Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, than the absorbed radiation. A perceptible example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the electromagnetic spectrum, while the emitted light is in the visible region; this gives the fluorescent substance a distinct color that can only be seen when the substance has been exposed to UV light. Fluorescent materials cease to glow nearly immediately when the radiation source stops, unlike phosphorescent materials, which continue to emit light for some time after.
Infrared is electromagnetic radiation (EMR) with wavelengths longer than those of visible light and shorter than radio waves. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around 1 millimeter (300 GHz) to the nominal red edge of the visible spectrum, around 700 nanometers (430 THz). IR is commonly divided between longer wavelength thermal infrared that is emitted from terrestrial sources and shorter wavelength near-infrared that is part of the solar spectrum. Longer IR wavelengths are sometimes included as part of the terahertz radiation range. Almost all black-body radiation from objects near room temperature is at infrared wavelengths. As a form of electromagnetic radiation, IR propagates energy and momentum, exerts radiation pressure, and has properties corresponding to both those of a wave and of a particle, the photon.
An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback from the cavity is suppressed. Optical amplifiers are important in optical communication and laser physics. They are used as optical repeaters in the long distance fiberoptic cables which carry much of the world's telecommunication links.
Wien's displacement law states that the black-body radiation curve for different temperatures will peak at different wavelengths that are inversely proportional to the temperature. The shift of that peak is a direct consequence of the Planck radiation law, which describes the spectral brightness or intensity of black-body radiation as a function of wavelength at any given temperature. However, it had been discovered by Wilhelm Wien several years before Max Planck developed that more general equation, and describes the entire shift of the spectrum of black-body radiation toward shorter wavelengths as temperature increases.
A helium–neon laser or He-Ne laser, is a type of gas laser whose high energetic medium gain medium consists of a mixture of ratio(between 5:1 and 20:1) of helium and neon at a total pressure of about 1 torr inside of a small electrical discharge. The best-known and most widely used He-Ne laser operates at a wavelength of 632.8 nm, in the red part of the visible spectrum.
The term biophotonics denotes a combination of biology and photonics, with photonics being the science and technology of generation, manipulation, and detection of photons, quantum units of light. Photonics is related to electronics and photons. Photons play a central role in information technologies, such as fiber optics, the way electrons do in electronics.
The Balmer series, or Balmer lines in atomic physics, is one of a set of six named series describing the spectral line emissions of the hydrogen atom. The Balmer series is calculated using the Balmer formula, an empirical equation discovered by Johann Balmer in 1885.
Fluorescence spectroscopy is a type of electromagnetic spectroscopy that analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit light; typically, but not necessarily, visible light. A complementary technique is absorption spectroscopy. In the special case of single molecule fluorescence spectroscopy, intensity fluctuations from the emitted light are measured from either single fluorophores, or pairs of fluorophores.
A fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds.
Stokes shift is the difference between positions of the band maxima of the absorption and emission spectra of the same electronic transition. It is named after Irish physicist George Gabriel Stokes. Sometimes Stokes shifts are given in wavelength units, but this is less meaningful than energy, wavenumber or frequency units because it depends on the absorption wavelength. For instance, a 50 nm Stokes shift from absorption at 300 nm is larger in terms of energy than a 50 nm Stokes shift from absorption at 600 nm.
Cyanines, also referred to as tetramethylindo(di)-carbocyanines are a synthetic dye family belonging to the polymethine group. Although the name derives etymologically from terms for shades of blue, the cyanine family covers the electromagnetic spectrum from near IR to UV.
Phthalaldehyde (sometimes also o-phthalaldehyde or ortho-phthalaldehyde, OPA) is the chemical compound with the formula C6H4(CHO)2. It is one of three isomers of benzene dicarbaldehyde, related to phthalic acid. This pale yellow solid is a building block in the synthesis of heterocyclic compounds and a reagent in the analysis of amino acids. OPA dissolves in water solution at pH < 11.5. Its solutions degrade upon UV illumination and exposure to air.
