Search

Gas sensors based on micro‐electromechanical systems (MEMS) offer advantages such as a broad spectrum of potentially sensitive materials and analytes, easy miniaturization and integration, high sensitivity, and low costs. This paper introduces a novel MEMS sensor platform utilizing a suspended gate field effect transistor (SGFET) transducer. In this approach, the flexible gate membrane of the SGFET is coated with a sensitive material exhibiting responsive swelling behavior. For the proof of concept, kraft lignin hydrogel is chosen as a biorenewable material for humidity sensing. A precision dispensing technique is used to deposit kraft lignin hydrogel on the SGFETs. The sensor measurements yield reversible shifts in the sensor's output current of up to 9% in response to 5000 ppm water vapor. The results successfully demonstrate the feasibility of this new sensing platform. A novel MEMS sensor platform utilizing a suspended gate field effect transistor (SGFET) transducer is introduced. In this approach, the flexible gate membrane of the SGFET is coated with a sensitive material exhibiting responsive swelling behavior. For the proof of concept, kraft lignin hydrogel is chosen as a biorenewable material for humidity sensing.

Thin films of cellulose ferulate were designed to study the formation of dehydrogenation polymers (DHPs) on anchor groups of the surface. Trimethylsilyl (TMS) cellulose ferulate with degree of substitution values of 0.35 (ferulate) and 2.53 (TMS) was synthesized by sophisticated polysaccharide chemistry applying the Mitsunobu reaction. The biopolymer derivative was spin-coated into thin films to yield ferulate moieties on a smooth cellulose surface. Dehydrogenative polymerization of coniferyl alcohol was performed in a Quartz crystal microbalance with a dissipation monitoring device in the presence of H2O2and adsorbed horseradish peroxidase. The amount of DHP formed on the surface was found to be independent of the base layer thickness from 14 to 75 nm. Pyrolysis-GC-MS measurements of the DHP revealed β-O-4 and β-5 linkages. Mimicking lignification of plant cell walls on highly defined model films enables reproducible investigations of structure–property relationships.

Graphical abstract:

Graphical abstract:

We study temperature-dependent charge transport in two-dimensional assemblies of copper sulfide nanodiscs in the covellite crystal phase (Cu1.1S). To enhance interparticle coupling, we cross-link the nanocrystals with the organic π-system Cu-4,4′,4″,4‴-tetraaminophthalocyanine and observe an increase in the conductivity by 6 orders of magnitude. The electrical properties of monolayers of this hybrid ensemble are consistent with a two-dimensional semiconductor and exhibit two abrupt changes at discrete temperatures (120 and 210 K), which may be interpreted as phase changes. X-ray scattering experiments serve to study the importance of electronic conjugation in the organic π-system vs interparticle spacing for efficient charge transport. Applying the hybrid ensemble as a chemiresistor in organic vapor sensing experiments reveals a strong selectivity between polar and nonpolar analytes, which we discuss in light of the role of the organic π-system and its metal center.

A triboelectric nanogenerator (TENG) is a promising approach to harvest electric power from the environment by converting mechanical energy into electrical energy. Various nanocomposites and nanofillers are incorporated to enhance triboelectric surface charge density. Researchers recently attempted to incorporate small molecules into TENGs and boost surface charge density after being used in drug delivery and solar cells. However, among the numerous small molecules, the fundamental physics for selecting small molecules has not been reported. Herein, approaches are carefully selected based on small molecules to enhance the surface charge density of the TENG. In addition to that, different surface and bulk approaches are also suggested to incorporate and assimilate small molecules into triboelectric layers. This systematic review provides the historical background, selection mechanisms, and fabrication methods of small‐molecule‐based TENGs to boost the surface charge density. Through a variety of surface and bulk manufacturing processes, small molecules can be integrated and infiltrated into triboelectric layers. This thorough review outlines the background, selection criteria, and fabrication processes for small‐molecule‐based triboelectric nanogenerators, which are designed to increase the density of the triboelectric surface charge and effectively capture mechanical energy.

