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An aggregation and crosslinking strategy is proposed for constructing high-relaxivity C-BM. The further increased r1, stabler FL, stronger PA and better PT effect are achieved in C-BM/I, which can be used for MR, NIR-II FL and PA imaging and PTT-PDT.

Single-cell interrogation with the solid-state nanoprobes enables understanding of the linkage between cellular behavior and heterogeneity. Herein, inspired by the charge property of the organic molecular probe (OMP), a generic ionic current rectification (ICR) single-cell methodology is established, exemplified by subcellular detection of glutathione (GSH) with high selectivity, sensitivity, and recyclability. The as-developed nanosensor can transduce the subcellular OMP-GSH interaction via a sensitive ionic response, which stems from the superior specificity of OMP and its essential charge property. In addition, the nanosensor exhibits good reversibility, since the subsequent tandem reaction after the recognition can well recover the sensing surface. Given the diverse structures and tailorable charge properties of OMP, this work underpins a new and general method of OMP-based ICR single-cell analysis.

Tumor-targeted and stimuli-activatable nanosensitizers are highly desirable for cancer theranostics. However, design of smart nanosensitizers with multiple imaging signals and synergistic therapeutic activities switched on is challenging. Herein, we report tumor-targeted and redox-activatable nanosensitizers (1-NPs) for sono-photodynamic immunotherapy of tumors by molecular co-assembly and redox-controlled disassembly. 1-NPs show a high longitudinal relaxivity (r1 = 18.7 ± 0.3 mM-1 s-1), but "off" dual fluorescence (FL) emissions (at 547 and 672 nm), "off" sono-photodynamic therapy and indoleamine 2,3-dioxygenase 1 (IDO1) inhibition activities. Upon reduction by glutathione (GSH), 1-NPs rapidly disassemble and remotely release small molecules 2-Gd, Zn-PPA-SH and NLG919, concurrently switching on (1) dual FL emissions, (2) sono-photodynamic therapy and (3) IDO1 inhibition activities. After systemic injection, 1-NPs are effective for bimodal FL and magnetic resonance (MR) imaging-guided sono-photodynamic immunotherapy of orthotropic breast and brain tumors in mice under combined ultrasound (US) and 671-nm laser irradiation.

Controlling delivery and release of therapeutic agents to accomplish on-demand synergistic therapy of orthotopic gliomas is desired but challenging. Here, we report a glioma targeting and redox activatable theranostic nanoprobe (

Ultrasound (US)-activated nanoagents capable of producing cytotoxic species have been promising for the treatment of deep-seated tumors; however, poor tumor uptake and insufficient generation of cytotoxic agents have largely limited their therapeutic efficacy in vivo. Herein, we report a hybrid FeCuS-lipid nanoparticle (AIBA@FeCuS-FeCO) by amphiphilic lipids-assisted emulsion of a free radical initiator (AIBA), a radical-sensitive CO donor (Fe3(CO)12), and radical-degradable FeCuS nanodisks for US-activated synergistic therapy of deep-located orthotopic gastric tumors in living mice. Upon US irradiation, AIBA@FeCuS-FeCO could be degraded and release cytotoxic AIBA radicals, CO, Fe2+, and Cu2+, allowing us to (1) enhance tumor uptake of AIBA@FeCuS-FeCO through CO-mediated vasodilation, (2) promote hydroxyl radical production and induce tumor ferroptosis via intracellular accumulation of Fe2+/Cu2+, and (3) kill tumor cells. Moreover, the subsequent administration of disulfiram (DSF) could further chelate with the liberated Cu2+, yielding toxic bis(N,N-diethyl dithiocarbamato)copper(II) chelates to synergize the therapeutic effect to ablate deep-seated orthotopic gastric tumors.

Multimodal imaging, which harnesses two or more imaging modalities to produce complementary anatomical and molecular information of a living subject, has become as a powerful tool in both basic biomedical research and clinical diagnosis. The progresses in multimodal imaging are paralleled by the advances in multimodal probes, particularly activatable multimodal imaging probes that can generate concurrent switches in different imaging modality signals upon interaction with a molecular target. These probes are extremely promising for in vivo imaging. In this Minireview, we summarize the recent progress in activatable multimodal probes for in vivo imaging and cancer theranostics, focusing on their design principle, signal activation mechanism and biomedical applications. The current challenges and perspectives for future developments of activatable multimodal probes are also briefly discussed. We hope that this Minireview will provide inspiration for the design of other activatable multimodal probes for improving in vivo imaging and theranostics.

