NIR‐II Chemiluminescence Molecular Sensor for In Vivo High‐Contrast Inflammation Imaging

Self-Illuminating NIR-II Chemiluminescence Nanosensor for In Vivo Tracking H2 O2 Fluctuation

Chemiluminescence (CL) imaging, as an excitation-free technique, exhibits a markedly improved signal-to-noise ratio (SNR) owing to the absence of an excitation light source and autofluorescence interference. However, conventional chemiluminescence imaging generally focuses on the visible and first near-infrared (NIR-I) regions, which hinders high-performance biological imaging due to strong tissue scattering and absorption. To address the issue, self-luminescent NIR-II CL nanoprobes with a second near-infrared (NIR-II) luminescence in the presence of hydrogen peroxide are rationally designed. A cascade energy transfer, including chemiluminescence resonance energy transfer (CRET) from the chemiluminescent substrate to NIR-I organic molecules and Förster resonance energy transfer (FRET) from NIR-I organic molecules to NIR-II organic molecules, occurs in the nanoprobes, contributing to NIR-II light with great efficiency and good tissue penetration depth. Based on excellent selectivity, high sensitivity to hydrogen peroxide, and long-lasting luminescence performance, the NIR-II CL nanoprobes are applied to detect inflammation in mice, showing a 7.4-fold enhancement in SNR compared with that of fluorescence.

Chemiluminescent polymeric nanoprobes for tumor diagnosis: A mini review

Chemiluminescence (CL), a distinct luminescent process by taking advantage of chemical reactions rather than external light source, has recently attracted considerable research interests due to its high sensitivity and low background signal. The sensitivity and specificity of chemiluminescent signals in complex tumor microenvironment provide a sound basis for accurate detection of tumors. Various chemiluminescent nanoprobes with superior performance have been obtained by structural modification of chemiluminescent units or introduction of fluorescent dyes. In this review, we focused on the recent progress of chemiluminescent polymeric systems based on various chromophore substrates, including luminol, peroxyoxalates, 1, 2-dioxetanes and their derivatives for tumor detecting. And we also emphasized the design strategies, mechanisms and diagnostic applications of representative chemiluminescent polymeric nanoprobes. Finally, the critical challenges and perspectives of chemiluminescent systems usage in tumor diagnosis were also discussed.

Design and application of organic contrast agents for molecular imaging in the second near infrared (NIR-II) window

Optical imaging in the second near-infrared (NIR-II) window has attracted interest in recent years because of the merits of reduced light scattering, minimal autofluorescence from biological tissues and deeper penetration depth in this wavelength range. In this review, we summarize NIR-II organic contrast agents reported in the past decade for photoacoustic and fluorescence imaging including members of the cyanine family, D-A-D structure dyes, phthalocyanines and semiconducting polymers. Improved imaging contrast and higher resolution could be favorably achieved by rational design of NIR-II fluorophores by tuning their properties including molar extinction coefficient, fluorescence quantum yield, emission wavelength and others. A wide variety of applications using NIR-II dyes has been realized including imaging of tumors, lymphatics, brains, intestines and others. Emerging applications such as targeted imaging and activable imaging with improved resolution and sensitivity have been demonstrated by innovative chemical modification of NIR-II dyes. Looking forward, rational design of improved NIR-II dyes for advanced bioimaging is likely to remain an area of interest for next-generation potential approaches to disease diagnosis.

Chemiexcitation-Triggered Prodrug Activation for Targeted Carbon Monoxide Delivery

Photolysis-based prodrug strategy can address some critical drug delivery issues, which otherwise are very challenging to tackle with traditional prodrug strategy. However, the need for external light irradiation significantly hampers its in vivo application due to the poor light accessibility of deep tissue. Herein, we propose a new strategy of chemiexcitation-triggered prodrug activation, wherein a photoresponsive prodrug is excited for drug payload release by chemiexcitation instead of photoirradiation. As such, the bond-cleavage power of photolysis can be employed to address some critical drug delivery issues while obviating the need for external light irradiation. We have established the proof of concept by the successful development of a chemiexcitation responsive carbon monoxide delivery platform, which exhibited specific CO release at the tumor site and pronounced tumor suppression effects. We anticipate that such a concept of chemiexcitation-triggered prodrug activation can be leveraged for the targeted delivery of other small molecule-based drug payloads.

Chemiluminescent 1,2-Dioxetane Iridium Complexes for Near-Infrared Oxygen Sensing

Chemiluminescent iridium-based sensors which demonstrate oxygen dependent responses have been developed. The molecular probes, named IrCL-1, IrCL-2 and IrCL-3 consist of oxygen-sensitive iridium complexes attached to a spiroadamantane 1,2 dioxetane and operate via energy transfer from the chemiexcited benzoate to the corresponding iridium(III) complex. Complexing the iridium(III) center with π-extended ligands results in emission in the biologically relevant, near-infrared (NIR) region. All probes demonstrate varying oxygen tolerance, with IrCL-1 being the most oxygen sensitive. These probes have been further utilized for in vitro ratiometric imaging of oxygen, as well as for intraperitoneal, intramuscular and intratumoral imaging in live mice. To our knowledge, these are the first iridium-based chemiluminescent probes that have been employed for in vitro ratiometric oxygen sensing, and for in vivo tumor imaging.

A Near-Infrared-II Polymer with Tandem Fluorophores Demonstrates Superior Biodegradability for Simultaneous Drug Tracking and Treatment Efficacy Feedback

NIR-II (1000-1700 nm) fluorescence imaging is continually attracting strong research interest. However, current NIR-II imaging materials are limited to small molecules with fast blood clearance and inorganic nanomaterials and organic conjugated polymers of poor biodegradability and low biocompatibility. Here, we report a highly biodegradable polyester carrying tandem NIR-II fluorophores as a promising alternative. The polymer encapsulated a platinum intercalator (56MESS, (5,6-dimethyl-1,10-phenanthroline) (1S,2S-diaminocyclohexane) platinum(II)) and was conjugated with both a cell-targeting RGD peptide and a caspase-3 cleavable peptide probe to form nanoparticles for simultaneous NIR-II and apoptosis imaging. In vitro, the nanoparticles were approximately 4-1000- and 1.5-10-fold more potent than cisplatin and 56MESS, respectively. Moreover, in vivo, they significantly inhibited tumor growth on a multidrug-resistant patient-derived mouse model (PDX^MDR). Finally, through label-free laser desorption-ionization mass spectrometry imaging (MALDI-MSI), in situ 56MESS release in the deeper tumors was observed. This work highlighted the use of biodegradable NIR-II polymers for monitoring drugs in vivo and therapeutic effect feedback in real-time.

NIR-II pH Sensor with a FRET Adjustable Transition Point for In Situ Dynamic Tumor Microenvironment Visualization

Monitoring the pH in tumor lesions provides abundant physiological information. However, currently developed pH sensors only achieve sensitive detection in the settled response region around the pH transition point (pHt ). To realize tumor pH monitoring with high sensitivity within a wider response region, reported here are serial pHt adjustable sensors (pTAS) that simply regulate the component ratio of second near-infrared (NIR-II) emission aza-BODIPY (NAB) donor and pH sensitive rhodamine-based pre-acceptor (NRh) in Förster resonance energy transfer system. Combining the pH response regions of pTAS, a twofold widened pH detection range (6.11-7.22) is obtained compared to the pHt settled sensor (6.38-6.94). With an adjustable pHt , in vivo tumor pH increase and decrease processes could be dynamically visualized through dual-channel ratiometric bioimaging within the NIR-II window, with a coefficient of variation under 1 % compared to the standard pH meter.