Trevor Rayment

A femtojoule calorimeter using micromechanical sensors

We describe a highly sensitive new type of calorimeter based on the deflection of a ‘‘bimetallic’’ micromechanical sensor as a function of temperature. The temperature changes can be due to ambient changes, giving a temperature sensor or, more importantly, due to the heat absorbed by a coating on the sensor, giving a heat sensor. As an example we show the results of using the sensor as a photothermal spectrometer. The small dimensions and low thermal mass of the sensor make it highly sensitive and we demonstrate a sensitivity of roughly 100 pW. By applying a simple model of the system the ultimate sensitivity is expected to be of the order of 10 pW. The thermal response time of the cantilever can also be determined, giving an estimate of the minimum detectable energy of the sensor. This we find to be 150 fJ and again from our model, expect a minimum value of the order of 20 fJ.

Nanomechanical detection of antibiotic mucopeptide binding in a model for superbug drug resistance

The alarming growth of the antibiotic-resistant superbugs methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) is driving the development of new technologies to investigate antibiotics and their modes of action. We report the label-free detection of vancomycin binding to bacterial cell wall precursor analogues (mucopeptides) on cantilever arrays, with 10 nM sensitivity and at clinically relevant concentrations in blood serum. Differential measurements have quantified binding constants for vancomycin-sensitive and vancomycin-resistant mucopeptide analogues. Moreover, by systematically modifying the mucopeptide density we gain new insights into the origin of surface stress. We propose that stress is a product of a local chemical binding factor and a geometrical factor describing the mechanical connectivity of regions activated by local binding in terms of a percolation process. Our findings place BioMEMS devices in a new class of percolative systems. The percolation concept will underpin the design of devices and coatings to significantly lower the drug detection limit and may also have an impact on our understanding of antibiotic drug action in bacteria.

The nature of the iron oxide-based catalyst for dehydrogenation of ethylbenzene to styrene. I, Solid-state chemistry and bulk characterization

Abstract The active catalyst for the dehydrogenation of ethylbenzene is generated from a precursor material consisting of hematite and potassium hydroxide (with additional promotors) during the initial phase of catalyst operation at 873 K in a steam atmosphere. The active phase is a thin layer of KFeO 2 supported on a solid solution of K 2 Fe 22 O 34 in Fe 3 O 4 . The ternary K 2 Fe 22 O 34 phase acts as storage medium from which the active surface is continuously supplied with a near-monolayer coverage of potassium ions in an environment of Fe 3+ ions. The catalyst undergoes a continuous solid-state transformation caused by the migration of potassium ions. This requires a certain degree of imperfection in the matrix lattice which originates from the catalyst preparation and from the addition of promotors which act on the iron oxide lattice rather than on the surface chemistry. The identity of the active phase with KFeO 2 was confirmed by independent synthesis of this phase and comparison of its catalytic activity with that of the technical catalyst.

Chiral discrimination by chemical force microscopy

Chirality is a fundamental aspect of chemical biology, and is of central importance in pharmacology. Consequently there is great interest in techniques for distinguishing between different chiral forms of a compound. Chemical force microscopy is a technique that combines chemical discrimination with atomic force microscopy by chemical derivatization of the scanning probe tip. It has been applied to the study of hydrophobic and hydrophilic interactions, the binding between biotin and streptavidin, and between DNA bases. Here we report on the use of chemical force microscopy to discriminate between chiral molecules. Using chiral molecules attached to the probe tip, we can distinguish the two enantiomers of mandelic acid arrayed on a surface, through differences in both the adhesion forces and the frictional forces measured by the probe.

An in situ X-ray diffraction study of the activation and performance of methanol synthesis catalysts derived from rare earth-copper alloys

Abstract The activation of NdCu, NdCu 2 , NdCu 5 , and CeCu 2 alloy precursors for methanol synthesis catalysts has been investigated by in situ XRD observations and concurrent measurements of methanol activity. Pressures of 2–30 bar and temperatures in the range 300–573 K were employed. It is shown that the formation of certain intermediate hydride phases is crucial to the eventual production of highly active catalysts and that methanol activity does not correlate with Cu crystallite size. CO 2 is a very effective poison which does not visibly affect the morphology of the metal phase. These findings strongly suggest that the reaction mechanism which obtains here is quite different from that which operates on conventional Cu  ZnO Al 2 O 3 methanol synthesis Catalysts.

Solvation forces near a graphite surface measured with an atomic force microscope

Solvation force interactions in a liquid near a solid wall (graphite) were investigated using an atomic force microscope. The general features of the data show the distinctive oscillatory force curve associated with solvation forces, with a mean periodicity approximately equal to the minimum dimensions of the molecules. Moreover, the graphite surface can still be imaged with atomic resolution; which suggests that the technique can be used for the detailed study of short range forces over specific parts of various surfaces.

Hybrid Scanning Ion Conductance and Scanning Near-Field Optical Microscopy for the Study of Living Cells

We have developed a hybrid scanning ion conductance and scanning near-field optical microscope for the study of living cells. The technique allows quantitative, high-resolution characterization of the cell surface and the simultaneous recording of topographic and optical images. A particular feature of the method is a reliable mechanism to control the distance between the probe and the sample in physiological buffer. We demonstrate this new method by recording near-field images of living cells (cardiac myocytes).

Atomic force microscopy stress sensors for studies in liquids

Simple, sensitive, and fast sensors can be constructed from standard atomic force microscopy cantilevers. For use in liquid environments, it is preferable to use changes in surface stress as the measurement basis of the sensor. We have constructed such a sensor in an electrochemical cell so that simultaneous cyclic voltammograms and strain measurements can be made. This is demonstrated with examples of underpotential deposition of Pb on Au(111) and electrocapillary effects in KCl.

Atomic force microscope study of boundary layer lubrication

An atomic force microscope is used to investigate the lubrication properties of a simple surfactant (n‐dodecanol) on mica at 24 °C. The liquid becomes strongly layered as it is confined between the tip and the mica and a bilayer structure was often observed. The lubrication properties of the adsorbed molecules are clearly evident in the very low friction forces observed at appreciable applied loads (∼100 MPa). It is only when the last layer of molecules is removed that a significant friction signal is observed. It appears that the tip‐mica interaction is dominated by adhesive forces and hence the measured friction and normal forces are strongly influenced by the effective contact area of the tip.

An in situ XRD investigation of singly and doubly promoted manganese oxide methane coupling catalysts

In situ X-ray diffraction (XRD) and concurrent measurements of catalytic performance have been used to characterize the solid phases present during various stages in the history of working methane coupling catalytic systems. Three such systems were studied: unpromoted, K-promoted, and KCl-promoted manganese oxide. In each case the effect of pulses of CHCl{sub 3} on the activity, selectivity, and catalyst structure was determined. Depending on the conditions, various oxides or mixed oxides of Mn were present. Of these, Mn{sub 3}O{sub 4} is an unselective total oxidation catalyst; K-promotion stabilizes this phase, drastically reducing CO{sub 2} formation and raising C{sub 2} activity. Chloride ions (added as KCl) prevent the formation of highly unselective potassium manganese oxides. Chlorine introduced from the gas phase has an additional effect: C{sub 2} activity is further enhanced leaving CO{sub 2} production unaffected. This form of chlorine promotion is greatly augmented by the presence of KCl. There are strong indications that the effects of chlorine involved substantial modification of the surface chemistry and are not purely due to Cl atom-induced homogeneous chemistry.