Pyrolysis Vacuum-Assisted Plasma Ionization Ion Mobility-Mass Spectrometry for Insoluble Polymer Analysis.

This Communication describes a new thermal desorption/pyrolysis vacuum-assisted plasma ionization (pyro-VaPI) ion source coupled to ion mobility-mass spectrometry (IM-MS) for insoluble polymer analysis. Pyro-VaPI combines a pyrolysis device, soft ambient plasma ionization, IM, and MS into a single platform for polymer analysis with minimal sample preparation. Nylons, a widely used and well-studied thermoplastic, were chosen to evaluate the pyro-VaPI performance. Six different nylon polymers were studied and characterized. With the application of IM-MS, two different isobars for the protonated cyclic dimers of 6-6, 6-9, 6-10, and 6-12 nylon and two isobars for the cyclic tetramer of nylon-6 were detected at 200 °C. These isobars were observed at different heating times, with the species drifting faster in the IM cell appearing several minutes after the slower drifting species. To the best of our knowledge, these isobaric dimers and tetramers have not been previously reported, indicating that pyro-VaPI IM-MS is a useful tool for the structural characterization of heated or pyrolyzed polymers.

Structural Analysis of the Complexation of Uranyl, Neptunyl, Plutonyl, and Americyl with Cyclic Imide Dioximes.

Knowledge-based design of extracting agents for selective binding of actinides is essential in stock-pile stewardship, environmental remediation, separations, and nuclear fuel disposal. Robust computational protocols are critical for in depth understanding of structural properties and to further advance the design of selective ligands. In particular, rapid radiochemical separations require predictive capabilities for binding in the gas phase. This study focuses on gas-phase binding preferences of cyclic imide dioximes to uranyl, neptunyl, plutonyl, and americyl. Structural properties, electron withdrawing effects, and their effects on binding preferences are studied with natural bond-order population analysis. The aromatic amidoximes are found to have a larger electron-donation effect than the aliphatic amidoximes. It is also found that plutonyl is more electron withdrawing than uranyl, neptunyl, and americyl when bound to the cyclic imide dioximes studied.

Surface Modification of Silicon Pillar Arrays To Enhance Fluorescence Detection of Uranium and DNA.

There is an ever-growing need for detection methods that are both sensitive and efficient, such that reagent and sample consumption is minimized. Nanopillar arrays offer an attractive option to fill this need by virtue of their small scale in conjunction with their field enhancement intensity gains. This work investigates the use of nanopillar substrates for the detection of the uranyl ion and DNA, two analytes unalike but for their low quantum efficiencies combined with the need for high-throughput analyses. Herein, the adaptability of these platforms was explored, as methods for the successful surface immobilization of both analytes were developed and compared, resulting in a limit of detection for the uranyl ion of less than 1 ppm with a 0.2 µL sample volume. Moreover, differentiation between single-stranded and double-stranded DNA was possible, including qualitative identification between double-stranded DNA and DNA of the same sequence, but with a 10-base-pair mismatch.

Nanopillar Based Enhanced-Fluorescence Detection of Surface-Immobilized Beryllium.

The unique properties associated with beryllium metal ensures the continued use in many industries despite the documented health and environmental risks. While engineered safeguards and personal protective equipment can reduce risks associated with working with the metal, it has been mandated by the Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) that the workplace air and surfaces must be monitored for toxic levels. While many methods have been developed to monitor levels down to the low µg/m(3), the complexity and expense of these methods have driven the investigation into alternate methodologies. Herein, we use a combination of the previously developed fluorescence Be(II) ion detection reagent, 10-hydroxybenzo[h]quinoline (HBQ), with an optical field enhanced silicon nanopillar array, creating a new surface immobilized (si-HBQ) platform. The si-HBQ platform allows the positive control of the reagent for demonstrated reusability and a pillar diameter based tunable enhancement. Furthermore, native silicon nanopillars are overcoated with thin layers of porous silicon oxide to develop an analytical platform capable of a 0.0006 µg/L limit of detection (LOD) using sub-µL sample volumes. Additionally, we demonstrate a method to multiplex the introduction of the sample to the platform, with minimal 5.2% relative standard deviation (RSD) at 0.1 µg/L, to accommodate the potentially large number of samples needed to maintain industrial compliance. The minimal sample and reagent volumes and lack of complex and highly specific instrumentation, as well as positive control and reusability of traditionally consumable reagents, create a platform that is accessible and economically advantageous.

