Dielectric microspheres with appropriate refractive index can image objects with super-resolution, that is, with a precision well beyond the classical diffraction limit. A microsphere is also known to generate upon illumination a photonic nanojet, which is a scattered beam of light with a high-intensity main lobe and very narrow waist. Here, we report a systematic study of the imaging of water-immersed nanostructures by barium titanate glass microspheres of different size. A numerical study of the light propagation through a microsphere points out the light focusing capability of microspheres of different size and the waist of their photonic nanojet. The former correlates to the magnification factor of the virtual images obtained from linear test nanostructures, the biggest magnification being obtained with microspheres of ∼6-7 μm in size. Analyzing the light intensity distribution of microscopy images allows determining analytically the point spread function of the optical system and thereby quantifies its resolution. We find that the super-resolution imaging of a microsphere is dependent on the waist of its photonic nanojet, the best resolution being obtained with a 6 μm Ø microsphere, which generates the nanojet with the minimum waist. This comparison allows elucidating the super-resolution imaging mechanism.

No abstract

Models and Data Analysis for Monitoring Single Cell Exocytosis 4379 Microfabricated Devices in the Measurement of Exocytosis at Single Cells 4380 Electrode Arrays 4380 Field Effect Transistors Used to Monitor Exocytosis at Cells 4380 Impedance Measurements 4380 Scanning Electrochemical Microscopy (SECM) Measurements at Single Cells 4380 Morphology 4380 Metabolism 4381 Release 4381 Uptake 4381 Ion Selective Electrodes 4381

We have compared the properties and resistance to DA fouling of a carbon nanotube fiber (CNTF) microelectrode to a traditional carbon fiber (CF) microelectrode. These two materials show comparable electrochemical activities for outer-sphere and inner-sphere redox reactions. Although the CNTF might have a higher intrinsic RC constant, thus limiting its high-frequency behavior, the CNTF show a significantly higher durability than the CF in terms of electrode stability. During constant oxidation of 100 μM DA, the signal measured by the CNTF microelectrode shows a 2-hour window over which no decrease in current is observed. Under the same conditions, the current obtained at the CF microelectrode decreases by almost 50 %. A model of the fouling process, assuming the formation of growing patches of insulator on the surface, has been compared to the data. This model is found to be in good agreement with our results, and indicates a growth rate of the patches in the 0.1 - 2 nm s−1 range.

The basis for communication between nerve cells lies in the process of exocytosis, the fusion of neurotransmitter filled vesicles with the cell membrane resulting in release of the signaling molecules. Even though much is known about this process, the extent that the vesicles are emptied upon fusion is a topic that is being debated. We have analyzed amperometric peaks corresponding to release at PC12 cells and find stable plateau currents during the decay of peaks, indicating closing of the vesicle after incomplete release of its content. Using lipid incubations to alter the amount of transmitter released we were able to estimate the initial vesicular content, and from that, the fraction of release. We propose a process for most exocytosis events where the vesicle partially opens to release transmitter and then closes directly again, leaving the possibility for regulation of transmission within events.