The room-temperature luminescence of single CdSe/ZnS core-shell quantum dots is investigated by spectrally and temporally resolved confocal microscopy. A large (30 nm) blue shift is observed in the emission wavelength during illumination in air. In nitrogen, no blue shift is observed. The blue shift in air is ascribed to a 1 nm shrinkage of the CdSe core by photooxidation. Photobleaching occurs about 4 times faster in air than in nitrogen, indicating the formation of nonradiative recombination centers during photooxidation. The initial light output is higher in air than in nitrogen, which may be due to a reduction of the defect state lifetime by oxygen.

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Four different conductive supports are analysed regarding their suitability for combined atomic force and scanning electrochemical microscopy (AFM-SECM) on biological membranes. Highly oriented pyrolytic graphite (HOPG), MoS(2), template stripped gold, and template stripped platinum are compared as supports for high resolution imaging of reconstituted membrane proteins or native membranes, and as electrodes for transferring electrons from or to a redox molecule. We demonstrate that high resolution topographs of the bacterial outer membrane protein F can be recorded by contact mode AFM on all four supports. Electrochemical feedback experiments with conductive cantilevers that feature nanometre-scale electrodes showed fast re-oxidation of the redox couple Ru(NH(3))(6)(3+/2+) with the two metal supports after prolonged immersion in electrolyte. In contrast, the re-oxidation rates decayed quickly to unpractical levels with HOPG or MoS(2) under physiological conditions. On HOPG we observed heterogeneity in the re-oxidation rate of the redox molecules with higher feedback currents at step edges. The latter results demonstrate the capability of conductive cantilevers with small electrodes to measure minor variations in an SECM signal and to relate them to nanometre-scale features in a simultaneously recorded AFM topography. Rapid decay of re-oxidation rate and surface heterogeneity make HOPG or MoS(2) less attractive for combined AFM-SECM experiments on biological membranes than template stripped gold or platinum supports.

We describe a method to perform dynamic-mode scanning force microscopy in liquid with true atomic resolution. A frequency-modulation technique is used to maintain constant amplitude, phase, and frequency shift of the cantilever oscillation. As a consequence, the tip-sample interaction force is well defined and quantitative. The force sensitivity is demonstrated by imaging and deliberate bending of a peptide loop connecting transmembrane helices of the membrane protein bacteriorhodopsin. The experimental setup allows further enhancement of the force sensitivity by the use of small cantilevers.

We have developed a Fabry-Perot interferometer detecting the deflection of micrometer-sized cantilevers and other micromechanical devices, at a working distance of 0.8 mm. At 1 MHz, a noise floor of 1 fm/ ͱ Hz is obtained. The detector is mounted on a piezo motor for three-axis alignment.The angular alignment is not critical. The interferometer can be operated in vacuum, air, and liquid. It is particularly suited for scanning force microscopy with small cantilevers, or with larger cantilevers simultaneously monitoring vertical and lateral forces.