The next generation of power sources for wearable electronics is anticipated to be nanogenerators based on triboelectric and piezoelectric mechanisms, which have proven to be effective at converting biomechanical energy into electrical energy. In this work, the piezoelectric and triboelectric effects of modeling clay were deeply explored. It is interestingly found that dry modeling clay possesses increasing β phase crystallinity when wet modeling clay undergoes annealing treatment. Based on the piezoelectric mechanism, the single-layer device of dry modeling clay delivers a power density of 1 W/m2, 250 times higher than the single-layer device of wet modeling clay. By piezoelectric mechanism, the single-layer device of polystyrene (PS) film delivers a power density of 0.35 W/m2. It is amazing that the nanogenerator composed of dry modeling clay and PS double layers achieves a high-power density of 3.75 W/m2. Through deep investigation, it is found that a synergetic piezo-triboelectric mechanism takes effect. The piezoelectric effects in each dry modeling clay, the porous structure of the polystyrene film, and the triboelectric effects occurring between the two layers are all involved. It was demonstrated that 200 and 300 commercial LED lights could be powered by the dry modeling clay-based device and the dry modeling clay-PS double layer device, respectively, showing that the devices have the potential to be used for energy harvesting.

Composite materials made of metallic nanoparticles embedded in an organic matrix are highly promising candidates as coatings for novel chemical sensors. Micromechanical cantilever measurements revealed that the Au-nanoparticle terphenyldithiol composite material swells upon dosing with toluene vapor. The mass increase was found to be linear with the toluene vapor concentration, ≈ 40 fg/ppm. Furthermore, significant differences in the mechanical transduction of ≈100 nm thick Au-nanoparticle terphenyldithiol composite material that was prepared on a 3-aminopropyldimethylmonoethoxysilane (APDMES) surface and on a Au surface were observed. The transduction of swelling of the composite film into a mechanical deflection was found to be more efficient for the composite film prepared on the Au surface attributed to covalent binding of the terphenyldithiol molecules with the Au surface. In contrast, the interface of the APDMES layer and the Au−terphenyldithiol composite material is based on electrostatic interaction between the Au nanoparticles and the amino interface. The analysis of the micromechanical cantilever sensor measurements lead to the conclusion that the composite film at the APDMES interface is more mobile compared to a similar film that was prepared on Au.

Networked films comprising gold nanoparticles (4 nm core diameter) and dodecanedithiol were deposited via layer-by-layer self-assembly. The film thickness was controlled by the number of deposition cycles and ranged from submonolayer to multilayer coverage with up to 60 nm thickness. FE-SEM and XPS revealed island growth during the first four to five deposition cycles. At room temperature, films based on islands showed slightly nonlinear current−voltage curves, whereas thicker films gave Ohmic behavior. Between 100 and 300 K, the temperature dependence of conductance was consistent with an Arrhenius model for activated charge transport. The chemical sensitivity of the films was characterized by dosing them with vapors of toluene, 4-methyl-2-pentanone, 1-propanol, and water while monitoring their relative differential resistances. Thin films responded with a decrease in the resistance, whereas thicker films responded with a resistance increase. The results indicate that swelling along the film normal may be important for the underlying sensing mechanism of homogeneous multilayer films. Changes in permittivity and/or swelling-induced decrease of the interisland distance can be responsible for the observed decrease in resistance of the thinner films.

In this study we investigated the response behavior of chemiresistors made from differently interlinked networks of gold nanoparticles. Our results show that the degree of flexibility and conductivity of the interlinkage between the nanoparticles has a profound impact on the response characteristics of such sensors. 1,12-Dodecanedithiol was used as a hydrophobic, flexible linker compound. For comparison, 4-staffane-3,3‘ ‘‘-dithiol provided a rigid, rodlike linkage, and 4,4‘-terphenyldithiol was used as a rigid linker with enhanced conductivity due to its delocalized aromatic moieties. As determined by AFM, all three sensor coatings had similar thicknesses (∼30 nm), but the degree of interlinkage, as measured by XPS, was significantly higher in the case of the flexible network. All three materials showed linear current−voltage characteristics. The vapor sensitivity was tested by dosing the sensors with toluene, 1-propanol, 4-methyl-2-pentanone, and water in the concentration range 100−5000 ppm at 0% relative humidity. The flexible 1,12-dodecanedithiol interlinked film responded with an increase in resistance to these analytes and with the highest sensitivity to toluene. In striking contrast, the rigid staffane interlinked film responded with a decrease in resistance to all four analytes and with the highest sensitivity to 4-methyl-2-pentanone. The rigid but more conductive 4,4‘-terphenyldithiol interlinked coating gave hardly any response, although microgravimetric measurements showed that similar amounts of analytes were absorbed as in the case of the other two sensor films. The different response characteristics are discussed in terms of film swelling and changes in permittivity.

