Clinical and field-portable diagnostic devices require the detection of atto-to zeptomoles of biological molecules rapidly, easily and at low cost, with stringent requirements in terms of robustness and reliability. Though a number of creative approaches to this difficult problem have been reported 1-9 , numerous unmet needs remain in the marketplace, particularly in resource-poor settings [10][11][12] . Using rational materials design, we investigated harnessing the amplification inherent in a radical chain polymerization reaction to detect molecular recognition. Polymerization-based amplification is shown to yield a macroscopically observable polymer, easily visible to the unaided eye, as a result of as few as ~1,000 recognition events (10 zeptomoles). Design and synthesis of a dual-functional macromolecule that is capable both of selective recognition and of initiating a polymerization reaction was central to obtaining high sensitivity and eliminating the need for any detection equipment. Herein, we detail the design criteria that were used and compare our findings with those obtained using enzymatic amplification. Most excitingly, this new approach is general in that it is readily adaptable to facile detection at very low levels of specific biological interactions of any kind.

A water vapor interference in ozone measurements by UV absorption was investigated using four different ozone monitors (TEI models 49 and 49C, Dasibi model 1003-AH, and a 2B Technologies model 202 prototype). In the extreme case of step changes between 0 and 90% relative humidity (RH), a large interference in the range of tens to hundreds of ppbv was found for all instruments tested, with the magnitude and sign depending on the manufacturer and model. Considering that water vapor does not absorb at the wavelength of the Hg lamp (253.7 nm) used in these instruments, another explanation is required. Based on experimental evidence and theoretical considerations, we conclude that the water vapor interference is caused by humidity effects on the transmission of uncollimated UV light through the detection cell. The ozone scrubber acts as a water reservoir, either adding or removing water from the air sample, thereby modulating the detector signal and producing a positive or negative offset. It was found for the 2B Technologies ozone monitor that use of a 1-m length of Nafion tubing just prior to the entrance to the detection cell reduces the water vapor interference to negligible levels (+/- 2 ppbv for step changes between 0 and 90% RH) while quantitatively passing ozone.

Abstract. Vertical profiles of volatile organic compounds (VOCs) within the convective boundary layer (CBL) were measured at a tropical forest site in the Peruvian Amazon during July 1996 from a tethered balloon sampling platform. A profiling technique based on the collection of VOCs onto solid adsorbent cartridges was used to take samples at altitudes up to 1600 m above ground. VOC analysis was performed by thermal desorption with gas chromatographic separation and mass spectrometric and flame ionization detection. A total of 26 VOCs were stmcturally identified. VOCs were dominated by biogenic compounds. Highest concentrations were observed for isoprene, followed by c•-pinene, p-cymene, and [3-pinene. Combined, all monoterpenes accounted for approximately 15-20% of the total carbon from biogenic VOCs (BVOCs). The isoprene oxidation products methacrolein (MAC), methylvinylketone (MVK), and 3-methylfuran were observed throughout the CBL. Besides the ubiquitous chlorofluorocarbons, anthropogenic VOC concentrations were at the lower end of concentration ranges observed in rural air. From the vertical profiles, BVOC surface flux estimates were derived. Emission rates were estimated from five vertical profiles using the mixed-layer gradient and CBL budget methods. Emission estimates

