In the case of the chickens it was related to avian flu. These are very worthwhile things to study. The fluorescent proteins were not added to have any influence on the research itself, but rather to make the work more efficient. The challenge is biology. The old-fashioned, time-consuming way to find out would be to draw blood from each one and analyze the DNA to read the gene sequence.
This is where the fluorescence comes in. This ability to add fluorescence to living things has been phenomenally valuable for modern biological research. What started with a curious observation in a small jellyfish has proved to be so important that several of the pioneers of the discovery and its application won the Nobel Prize in Chemistry in These are the guys that started it all — naturally occurring green fluorescent protein in the jellyfish Aequorea aequorea c Charles Mazel.
Fluorescence is a wonderful thing. Both fluorescence and phosphorescence are spontaneous emissions of electromagnetic radiation. The difference is that the glow of fluorescence stops right after the source of excitatory radiation is switched off, whereas for phosphorescence, an afterglow with durations of fractions of a second up to hours can occur [6,7].
To compare the photo-physical processes behind both phenomena, there are some facts about electrons that are helpful for understanding: Electrons are particles that have a so-called spin and a spin quantum number.
This number is a property that we actually cannot imagine or describe easily. It is often compared with a spinning top, either spinning in a clockwise or anti-clockwise direction. However, this description is neither mathematically nor physically quite correct.
In the Jablonski diagram for fluorescence see Fig. Within those states, there are several energy levels. The higher the level is, the more energy an electron possesses when being in that level. In the case of singlet states, the electrons have antiparallel spins. The electrons are lifted from the ground state S 0 , for example, to an energy level of the second excited state S 2 , when excited by electromagnetic radiation. After excitation stops, the electrons only stay in that excited state for a short period of time ca.
In doing so, energy initially can be released to the surroundings by vibrational relaxation. That means thermal energy is released by the motion of the atom or molecule until the lowest level of the second excited state is reached. The bigger gap between the second and first excited state is overcome by internal conversion.
That describes an electronic transition between two states while the spin of electrons is maintained. Now, the electrons can relax further due to more vibrational relaxation until they reach the lowest energy level of the S 1 state. Theoretically, the electrons could relax even further in a non-radiative way until they eventually reach the ground state again. However, it can be the case that the last amount of energy is too large to be released to the surroundings because the surrounding molecules cannot absorb this much energy.
Then, fluorescence occurs, which leads to an emission of photons possessing a certain wavelength. The emission lasts only until the electrons are back in the ground state.
Since during all those transitions the electron spin is kept the same, they are described as spin-allowed [6,7,10]. For phosphorescence, things are a bit different see Fig. There are again an S 0 ground state and the two excited states, S 1 and S 2.
Additionally, there is an excited triplet T 1 state which lies energetically between the S 0 and S 1 state. The electrons again have antiparallel spins in the ground state. Excitation happens in the same way as in fluorescence, namely through electromagnetic radiation.
The release of energy through vibrational relaxation and internal conversion while maintaining the same spin is the same here, as well, but only until the S 1 state is reached. Alongside the singlet states, a triplet state exists and so-called intersystem crossing ISC can occur since the T 1 state is energetically more favorable than the S 1 state.
This crossing, like internal conversion, is an electronic transition between two excited states. But contrary to internal conversion, ISC is associated with a spin reversal from singlet to triplet. This ISC process is described as "spin-forbidden". It is not completely impossible — due to a phenomenon called "spin-orbit coupling" — however, it is rather unlikely [7]. In the T 1 state, non-radiative decay is possible as well. However, a transition between the lowest energy level of the triplet state and the S 0 state is not readily possible, because that transition is spin-forbidden, too.
Still, it can happen anyway with a small possibility. It causes a rather weak emission of photons because the electron spin has to be reversed again. DayGlo Color Corp. These pigments have the ability to absorb energy from the light source and store it for a short period of time. After removing the light source, the object starts to glow. The object is now giving up the stored energy in the form of light. The charged pigments can glow for anywhere from seconds to hours depending on the strength.
This pigment will appear as a bright greenish shade until the stored energy is used. Fluorescent colors appear intense in daylight but will not be visible in the dark unless exposed to a black light.
Phosphorescent pigments will glow in the dark but only after being exposed to a light source, including sunlight or by placing under a light bulb. The easiest way to remember their differences? With no light source, fluorescent color has no color.
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