Wicking nanopillar arrays with dual roughness for selective transport and fluorescence measurements.

Silicon nanopillars are important building elements for innovative nanoscale systems with unique optical, wetting, and chemical separation functionalities. However, technologies for creating expansive pillars arrays on the submicron scale are often complex and with practical time, cost, and method limitations. Herein we demonstrate the rapid fabrication of nanopillar arrays using the thermal dewetting of Pt films with thicknesses in the range from 5 to 19 nm followed by anisotropic reactive ion etching (RIE) of the substrate materials. A second level of roughness on the sub-30 nm scale is added by overcoating the silicon nanopillars with a conformal layer of porous silicon oxide (PSO) using room temperature plasma enhanced chemical vapor deposition (PECVD). This technique produced environmentally conscious, economically feasible, expansive nanopillar arrays with a production pathway scalable to industrial demands. The arrays were systematically analyzed for size, density, and variability of the pillar dimensions. We show that these stochastic arrays exhibit rapid wicking of various fluids and, when functionalized with a physiosorbed layer of silicone oil, act as a superhydrophobic surface. We also demonstrate high brightness fluorescence and selective transport of model dye compounds on surfaces of the implemented nanopillar arrays with two-tier roughness. The demonstrated combination of functionalities creates a platform with attributes inherently important for advanced separations and chemical analysis.

Silicon nanopillars as a platform for enhanced fluorescence analysis.

The importance of fluorescent detection in many fields is well established. While advancements in instrumentation and the development of brighter fluorophore have increased sensitivity and lowered the detection limits of the method, additional gains can be made by manipulating the local electromagnetic field. Herein we take advantage of silicon nanopillars that exhibit optical resonances and field enhancement on their surfaces and demonstrate their potential in improving performance of biomolecular fluorescent assays. We use electron beam lithography and wafer scale processes to create silicon nanoscale pillars with dimensions that can be tuned to maximize fluorescence enhancement in a particular spectral region. Performance of the nanopillar based fluorescent assay was quantified using two model bioaffinity systems (biotin-streptavidin and immunoglobulin G-antibody) as well as covalent binding of fluorescently tagged bovine serum albumin (BSA). The effects of pillar geometry and number of pillars in arrays were evaluated. Color specific and pillar diameter dependent enhancement of fluorescent signals is clearly demonstrated using green and red labels (FITC, DyLight 488, Alexa 568, and Alexa 596). The ratios of the on pillar to off pillar signals normalized by the nominal increase in surface area due to nanopillars were found to be 43, 75, and 292 for the IgG-antibody assay, streptavidin-biotin system, and covalently attached BSA, respectively. Applicability of the presented approaches to the detection of small numbers of molecules was evaluated using highly diluted labeled proteins and also control experiments without biospecific analytes. Our analysis indicates that detection of fewer than 10 tagged proteins is possible.

Adsorption of water molecules on selected charged sodium-chloride clusters.

