Utilizing the power of Cerenkov light with nanotechnology

Progressive Optimization of Lanthanide Nanoparticle Scintillators for Enhanced Triple-Activated Radioluminescence Imaging

Lanthanide nanoparticle (LnNP) scintillators exhibit huge potential in achieving radionuclide-activated luminescence (radioluminescence, RL). However, their structure-activity relationship remains largely unexplored. Herein, progressive optimization of LnNP scintillators is presented to unveil their structure-dependent RL property and enhance their RL output efficiency. Benefiting from the favorable host matrix and the luminescence-protective effect of core-shell engineering, NaGdF4 : 15 %Eu@NaLuF4 nanoparticle scintillators with tailored structures emerged as the top candidates. Living imaging experiments based on optimal LnNP scintillators validated the feasibility of laser-free continuous RL activated by clinical radiopharmaceuticals for tumor multiplex visualization. This research provides unprecedented insights into the rational design of LnNP scintillators, which would enable efficient energy conversion from Cerenkov luminescence, γ-radiation, and β-electrons into visible photon signals, thus establishing a robust nanotechnology-aided approach for tumor-directed radio-phototheranostics.

Superluminal Molecular and Nanomaterial Probes Based on Fast Ions or Electrons

This work reviews the progression of chemical analysis via Cherenkov emissions, i.e., Cherenkov Photometry and Cherenkov Emission Spectroscopy, from its introduction in the literature up to modern developments. In presenting the history of this field, we aim to consolidate the literature, both for reference and contextualization. We present an argument aiming to untangle why this corner of research has seen little progress while so many other directly related aspects of Cherenkov research have flourished, as well as speak to the progress of the field in recent years and prospective direction in years to come.

131I Induced In Vivo Proteolysis by Photoswitchable azoPROTAC Reinforces Internal Radiotherapy

Photopharmacology, incorporating photoswitches such as azobenezes into drugs, is an emerging therapeutic method to realize spatiotemporal control of pharmacological activity by light. However, most photoswitchable molecules are triggered by UV light with limited tissue penetration, which greatly restricts the in vivo application. Here, this study proves that 131I can trigger the trans-cis photoisomerization of a reported azobenezen incorporating PROTACs (azoPROTAC). With the presence of 50 µCi mL-1 131I, the azoPROTAC can effectively down-regulate BRD4 and c-Myc levels in 4T1 cells at a similar level as it does under light irradiation (405 nm, 60 mW cm-2). What's more, the degradation of BRD4 can further benefit the 131I-based radiotherapy. The in vivo experiment proves that intratumoral co-adminstration of 131I (300 µCi) and azoPROTC (25 mg kg-1) via hydrogel not only successfully induce protein degradation in 4T1 tumor bearing-mice but also efficiently inhibit tumor growth with enhanced radiotherapeutic effect and anti-tumor immunological effect. This is the first time that a radioisotope is successfully used as a trigger in photopharmacology in a mouse model. It believes that this study will benefit photopharmacology in deep tissue.

Acidity-activatable upconversion afterglow luminescence cocktail nanoparticles for ultrasensitive in vivo imaging

Activatable afterglow luminescence nanoprobes enabling switched "off-on" signals in response to biomarkers have recently emerged to achieve reduced unspecific signals and improved imaging fidelity. However, such nanoprobes always use a biomarker-interrupted energy transfer to obtain an activatable signal, which necessitates a strict distance requisition between a donor and an acceptor moiety (<10 nm) and hence induces low efficiency and non-feasibility. Herein, we report organic upconversion afterglow luminescence cocktail nanoparticles (ALCNs) that instead utilize acidity-manipulated singlet oxygen (1O2) transfer between a donor and an acceptor moiety with enlarged distance and thus possess more efficiency and flexibility to achieve an activatable afterglow signal. After in vitro validation of acidity-activated afterglow luminescence, ALCNs achieve in vivo imaging of 4T1-xenograft subcutaneous tumors in female mice and orthotopic liver tumors in male mice with a high signal-to-noise ratio (SNR). As a representative targeting trial, Bio-ALCNs with biotin modification prove the enhanced targeting ability, sensitivity, and specificity for pulmonary metastasis and subcutaneous tumor imaging via systemic administration of nanoparticles in female mice, which also implies the potential broad utility of ALCNs for tumor imaging with diverse design flexibility. Therefore, this study provides an innovative and general approach for activatable afterglow imaging with better imaging performance than fluorescence imaging.