10,11-Bis[bis(4-dimethylaminophenyl)methylene]dibenzo[bf]thiepin (1) and -oxepin (2) were prepared as stable yellow crystalline compounds, which are the cyclic analogues of electron-donating hexaarylbutadienes. Upon two-electron oxidation, they are reversibly transformed into the title dications (1

Reversible imaging probes that allow for the dynamic visualization of the redox cycle between hydroxyl radical (⋅OH) and hydrogen sulfide (H

Pretargeted imaging has emerged as a promising approach to advance nuclear imaging of malignant tumors, however, the application of pretargeted strategy for multimodality imaging of enzyme activity in vivo is challenging. Herein, we combine the enzyme-mediated fluorogenic reaction and in situ self-assembly with the inverse electron demand Diels-Alder (IEDDA) reaction to develop an activatable pretargeted strategy for multimodality imaging. The trans -cyclooctene (TCO) bearing small-molecule probe, P-FFGd-TCO , can be activated by alkaline phosphatase and in situ self-assembles into nanoaggregates ( FMNPs-TCO ) retained on the membranes, permitting to (1) amplify near-infrared (NIR) fluorescence (FL) and magnetic resonance imaging (MRI) signals, and (2) enrich TCOs to promote IEDDA ligation. The Gallium-68 ( 68 Ga) labeled tetrazine can readily conjugate the tumor-retained FMNPs-TCO to enhance radioactivity uptake in tumors. Hence, strong NIR FL, MRI and positron emission tomography (PET) signals are concomitantly achieved, allowing for pretargeted multimodality imaging of ALP activity in HeLa tumor-bearing mice.

Near-infrared (NIR)-II light-excitable photonic agents capable of generating tumor hyperthermia and cytotoxic free radicals are promising for synergistic phototherapy of tumors. However, the lack o...

For cancer therapy, drug delivery systems are often limited by insufficient drug loading capacity, which usually results in systemic toxicity and heavy metabolic burden to excrete the carriers. Her...

Stimuli-responsive in situ self-assembly of small molecule probes into nanostructures has been promising for the construction of molecular probes for in vivo imaging. In the past few years, a number of intelligent molecular imaging probes with fluorescence, magnetic resonance imaging (MRI), positron electron tomography (PET) or photoacoustic imaging (PA) modality have been developed based on the in situ self-assembly strategy. In this minireview, we summarize the recent advances in the development of different modality imaging probes through controlling in situ self-assembly for in vivo imaging of enzymatic activity. This review starts from the brief introduction of two different chemical approaches amenable for in situ self-assembly, including (1) stimuli-mediated proteolysis and (2) stimuli-triggered biocompatible reaction. We then discuss their applications in the design of fluorescence, MRI, PET, PA, and bimodality imaging probes for in vivo imaging of different enzymes, such as caspase-3, furin, gelatinase and phosphatase. Finally, we discuss the current and prospective challenges in the stimuli-responsive in situ self-assembly strategy for in vivo imaging.

γ-Glutamyltranspeptidase (GGT) is an important aminopeptidase overexpressed in many malignant tumors, and accurate detection of its activity is useful for the diagnosis and treatment of tumors. Herein, we report a GGT-activatable ratiometric fluorescent probe (1) constructed by covalently linking an 'always-on' BODIPY fluorophore with a GGT-activatable near-infrared (NIR) fluorescent substrate. Upon interaction with GGT, the NIR fluorescence at 735 nm in probe 1 is significantly enhanced, while the fluorescence of BODIPY at 517 nm remains unchanged. Using BODIPY fluorescence as an internal standard, significantly enhanced ratiometric fluorescence between 735 nm and 517 nm could be achieved, allowing accurate detection of the activity of GGT in living subjects independent of probe concentration. We demonstrate that probe 1 is feasible for the evaluation of GGT levels in different tumor cells and differentiation of GGT-positive tumor cells from GGT-negative normal tissue cells. Moreover, probe 1 is further applied for the visualization of tumor via noninvasive ratiometric fluorescence imaging of GGT activity, which could facilitate the detection of GGT-positive tumor tissues and study of GGT-related pathological processes.

