Abstract
Highly environment-sensitive fluorophores have been desired for many biomedical applications. Because of the noninvasive operation, high sensitivity, and high specificity to the microenvironment change, they can be used as excellent probes for fluorescence sensing/imaging, cell tracking/imaging, molecular imaging for cancer, and so on (i.e., polarity, viscosity, temperature, or pH measurement). In this work, investigations of the switching mechanism of a recently reported near-infrared environment-sensitive fluorophore, ADP(CA)2, were conducted. Besides, multiple potential biomedical applications of this switchable fluorescent probe have been demonstrated, including wash-free live-cell fluorescence imaging, in vivo tissue fluorescence imaging, temperature sensing, and ultrasound-switchable fluorescence (USF) imaging. The fluorescence of the ADP(CA)2 is extremely sensitive to the microenvironment, especially polarity and viscosity. Our investigations showed that the fluorescence of ADP(CA)2 can be switched on by low polarity, high viscosity, or the presence of protein and surfactants. In wash-free live-cell imaging, the fluorescence of ADP(CA)2 inside cells was found much brighter than the dye-containing medium and was retained for at least two days. In all of the fluorescence imaging applications conducted in this study, high target-to-noise (>5-fold) was achieved. In addition, a high temperature sensitivity (73-fold per Celsius degree) of ADP(CA)2-based temperature probes was found in temperature sensing.
Highlights
Fluorescence imaging and sensing in cells or tissues gain great interest due to the unique features, such as non-physical-contact operation, high sensitivity and specificity, unique fluorescence spectrum and lifetime, etc. [1,2,3,4,5,6,7]
When the temperature is below the LCST, the dye fluoresces weakly in the water-rich microenvironments because water provides a high polar and nonviscous microenvironment that increases the rate of the non-radiation relaxation of the excited fluorophores
Besides the temperature imaging, based on the same type of switchable fluorescent probes (SFPs), we recently developed a new imaging technique, ultrasound-switchable fluorescence (USF), for visualizing tissue microstructures in centimeter-deep tissues
Summary
Fluorescence imaging and sensing in cells or tissues gain great interest due to the unique features, such as non-physical-contact operation, high sensitivity and specificity, unique fluorescence spectrum and lifetime, etc. [1,2,3,4,5,6,7]. When the temperature is below the LCST, the dye fluoresces weakly in the water-rich microenvironments because water provides a high polar and nonviscous microenvironment that increases the rate of the non-radiation relaxation of the excited fluorophores. When the temperature is above the LCST, the dye fluoresces strongly in the polymer-rich microenvironment because the polymer provides a relatively low polar and viscous microenvironment, which can suppress the nonradiative decay rate of the excited fluorophores [20,21] This type of fluorescence switching is reversible and can be used for temperature imaging in cells or tissues. We investigated the switching mechanism of a recently reported NIR aza-BODPIY-based fluorescent dye (ADP(CA)2) [19] and its potential applications as a SFP in different formats (dye itself and dye-conjugated polymers), including wash-free cell imaging, in vivo tissue imaging, temperature sensing, and tissue USF imaging. Its peak excitation and emission wavelengths are located at 683 and 717 nm, rweshpicehctmivealkye,swithiscuhitmabalkeefsoritcseullitaanblde tfiosrsuceelsl taunddietsi.ssLuaestslytu, dthieiss.dLyaesthlya,s tthwisodcyaerbhoaxsytlwcooncjaurgbaotxioynl cgornoujupgsatainodn cgarnoubpes uasnedd cfaonr cboenujusgeadtifoonr wcointhjuogtahteiornuwniittshvoiathaemr uinneitgsrvoiuapasm(siuncehgarosutpems p(seurcahtuarse tseemnspiteirvaetuproelysmenesristiivnetphoislysmtuedrys).inInthsuismsmtuadryy),. thInissduymemisaarny, etxhciesldleynet cisanadnidexacteelfloerntwcaasnhd-fidreaetelivfoerwceallshim-fraegeinligv,e-icnelvl iivmoafgliunogr,eisncevnivceo flimuoagreinscge,ntceemimpeargaitnugre, tesemnpsienrga,tutrisessueensUinSgF, timissaugeinUgS, Fanimdaogtihnegr, apnodteontthiaelrSpFoPteanptpiallicSaFtiPonaps.plications
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