Molecularly generated light and its biomedical applications

Molecularly generated light, referred to here as "molecular light", mainly includes bioluminescence, chemiluminescence, and Cerenkov luminescence. Molecular light possesses unique dual features of being both a molecule and a source of light. Its molecular nature enables it to be delivered as molecules to regions deep within the body, overcoming the limitations of natural sunlight and physically generated light sources like lasers and LEDs. Simultaneously, its light properties make it valuable for applications such as imaging, photodynamic therapy, photo-oxidative therapy, and photobiomodulation. In this review article, we provide an updated overview of the diverse applications of molecular light and discuss the strengths and weaknesses of molecular light across various domains. Lastly, we present forward-looking perspectives on the potential of molecular light in the realms of molecular imaging, photobiological mechanisms, therapeutic applications, and photobiomodulation. While some of these perspectives may be considered bold and contentious, our intent is to inspire further innovations in the field of molecular light applications.

Nanocrystals for Deep-Tissue In Vivo Luminescence Imaging in the Near-Infrared Region

In vivo imaging technologies have emerged as a powerful tool for both fundamental research and clinical practice. In particular, luminescence imaging in the tissue-transparent near-infrared (NIR, 700-1700 nm) region offers tremendous potential for visualizing biological architectures and pathophysiological events in living subjects with deep tissue penetration and high imaging contrast owing to the reduced light-tissue interactions of absorption, scattering, and autofluorescence. The distinctive quantum effects of nanocrystals have been harnessed to achieve exceptional photophysical properties, establishing them as a promising category of luminescent probes. In this comprehensive review, the interactions between light and biological tissues, as well as the advantages of NIR light for in vivo luminescence imaging, are initially elaborated. Subsequently, we focus on achieving deep tissue penetration and improved imaging contrast by optimizing the performance of nanocrystal fluorophores. The ingenious design strategies of NIR nanocrystal probes are discussed, along with their respective biomedical applications in versatile in vivo luminescence imaging modalities. Finally, thought-provoking reflections on the challenges and prospects for future clinical translation of nanocrystal-based in vivo luminescence imaging in the NIR region are wisely provided.

Free-electron crystals for enhanced X-ray radiation

Bremsstrahlung-the spontaneous emission of broadband radiation from free electrons that are deflected by atomic nuclei-contributes to the majority of X-rays emitted from X-ray tubes and used in applications ranging from medical imaging to semiconductor chip inspection. Here, we show that the bremsstrahlung intensity can be enhanced significantly-by more than three orders of magnitude-through shaping the electron wavefunction to periodically overlap with atoms in crystalline materials. Furthermore, we show how to shape the bremsstrahlung X-ray emission pattern into arbitrary angular emission profiles for purposes such as unidirectionality and multi-directionality. Importantly, we find that these enhancements and shaped emission profiles cannot be attributed solely to the spatial overlap between the electron probability distribution and the atomic centers, as predicted by the paraxial and non-recoil theory for free electron light emission. Our work highlights an unprecedented regime of free electron light emission where electron waveshaping provides multi-dimensional control over practical radiation processes like bremsstrahlung. Our results pave the way towards greater versatility in table-top X-ray sources and improved fundamental understanding of quantum electron-light interactions.

Current clinical applications of Cerenkov luminescence for intraoperative molecular imaging

BACKGROUND

Cerenkov luminescence imaging (CLI) is a new emerging technology that can be used for optical imaging of approved radiotracers, both in a preclinical, and even more recently, in a clinical context with rapid imaging times, low costs, and detection in real-time (Grootendorst et al. Clin Transl Imaging 4(5):353-66, 2016); Wang et al. Photonics 9(6):390, 2022). This brief review provides an overview of clinical applications of CLI with a focus on intraoperative margin assessment (IMA) to address shortcomings and provide insight for future work in this application.

METHODS

A literature review was performed using PubMed using the search words Cerenkov luminescence imaging (CLI), intraoperative margin assessment (IMA), and image-guided surgery. Articles were selected based on title, abstract, content, and application.