Enzyme-triggered macrocyclization and in situ self-assembly of small molecules into nanoparticles has shown promise to design activatable probes for molecular imaging. However, controlling macrocyclization and self-assembly to concurrently augment positron emission tomography (PET) and photoacoustic (PA) signals for bimodality imaging is challenging. Herein, we report the engineering of a triazole-IR780 fluorophore as a versatile macrocyclization scaffold for controlling in situ self-assembly and design a caspase-3-activatable PA/PET bimodal probe ([

Stimuli-responsive smart photosensitizer (PS) nanoassemblies that allow enhanced delivery and controlled release of PSs are promising for imaging-guided photodynamic therapy (PDT) of tumors. However, the lack of high-sensitivity and spatial-resolution signals and fast washout of released PSs from tumor tissues have impeded PDT efficacy in vivo. Herein, we report tumor targeting, redox-responsive magnetic and fluorogenic PS nanoassemblies (NP-RGD) synthesized via self-assembly of a cRGD- and disulfide-containing fluorogenic and paramagnetic small molecule (1-RGD) for fluorescence/magnetic resonance bimodal imaging-guided tumor PDT. NP-RGD show high r1 relaxivity but quenched fluorescence and PDT activity; disulfide reduction by glutathione (GSH) promotes efficient disassembly into a small-molecule probe (2-RGD) and an organic PS (PPa-SH), which could further bind with intracellular albumin, allowing prolonged retention and cascade activation of fluorescence and PDT to ablate tumors.

Ratiometric fluorescent probes hold great promise for in vivo imaging; however, stimuli-activatable ratiometric probes with fluorescence emissions in near-infrared (NIR) region are still very few. Herein, we report a hydrogen sulfide (H2S)-activatable ratiometric NIR fluorescent probe ( 1 -SPN) by integrating a H2S-responsive NIR fluorescent probe 1 into a H2S-inert poly[2,6-(4,4-bis-(2-ethylhexyl)-4 H -cyclopenta[2,1-b;3,4-b′]dithiophene)- alt -4,7(2,1,3-benzothiadiazole)] (PCPDTBT)-based NIR semiconducting polymer nanoparticle (SPN). 1 -SPN shows “always on” PCPDTBT fluorescence at 830 nm and weak probe 1 fluorescence at 725 nm under excitation at 680 nm. The ratio of NIR fluorescence intensities between 725 and 830 nm ( I 725/ I 830) is small. Upon interaction with H2S, the fluorescence at 725 nm is rapidly switched on, resulting in a large enhancement of I 725/ I 830, which is allowed for sensitive visualization and quantification of H2S concentrations in living cells. Taking advantage of enhanced tissue penetration depth of NIR fluorescence, 1 -SPN is also applied for real-time ratiometric fluorescence imaging of hepatic and tumor H2S in living mice. This study demonstrates that activatable ratiometric NIR fluorescent probes hold great potential for in vivo imaging.

Near-infrared (NIR) probes are ideal for fluorescence labeling and imaging of biological targets in living animals. However, the instability of common NIR dyes hampers the construction of NIR probes bearing multiple functional components such as biomolecules for specific targeting and imaging reagents for multimodality imaging. To overcome these limitations, we designed a novel NIR scaffold bearing two terminal alkynes as clickable handles and a chloride on the heptamethine backbone that allows nucleophilic substitution with an azide to generate the third clickable handle. This unique scaffold allows for facile installation of multiple functional arms for the construction of multifunctional NIR probes. Various biomacromolecules or imaging reagents can be introduced to the NIR scaffold by sequential one-pot click reactions under biocompatible conditions. The preclickable handle chloride on the NIR backbone does not interfere with the initial click reactions, and it can be easily transformed into an azide for a following click reaction. On the basis of this unique NIR scaffold, we developed a highly efficient method to construct diverse NIR probes containing multiple functional biomolecules including peptides, antibodies, nucleic acids, and NIR/PET (positron emission tomography) dual-modality imaging probes bearing tumor-targeting groups. NIR imaging or multimodality imaging using these probes was performed on live cells or tumor models on living mice.

