A Biocompatible and Near‐Infrared Liposome for In Vivo Ultrasound‐Switchable Fluorescence Imaging

Abstract

Fluorescence imaging is a remarkable tool for molecular targeting and multicolor imaging, but it suffers from low resolution in centimeter‐deep tissues. The recently developed ultrasound‐switchable fluorescence (USF) imaging has overcome this challenge and achieved in vivo imaging in a mouse with help from the indocyanine green (ICG) dye encapsulated poly(N‐isopropylacrylamide) (ICG‐PNIPAM) contrast agent. However, the ICG‐PNIPAM has shortcomings, such as concerns about cytotoxicity and blueshifted excitation and emission spectra. This study introduces a newly developed ICG‐encapsulated liposome to broaden the contrast agent selection for USF imaging and resolve the issues mentioned above. The emission peak of the ICG‐liposome is 836 nm with excellent biostability and USF imaging capability. Furthermore, the cell viability test verifies the low cytotoxicity feature. Eventually, both ex vivo and in vivo USF imaging are successfully achieved and 3D USF images are acquired. The ex vivo result confirms that the ICG‐liposome maintains the thermoresponsive characteristic at the right lobe of the liver and is able to conduct the USF imaging. The further in vivo USF imaging demonstrates that although the whole liver emitted fluorescence, only the right lobe of the liver contains the working ICG‐liposome.

Recent advances in ultrasound-controlled fluorescence technology for deep tissue optical imaging

“…This also indicates that the spatial resolution of UCF imaging primarily relies on the size of confined thermal space. Besides, the outgoing fluorescence signal can be readily regulated by changing the ultrasound parameters and can only be generated from the confined UCF probes [ 39 ].…”

“…An NIR-UCF probe with multifunctional applications has the following properties: low toxicity, a reasonable on-to-off ratio of fluorescence intensity (I ON /I OFF ), low critical solution temperature at around normal body temperature, narrow temperature transition bandwidth, high photo- and chemical-stability, and easy functionalization by targeted molecules or peptides for achieving specific targeting of lesion tissues. Until now, three types of NIR-UCF probes have been reported: temperature-sensitive polymer NPs [ 16 ], temperature-responsive micelles [ 17 , 21 ], and thermosensitive liposomes [ 39 , 41 ]. Only ICG-loaded thermosensitive liposome and ICG-encapsulated PNIPAM NPs have been triumphantly used for in vivo NIR-UCF imaging until now; other types of temperature-sensitive polymer NPs have not been reported yet.…”

Enhanced photodynamic therapy/photothermo therapy for nasopharyngeal carcinoma via a tumour microenvironment-responsive self-oxygenated drug delivery system

“…To address these limitations, researchers have developed various methods to deliver ICG, including polymeric nanoparticles, liposomes, lipid-polymer nanoparticles, inorganic particles, carbon nanomaterials, bioconjugates and other formulations [31] , [32] , [33] , [34] , [35] , [36] . Amongst these, liposomes are a commonly used strategy for ICG delivery [ 37 , 38 ]. Thus, in this study, the intention was to add ICG to liposomes.…”

Bio-engineered nano-vesicles for IR820 delivery: a therapy platform for cancer by surgery and photothermal therapy

“…11,12 However, the shortcoming of ICG is the limited penetration depth of emitted light in tissue, resulting in an almost invisible fluorescent signal. 13,14 By contrast, the supra-molecular assembly of human serum albumin protein with a sulfonated NIR-I organic dye (IR820) can significantly increase by 21 times the fluorescence of NIR-II imaging and high-resolution photo-acoustic imaging. 14 Compared with IGG, a new indocyanine green IR820 has longer emission and clearance plasma half-life.…”