Analyte detection with Cu-BTC metal-organic framework thin films by means of mass-sensitive and work-function-based readout.

Metal-organic frameworks (MOFs) constitute a new generation of porous crystalline materials, which have recently come into focus as analyte-specific active elements in thin-film sensor devices. Cu-BTC--also known as HKUST-1--is one of the most theoretically and experimentally investigated members of the MOF family. Its capability to selectively adsorb different gas molecules renders this material a promising candidate for applications in chemical gas and vapor sensing. Here, we explore details of the host-guest interactions between HKUST-1 and various analytes under different environmental conditions and study the vapor adsorption mechanism by mass-sensitive and work-function-based readouts. These complementary transduction mechanisms were successfully applied for the detection of low ppm (2 to 50 ppm) concentrations of different alcohols (methanol, ethanol, 1-propanol, and 2-propanol) adsorbed into Cu-BTC thin films. Evaluation of the results allows for the comparison of the amounts of adsorbed vapors and the contribution of each vapor to the changes of the electronic properties of Cu-BTC. The influence of the length of the alcohol chain (C1-C3) and geometry (1-propanol, 2-propanol) as well as their polarity on the sensing performance was investigated, revealing that in dry air, short chain alcohols are more likely adsorbed than long chain alcohols, whereas in humid air, this preference is changed, and the sensitivity toward alcohols is generally decreased. The adsorption mechanism is revealed to differ for dry and humid atmospheres, changing from a site-specific binding of alcohols to the open metal sites under dry conditions to weak physisorption of the analytes dissolved in surface-adsorbed water reservoirs in humid air, with the signal strength being governed by their relative concentration.

Blood platelet adhesion to printed von Willebrand factor.

Von Willebrand factor (vWF), a glycoprotein in blood, mediates the adhesion of blood platelets and thus plays a crucial role in hemostasis and thrombosis. Functional coating of surfaces with vWF allows the investigation of in vitro adhesion of blood platelet. We used soft lithography to create a functional patterned substrate. vWF was printed on plasma-treated glass and mica surfaces, producing elongated network-like fibril structures. A minimum layer thickness of 3 nm was observed, corresponding to the height of a monolayer of vWF. The stability of the patterns was verified in a laminar fluid flow, and the bioactivity of the structures was tested with platelet adhesion experiments. Platelets adhered to and spread on printed vWF. These results indicate that printed vWF substrates are stable and functional in typical perfusion experiments, and thus provide a useful tool for studying thrombus formation in vitro.

Anisotropic Raman scattering in collagen bundles.

Collagen is the main connective tissue protein of vertebrates and shows exceptional mechanical and optical properties. The alignment of collagen fibrils correlates to the function of a specific tissue and leads to optical anisotropy. The effect of the molecular alignment on Raman scattering, however, has barely been investigated. We found that the peak intensities of the C-C, C=O, and N-H vibrational modes, which are typical for the Raman bands of the protein backbone, change with the orientation of the collagen fibrils. These observations demonstrate that Raman spectra contain specific information regarding molecular and fiber alignment.