Mitochondria-targeting probes that allow us to induce and report mitochondrial dysfunction have become promising theranostic agents for cancer; however, the lack of selectivity toward tumor cells over normal tissue cells has impeded the treatment outcome. Herein, we develop 10 fluorescent dehydroberberine derivatives (

Hydrogen sulfide (H2S) is an important endogenous gasotransmitter, but the targeted delivery and real-time feedback of exogenous H2S are still challenging. With the aid of density functional theory (DFT) calculations, we designed a new 1,3-dithiolium-4-olate (DTO) compound, which can react with a strained alkyne via the 1,3-dipolar cycloaddition and the retro-Diels-Alder reaction to generate carbonyl sulfide (COS) as the precursor of H2S, and a thiophene derivative with turn-on fluorescence. Moreover, the diphenylamino substituent in DTO greatly increases the mitochondrial targeting of this H2S delivery system. Such a bioorthogonal click-and-release reaction has integrated three functions in one system for the first time: (1) in-situ controllable H2S release, (2) concomitant fluorescence response, and (3) mitochondria-targeted delivery. In addition, we investigated the mitochondrial membrane potential loss alleviation by using this system in H9c2 cells under oxidative stress.

Accurate detection of hepatic hydrogen sulfide (H 2 S) to monitor H 2 S-related enzymes' activity is critical for acute hepatitis diagnosis, but remains a challenge due to the dynamic and transient nature of H 2 S. Here, we report a H 2 S-activatable near-infrared afterglow/MRI bimodal probe F1 -GdNP, which shows an "always-on" MRI signal and "off-on" afterglow signal toward H 2 S. F1 -GdNP shows fast response, high sensitivity and specificity toward H 2 S, permitting afterglow imaging of H 2 S and evaluation of cystathionine γ -lyase's activity in living mice. We further employ the high spatial-resolution MRI signal of F1 -GdNP to track its delivery and accumulation in liver. Importantly, F1 -GdNP offers a high signal-to-background ratio (SBR = 86.2 ± 12.0) to sensitively report on the increased hepatic H 2 S level in the acute hepatitis mice via afterglow imaging, which correlated well with the upregulated CSE activity in the liver, showcasing the good potential of F1 -GdNP for monitoring of acute hepatitis process in vivo.

Near-infrared (NIR) fluorescent imaging of both soluble and insoluble Aβ species in the brain of Alzheimer's disease (AD) is crucial for the early diagnosis and intervention of AD. To date, a variety of NIR fluorescent probes have been reported for the detection of Aβ species. Among these probes, CRANAD-58 was reported to have the capability to detect both soluble and insoluble Aβ species, which is vital to monitor the changes of Aβ species during the pathological course of the disease. Though CRANAD-58 has shown promise to noninvasively detect Aβ species in transgenic AD mice, the emission wavelength (~670 nm) is still too short for further applications. Therefore, new probes with longer emission wavelength and improved physiological properties are in highly demand. Herein, we report the design and engineering of nine donor-acceptor-donor molecules as "off-on" near-infrared fluorescent probes for

Multimodal imaging probes have shown promise in both biomedical research and clinical diagnosis. However, the development of molecular probes capable of being switched on multimodality imaging signals in response to a biomarker of interest remains challenging. In this paper, we report a caspase-3-activatable small-molecule bimodal probe (Gd-IR780) for photoacoustic imaging (PAI) and magnetic resonance imaging (MRI) of tumor apoptosis via caspase-3-triggered intramolecular macrocyclization and in situ self-assembly process. Upon interaction with caspase-3, Gd-IR780 can be efficiently converted into a macrocyclic product, Gd-IR780-MC, which subsequently self-assembles into near-infrared absorptive and paramagnetic nanoparticles (Gd-IR780-NPs), allowing to concurrently switch on PAI (∼4.3-fold at 855 nm) and MRI (r

