Analysis of a sample to determine its characteristic cycle time
View Patent ↗An analysis for determining a characteristic cycle time of a sample. Active elements in the sample are excited with sufficient intensity and duration larger than the characteristic cycle time that at least some of the active elements are re-excited to an excited state substantially immediately following relaxation to a ground state, detecting quanta emitted by the active elements in the sample to obtain a detected signal, and analyzing the detected signal to derive the characteristic cycle time. The number of active elements in the sample and the intensity of the excitation are such that quanta are detected in a stream in which individual quanta are distinguishable from each other.
1. A method of analysis for determining a characteristic cycle time of a sample, the method comprising:
exciting active elements in the sample with sufficient intensity and duration that at least some of the active elements are re-excited to an excited state substantially immediately following relaxation to a ground state,
detecting quanta emitted by the active elements in the sample to obtain a detected signal, and
analyzing the detected signal to derive the characteristic cycle time,
wherein the number of active elements in the sample and the intensity of the excitation are such that quanta are detected in a stream in which individual quanta are distinguishable from each other.
2. A method according to claim 1 , wherein the analysis of the detected signal includes auto correlation of the detected signal.
3. A method according to claim 1 , wherein the characteristic cycle time of the sample is modified by chemical or physical modification of the active elements' environment, and the modified characteristic cycle time is determined.
4. A method according to claim 1 , wherein:
at least some of the active elements have an excited level, an upper level of an emission transition and a lower level of the emission transmission, and emit a detectable quanta upon relaxation from the upper level of the emission transition to the lower level of the emission transition,
the lifetime of the lower level of the emission transition or another energy level having a lesser energy than the lower level of the emission transition is influenced by modification of the active elements' environment, and
the effect of such modification is determined.
5. A method according to claim 4 , wherein:
at least some of the active elements are bound to a substrate by a member that permits vibrational motion of the active element wherein the lifetime of the lower level of the emission transition or another energy leel having a lesser energy than the lower level of the emission transition, is altered by modifying the electronic environment of the active element.
6. A method according to claim 5 , wherein:
the modification of the electronic environment is effected by the presence of at least one modifying moiety which influences the electronic environment of the active element.
7. A method according to claim 6 , wherein:
a change in cycle time is caused by transfer to energy to the modifying moiety from the lower level of the emission transition or another energy level having a lesser energy than the lower level of the emission.
8. A method according to claim 3 , wherein:
the cycle time is modified by changes in conformation of the active element relative to a modifying moiety.
9. A method according to claim 3 , wherein:
each active element comprises part of a probe, whereby the probe is moved between different dielectric environments, including those occurring in a molecule or its solvent,
the characteristic cycle time of the probe is affected by time scales of the motion of the active element between different dielectric environments, and
the motion is affected by modifications including at least one of the following:
(e) altering the size of the probe;
(f) altering the distance between the active element and the remainder of the probe;
(g) altering the rigidity of a spacer molecule between the active element and the remainder of the probe; or
(h) modifying the probe or part thereof with hydrophilic, polar, charged or hydrophobic moieties.
10. A method according to claim 3 , wherein:
the active element comprises part of a species which periodically interacts with a modifying moiety, and the periods during which the species interacts with the modifying moiety and the periods during which the species does not interact with the modifying moiety are measures.
11. A method according to claim 3 , wherein:
the active element comprises part of a species which periodically interacts with a quenching moiety and is thereby quenched by a static quenching mechanism, and
the periods during which the species is active and the periods during which the species is inactive are measured.
12. A method according to claim 3 , wherein:
the active element comprises part of a species which periodically interacts with a quenching moiety and is thereby quenched by a collisional quenching mechanism, and
the periods during which the species is active and the periods during which the species is inactive are measured.
13. A method according to claim 11 , wherein
the period of the periodical interaction is influenced by modification of a property of the species or the modifying moiety or quenching moiety.
14. A method according to claim 13 , wherein
the modification comprises changing the length of a spacer molecule upon which the active element is located, or the length of the spacer molecule upon which the modifying moiety or quenching moiety is located.
15. A method according to claim 13 , wherein
the modification comprises changing the flexibility of a spacer molecule upon which the active element is located, or the flexibility of the spacer molecule upon which the modifying moiety or quenching moiety is located.
16. A method according to claim 13 , wherein
the modification comprises adding a modifying moiety to a spacer molecule upon which the active element is located, or to a spacer molecule upon which the modifying moiety or quenching moiety is located.
17. A method according to claim 13 , wherein:
the active element is attached via a spacer molecule to a binding site, and the modification results from an interaction with the binding site.
18. A method according to claim 13 , wherein:
the modification results from a restriction of periodic movement of the spacer molecule upon which the active element is located, or the spacer molecule upon which the modifying moiety or quenching moiety is located.
19. A method according to claim 13 , wherein
the active element is attached via a spacer molecule to a binding site, and the modification results from an interaction with a modifying moiety attached to the binding site.
20. A method according to claim 13 , wherein
the active element is attached via a first spacer molecule to a first binding site, and a modifying moiety or quenching moiety is attached via a second spacer molecule to a second binding site, and
the separation of the first and second binding sites determines the periodicity of the interaction between the active element and the modifying moiety or quenching moiety.
21. A method according to claim 3 , wherein
first and second elements which periodically interact to form the active element, and
the period during which the first and second elements interact to form the active element and the periods during which the first and second elements do not interact to form the active element are measured.
22. A method according to claim 21 , wherein
the active element is a fluorescence resonant energy transfer species.
23. A method according to claim 21 , wherein the active element is an excimer or an exciplex.
24. A method according to claim 1 , wherein
an excitation cross section of a ground state of an active element is varied periodically, and
the period of variation is measured.
25. A method according to claim 1 , wherein:
the active element emits fluorescence photons which interact with a solution in which the active elements are held, and
the effect of the solution is monitored by modulating properties of the solution.
26. A method according to claim 1 further comprising
exciting the active elements using an excitation pulse and determining the time elapsed between excitation and the emission of a quanta from the active element, and
subtracting that elapsed time from the characteristic cycle time.
27. A method according to claim 1 , wherein
excitation of active element in the sample is by a chemical reaction.
28. A method according to claim 1 , wherein the active elements have an upper excited state, a lower excited state and a ground state, and emit a detectable quanta upon relaxation from the upper excited state to the lower excited state, the method further comprising:
exciting second elements to an excited state such that the second elements transfer excitation energy to the active elements, thereby exciting the active elements to the upper excited state.
29. An analysis apparatus for determining the characteristic cycle time of active elements in a sample, said apparatus comprising:
means for exciting active elements in the sample with sufficient intensity and duration that at least some of the active elements are re-excited to an excited state substantially immediately following relaxation to a ground state,
means for detecting quanta emitted by the sample to obtain a detected signal,
analyzing means for analyzing the detected signal to derive the characteristic cycle time,
wherein the number of active elements in the sample and the intensity of the excitation are such that quanta are detected in a stream in which individual quanta are distinguishable from each other.