Identification of iron sulphide grains in protoplanetary disks.

Sulphur is depleted in cold dense molecular clouds with embedded young stellar objects, indicating that most of it probably resides in solid grains. Iron sulphide grains are the main sulphur species in cometary dust particles, but there has been no direct evidence for FeS in astronomical sources, which poses a considerable problem, because sulphur is a cosmically abundant element. Here we report laboratory infrared spectra of FeS grains from primitive meteorites, as well as from pyrrhotite ([Fe, Ni](1-x)S) grains in interplanetary dust, which show a broad FeS feature centred at approximately 23.5 micrometres. A similar broad feature is seen in the infrared spectra of young stellar objects, implying that FeS grains are an important but previously unrecognized component of circumstellar dust. The feature had previously been attributed to FeO. The observed astronomical line strengths are generally consistent with the depletion of sulphur from the gas phase, and with the average Galactic sulphur/silicon abundance ratio. We conclude that the missing sulphur has been found.

An infrared spectral match between GEMS and interstellar grains.

Infrared spectral properties of silicate grains in interplanetary dust particles (IDPs) were compared with those of astronomical silicates. The approximately 10-micrometer silicon-oxygen stretch bands of IDPs containing enstatite (MgSiO3), forsterite (Mg2SiO4), and glass with embedded metal and sulfides (GEMS) exhibit fine structure and bandwidths similar to those of solar system comets and some pre-main sequence Herbig Ae/Be stars. Some GEMS exhibit a broad, featureless silicon-oxygen stretch band similar to those observed in interstellar molecular clouds and young stellar objects. These GEMS provide a spectral match to astronomical "amorphous" silicates, one of the fundamental building blocks from which the solar system is presumed to have formed.

The delivery of organic matter from asteroids and comets to the early surface of Mars.

Carbon delivered to the Earth by interplanetary dust particles may have been an important source of pre-biotic organic matter (Anders, 1989). Interplanetary dust is shown to deliver an order-of-magnitude higher surface concentration of carbon onto Mars than onto Earth, suggesting interplanetary dust may be an important source of carbon on Mars as well.

Laser induced fluorescence identification of sinoatrial and atrioventricular nodal conduction tissue.

UNLABELLED: Transcatheter ablation of nodal tissue is used for the treatment of arrhythmia resistant to medical therapy. We have investigated the use of laser induced fluorescence spectroscopy for the in vitro recognition of nodal conduction tissue. Twelve fresh human necropsy specimens (< 48 hours) were obtained from sinoatrial node and atrioventricular node areas. Spectra were recorded during excitation at 308 nm (XeCl excimer laser, 1.5-2.0 mJ/pulse, 10 Hz). Ech area examined was marked for subsequent histologic examination. Four hundred eleven spectra were obtained, of which 37 contained nodal conduction tissue (21 sinoatrial, 16 atrioventricular node). Normalized fluorescence emission intensity from these areas was compared with that of surrounding endomyocardial tissue at 18 wavelengths and 35 ratios of fluorescence intensity at selected wavelengths. Spectra recorded from nodal tissue could be clearly distinguished by a visible decrease in fluorescence emission intensity at wavelengths from 440 to 500 nm (P < 0.0006 at 450 nm), peak area, and peak width when compared to that of adjacent atrial endomyocardial tissue. Nodal conduction tissue was also distinguished from ventricular endocardium (14 spectra) by an increase in fluorescence emission at 430 to 550 nm (P < 0.0001). The specificity was 73% and 88% and the sensitivity was 73% and 60% for sinus nodal and atrioventricular nodal conduction tissue identification, respectively. A ratio of fluorescence emission intensity > 1.3 for 380/475 nm was able to detect nodal conduction tissue (P < 0.001). CONCLUSION: Laser induced fluorescence can differentiate nodal conduction tissue from atrial and ventricular endocardium and may provide a new diagnostic tool for the recognition and subsequent ablation of nodal conduction tissue.

In vitro staining of islets of Langerhans for fluorescence-activated cell sorting.

A previously described technique from the author's laboratories for purification of pancreatic islets by fluorescence-activated cell sorting used the dye neutral red (NR) to obtain specific fluorescence of islets sufficient to give a sorting signal. A major drawback with this technique was the need to inject the dye intravascularly before excision of the pancreas. Preliminary investigations showed that NR would produce selective staining of islets by topical application in vitro but only at low concentrations that were insufficient to give fluorescence strong enough for sorting. The chelating agent dithizone (DTZ) produces bright red staining of islets by topical application in vitro. Further studies showed that dithizone-stained islets exhibited moderately strong fluorescence that faded too quickly for reliable sorting. By combining both NR and DTZ staining in vitro, selective fluorescence of islets was obtained that was sufficient to allow efficient sorting. Using the combined DTZ/NR stain the yield of islets obtained by sorting from a single rat pancreas was 569 +/- 72 (n = 16), corresponding to 83% of the islets present in the digest. The mean purity of the preparation, confirmed by histologic examination, was 80%. The viability of the islets was shown to be good both by supravital staining and by the successful correction of streptozotocin diabetes in syngeneic rats following transplantation of sorted islets.

Laser-induced fluorescence emission: I. The spectroscopic identification of fibrotic endocardium and myocardium.

UNLABELLED: Laser-induced fluorescence has been developed as a guidance system for laser angioplasty. Laser ablation has been used for resection of arrhythmogenic ventricular scar. We have investigated the use of laser-induced fluorescence for the detection of fibrotic and ischemic changes in endocardium and myocardium. Fluorescence emission spectra from human necropsy specimens were correlated with histologic examination. Normalized fluorescence intensity detected from both the endocardial and the myocardial surfaces of the fibrotic ventricular specimens was significantly higher than that of corresponding normal specimens at 440 to 475 nm. Fibrotic endocardium could be identified by a fluorescence emission intensity ratio less than 1.5 for wavelength ratio 375/450nm. Acutely infarcted endocardium was recognizable by a ratio of 1.5 to 2.0. The specificity and sensitivity of detection of scarred endocardium was 70 and 100%, respectively. Fibrotic myocardium was also consistently identified by fluorescence spectroscopy. CONCLUSION: Fluorescence emission spectroscopy can differentiate normal and fibrotic endocardium and myocardium, in vitro. This technique may be useful for guidance during laser ablation of arrhythmogenic ventricular scar.

Noble gases in stratospheric dust particles: confirmation of extraterrestrial origin.

Noble gas elemental and isotopic ratios were measured in a group of 13 "chondritic" stratospheric dust particles. Neon and argon are present in "solar" proportions; xenon appears to be dominated by contributions from "planetary" sources. The apparent xenon concentration is higher than that measured in any bulk meteorite, approaching the concentration found in the noble gas-rich, acid-insoluble residues from carbonaceous chondrites.