We present the basis for an entirely new approach to in situ nanoparticle sizing. Nanoparticles containing just 12 zeptomoles (1 zeptomole = 10(-21) moles) of silver, are detected via in situ particle coulometry. These stochastic charge measurements correspond to the transfer of only 7000-8000 electrons, yielding direct information relating to the individual nanoparticle volumes. The resulting particle size distribution (average equivalent radius 5 nm) obtained via nanoparticle coulometry is in excellent correspondence with that attained from TEM analysis. Moreover, the measurable particle size limit by this electrochemical method is shown to be significantly below that of more common optical nanoparticle tracking techniques, and as such can be viewed as a potential disruptive nano-technology.
A portable and compact device is demonstrated for measuring acetone in breath samples. The device features a 7 cm long high finesse optical cavity as an optical sensor that is coupled to a miniature adsorption preconcentrator containing 0.5 g of polymer material. Acetone is trapped out of breath and released into the optical cavity where it is probed by a near-infrared diode laser operating at ∼1670 nm. With an optical cavity mirror reflectivity of 99.994%, a limit of detection of 159 ppbv (1σ) is demonstrated on samples from breath bags. Initial results on direct breath sampling are presented with a precision of 100 ppbv. The method is validated with measurements made using an ion-molecule reaction mass spectrometer. Data are presented on elevated breath acetone from two individuals following an overnight fast and exercise, and from a third individual during several days of routine behavior.
A handheld electrochemical sensor has been demonstrated for the quantification of the strength of garlic. The device is based on the enhanced voltammetric response in the presence of organosulfur compounds extracted from garlic. Convenient and disposable platinum screen-printed electrodes are employed. All measurements and data analyses are performed within the device. A linear response of the voltammetric peak current enhancement as a function of garlic concentration was observed, indicating the ability of the device to be applied to garlic samples of any strength. Importantly, this portable sensor can be used by non-scientifically skilled personnel and does not require expensive laboratory equipment. It is thus suitable for application in the food industry.
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