Review—Advances in the Application of Microenvironment-Responsive NIR-II Fluorescent Probes in Organisms

Abstract

Near-infrared fluorescence imaging plays an important role in the diagnosis and treatment of major diseases by virtue of its high sensitivity and specificity. However, compared with the traditional NIR-I (700∼900 nm) fluorescence imaging, NIR-II (900∼1400 nm) fluorescence imaging has the advantages of higher tissue penetration depth and higher imaging signal-to-noise ratio in vivo imaging studies. The review focuses on the development of NIR-II fluorescent probes in recent years, classifies and discusses the activable NIR-II fluorescent probes, and systematically introduces the microenvironment-responsive fluorescent probes. The research results of redox activated probes, pH activated probes, hypoxic activated probes, enzyme activated probes, viscosity activated probes, ATP and metal ion activated probes in the field of biological applications are included. Finally, the development prospect of NIR-II fluorescent probe is prospected.

Recent Progress of Cyanine Fluorophores for NIR‐II Sensing and Imaging

“…In the past few decades, many NIR-II cyanine fluorophores and fluorescent probes have been established for deep-tissue bioimaging with high contrast and sensitivity. [57] However, most of the existing NIR-II cyanine fluorophores and probes are still in their infancy and their clinical applications are limited. To extend their applications in bioimaging or biosensing, several limitations of the NIR-II cyanine fluorophores must be overcome: 1) the current cyanine fluorophores whose excitation wavelength and emission wavelength both exceed 1000 nm still face the problems of low quantum yield and poor stability; 2) due to the large structure of NIR-II cyanine dyes and the steric sensitivity of the enzymes, [58] achieving the NIR-II cyanine probes with highly sensitive enzyme-catalyzed responses is still a challenge; 3) poor water solubility and lack of adjustable sites also limits the application of fluorophores in biological detection.…”

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

“…[29][30][31][32][33][34] Particularly, organic fluorophores that emit light in the first near-infrared (NIR) range (NIR-I; 700-900 nm) have received ever-growing attention for in vitro and in vivo bioimaging because NIR fluorescent dyes possess unique advantageous features compared to others with shorter emission wavelengths. [35][36][37][38][39][40][41][42] For example, NIR photons penetrate relatively deeply into tissues and cause low levels of damage to biological samples. In addition, the use of NIR light minimizes tissue auto-fluorescence associated with biomolecules in living systems and reduces light scattering.…”

Bioimaging of Dissolvable Microneedle Arrays: Challenges and Opportunities

“…Given the important role of fluorescent contrast agents in TPM and tissue slices, confocal, fluorescence microscope, and live animal imaging, nanomaterials [ 108 ] including semiconductor quantum dots, metal nanoclusters, carbon nanomaterials, upconversion nanoparticles, and fluorescent silicon nanoparticles [ 55 , 100 , 109 , 110 ], in addition to a variety of functionally different dyes, have been developed and used successively in the last decade. Fluorescent probes with high fluorescence quantum yields and high absorption coefficients are more desirable in the future [ 111 ].…”

“…Nanoparticles can increase circulation time and imaging brightness relative to single molecule imaging agent, which promotes the rapid development of nanocarriers for NIR imaging with long excitation and emission wavelengths. Additionally, it is important to choose the right fluorescent imaging agent in conjunction with the characteristics of materials used to construct MNAs, especially those fluorescent nanomaterials [ 109 , 110 ] with increased mechanical properties of MNAs [ 112 , 113 ] and various microenvironment-responsive fluorescent probes activated by redox, pH, hypoxic, enzyme, viscosity, ATP, and metal ions [ 111 ].…”