The adsorption of water molecules (H(2)O) on sodium chloride cluster cations and anions was studied at 298 K over a mass range of 100-1200 amu using a custom-built laser desorption ionization reactor and mass spectrometer. Under the conditions used, the cations Na(3)Cl(2)(+) and Na(4)Cl(3)(+) bind up to three water molecules, whereas the larger cations, Na(5)Cl(4)(+) to Na(19)Cl(18)(+), formed hydrates with one or two only. The overall trend is a decrease in hydration with increasing cluster size, with an abrupt drop occurring at the closed-shell Na(14)Cl(13)(+). As compared to the cluster cations, the cluster anions showed almost no adsorption. Among smaller clusters, a weak adsorption of one water molecule was observed for the cluster anions Na(6)Cl(7)(-) and Na(7)Cl(8)(-). In the higher mass region, a substantial adsorption of one water molecule was observed for Na(14)Cl(15)(-). Density functional theory (DFT) computations were carried out for the adsorption of one molecule of H(2)O on the cations Na(n)Cl(n-1)(+), for n = 2-8, and the anions Na(n)Cl(n+1)(-), for n = 1-7. For each ion, the structure of the hydrate, the hydration energy, and the standard-state enthalpy, entropy, and Gibbs energy of hydration at 298 K were computed. In addition, it was useful to compute the distortion energy, defined as the electronic energy lost due to weakening of the Na-Cl bonds upon adsorption of H(2)O. The results show that strong adsorption of a H(2)O molecule occurs for the linear cations only at an end Na ion and for the nonlinear cations only at a corner Na ion bonded to two Cl ions. An unexpected result of the theoretical investigation for the anions is that certain low-energy isomers of Na(6)Cl(7)(-) and Na(7)Cl(8)(-) bind H(2)O strongly enough to produce the observed weak adsorption. The possible implications of these results for the initial hydration of extended NaCl surfaces are discussed.

Combined atomic force microscope-based topographical imaging and nanometer-scale resolved proximal probe thermal desorption/electrospray ionization-mass spectrometry.

Nanometer- scale proximal probe thermal desorption/electrospray ionization mass spectrometry (TD/ESI-MS) was demonstrated for molecular surface sampling of caffeine from a thin film using a 30 nm diameter nanothermal analysis (nano-TA) probe tip in an atomic force microscope (AFM) coupled via a vapor transfer line and ESI interface to a MS detection platform. Using a probe temperature of 350 °C and a spot sampling time of 30 s, conical desorption craters 250 nm in diameter and 100 nm deep were created as shown through subsequent topographical imaging of the surface within the same system. Automated sampling of a 5 × 2 array of spots, with 2 µm spacing between spots, and real time selective detection of the desorbed caffeine using tandem mass spectrometry was also demonstrated. Estimated from the crater volume (∼2 × 10(6) nm(3)), only about 10 amol (2 fg) of caffeine was liberated from each thermal desorption crater in the thin film. These results illustrate a relatively simple experimental setup and means to acquire in an automated fashion submicrometer scale spatial sampling resolution and mass spectral detection of materials amenable to TD. The ability to achieve MS-based chemical imaging with 250 nm scale spatial resolution with this system is anticipated.

Combined chemical and topographic imaging at atmospheric pressure via microprobe laser desorption/ionization mass spectrometry-atomic force microscopy.

The operational characteristics and imaging performance are described for a new instrument comprising an atomic force microscope coupled with a pulsed laser and a linear ion trap mass spectrometer. The operating mode of the atomic force microscope is used to produce topographic surface images having sub-micrometer spatial and height resolution. Spatially resolved mass spectra of ions, produced from the same surface via microprobe-mode laser desorption/ionization at atmospheric pressure, are also used to create a 100 x 100 microm chemical image. The effective spatial resolution of the image (approximately 2 microm) was constrained by the limit of detection (estimated to be 10(9)-10(10) molecules) rather than by the diameter of the focused laser spot or the step size of the sample stage. The instrument has the potential to be particularly useful for surface analysis scenarios in which chemical analysis of targeted topographic features is desired; consequently, it should have extensive application in a number of scientific areas. Because the number density of desorbed neutral species in laser desorption/ionization is known to be orders-of-magnitude greater than that of ions, it is expected that improvements in imaging performance can be realized by implementation of post-ionization methods.

Portal venous gas and surgical outcome of neonatal necrotizing enterocolitis.

