DNA and peptide nucleic acid (PNA) molecular beacons were successfully used to detect rRNA in solution. In addition, PNA molecular beacon hybridizations were found to be useful for the quantification of rRNA: hybridization signals increased in a linear fashion with the 16S rRNA concentrations used in this experiment (between 0.39 and 25 nM) in the presence of 50 nM PNA MB. DNA and PNA molecular beacons were successfully used to detect whole cells in fluorescence in situ hybridization (FISH) experiments without a wash step. The FISH results with the PNA molecular beacons were superior to those with the DNA molecular beacons: the hybridization kinetics were much faster, the signal-to-noise ratio was much higher, and the specificity was much better for the PNA molecular beacons. Finally, it was demonstrated that the combination of the use of PNA molecular beacons in FISH and flow cytometry makes it possible to rapidly collect quantitative FISH data. Thus, PNA molecular beacons might provide a solution for limitations of traditional FISH methods, such as variable target site accessibility, poor sensitivity for target cells with low rRNA content, background fluorescence, and applications of FISH in microfluidic devices.

Fluorescent reactions of a heterogeneous sandwich enzyme-linked immunoassay (ELISA) in an all-PDMS [poly (dimethylsiloxane)] microfluidic device were detected using a cooled charge coupled device (CCD) camera interfaced with an epifluorescence microscope. The study represents preliminary efforts to integrate biochemical reactions and detection on-chip using the "hybrid" detection approach. In initial experiments, the PDMS chip microsensor was successfully used to quantify a model analyte (sheep IgM) with sensitivity down to 17nM. Thus, we demonstrate here the extension of this hybrid integrated technique to on-chip imaging and quantification of light emission from a biochemical immunoassay in PDMS chip.

We describe a modified confocal microscope in which depth discrimination results from matched filtering by a volume hologram instead of a pinhole filter. The depth resolution depends on the numerical aperture of the objective lens and the thickness of the hologram, and the dynamic range is determined by the diffraction efficiency. We calculate the depth response of the volume holographic confocal microscope, verify it experimentally, and present the scanned image of a silicon wafer with microfabricated surface structures.

Following the lack of microscopic information about the intriguing well-known electrical-thermal switching mechanism in carbon-black-polymer composites, we applied atomic force microscopy in order to reveal the local nature of the process and correlated it with the characteristics of the widely used commercial switches. We conclude that the switching events take place in critical interparticle tunneling junctions that carry most of the current. The macroscopic switched state is then a result of a dynamic-stationary state of fast switching and slow reconnection of the corresponding junctions.

We developed a new method to identify the separate cellular compartments in the optical path delay (OPD) maps of un-labeled spermatozoa. This was conducted by comparing OPD maps of fixed, un-labeled spermatozoa to bright field images of the same cells following labeling. The labeling enabled us to identify the acrosomal and nuclear compartments in the corresponding OPD maps of the cells. We then extracted the refractive index maps of fixed cells by dividing the OPD maps of spermatozoa by the corresponding thickness maps of the same cells, obtained with AFM. Finally, the dry mass of the head, nucleus and acrosome of un-labeled immobile spermatozoa, was measured. This method provides the ability to quantitatively measure the dry mass of cellular compartments within human spermatozoa. We expect that these measurements will assist label-free selection of sperm cells for fertilization.