Towards T1-limited magnetic resonance imaging using Rabi beats

Two proof-of-principle experiments towards T1-limited magnetic resonance imaging with NV centers in diamond are demonstrated. First, a large number of Rabi oscillations is measured and it is demonstrated that the hyperfine interaction due to the NV's 14N can be extracted from the beating oscillations. Second, the Rabi beats under V-type microwave excitation of the three hyperfine manifolds is studied experimentally and described theoretically.Comment: 6 pages, 8 figure

Workgroup report: Public health strategies for reducing aflatoxin exposure in developing countries

10.1289/ehp.9302Environmental Health Perspectives114121898-190

Fluorescence fluctuation spectroscopy in subdiffraction focal volumes.

Contains fulltext : 47864.pdf (publisher's version ) (Open Access)We establish fluorescence fluctuation spectroscopy (FFS) with nanoscale detection volumes generated by stimulated emission depletion. Our method applies fluorescence correlation spectroscopy and fluorescence intensity distribution analysis to extract molecular information about mobilities and fluorescence emission in solution. The combination of correlation analysis with that of photon intensity distributions reveals a fivefold squeezing of the detection volume over current diffraction-limited systems, which is in full agreement with the simultaneously demonstrated 25-fold reduction in (axial) focal transit time. Our method significantly extends the potential of far-field FFS, including for the noninvasive investigation of molecular reactions at higher concentrations

Synthesis and characterization of photoswitchable fluorescent silica nanoparticles

We have designed and synthesized a new functional (amino reactive) highly efficient fluorescent molecular switch (FMS) with a photochromic diarylethene and a rhodamine fluorescent dye. The reactive group in this FMS -N-hydroxysuccinimide ester- allows selective labeling of amino containing molecules or other materials. In ethanolic solutions, the compound displays a large fluorescent quantum yield of 52 % and a large fluorescence modulation ratio (94 %) between two states that may be interconverted with red and near-UV light. Silica nanoparticles incorporating the new FMS were prepared and characterized, and their spectroscopic and switching properties were also studied. The dye retained its properties after the incorporation into the silica, thereby allowing light-induced reversible high modulation of the fluorescence signal of a single particle for up to 60 cycles, before undergoing irreversible photobleaching. Some applications of these particles in fluorescence microscopy are also demonstrated. In particular, subdiffraction images of nanoparticles were obtained, in the focal plane of a confocal microscope