backscatter from the surface as energetic neutral atoms (ENAs). The first observations of these ENA emissions from the Moon were recently reported from the Interstellar Boundary Explorer (IBEX). These observations yielded a lunar ENA albedo of ˜10% and showed that the Moon reflects ˜150 metric tons of neutral hydrogen per year. More recently, a survey of the first 2.5 years of IBEX observations of lunar ENAs was conducted for times when the Moon was in the solar wind. Here, we present the first IBEX ENA observations when the Moon is inside the terrestrial magnetosheath and compare them with observations when the Moon is in the solar wind. Our analysis shows that: (1) the ENA intensities are on average higher when the Moon is in the magnetosheath, (2) the energy spectra are similar above ~0.6* solar wind energy but below there are large differences of the order of a factor of 10, (3) the energy spectra resemble a power law with a "hump" at ˜0.6 * solar wind energy, and (4) this "hump" is broader when the Moon is in the magnetosheath. We explore potential scenarios to explain the differences, namely the effects of the topography of the lunar surface and the consequences of a very different Mach number in the solar wind versus in the magnetosheath.

Remote energetic neutral atom imaging of electric potential over a lunar magnetic anomaly

The formation of electric potential over lunar magnetized regions is essential for understanding fundamental lunar science, for understanding the lunar environment, and for planning human exploration on the Moon. A large positive electric potential was predicted and detected from single point measurements. Here, we demonstrate a remote imaging technique of electric potential mapping at the lunar surface, making use of a new concept involving hydrogen neutral atoms derived from solar wind. We apply the technique to a lunar magnetized region using an existing dataset of the neutral atom energy spectrometer SARA/CENA on Chandrayaan-1. Electrostatic potential larger than +135 V inside the Gerasimovic anomaly is confirmed. This structure is found spreading all over the magnetized region. The widely spread electric potential can influence the local plasma and dust environment near the magnetic anomaly.