Renal-clearable and target-responsive near-infrared (NIR) fluorescent imaging probes have been promising for in vivo diagnosis of acute kidney injury (AKI). However, designing an imaging probe that is renal-clearable and concurrently responsive toward multiple molecular targets to facilitate early detection of AKI with improved sensitivity and specificity is challenging. Herein, by leveraging the receptor-mediated binding and retention effect along with enzyme-triggered fluorescence activation, we design and synthesize an activatable small-molecule NIR fluorescent probe (1-DPA2) using a "one-pot sequential click reaction" approach. 1-DPA2 can target both the externalized phosphatidylserine (PS) and active caspase-3 (Casp-3), two essential biomarkers of apoptosis, producing enhanced 808 nm NIR fluorescence and a high signal-to-background ratio (SBR) amenable to detecting the onset of cisplatin-induced AKI in mice as early as 24 h post-treatment with cisplatin. We not only monitor the gradual activation of Casp-3 in the kidney of mice upon AKI progression but also can report on the progressive recovery of kidney functions in AKI mice following N-acetyl-l-cysteine (NAC) therapy via real-time fluorescence imaging by 1-DPA2. This study demonstrates the ability of 1-DPA2 for longitudinal monitoring of renal cell apoptosis by concurrently targeting PS externalization and Casp-3 activation, which is efficient for early diagnosis of AKI and useful for prediction of potential drug nephrotoxicity as well as in vivo screening of anti-AKI drugs' efficacy.

Tumor response to radiotherapy or ferroptosis is closely related to hydroxyl radical (•OH) production. Noninvasive imaging of •OH fluctuation in tumors can allow early monitoring of response to therapy, but is challenging. Here, we report the optimization of a diene electrochromic material (1-Br-Et) as a •OH-responsive chromophore, and use it to develop a near-infrared ratiometric fluorescent and photoacoustic (FL/PA) bimodal probe for in vivo imaging of •OH. The probe displays a large FL ratio between 780 and 1113 nm (FL780/FL1113), but a small PA ratio between 755 and 905 nm (PA755/PA905). Oxidation of 1-Br-Et by •OH decreases the FL780/FL1113 while concurrently increasing the PA755/PA905, allowing the reliable monitoring of •OH production in tumors undergoing erastin-induced ferroptosis or radiotherapy., The hydroxyl radical is generated during radiotherapy and ferroptosis and accurate imaging of this reactive oxygen species may permit the monitoring of response to therapy. Here, the authors develop a ratiometric probe for accurate imaging of hydroxyl radical generation in vivo.

Accurate detection of hepatic hydrogen sulfide (H

A facile access to highly fused tetracyclic indeno-1,2-benzothiazines has been established via a Rh(III)-catalyzed C-H bond activation and intramolecular annulation cascade between sulfoximides and all-carbon diazo indandiones. This strategy is characterized by the fact that the diazo coupling partners do not require preactivation, along with its high efficiency, broad substrate generality, and facile transformation. Particularly, the highly conjugated tetracyclic products demonstrate good optical properties and can easily enter cells to emit bright fluorescence for live cell imaging.

Ultrasound (US)-activated nanoagents capable of producing cytotoxic species have been promising for the treatment of deep-seated tumors; however, poor tumor uptake and insufficient generation of cytotoxic agents have largely limited their therapeutic efficacy

Photoacoustic (PA) imaging is an emerging imaging technique, which combines high spatial resolution and deep tissue penetration of ultrasound imaging with high sensitivity of fluorescence imaging. In the past few years, PA has shown promise for noninvasive imaging of biomolecules in vivo. In this chapter, we present the synthesis and application of a tumor targeting and caspase-3 activatable PA probe (1-RGD) for real-time and noninvasive imaging of tumor apoptosis. 1-RGD can be efficiently delivered into tumor tissues and recognized by caspase-3, which triggered efficient proteolysis of DEVD substrate and subsequent intramolecular macrocyclization, followed by in situ self-assembly into nanoparticles, leading to prolonged retention in apoptotic tumors and enhanced PA signals. With 1-RGD, high-resolution 3D PA images of tumor tissues can be obtained, allowing to report on the activity and distribution of caspase-3 within DOX-treated tumors, which was helpful for early monitoring of tumor response to therapy. We provide detailed protocols for the synthesis, in vitro characterization and in vivo applications of 1-RGD.

