In this chapter, we describe the technological challenges in the development of modern SiPM in CMOS technology. The voltage amplitude of the signal from the SiPM is measured on a 50 ohm load resistor.
The light response of the SiPM
The common output of the SiPM is the analog sum of the signals from each avalanche pixel. The area under each peak reflects the Poisson statistics of the photon detection in the SiPM structure.
Application of SiPM to digital positron emission tomography
As an example of an easy combination of the P&I elements, Positron Emission Tomography can be used for the correct determination of the proton range in proton therapy. PET systems will be dedicated to reconstructing the position of such a nuclear interaction.
Conclusions
In Low-Noise Single-Photon Avalanche Diodes in 0.15 µm CMOS Technology, Solid State Devices Research Conference (ESSDERC). Low number dark single photon avalanche diode structure compatible with standard cmos nanoscale technology.
Parallelized Integrated Time-Correlated Photon Counting System for High Photon Counting Rate
- Introduction
- A parallelized macropixel structure for SNR optimization
- Efficiency improvement of TCSPC systems
- Conclusion
To simplify the study of the TCSPC system, the readout period is considered to be equal to the dead time of the system. It is clear that the efficiency of the system increases with FIFO depth, although the rate of growth decreases.
Application of Fluorescence Spectroscopy for Microbial Detection to Enhance Clinical Investigations
- Fluorescence phenomena
- Fluorescence spectroscopy
- Photomultiplier tube
- Fluorimeter equipment
- Fluorescence analysis software
- Bacterial biofilms
- Porphyrins and biofilm fluorescence
- Conclusions
In fluorescence, the absorption of light of a particular wavelength results in the emission of light of a longer wavelength. Likewise, porphyrins emit light in the near-infrared region when excited by wavelengths of visible light. There is a reference photodiode which is used to correct for variations in the intensity of the emissions from the xenon lamp at different wavelengths.
For in-tube biofilm detection, issues such as fluorescence from the fluid carried in the tube and from the tube itself must be addressed. A challenge in using fluorescence in very small confined environments where there are low levels of microorganisms is the detection limit of the system used to detect fluorescence emissions. Using such an approach, it should be possible to achieve detection of a single organism, provided it is within range of the optical detection system.
These are involved in the synthesis of metalloporphyrin heme [ferro protoporphyrin (Fe2+)], hemin [ferriprotoporphyrin (Fe3+)] and chlorophyll [54].
Acknowledgements
In general, visible light is useful for inducing fluorescence from porphyrins to detect bacteria and their products present in infected tissues by emissions in the visible red region.
Author details
Biofilm removal from silicone tubing: An assessment of the effectiveness of dialysis machine decontamination procedures using an in vitro model. An assessment of changes in dentin permeability after irradiation with a pulsed erbium:YAG laser. DIAGNOdent pen versus tactile sense for detection of subgingival calculus: An in vitro study.
Violet and blue light-induced green fluorescence emissions from dental calculus: A new approach to dental diagnosis. Validity and reliability of laser-induced fluorescence measurements on carious root surfaces in vitro. Clinical evaluation of an Er:YAG laser combined with scaling and root planing for nonsurgical periodontal treatment.
Fluorescence-controlled Er:YAG laser for caries removal in permanent teeth: A randomized clinical trial.
High-Speed and High-Resolution Photon Counting for Near-Range Lidar
- Lidar principle and photon counting
- Near-range Lidar
- High-speed and high-resolution photon counting
- Lidar applications
- Summary
The close-range lidars for hard target and atmosphere detection must track the rapid movement/activity of the target material. To track and visualize the rapid movement of the target, fast and high-resolution photon counters (multichannel scalers) were developed. At the end, the next step of high-speed photon counting is finally discussed.
Here the lidar echo power increases until the entire beam enters the field of view. It is a photon counting mode (digital mode). Figure 2 shows such a behavioral difference on analog mode and photon counting mode for the lidar echo. The balance between the BIN width, its number and repetition rate is important for the photon counter device.
In order to increase the signal-to-noise ratio while limiting the transmit power, the pulse repetition frequency is increased.
Detectors for Super-Resolution & Single-Molecule Fluorescence Microscopies
Principles of fluorescence microscopy
In confocal microscopy, out-of-focus light is rejected by an adjustable pinhole placed in front of the detector, allowing optical sectioning of the sample and improved image quality, especially for thick samples. The resolution of fluorescence microscopes, or in general all light microscopes, is limited by the diffraction properties and wavelength of light. The full width at half maximum (FWHM) of the PSF is a convenient measurement to characterize resolution.
However, in biological samples many subcellular structures are closer together or smaller than the FWHM of the PSF resulting in a less than true representation of the sample being imaged. Ernst Abbe first described the diffraction properties of light in 1873 and established that resolution depends on both the wavelength of light used and the numerical aperture (NA), or light-gathering power, of the objective used in the microscope [2]. Lord Rayleigh further defined resolution as the distance where the center of the diffraction pattern of image one overlaps with the first minima of the diffraction pattern of image two, and his equation (Rayleigh resolution criterion) is widely used today and is R = 0.61λ / NA [2, 3].