A new instrument for the detection of nitric oxide has been developed and applied to the analysis of exhaled breath. The instrument is based on conversion of NO to NO2, using the oxidant chromium trioxide, followed by detection of chemiluminescence in the reaction of NO2 with an alkaline luminol/H2O2 solution. The presence of H2O2 is found to enhance the sensitivity of NO2 detection by a factor of approximately 20. A bundle of porous polypropylene hollow fiber membranes is used to bring the gaseous sample into contact with the luminol solution. Chemiluminescence occurring within the translucent hollow fibers is detected using a miniature photomultiplier tube. The limit of detection for NO is 0.3 ppbv for S/N = 3, and the 1/e response time is 2 s. A large interference resulting from the 4-6% CO2 concentration in exhaled breath is removed by use of an ascarite scrubber in the air stream. Breath measurements of NO were made using a sampling technique developed by Sensor Medics (Yorba Linda, CA) with simultaneous detection using the luminol/H2O2 and NO + O3 chemiluminescence techniques. The two instruments were found to be in excellent agreement. Nitric oxide levels were in the range 6.0-22.0 ppbv for healthy individuals and 40.0-80.0 ppbv for individuals with asthma or a respiratory infection. This new detector offers the advantages of compact size, low cost, and a simple configuration compared to NO detectors based on NO + O3 chemiluminescence.

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A new laboratory source of gaseous hypochlorous acid (HOCI) is described. The new source is dynamic, whereby HOCI is formed by reaction of Cl2 with aqueous CaC03 and used before it equilibrates to form C120 and H20. When compared to the conventional static preparation of HOCI by C120-H20-HOC1 equilibration, the dynamic HOCI source has a substantially lower C120 impurity level. We have applied the new source to the measurement of the product distribution in the reaction of Cl + HOCI in a low-pressure mass spectrometry-discharge flow system. The major reaction channel gives the products Cl2 and OH, with a yield of 91 ± 6% at 298 K. In combination with other thermochemical and kinetic data, this result yields a value of -18.0 kcal mol"1 for the standard heat of formation (AH°) of HOCI. In addition, we have used the dynamic source to achieve an absolute calibration of the response of the mass spectrometer to HOCI. Making use of this calibration and conventional equilibrium Cl20-H20-HOCl mixtures, we determined the equilibrium constant (K^) of the reaction C120 + H20 = 2HOC1 to be 0.092 ± 0.011 at 298 K, where the uncertainty reflects both random errors and our estimate of possible systematic errors of the measurement.

It has been shown that 1,1'-oxalyldiimidazole (ODI) is formed as an intermediate in the imidazole-catalyzed reaction of oxalate esters with hydrogen peroxide. Therefore, the kinetics of the chemiluminescence reaction of 1,1'-oxalyldiimidazole (ODI) with hydrogen peroxide in the presence of a fluorophore was investigated in order to further elucidate the mechanism of the peroxyoxalate chemiluminescence reaction. The effects of concentrations of ODI, hydrogen peroxide, imidazole (ImH), the general-base catalysts lutidine and collidine, and temperature on the chemiluminescence profile and relative quantum efficiency in the solvent acetonitrile were determined using the stopped-flow technique. Pseudo-first-order rate constant measurements were made for concentrations of either H2O2 or ODI in large excess. All of the reaction kinetics are consistent with a mechanism in which the reaction is initiated by a base-catalyzed substitution of hydrogen peroxide for imidazole in ODI to form an imidazoyl peracid (Im(CO)2OOH). In the presence of a large excess of H2O2, this intermediate rapidly decays with both a zero- and first-order dependence on the H2O2 concentration. It is proposed that the zero-order process reflects a cyclization of this intermediate to form a species capable of exciting a fluorophore via the "chemically initiated electron exchange mechanism" (CIEEL), while the first-order process results from the substitution of an additional molecule of hydrogen peroxide to the imidazoyl peracid to form dihydroperoxyoxalate, reducing the observed quantum yield. Under conditions of a large excess of ODI, the reaction is more than 1 order of magnitude more efficient at producing light, and the quantum yield increases linearly with increasing ODI concentration. Again, it is proposed that the slow initiating step of the reaction involves the substitution of H2O2 for imidazole to form the imidazoyl peracid. This intermediate may decay by either cyclization or by reaction with another ODI molecule to form a cyclic peroxide that is much more efficient at energy transfer with the fluorophore. The reaction kinetics clearly distinguishes two separate pathways for the chemiluminescent reaction.

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