Dansyl chloride or 5-(DimethylAmino)Naphthalene-1-SulfonYL chloride is a reagent that reacts with primary amino groups in both aliphatic and aromatic amines to produce stable blue- or blue-green–fluorescent sulfonamide adducts. It can also be made to react with secondary amines. Dansyl chloride is widely used to modify amino acids; specifically, protein sequencing and amino acid analysis. Dansyl chloride may also be denoted DNSC. Likewise, a similar derivative, dansyl amide is known as DNSA.
EosFP is a photoactivatable green to red fluorescent protein. Its green fluorescence (516 nm) switches to red (581 nm) upon UV irradiation of ~390 nm due to a photo-induced modification resulting from a break in the peptide backbone near the chromophore. Eos was first discovered as a tetrameric protein in the stony coral Lobophyllia hemprichii. Like other fluorescent proteins, Eos allows for applications such as the tracking of fusion proteins, multicolour labelling and tracking of cell movement. Several variants of Eos have been engineered for use in specific study systems including mEos2, mEos4 and CaMPARI.
Fluorescence is used in the life sciences generally as a non-destructive way of tracking or analysing biological molecules. Some proteins or small molecules in cells are naturally fluorescent, which is called intrinsic fluorescence or autofluorescence. Alternatively, specific or general proteins, nucleic acids, lipids or small molecules can be "labelled" with an extrinsic fluorophore, a fluorescent dye which can be a small molecule, protein or quantum dot. Several techniques exist to exploit additional properties of fluorophores, such as fluorescence resonance energy transfer, where the energy is passed non-radiatively to a particular neighbouring dye, allowing proximity or protein activation to be detected; another is the change in properties, such as intensity, of certain dyes depending on their environment allowing their use in structural studies.
eFluor nanocrystals are a class of fluorophores made of semiconductor quantum dots. The nanocrystals can be provided as either primary amine, carboxylate, or non-functional groups on the surface, allowing conjugation to biomolecules of a researcher's choice. The nanocrystals can be conjugated to primary antibodies which are used for flow cytometry, immunohistochemistry, microarrays, in vivo imaging and microscopy.
Photo-activated localization microscopy and stochastic optical reconstruction microscopy (STORM) are widefield fluorescence microscopy imaging methods that allow obtaining images with a resolution beyond the diffraction limit. The methods were proposed in 2006 in the wake of a general emergence of optical super-resolution microscopy methods, and were featured as Methods of the Year for 2008 by the Nature Methods journal. The development of PALM as a targeted biophysical imaging method was largely prompted by the discovery of new species and the engineering of mutants of fluorescent proteins displaying a controllable photochromism, such as photo-activatible GFP. However, the concomitant development of STORM, sharing the same fundamental principle, originally made use of paired cyanine dyes. One molecule of the pair, when excited near its absorption maximum, serves to reactivate the other molecule to the fluorescent state.
Fluorescence guided surgery (FGS), also called fluorescence image-guided surgery, or in the specific case of tumor resection, fluorescence guided resection, is a medical imaging technique used to detect fluorescently labelled structures during surgery. Similarly to standard image-guided surgery, FGS has the purpose of guiding the surgical procedure and providing the surgeon of real time visualization of the operating field. When compared to other medical imaging modalities, FGS is cheaper and superior in terms of resolution and number of molecules detectable. As a drawback, penetration depth is usually very poor in the visible wavelengths, but it can reach up to 1–2 cm when excitation wavelengths in the near infrared are used.
3-Hydroxyisonicotinaldehyde (HINA), also known as 3-hydroxypyridine-4-carboxaldehyde, is a derivative of pyridine, with hydroxyl and aldehyde substituents. It has been studied as a simple analogue of vitamin B6. In 2020, it was reported as having the lowest molecular weight of all dyes which exhibit green fluorescence.
3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQCA) is a fluorogenic amine labeling dye that is not fluorescent itself, but covalently reacts with primary amines to form fluorescent products. It was first reported in 1991. Today, it is largely used in the context of quantifying peptides or proteins. Either cyanide or thiols are required as a co-substrate in the fluorogenic reaction, although thiols also react with & mask the CBQCA aldehyde thereby preventing the fluorogenic reaction against the targeted primary amines. Once bound to protein the excitation wavelength is 465 nm (blue) and the emission wavelength is ~550 nm (green).