If adsorption is reversible and sufficiently fast, isotherms or isobars can be measured in adsorption–desorption equilibrium at low pressures on single crystal surfaces. The isosteric heat of adsorption can easily be derived from them using the Clausius–Clapeyron equation. Reaction orders and frequency factors can, in principle, be deduced from a fit of the isobars (or isotherms) using the kinetic equations for adsorption and desorption. Immobile and mobile precursor kinetics can be included in the analysis but the fit fails when structural phase transitions in the substrate or the adlayer cause the kinetics to become complex. We review the methods, strong points and limitations of isobar (isotherm) measurements and of their kinetic fits by discussing the adsorption of water, ethylbenzene and styrene on FeO(111), Fe₃O₄(111) and Pt(111) and the adsorption of ammonia on germanium surfaces. Where the kinetic fit was successful, mobile precursor kinetics is quite common and frequency factors for desorption deviate considerably from the often assumed value of 1013 s−1.

The adsorption of ethylbenzene and styrene on well ordered epitaxial iron oxide model catalyst films with different stoichiometries was investigated using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). On the iron-terminated Fe₃O₄(111) and α-Fe₂O₃(0001) surfaces chemisorption of ethylbenzene and styrene is observed occurring initially on the iron sites via the π-electron system of the phenyl ring. This forces the molecules into an almost flat configuration (η⁶-like ring adsorption geometry). In the case of ethylbenzene this adsorption complex is supposed to lead to an activation of the C–H bonds, thus facilitating the dehydrogenation to styrene. The tilt angle of the aromatic ring systems increases to about 40° when approaching monolayer saturation. In contrast, the interaction with the oxygen-terminated FeO(111) surface is weak and of the physisorption type. The adsorbate–adsorbate interaction dominates and causes a tilted adsorption of the molecules from the beginning.

CD28 has been demonstrated to provide the major costimulatory signal for CD4-positive T cells. Ligation with its natural ligands CD80 (B7-1) and CD86 (B7-2) leads to signals during activation that are required for the production of interleukin-2, and this process has been implicated in the regulation of T-cell anergy and programmed cell death. This article describes the assay development, assay validation, and primary screening for small molecule antagonists of this interaction, which could be potential drug candidates. The assay uses homogeneous time-resolved fluorescence based on energy transfer from excited europium ions to cross-linked allophycocyanin, which then subsequently emits a fluorescent signal. An “indirect” approach was taken, whereby the cross-linked allophycocyanin (XL665) is covalently linked to an antihuman antibody that binds to a human immunoglobulin (Ig) domain fused to CD28. The CD86 that is expressed as a fusion protein with a rat Ig domain is bound to biotinylated sheep antirat antibody, which is complexed with streptavidin-europium cryptate. This “cassette” format facilitates the development of related assays using CTLA-4 in place of CD28 and/or CD80 in place of CD86, allowing easy determination of the selectivity of active compounds. When the CD28 and CD86 are in close proximity (i.e., bound), there is a specific time-resolved emission at 665 nm that is largely absent in either unbound partner. Experiments to optimize the reagent concentrations, incubation time, solvent effects and quench effects by colored compounds are discussed, as are the results from robustness testing and data from primary screening.

CD28 has been demonstrated to provide the major costimulatory signal for CD4-positive T cells. Ligation with its natural ligands CD80 (B7-1) and CD86 (B7-2) leads to signals during activation that are required for the production of interleukin-2, and this process has been implicated in the regulation of T-cell anergy and programmed cell death. This article describes the assay development, assay validation, and primary screening for small molecule antagonists of this interaction, which could be potential drug candidates. The assay uses homogeneous time-resolved fluorescence based on energy transfer from excited europium ions to cross-linked allophycocyanin, which then subsequently emits a fluorescent signal. An "indirect" approach was taken, whereby the cross-linked allophycocyanin (XL665) is covalently linked to an antihuman antibody that binds to a human immunoglobulin (Ig) domain fused to CD28. The CD86 that is expressed as a fusion protein with a rat Ig domain is bound to biotinylated sheep antirat antibody, which is complexed with streptavidin-europium cryptate. This "cassette" format facilitates the development of related assays using CTLA-4 in place of CD28 and/or CD80 in place of CD86, allowing easy determination of the selectivity of active compounds. When the CD28 and CD86 are in close proximity (i.e., bound), there is a specific time-resolved emission at 665 nm that is largely absent in either unbound partner. Experiments to optimize the reagent concentrations, incubation time, solvent effects and quench effects by colored compounds are discussed, as are the results from robustness testing and data from primary screening.