For light microscopes, the resolution is approximately half the wavelength of the light used, corresponding to 150-200 nm.
Review of super-resolution microscopy
This process allows the moiré fringes to be "recorded" and high-resolution images can be acquired using computer algorithms. PSF techniques attempt to limit image overlap of objects through changes in the geometry of the exciting light. This process is repeated thousands of times to localize nearly all fluorescent molecules, leading to a point-by-point construction of the super-resolution image.
Multi-color SRM (i.e. two or more fluorescent molecules) has been realized for many of the aforementioned techniques [24-26]. The introduction of an astigmatic lens leads to improved axial resolution for STORM because it allows precise 3D localization of molecules, and this technique has been called 3D STORM [28]. Importantly, the performance of pointillism techniques (2D or 3D versions) is highly dependent on the density of fluorophore labeling and the nature of the biological structure.
The type of SRM employed depends on proper matching of the experimental requirements with the technical capabilities of the SR technique.
Review of fluorescence fluctuation techniques (FFTs)
As mentioned earlier, the average number of molecules can be determined from the amplitude of the FCS curve (Go ≈ 1/N), and changes in the amplitude of the curve have been used to infer protein-ligand binding and protein-protein dimerization [43]. For example, as the protein dimerizes, the concentration of individual monomers decreases, leading to a doubling of the amplitude. The amplitude and shape of the histogram plot is affected by the PSF of the microscope, detector noise and fluctuation in molecular number.
Careful fitting of the histogram returns the first and second moments for the entire photon distribution. This enables measurements of complex samples and the determination of the number of molecules per second (cpsm) or molecular brightness. Like RICS, an adequate scan rate (pixel dwell time) is required to "capture" the oscillation of the molecules.
New genetic approaches such as CRISPR make it possible to replace endogenous proteins with fluorescently labeled versions in the genome of the cell or organism [53].
Detector technologies used in SRM & FFTs
- Brief history of photodetectors
- Photomultiplier tubes (PMTs)
- Avalanche photodiodes (APDs)
- Hybrid photodetectors
- Charged coupled devices (CCDs)
- Complementary metal oxide semiconductors (CMOS)
- Next generation photodetectors
The composition of the photocathode determines the PMT's spectral response, quantum efficiency (QE), and dark current levels. Avalanche photodiodes have better QE and better sensitivity in the green and red regions of the visible spectrum compared to PMTs [64]. The charge in the unmasked rows is transferred to the masked row, allowing a second round of exposure while reading the previous first exposure.
Finally, an intensifier screen can be placed in front of the CCD sensor (ICCD) to increase the sensitivity for single photon detection [76]. EMCCD cameras have built-in excess noise due to the amplification process, which contributes to about 50% of the total noise. One of the solutions to this problem is to parallelize the point detector (i.e. an array of point detectors).
In contrast, wide-field detectors that have pico-second responses, such as Time-limited ICCDs are photon inefficient due to the coupling of the intensifying screen lens to the CCD sensor.
Examples of photodetector used in SRM & FFTs
The wild-type receptor formed higher order oligomers in the Golgi membrane and dimers at the plasma membrane (Figure 3). In contrast, the mutant proteins that failed to move to the apical membrane did not form higher order oligomers at the Golgi (Figure 3). Hybrid detectors have been used to measure lipid raft formation in a cell model of Fabry disease [110].
In Fabry disease, lysosomal function is disrupted due to decreased activity of a specific enzyme (alpha-galactosidase A), which leads to the accumulation of neutral glycosphingolipids such as globotriaosylceramide (Gb3). N&B analysis was performed on wild-type and alpha-galactosidase-deficient cells, which serve as a model of Fabry disease. Antibody-induced clustering of a model lipid raft protein was increased in the mutant compared to control cells [110].
These results suggested that accumulated Gb3 may alter lipid raft-protein interactions in membranes of alpha-galactosidase-deficient cells.
Summary and concluding remarks
These two examples are just a few of the many experiments that have used a variety of low-light photodetectors. Point by Point: An Introductory Guide to Sample Preparation for Single-Molecule, Super-Resolution Fluorescence Microscopy: Sample Preparation for Single-Molecule, Super-Resolution Fluorescence Microscopy. Application Note, ANDOR Technology http://www.andor.com/learning-academy/emccd-vs-scmos- cameras-for-spinning-disk-confocal-microscopy-application-note (accessed 15 August 2017).
Localization-based super-resolution microscopy with an sCMOS camera part II: Experimental method for comparing sCMOS with EMCCD cameras. Experimental comparison of the high-speed imaging performance of an EM-CCD and sCMOS camera in a dynamic live-cell imaging test case.
