Fractional exhaled nitric oxide measurement with a handheld device.

A sensing system for fractional exhaled nitric oxide (FeNO) measurement is presented, which is characterized by a compact setup and a cost potential to be made available for the patient at home. The sensing is based on the work function measurement of a phthalocyanine-type sensing material, which is shown to be sufficiently sensitive for NO(2) in the ppb range. The transducer used to measure the work function is a field effect transistor with a suspended gate electrode. Selectivity is given with respect to other breath components including typically metabolic by-products. The measurement system includes breath treatments in a simple setup, which essentially are dehumidification and a quantitative conversion of NO to NO(2) with a conversion rate of approx. 95%, using a disposable oxidation catalyst. The accomplishment of the correct exhalation maneuver and feeding of the suited portion of exhaled air to the sensor is provided by breath sampling means. The sensor is not gas consuming. This allows us to fill the measurement chamber once, instead of establishing a gas flow for the measurement. This feature simplifies the device architecture. In this paper, we report on sensor characteristics, system architecture and measurement with artificial breath-gas as well as with human breath with the device.

Torsional noise of a colloidal probe in contact with surface-grafted PEG layers.

Surface coatings modify the interaction between microparticles and surfaces. To analyze the effect of a PLL-g-PEG surface coating on the sticktion of a microparticle, we analyzed the torsional Brownian fluctuations of a colloidal probe attached to an atomic force microscope (AFM) cantilever. Results obtained with uncoated surfaces indicate that the torsional oscillation due to noise was only weakly affected by hydrodynamic effects. Upon mechanical contact, however, the uncoated probe stuck to the uncoated surface. Coating probe or surface with a PLL-g-PEG brush polymer reduced the lateral interaction (sticktion and friction) of the colloidal probe. For such a combination, the torsional fluctuations persisted during mechanical compression of the brush layer. The results demonstrate that a PLL-g-PEG coating can effectively reduce the lateral interaction of a microparticle with a surface and prevent sticktion.