Super-stable cyanine@albumin fluorophore for enhanced NIR-II bioimaging

Abstract

Near-infrared-II (NIR-II) dyes could be encapsulated by either exogenous or endogenous albumin to form stable complexes for deep tissue bioimaging. However, we still lack a complete understanding of the interaction mechanism of the dye@albumin complex. Studying this principle is essential to guide efficient dye synthesis and develop NIR-II probes with improved brightness, photostability, etc . Methods: Here, we screen and test the optical and chemical properties of dye@albumin fluorophores, and systematically investigate the binding sites and the relationship between dye structures and binding degree. Super-stable cyanine dye@albumin fluorophores are rationally obtained, and we also evaluate their pharmacokinetics and long-lasting NIR-II imaging abilities. Results: We identify several key parameters of cyanine dyes governing the supramolecular/covalent binding to albumin, including a six-membered ring with chlorine (Cl), the small size of side groups, and relatively high hydrophobicity. The tailored fluorophore (IR-780@albumin) exhibits much-improved photostability, serving as a long-lasting imaging probe for NIR-II bioimaging. Conclusion: Our study reveals that the chloride-containing cyanine dyes with the above-screened chemical structure (e.g. IR-780) could be lodged into albumin more efficiently, producing a much more stable fluorescent probe. Our finding partly solves the photobleaching issue of clinically-available cyanine dyes, enriching the probe library for NIR-II bioimaging and imaging-guided surgery.

NIR fluorescence imaging and treatment for cancer immunotherapy

“…In addition to NIR-II fluorophores, the long non-negligible emission tail of existing NIR-I dyes (eg, indocyanine green, ICG) allows them to be repurposed for NIR-II fluorescence imaging, which yields even higher signal intensities than commercially available NIR-II dyes (eg, IR-E1050). [28][29][30] In this way, the clinically approved fluorophore ICG has been demonstrated for NIR-II imaging Open access in preclinical and clinical settings. 31 32 Recently, Kang et al repurposed heptamethine fluorophores to NIR-II tail imaging and demonstrated the ability to target tumor-associated immune cells with high sensitivity and accuracy.…”

Luminescent Gold Nanoclusters for Bioimaging: Increasing the Ligand Complexity

“…Organic fluorophores [ 19 , 20 , 21 ], quantum dots [ 22 , 23 ], and polymeric materials [ 24 , 25 ] were tested as potential luminescent chemicals for applications in the fluorescence imaging. However, in the most recent developments, these emitters have sometimes suffered from certain drawbacks, such as low quantum yield [ 26 ], scarce photostability [ 27 ], photobleaching [ 28 ], or insufficient biocompatibility [ 29 ]. AuNCs have been recognized to be more biocompatible than other nanomaterials, while they exhibit acceptable quantum yields in the NIR region [ 30 , 31 ].…”

Ultrabright Renal-Clearable Cyanine-Protein Nanoprobes for High-Quality NIR-II Angiography and Lymphography

“…We selected IR-780 because of its better photostability compared to other cyanine fluorophores. 46 BSA and HSA had been proven to covalently bind IR-780 to form stable complexes with elevated NIR brightness. 49−52 Plotting the NIR-II signal of the protein@IR-780 complex in the series against reaction temperature revealed that β-LG also exhibited a significant fluorescence enhancement, particularly at higher reaction temperature.…”

“…Clinical NIR imaging primarily depends on cyanine dyes, − and ICG is the only NIR contrast agent approved by the FDA and EMA . To improve the brightness and photostability of cyanine dyes, previous studies used exogenous/endogenous albumin to encapsulate the small molecular dyes to improve their in vivo imaging outcomes. − Cyanine dyes could be stably embedded in the hydrophobic pocket of albumin through a covalent bond, − so that the nonradiative transition caused by internal rotation/vibration of dye molecules was effectively suppressed, thus significantly increasing their physiological brightness. , The preferential conformation of cyanine dyes in the pocket of albumin also promotes the twisted intramolecular charge transfer (TICT), resulting in the enhancement of NIR-II emission. ,, In addition, the protein shell also protects cyanine dyes from collisional quenching, effectively improving their biocompatibility and photostability . While critical advances, the albumin-encapsulated strategy produced protein@dye complex with relatively large size and long blood half-life, losing the advantage of inherently fast clearance from the body of cyanine dye counterparts and potentially increasing background signals.…”

“…To construct a stable protein@cyanine dye with bright NIR-II emission and renal clearance, we selected a set of functional proteins, including bovine serum albumin (BSA), human serum albumin (HSA), ovalbumin (OVA), hemoglobin (Hb), transferrin (Tf), β-lactoglobulin (β-LG), lactoferrin (Lf), and α-lactalbumin (α-LA), to explore the fluorescence enhancement to IR-780 (Figure a, b). We selected IR-780 because of its better photostability compared to other cyanine fluorophores . BSA and HSA had been proven to covalently bind IR-780 to form stable complexes with elevated NIR brightness. − Plotting the NIR-II signal of the protein@IR-780 complex in the series against reaction temperature revealed that β-LG also exhibited a significant fluorescence enhancement, particularly at higher reaction temperature.…”