Controlled generation of reactive oxygen species (ROS) is essential in biological, chemical, and environmental fields, and piezoelectric catalysis is an emerging method to generate ROS, especially in sonodynamic therapy due to its high tissue penetrability, directed orientation, and ability to trigger in situ ROS generation. However, due to the low piezoelectric coefficient, and environmental safety and chemical stability concerns of current piezoelectric ROS catalysts, novel piezoelectric materials are urgently needed. Here, we demonstrate a method to induce polarization of inert poly(tetrafluoroethylene) (PTFE) particles ( ~ 1–5 μm) into piezoelectric electrets with a mild and convenient ultrasound process. Continued ultrasonic irradiation of the PTFE electrets generates ROS including hydroxyl radicals (•OH), superoxide (•O2−) and singlet oxygen (1O2) at rates significantly faster than previously reported piezoelectric catalysts. In summary, ultrasonic activation of inert PTFE particles is a simple method to induce permanent PTFE polarization and to piezocatalytically generate aqueous ROS that is desirable in a wide-range of applications from environmental pollution control to biomedical therapy., Controlled generation of reactive oxygen species (ROS) is essential in biological, chemical, and environmental fields. Here, the authors report that ultrasonication can induce polarization of inert poly(tetrafluoroethylene) to a piezoelectric electret and drive piezocatalytic generation of aqueous ROS.

Plasmonic metal/semiconductor nanohybrids hold great promise in photocatalysis and biosensor development; however, their potential phototherapeutic applications are yet fully unexplored. On the other hand, the demand of high laser power density to induce antibacterial photothermal therapeutic effects greatly restricts the practical applicability of the previously developed photothermal nanoagents (PTAs) for anticancer photothermal therapy (PTT). Here, we develop a plasmonic nanohybrid by integrating plasmonic noble metal gold nanorods (AuNRs) with a two-dimensional graphene oxide (2-D GO), capable to perform photothermal ablation of both bacterial pathogens as well as tumor cells, respectively, under low power single near-infrared (NIR) laser activation. Owing to the synergistic plasmonic photothermal effect (PPTT) of dual plasmonic PTAs, the plasmonic AuNR/GO nanohybrid exhibits remarkably higher photothermal conversion efficiency (PCE, 72.59%) than either individual AuNRs or GO under low laser power density (300 mW), leading to enhanced antibacterial/anticancer PTT. In addition, the synergistic plasmonic antibacterial/anticancer PTT induced by the plasmonic nanohybrid is also far superior to individual PTAs (AuNRs or GO), whereas the flow cytometric analysis of heat shock proteins (HSP 70) clearly dictates that the substantial killing of bacterial pathogens/tumor cells is solely due to the synergistic PPTT. Thus, the plasmonic AuNR/GO nanohybrid is a standalone PTA to perform simultaneous antibacterial/anticancer PTT under low power NIR laser activation for only 5 min, without any systemic side effects. The present study provides a clear demonstration about the potential therapeutic impact of plasmonic nanohybrids and thus will surely pave the way to design other hybrid nanoagents with enhanced PCE and integrate them with chemotherapeutic agents, leading to dual-modal chemo-/photothermal antibacterial/anticancer therapy under low power single laser excitation for a short duration.

Stimuli-responsive in situ self-assembly of small molecules to form nanostructures in living subjects has produced promising tools for molecular imaging and tissue engineering. However, controlling the self-assembly process to simultaneously activate multimodality imaging signals in a small-molecule probe is challenging. In this paper, we rationally integrate a fluorogenic reaction into enzyme-responsive in situ self-assembly to design small-molecule-based activatable near-infrared (NIR) fluorescence and magnetic resonance (MR) bimodal probes for molecular imaging. Using alkaline phosphatase (ALP) as a model target, we demonstrate that probe (P-CyFF-Gd) can be activated by endogenous ALP overexpressed on cell membranes, producing membrane-localized assembled nanoparticles (NPs) that can be directly visualized by cryo-SEM. Simultaneous enhancements in NIR fluorescence (>70-fold at 710 nm) and r1 relaxivity (∼2.3-fold) enable real-time, high-sensitivity, high-spatial-resolution imaging and localization of the ALP activity in live tumor cells and mice. P-CyFF-Gd can also delineate orthotopic liver tumor foci, facilitating efficient real-time, image-guided surgical resection of tumor tissues in intraoperative mice. This strategy combines activatable NIR fluorescence via a fluorogenic reaction and activatable MRI via in situ self-assembly to promote ALP activity imaging, which could be applicable to design other activatable bimodal probes for in vivo imaging of enzyme activity and locations in real time.

