Solution-based single-molecule fluorescence spectroscopy is a powerful new experimental approach with applications in
all fields of natural sciences. The basic concept of this technique is to excite and collect light from a very small volume
(typically femtoliter) and work in a concentration regime resulting in rare burst-like events corresponding to the transit
of a single-molecule. Those events are accumulated over time to achieve proper statistical accuracy. Therefore the
advantage of extreme sensitivity is somewhat counterbalanced by a very long acquisition time. One way to speed up data
acquisition is parallelization. Here we will discuss a general approach to address this issue, using a multispot excitation
and detection geometry that can accommodate different types of novel highly-parallel detector arrays. We will illustrate
the potential of this approach with fluorescence correlation spectroscopy (FCS) and single-molecule fluorescence
measurements obtained with different novel multipixel single-photon counting detectors.
A Complementary Metal Oxide Semiconductor (CMOS) camera (1024×1024 pixels) is used to record spontaneous
oscillations of hair cell stereocillia in an in-vitro preparation of the bullfrog sacculus with the otolithic membrane
removed. The CMOS camera is attached to an Olympus BX51WI Microscope inside of a sound-isolation chamber, with
white light transmission illumination using an X-Cite 120 metal halogenide lamp. The combination of the parallel
readout of the CMOS chip and the high intensity of illumination allows full frame images of the oscillations to be taken
at 1000 frames per second. A weighted, time averaged differential algorithm is used to aid in the visualization of the hair
cell movement. To detect the displacement from its center of the stereocillia tip with nanometer position resolution and
millisecond time resolution, an average background intensity value was subtracted from each image to remove lamp
intensity fluctuations and then a center of intensity algorithm was applied. This combination of our imaging system and
data analysis allows for the oscillations of more than one hair cell to be recorded during the same time period, and their
frequency components extracted.
We report benchmark tests of a new single-photon counting detector based on a GaAsP photocathode and an electron-bombarded
avalanche photodiode developed by Hamamatsu Photonics. We compare its performance with those of
standard Geiger-mode avalanche photodiodes. We show its advantages for FCS due to the absence of after-pulsing and
for fluorescence lifetime measurements due to its excellent time resolution. Its large sensitive area also greatly simplifies
setup alignment. Its spectral sensitivity being similar to that of recently introduced CMOS SPADs, this new detector
could become a valuable tool for single-molecule fluorescence measurements, as well as for many other applications.
We have begun developing an innovative ultra-fast single-photon counting imager which comprises a mega-pixel CMOS array and a newly-designed Image Intensifier. It is expected to have single photon sensitivity with 100 psec time resolution, operational at a total counting rate exceeding 1MHz. The readout is based on dead-time-free flash ADC, running at 1-2GS/s, followed by a FPGA for real-time parallel data processing. Such a device has not been realized
before and is expected to revolutionize time-resolved fluorescence imaging and spectroscopy from a single-molecule to whole animal level. To evaluate the design principle, an Image Intensifier with a GaAsP photocathode (>40% quantum efficiency at 400-600 nm) followed by double MCP was evaluated together with an existing CMOS camera. In our future design, the image from CMOS Camera will be combined with the MCP output, followed by a set of FPGA and CPU for real time data processing. This stream line method will allow ultra fast single-photon counting with 100 psec time resolution and 20 μm position resolution (1M pixel imaging). In this paper, we present the design principle and preliminary results on its performance. Our future plan and the design goals are also described.
The FiberGLAST scintillating fiber telescope is a large-area instrument concept for NASA's GLAST program. The detector is designed for high-energy gamma-ray astronomy, and uses plastic scintillating fibers to combine a photon pair tracking telescope and a calorimeter into a single instrument. A small prototype detector has been tested with high energy photons at the Thomas Jefferson National Accelerator Facility. We report on the result of this beam test, including scintillating fiber performance, photon track reconstruction, angular resolution, and detector efficiency.
A scintillating fiber detector is currently being studied for the NASA Gamma-Ray Large Area Space Telescope (GLAST) mission. This detector utilizes modules composed of a thin converter sheet followed by an x, y plane of scintillating fibers to examine the shower of particles created by high energy gamma-rays interacting in the converter material. The detector is composed of a tracker with 90 such modular planes and a calorimeter with 36 planes. The two major component of this detector are the scintillating fibers and their associated photodetectors. Here we present current status of development and test result of both of these. The Hamamatsu R5900-00-M64 multianode photomultiplier tube (MAPMT) is the baseline readout device. A characterization of this device has been performed including noise, cross- talk, gain variation, vibration, and thermal/vacuum test. A prototype fiber/MAPMT system has been tested at the Center for Advanced Microstructures and Devices at Louisiana State University with a photon beam and preliminary results are presented.