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ticularlyforthoseinwhichthedyesareusedaslabels.Theseconddistin-
guishingfeatureoffluorescenceisthehighspeedofresponse.Thisresponse
canbeasfastasnanosecondsandislimitedbyfluorescencelifetimeandthe
speedofphotophysicalorphotochemicaleventcreatingtheresponse.Im-
portantisveryhighspatialresolutionthatcanbeachievedwithfluorescence.It
allowsdetectingcellularimagesandoperatingwithdensemulti-analyte
sensorarrays.Thisresolutionincommonmicroscopyislimiteddiffraction
oflighttoabout500nm(invisiblelight)andeventhislimitcanbeovercome
inspecialconditionswhenoneemploytwophotonexcitationorstimulated
emissiondepletion(STED)microscopy.Thenon-destructiveandnon-invasive
characteroffluorescencesensingmaybebeneficialmainlyforbiologicaland
medicalapplications.Influorescencesensingthereporterdyeandthede-
tectinginstrumentarelocatedatacertaindistanceandconnectedvialight
signal.Thisiswhyfluorescencedetectionisequallywellsuitedtoremote
controlofchemicalreactionsinindustryandtosensingdifferenttargets
withinlivingcells.Inmicrofluidicdevicesthedetectionvolumecanbere-
ducedtonanoliters.Heterogeneousassaysdevelopintomulti-analytemi-
croarrays(sensorchips),whichallowsimultaneousdetectionofseveral
hundredsandthousandsofanalytes(Demchenko2009).Two-photonand
confocalmicroscopiessuggestonetoobtain3-dimensionalimages,whichal-
lowslocalizingtargetcompoundsinspacestructures.Fluorescencebelongs
tothegroupofphysicalphenomenaassociatedwithlightandlightinterac-
tionwithmatter,fluorescentrechniqueexploreslightsignalsfordistance
noncontactstudyofdifferentmaterialsandobjectsinallfieldsofhumanactiv-
ity,andingeneralaspectbelongstothefieldofPhotonics.Remarkablythatto
underlineimportanceandanexclusiveroleoflighttechnologiesandphenom-
enathis2015yearisInternationalYearofLightasannouncedbytheUnited
NationsEducational,ScientificandCulturalOrganization,UNESCO.
Nowletuscomedirectlytothesubjectofthismonography.Inherentpe-
culiaritiesofliquidmolecularsystemsincludingorganiconesarefluctua-
tionsofmicrodensity,micropolarityandothermicrocharacteristicsofmedi-
umowingtothermalmotionsofmoleculesandtheirsegments.Inpolymer
andbiologicalsamplestogetherwiththermalfluctuationstherealsoexist
gradientsofpolarity,density,viscosityandsoon,thenatureofwhichisdue
toconsiderablespatialheterogeneityofthementionedstructures.Allthese
characteristicsmaymodifyessentiallyspectralcharacteristicsoffluorescent
probesinsuchmediaand,hence,knowledgeofspectralcharacteristicsin
suchconditionsopensthedoorforsolvingthereverseproblem,namely,
studyingsuchstructurefeatureswiththeproperfluorescentprobesthatis
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