Photoacoustic (PA) imaging shows promise in the sensitive detection of caspase-3 activated in early tumor apoptosis in response to chemotherapy; smart PA probes are thus in high demand. Herein, we report the first smart PA probe (1-RGD) responsive to caspase-3, enabling real-time and high-resolution imaging of tumor apoptosis. 1-RGD is designed to leverage the synergetic effect of active delivery and caspase-3 activation. It is selectively recognized by active caspase-3 to trigger peptide substrate cleavage and biocompatible macrocyclization-mediated self-assembly, leading to an amplified PA imaging signal and prolonged retention in apoptotic tumor cells. Strong, high-resolution PA images are obtained in chemotherapy-induced apoptotic tumors in living mice after intravenous administration with 1-RGD, facilitating sensitive reporting of caspase-3 activity and distribution within tumor tissues.

Targeted delivery of enzyme-activatable probes into cancer cells to facilitate accurate imaging and on-demand photothermal therapy (PTT) of cancers with high spatiotemporal precision promises to advance cancer diagnosis and therapy. Here, we report a tumor-targeted and matrix metalloprotease-2 (MMP-2)-activatable nanoprobe (T-MAN) formed by covalent modification of Gd-doping CuS micellar nanoparticles with cRGD and an MMP-2-cleavable fluorescent substrate. T-MAN displays a high r1 relaxivity (∼60.0 mM–1 s–1 per Gd3+ at 1 T) and a large near-infrared (NIR) fluorescence turn-on ratio (∼185-fold) in response to MMP-2, allowing high-spatial-resolution magnetic resonance imaging (MRI) and low-background fluorescence imaging of gastric tumors as well as lymph node (LN) metastasis in living mice. Moreover, T-MAN has a high photothermal conversion efficiency (PCE, ∼70.1%) under 808 nm laser irradiation, endowing it with the ability to efficiently generate heat to kill tumor cells. We demonstrate that T-MAN can ac...

Enzyme-activatable ratiometric near-infrared (NIR) fluorescent probes enabling noninvasive imaging of enzyme activity in vivo are promising for biomedical research; however, such probes with ratiometric fluorescence emissions both in NIR window under a single NIR light excitation are largely unexplored. Here, a quenched NIR fluorophore of Cy5.5 is integrated with NIR fluorescent poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT)-based semiconducting polymer nanoparticles (SPNs), and an αv β3 integrin-targeting and matrix metalloproteinase-2 (MMP-2)-activatable ratiometric fluorescent probe (SPN-MMP-RGD) is developed. Under excitation at 660 nm, SPN-MMP-RGD shows "always-on" fluorescence of PCPDTBT (830 nm) and activatable fluorescence of Cy5.5 (690 nm) toward MMP-2, affording a remarkable ≈176-fold enhancement in fluorescence intensity ratio between 690 and 830 nm (I690 /I830 ) for sensitive detection of MMP-2 activity in vitro and in tumor cells. By virtue of ratiometric fluorescence imaging independently of probe's concentration, SPN-MMP-RGD can not only accurately report on MMP-2 levels regarding different tumor sizes, but also noninvasively delineate MMP-2-positive tiny gastric tumors metastasis in vivo. The authors' study reveals the potential of SPN-MMP-RGD for ratiometric fluorescence imaging of MMP-2 activity via combining two independent NIR fluorophores, which can be amenable for the design of other enzyme-activatable ratiometric NIR fluorescent probes for reliable in vivo imaging.