RESULTS

Original research was summarized to examine advantages and limitations of CLI compared to other modalities for IMA. The characteristics of Cerenkov luminescence (CL) are defined, and results from relevant clinical trials are discussed. Prospects of ongoing clinical trials are reviewed, along with technological advancements related to CLI.

CONCLUSION

CLI is a proven method for molecular imaging and shows feasibility for determining intraoperative margins if future work involves establishing quantitative approaches for attenuation and scattering, depth analysis, and radiation safety for CLI at a larger scale.

Self-Luminous Probe with One-Step Energy Conversion from Bioluminescence to NIR-IIb

Self-luminous probes with near-infrared (NIR) emission are powerful tools for deep-penetration and autofluorescence-free imaging, owing to the joint optimization of both excitation and emission. However, the limited emission wavelength and requirement for multistep energy transfer limit its potency. In this study, the concept of direct wavelength conversion is established from visible light (vis) to NIR-IIb using an exquisitely designed sensitizer-activator ion pair. The manipulation of the doping hosts enables a pair of energy levels between the sensitizer and activator. Based on this a class of broadband vis-responsive nanocrystals with intense NIR-II emission is prepared. The stability and quantum yield (up to 7.4%) of the nanocrystals are further enhanced by ZnS passivation via coherent epitaxial growth. By coupling luciferase, the self-luminous probe can convert bioluminescence to NIR-IIb luminescence (>1500 nm) through a one-step energy transfer. A maximum penetrable thickness of 6 mm is achieved in the porcine tissue model. Collectively, the distinctive photon-conversion performance of this probe offers the prospect of high-resolution labeling of deep-seated lesions.

Prodrug-based strategy with a two-in-one liposome for Cerenkov-induced photodynamic therapy and chemotherapy

Cerenkov radiation induced photodynamic therapy (CR-PDT) can tackle the tissue penetration limitation of traditional PDT. However, co-delivery of radionuclides and photosensitizer may cause continuous phototoxicity in normal tissues during the circulation. 5-aminolevulinic acid (ALA) which can intracellularly transform into photosensitive protoporphyrin IX (PpIX) is a cancer-selective photosensitizer with negligible side effect. However, the hydrophilic nature of ALA and the further conversion of PpIX to photoinactive Heme severely hinder the therapeutic benefits of ALA-based PDT. Herein, we developed an 89Zr-labeled, pH responsive ALA and artemisinin (ART) co-loaded liposome (89Zr-ALA-Liposome-ART) for highly selective cancer therapy. 89Zr can serve as the internal excitation source to self-activate PpIX for CR-PDT, and the photoinactive Heme can activate the chemotherapeutic effect of ART. The 89Zr-ALA-Liposome-ART exhibited excellent tumor inhibition capability in subcutaneous 4T1-tumor-bearing Balb/c mice via CR-PDT and chemotherapy. Combined with anti-PD-L1, the 89Zr-ALA-Liposome-ART elicited strong antitumor immunity to against tumor recurrence.

Cerenkov radiation-mediated in situ activation of silicon nanocrystals for NIR optical imaging

Cerenkov radiation from radiopharmaceuticals (18F-FDG) serves as an internal light source to excite UV-responsive silicon nanocrystals for near-infrared luminescence imaging that offers deeper tissue penetration and high signal-to-noise ratio.

Beyond External Light: On-Spot Light Generation or Light Delivery for Highly Penetrated Photodynamic Therapy

External light sources, such as lasers, light emitting diodes (LEDs) and lamps, are widely applied in photodynamic therapy (PDT); however, their use is severely limited by the nature of shallow tissue penetration depth. The recent exploration of light delivery or local generation on tumor sites has attracted much attention, owing to the fact that these systems are significantly endowed with high tissue penetration. In this review, we briefly introduced the principle of "on-spot light generation or delivery systems" in PDT. These systems are divided into different categories: (1) implantable luminescence, (2) mechanoluminescence, (3) electrochemiluminescence, (4) Cerenkov luminescence, (5) chemiluminescence, and (6) bioluminescence. Finally, their applications, advantages, and disadvantages in PDT will be appropriately summarized and further discussed in detail. We believe that this review will provide general guidance for the further design of light generation or delivery systems and clinical studies for PDT-mediated cancer treatments with unparalleled merits.