PURPOSE: The prognostic significance of portal venous gas (PVG) in neonatal necrotizing enterocolitis (NEC) for operative intervention (OP), neonatal complications, and mortality remains uncertain. The authors designed a long-term prospective study to describe the natural history of PVG related to these outcomes and to test the hypothesis that PVG does not mandate OP. METHODS: All infants admitted to a single center between October 1991 and February 2003 were evaluated weekly to identify all cases of NEC (defined as Bell stage II or higher). Demographic, radiological, surgical, and outcome data were abstracted prospectively. Radiographic studies were performed at the onset of illness and at subsequent 6- to 8-hour intervals or as clinically indicated. A single pediatric radiologist reviewed all radiographs. Values are expressed as mean +/- SD. Odds ratios and relative risk ratios are reported with 95% CIs. The level of significance was P < or = .05. RESULTS: After the exclusion of 24 infants with lethal diseases, major congenital or chromosomal anomalies, or recurrent episodes of NEC, 194 of 5891 infants developed NEC. The overall incidence of NEC was 3.7%. In 194 infants with NEC, the incidence of PVG was 33% (n = 64). Gestational age (30.8 +/- 4 vs 29.3 +/- 4.2 weeks; P = .02) but not birth weight (1609 +/- 761 vs 1434 +/- 810 g; P = NS) was greater in infants with PVG compared with infants without PVG (n = 130). Sixty-six (34%) infants with NEC underwent OP. Operative intervention occurred more frequently in infants with PVG compared with infants without PVG (OR, 2.5; CI, 1.37-4.76; P = .003)--only 48% of infants with PVG underwent OP. Among the variables, gestational age, severe NEC (Bell stage III), severe intramural gas (in all 4 abdominal quadrants), and the presence of PVG, severe NEC was most highly associated with OP (OR, 77.47; CI, 10.36-580.16; P < .0001). Bell stage III NEC was present in 98% of infants who underwent OP compared with 40% of infants without OP ( P < .0001). Of all infants with NEC, 37 (19%) died. Mortality was higher among infants who underwent OP (33% vs 12%; P < .0003). A multivariate regression model identified Bell stage III (OR, 3.74; CI, 1.20-11.62; P = .02), but neither PVG nor OP, to be significantly associated with mortality. Of interest is that survival in infants with PVG was greater (but not significantly so) than in infants without PVG in both OP (74% vs 59%) and non-OP (91% vs 87%) groups. Furthermore, 30 of 64 (47%) infants with PVG survived without OP, and of all 33 infants with PVG who did not undergo OP, 30 (91%) infants survived. CONCLUSIONS: Decision for OP should be based on the severity of NEC and not on the presence of PVG alone because nearly half of infants with PVG survive without OP. Overall, the presence of PVG does not increase the risk of mortality among infants with NEC. Severe NEC, but not OP, is associated with higher mortality.

Rotavirus-associated necrotizing enterocolitis: an insight into a potentially preventable disease?

PURPOSE: The aim of this study was to test the hypothesis that rotavirus-associated necrotizing enterocolitis (NEC + RV) differs from NEC associated with other organisms (NEC-RV). METHODS: Neonates with modified Bell stage II or higher NEC were identified. Demographic, clinical, and outcome information was collected prospectively. Fecal specimens from all infants were tested for confirmation of rotavirus infection (RVI) by immunoelectron microscopy (IEM). RESULTS: Of 2,444 admissions in the neonatal intensive care unit (NICU), 129 (5.3%) had NEC. Thirty-eight (29%) were rotavirus positive. The 2 groups did not differ in maternal or neonatal characteristics. Stage III or higher NEC was more common in the NEC-RV infants (62% v. 39%; P =.032), whereas recurrence was more common in NEC + RV group (P <.0001). The predominant distribution of nondiffuse pneumatosis (n = 52) was right sided in NEC-RV group and left sided in NEC + RV group (P <.0001). Surgical intervention (SI) did not differ between the 2 groups. The complications and mortality rates also were similar. Severe pneumatosis (P =.009) and severe thrombocytopenia (Platelet count < 50,000/mm3; P <.0001) increased, while human milk feedings decreased (P =.022) the odds for surgery. The annual distribution of NEC + RV paralleled RVI in the community. CONCLUSIONS: Generally, NEC + RV is a less severe disease than NEC - RV as classified by modified Bell staging. However, it can reach advanced stages obscuring distinction from NEC - RV. Indications for surgery should not be altered by identification of RVI in these infants. Monitoring RVI in the community, adhering to infection control measures, human milk feedings, and improving neonatal immunity against RVI may reduce the incidence of NEC + RV.

