No abstract

In this work, silver film over silica nanosphere (AgFON) surfaces are shown to be thermally stable, SERS-active substrates that are suitable for use in ultrahigh vacuum (UHV) conditions. The metal FON surface is a materials general, cost-effective, and highly SERS-active surface. The SERS activity and thermal stability were investigated by adsorbing benzene, pyridine, and C60 onto the AgFON surface. We chose these adsorbates for the following reasons:  (1) vibrational spectroscopy and temperature-programmed desorption (TPD) behavior of benzene adsorbed onto metal surfaces has been widely investigated and is a simple system to study, respectively; (2) characteristics of pyridine adsorption on the AgFON surface can be compared to a large body of previous studies; and (3) high-temperature studies of C60 adsorption can be performed. TPD demonstrates that the AgFON surface has two classes of adsorption sites:  (1) those that mimic the behavior of single crystal surfaces and (2) defect sites with higher adsorbate binding energies. Room temperature annealing does not irreversibly destroy the SERS enhancement capability of this surface, thereby permitting for repeated use in UHV experiments. The AgFON surface morphology and localized surface plasmon resonance frequencies, as monitored by UV-vis extinction, change as the AgFON surface temperatures increases from 300 to 548 K, and the SERS activity corresponds with these changes. Because the AgFON surface is thermally stable at room temperature and retains high SERS-activity following temperature annealing to 573 K, it is unlikely that adatoms or adatom clusters play a significant role as adsorption sites supporting the chemical enhancement mechanism. Rather, one can conclude that the electromagnetic enhancement mechanism is the most likely origin of the SER spectra from benzene, pyridine, and C60 adsorbed on AgFON surfaces.

The appearance energy of the CH2 + fragment from CH2CO has been carefully remeasured and fitted by a model curve, producing EA0(CH2 +/CH2CO) = 13.743 ± 0.005 eV. This value can be sequentially propagated through selected thermochemical cycles to yield individual values for EI(CH2), D0(H−CH2), ΔH°f   0(CH2), and ΔH°f   0(CH2CO). A set of values with a statistically larger weight is produced by analyzing a local thermochemical network, which combines the present measurement with thirteen other experimental determinations from the literature and encompasses the enthalpies of formation of CH3, CH3 +, CH2, CH2 +, and CH2CO. The recommended simultaneously adjusted thermochemical values are:  ΔH°f   0(CH3) = 35.86 ± 0.07 kcal/mol (35.05 ± 0.07 kcal/mol at 298 K), ΔH°f   0(CH3 +) = 262.73 ± 0.06 kcal/mol (261.83 ± 0.06 kcal/mol at 298 K), ΔH°f   0(CH2) = 93.18 ± 0.20 kcal/mol (93.31 ± 0.20 kcal/mol at 298 K), ΔH°f   0(CH2 +) = 332.92 ± 0.19 kcal/mol (333.04 ± 0.19 kcal/mol at 298 K), ΔH°f   0(CH2CO) = −11.10 ± 0.21 kcal/mol (−11.85 ± 0.21 kcal/mol at 298 K), as well as D0(H3C−H) = 103.42 ± 0.03 kcal/mol (104.99 ± 0.03 kcal/mol at 298 K), D0(H2C−H) = 108.95 ± 0.20 kcal/mol (110.35 ± 0.20 kcal/mol at 298 K), D0(H2CCO) = 77.08 ± 0.02 kcal/mol (78.73 ± 0.02 kcal/mol at 298 K), EI(CH3) = 9.3830 ± 0.0005 eV, and EI(CH2) = 10.3962 ± 0.0036 eV. These values are in excellent agreement with current and several previous experimental measurements. The recommended enthalpy of formation of CH2 implies that the reaction of singlet methylene with water is essentially thermoneutral (to within ±0.2 kcal/mol) at 0 and 298 K, and slightly endothermic (0.5 ± 0.2 kcal/mol) at 1000 K.

Research involving bacterial pathogens often requires enumeration of bacteria colonies.Here, we present a low-cost, high-throughput colony counting system consisting of colony counting software and a consumer-grade digital camera or document scanner. We demonstrate that this software, called ''NICE'' (NIST's Integrated Colony Enumerator), can count bacterial colonies as part of a high-throughput multiplexed opsonophagocytic killing assay used to characterize pneumococcal vaccine efficacy. The results obtained with NICE correlate well with the results obtained from manual counting, with a mean difference of less than 3%. NICE is also rapid; it can count colonies from multiple reaction wells within minutes and export the results to a spreadsheet for data processing. As this program is freely available from NIST, NICE should be helpful in bacteria colony enumeration required in many microbiological studies, and in standardizing colony counting methods. Published 2010 Wiley-Liss, Inc.

We describe a liquid-core optical fiber based on capillary tubing of Teflon AF 2400, which is a clear, amorphous fluoropolymer having a refractive index of 1.29. When filled with virtually any transparent liquid, the fiber is capable of transmitting light by total internal reflection. Loss below 3 dB/microm is demonstrated throughout much of the visible region for a 250-microm-i.d. fiber filled with water. The utility of this device in enhancing the intensity of Raman spectra of core liquids is demonstrated.