Targeted, Molecular Europium(III) Probes Enable Luminescence-Guided Surgery and 1 Photon Post-Surgical Luminescence Microscopy of Solid Tumors

Discrete luminescent lanthanide complexes represent a potential alternative to organic chromophores due to their tunability of optical properties, insensitivity to photobleaching, and large pseudo-Stokes shifts. Previously, we demonstrated that the lack of depth penetration of UV excitation required to sensitize discrete terbium and europium complexes can be overcome using Cherenkov radiation emitted by clinically employed radioisotopes in situ. Here, we show that the second-generation europium complexes [Eu(III)(pcta-PEPA2)] and [Eu(III)(tacn-pic-PEPA2)] (Φ = 57% and 76%, respectively) lower the limit of detection (LoD) to 1 nmol in the presence of 10 μCi of Cherenkov emitting isotopes, 18F and 68Ga. Bifunctionalization provides access to cysteine-linked peptide conjugates with comparable brightness and LoD. The conjugate, [Eu(tacn-(pic-PSMA)-PEPA2)], displays high binding affinity to prostate-specific membrane antigen (PSMA)-expressing PC-3 prostate cancer cells in vitro and can be visualized in the membrane-bound state using confocal microscopy. Biodistribution studies with the [86Y][Y(III)(tacn-(pic-PSMA)-PEPA2)] analogue in a mouse xenograft model were employed to study pharmacokinetics. Systemic administration of the targeted Cherenkov emitter, [68Ga][Ga(III)(PSMA-617)], followed by intratumoral injection or topical application of 20 or 10 nmol [Eu(III)(tacn-(pic-PSMA)-PEPA2)], respectively, in live mice resulted in statistically significant signal enhancement using conventional small animal imaging (620 nm bandpass filter). Optical imaging informed successful tumor resection. Ex vivo imaging of the fixed tumor tissue with 1 and 2 photon excitation further reveals the accumulation of the administered Eu(III) complex in target tissues. This work represents a significant step toward the application of luminescent lanthanide complexes for optical imaging in a clinical setting.

Interfacial Cherenkov radiation from ultralow-energy electrons

Cherenkov radiation occurs only when a charged particle moves with a velocity exceeding the phase velocity of light in that matter. This radiation mechanism creates directional light emission at a wide range of frequencies and could facilitate the development of on-chip light sources except for the hard-to-satisfy requirement for high-energy particles. Creating Cherenkov radiation from low-energy electrons that has no momentum mismatch with light in free space is still a long-standing challenge. Here, we report a mechanism to overcome this challenge by exploiting a combined effect of interfacial Cherenkov radiation and umklapp scattering, namely the constructive interference of light emission from sequential particle-interface interactions with specially designed (umklapp) momentum-shifts. We find that this combined effect is able to create the interfacial Cherenkov radiation from ultralow-energy electrons, with kinetic energies down to the electron-volt scale. Due to the umklapp scattering for the excited high-momentum Bloch modes, the resulting interfacial Cherenkov radiation is uniquely featured with spatially separated apexes for its wave cone and group cone.

Amplification of Cerenkov luminescence using semiconducting polymers for cancer theranostics

The therapeutic efficacy of photodynamic therapy is limited by the ability of light to penetrate tissues. Due to this limitation, Cerenkov luminescence (CL) from radionuclides has recently been proposed as an alternative light source in a strategy referred to as Cerenkov radiation induced therapy (CRIT). Semiconducting polymer nanoparticles (SPNs) have ideal optical properties, such as large absorption cross-sections and broad absorbance, which can be utilized to harness the relatively weak CL produced by radionuclides. SPNs can be doped with photosensitizers and have nearly 100% energy transfer efficiency by multiple energy transfer mechanisms. Herein, we investigated an optimized photosensitizer doped SPN as a nanosystem to harness and amplify CL for cancer theranostics. We found that semiconducting polymers significantly amplified CL energy transfer efficiency. Bimodal PET and optical imaging studies showed high tumor uptake and retention of the optimized SPNs when administered intravenously or intratumorally. Lastly, we found that photosensitizer doped SPNs have excellent potential as a cancer theranostics nanosystem in an in vivo tumor therapy study. Our study shows that SPNs are ideally suited to harness and amplify CL for cancer theranostics, which may provide a significant advancement for CRIT that are unabated by tissue penetration limits.