Acute esophageal coin ingestions: is immediate removal necessary?

AIMS: Coins are the most commonly encountered foreign body ingestions presenting to the emergency department (ED). The purpose of our study was to retrospectively evaluate a new institutional protocol implemented in 1998, in which healthy patients with acute (less than 24 h) coin ingestions located below the thoracic inlet, were observed at home with next-day follow-up. If repeat radiographs revealed a persistent esophageal foreign body, then the coin was removed. METHODS: The charts of all patients who presented to the ED with a complaint of esophageal foreign body were reviewed from 1 January 1998 until 31 December 2001. Patients were excluded if they had non-acute ingestions, known esophageal pathology, severe symptoms such as stridor or inability to tolerate oral fluids, or incomplete records. RESULTS: Of 31 patients with esophageal coin ingestions, 16 had coins above the thoracic inlet. Three of these patients were asymptomatic and all experienced spontaneous coin passage into the stomach within 2 h of ED presentation while awaiting coin removal. There were eight eligible patients with coins located below the thoracic inlet. Three of five patients with mid-esophageal coins experienced spontaneous coin passage while the remaining two required coin removal on next-day follow-up for persistent esophageal coins. Three of three patients with distal-esophageal coin ingestions experienced spontaneous coin passage. There were no complications in any of the patients who underwent delayed coin removal either due to the procedure itself or to a delay in therapy. CONCLUSIONS: Patients with acute esophageal coin ingestions may experience spontaneous coin passage and therefore, patients with coins located below the thoracic inlet with minor symptoms may be candidates for next-day follow-up. If repeat radiographs reveal a persistent esophageal coin, then the coin should be immediately removed. Furthermore, asymptomatic patients with coins above the thoracic inlet should undergo repeat radiographs in 2-5 h, as spontaneous coin passage may occur. Our protocol may also be more convenient and cost-effective as patients can be observed at home.

Clinical manifestations of rotavirus infection in the neonatal intensive care unit.

OBJECTIVES: This report describes clinical signs of rotavirus infection (RVI) among neonates admitted to a neonatal intensive care unit (NICU), compares these signs between term and preterm neonates and assesses the seasonal distribution of RVI in the NICU with that of the community. METHODS: After an initial prevalence study of 28 days, a prospective longitudinal study in the NICU was conducted. During the next 48 months from December 1, 1991 to November 30, 1995, term and preterm NICU patients were evaluated daily for pre-defined deviations in their baseline gastrointestinal status. Fecal specimens of neonates who fulfilled the entry criteria were tested for rotavirus by a monoclonal antibody-based enzyme immunoassay and by immunoelectron microscopy. Demographic and outcome data for these neonates were collected. In addition data assessing RVI in the community were collected during this period. RESULTS: The prevalence of RVI among NICU patients was 18.4%. Of 194 neonates included in the longitudinal study, 95 had RVI. Neonates with RVI differed from those without RVI with respect to frequent stooling (P = 0.0005), higher percentage of bloody mucoid stools (P = 0.003) and higher percentage of watery stools (P = 0.023). The odds of these three clinical outcomes were approximately 2.5 times higher in neonates with RVI than in neonates without RVI. Among neonates included in the study advanced necrotizing enterocolitis occurred at the same rate (15%) among those with and without RVI. Comparisons between term and preterm neonates with RVI showed that frequent stooling (P = 0.003) and watery stools (P = 0.0001) occurred more often among term neonates, whereas bloody mucoid stools (P = 0.001), abdominal distention (P = 0.03) and intestinal dilatation (P = 0.016) were more common in preterm neonates. The seasonal distribution of RVI in NICU paralleled its distribution in the community. CONCLUSION: RVI appears prevalent in the NICU setting. An absence of watery stools in a neonate should not preclude consideration of RVI when evaluating gastrointestinal signs among neonates. The clinical spectrum of RVI differs in term and preterm infants.