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Michael Wahl

Publications and source records attributed to Michael Wahl.

10 recordsLinked to original sources
PubMed2006

DNA-based molecular wires: multiple emission pathways of individual constructs.

The extent of photon energy transfer through individual DNA-based molecular wires composed of five dyes is investigated at the single molecular level. Combining single-molecule spectroscopy and pulse interleaved excitation imaging, we have directly resolved the time evolution spectral response of individual constructs, while simultaneously probing DNA integrity. Our data clearly show that intact wires exhibit photon-transfer efficiencies close to 100% across five dyes. Dynamical and multiple pathways for the photon emission resulting from conformational freedom of the wire are readily uncovered. These results provide the basis for guiding the synthesis of DNA-based supramolecular arrays with improved photon transport at the nanometer scale.

DNA, Single-Stranded↗
PubMed2006

Fluorescence lifetime correlation spectroscopy.

This article explains the basic principles of FLCS, a genuine fusion of Time-Correlated Single Photon Counting (TCSPC) and Fluorescence Correlation Spectroscopy (FCS), using common terms and minimum mathematics. The usefulness of the method is demonstrated on simple FCS experiments. The method makes possible to separate the autocorrelation function of individual components of a mixture of fluorophores, as well as purging the result from parasitic contributions like scattered light or detector afterpulsing.

Journal Article↗
PubMed2006

Mental chronometry of target detection: human thalamus leads cortex.

Attentive monitoring of environmental stimuli is most fundamental for rapid target detection. The aim of this study was to assess the timing of thalamic versus cortical processes involved in this cognitive operation. To this end, simultaneous depth and scalp EEG was recorded in eight patients with essential tremor, undergoing thalamic deep brain stimulation (DBS), when the DBS electrodes could be accessed via their temporarily externalized leads. The patients performed an oddball task consisting of 300 presentations of one frequent and two rare visual cues, appearing in randomized order. One of the rare cues was defined as a target, the occurrences of which had to be indicated by a button press (motor condition) or silently counted (non-motor condition). At the scalp and the thalamus, event-related potentials (ERP) were largest upon target presentation, with peak latencies in the time domain of classical P300 responses. Remarkably, target-specific thalamic ERP emerged significantly prior to scalp P300. Furthermore, whereas scalp ERP had a higher amplitude upon rare than upon frequent non-target signals, thalamic ERP were independent of stimulus probability. This pattern was identified during motor and non-motor task execution. We conclude that the human thalamus specifically supports the early recognition of target events and can widely distribute this label through its divergent cortical projections.

Adult↗