signature=0d4872ddad95e30c669f29d8002c2e80,Small-molecule fluorophores and fluorescent probes for bi...

INVITED REVIEW

Small-molecule fluorophores and fluorescent probes for bioimaging

Takuya Terai &Tetsuo Nagano

Received:7August 2012/Revised:31January 2013/Accepted:31January 2013/Published online:15February 2013#Springer-Verlag Berlin Heidelberg 2013

Abstract Fluorescent compounds based on synthetic small molecules are powerful tools to visualize biological events in living cells and organisms.Ever since the discovery of organic fluorescent compounds in the late nineteenth centu-ry,efforts have been made to “see ”the behaviors of specific biomolecules in living systems by using these dyes as labels.Also,following the development of fluorescent Ca 2+indicators in the 1980s,many fluorescent probes or biosensors,which are defined as molecules that show a change in fluorescence properties in the presence of their target molecule,have been reported and applied in biological research.Today,a variety of probes are available that target metal ions,pH,enzyme activities,and signaling molecules.In this review,we first consider the history of organic fluo-rescent molecules and discuss their utility for labeling bio-molecules and staining cells.Then,we review recent progress in small-molecule fluorescent probes for metal ions and re-active oxygen species,focusing on representative work in each category.Finally,we briefly discuss attempts to create novel kinds of probes,including hybrids of small molecules and genetically encoded proteins,with the potential to over-come some of the limitations of current probes.Keywords Fluorescence .Imaging .Ca 2+signaling .Reactive oxygen species .Protein labeling

Introduction

It is said that humans rely on vision for approximately 80%of all the information they receive from the external world.

Hence,as the proverb “seeing is believing ”suggests,an appeal to the eye should be most effective and informative even in the world of science.Unfortunately,however,our body and cells generally do not supply enough visual infor-mation detectable with the naked eye to allow us to under-stand specific biological events,such as cell signaling and protein expression.Therefore,tools that allow us to “see into the body ”or “see into cells ”are essential not only for basic biology research,but also for the diagnosis and treat-ment of diseases.Suitable methods must meet several con-ditions.First,the technique should be sensitive enough to visualize biological compounds at physiological concentra-tions,which in most cases range from nanomolars to micro-molars.Second,the method should have sufficient spatial and temporal resolution to analyze dynamic cell signaling processes.Third,the method should not be invasive,i.e.,detection should be possible from outside of the http://www.doczj.com/doc/53540382581b6bd97e19ea4f.htmlst,but not the least,it should rely on instruments that are not too special or expensive.At least for cells and dissected tissues,fluorescence imaging is an ideal methodology that satisfies all these requirements,compared with other tech-nologies based on radioactivity,bioluminescence,electro-magnetism,and electrochemistry.This is the reason why fluorescence live imaging is coming into widespread use in cell biology.Another advantage of the technology that we should emphasize here is that the fluorescence signal of a molecule can be drastically modulated by design,so probes that exhibit activation of the signal,not just accumulation of the compound,can be exploited,as we will describe later.Needless to say,to perform fluorescence imaging,fluo-rescent molecules must be present in the sample.Although some researchers have used internal or endogenous fluores-cent molecules in cells [11,12,38,122,133],including tryp-tophan,NAD(P)H,and flavins,in most cases,external fluorophores are added to the samples,either chemically or genetically.Before the middle of the 1990s,when fusion of green fluorescent protein [131]was introduced as a labeling

T.Terai :T.Nagano (*)

Graduate School of Pharmaceutical Sciences,The University of Tokyo,Tokyo,Japan e-mail:tlong@mol.f.u-tokyo.ac.jp

URL:http://www.f.u-tokyo.ac.jp/~tlong/en/

Pflugers Arch -Eur J Physiol (2013)465:347–359DOI 10.1007/s00424-013-1234-z