Free-electron Brewster-transition radiation

We reveal a mechanism to enhance particle-matter interactions by exploiting the pseudo-Brewster effect of gain materials, presenting an enhancement of at least four orders of magnitude for light emission. This mechanism is enabled by the emergence of an unprecedented phase diagram that maps all phenomena of free-electron transition radiation into three distinct phases in a gain-thickness parameter space, namely, the conventional, intermediate, and Brewster phases, when an electron penetrates a dielectric slab with a modest gain and a finite thickness. Essentially, our revealed mechanism corresponds to the free-electron transition radiation in the Brewster phase, which also features ultrahigh directionality, always at the Brewster angle, regardless of the electron velocity. Counterintuitively, we find that the intensity of this free-electron Brewster-transition radiation is insensitive to the Fabry-Pérot resonance condition and, thus, the variation of slab thickness, and moreover, a weaker gain could lead to a stronger enhancement for light emission.

Aggregation-Induced Emission Photosensitizer/Bacteria Biohybrids Enhance Cerenkov Radiation-Induced Photodynamic Therapy by Activating Anti-Tumor Immunity for Synergistic Tumor Treatment

Cerenkov radiation-induced photodynamic therapy (CR-PDT) gets rid of the limited tissue penetration depth of the external light source and provides a feasible scheme for the PDT excited by the internal light. However, due to the low luminescence intensity of Cerenkov radiation, CR-PDT alone cannot effectively inhibit tumor growth, curbing the potential clinical translation of CR-PDT. Herein, we reported an AIE-PS/bacteria biohybrid (EcN@TTVP) composed of Escherichia coli Nissle 1917 (EcN) loaded with aggregation-induced emission photosensitizer (AIE-PS) termed TTVP, which enhanced CR-PDT by activating anti-tumor immunity for synergistic tumor treatment. The preferential tumor-colonized EcN@TTVP and radiopharmaceutical ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) were administered sequentially to enable them to co-enrich in the tumor site, thereby triggering CR-PDT and promoting immunogenic tumor cell death. Most importantly, EcN acting as immunoadjuvants enhanced the maturation of dendritic cells (DCs) and priming of cytotoxic T cells (CTLs). Therefore, under the synergistic treatment of CR-PDT and immunotherapy, AIE-PS/bacteria biohybrids resulted in either efficient tumor remission or a survival prolongation in tumor-bearing mice, which presented significant advantages over single CR-PDT. Remarkably, no obvious toxic effects were observed during the treatment. In this study, we proposed a synergistic therapeutic strategy based on EcN@TTVP for combined CR-PDT and immunotherapy against tumors. Moreover, this strategy may have great potential in clinical translation and provide references for deep-seated tumor treatment. STATEMENT OF SIGNIFICANCE: PDT is restricted due to the shallow penetration depth of light into tumor tissues. Using CR as the excitation light source for PDT can overcome the aforementioned issue and greatly expand the application of PDT. However, the low efficacy of single CR-PDT limits further its applications. Therefore, the design and development of feasible strategies to improve the efficacy of CR-PDT are of immediate importance. Introducing probiotics to our study can be used not only as tumor-targeting carriers of photosensitizers but also as immunoadjuvants. Under co-stimulation by immunogenic tumor cell death triggered by CR-PDT and probiotics acting as immunoadjuvants, anti-tumor immune responses were effectively activated, thus remarkably enhancing the efficacy of CR-PDT.

Mid-infrared analogue polaritonic reversed Cherenkov radiation in natural anisotropic crystals

Cherenkov radiation (CR) excited by fast charges can serve as on-chip light sources with a nanoscale footprint and broad frequency range. The reversed CR, which usually occurs in media with the negative refractive index or negative group-velocity dispersion, is highly desired because it can effectively separate the radiated light from fast charges thanks to the obtuse radiation angle. However, reversed CR at the mid-infrared remains challenging due to the significant loss of conventional artificial structures. Here we observe mid-infrared analogue polaritonic reversed CR in a natural van der Waals (vdW) material (i.e., α-MoO₃), whose hyperbolic phonon polaritons exhibit negative group velocity. Further, the real-space image results of analogue polaritonic reversed CR indicate that the radiation distributions and angles are closely related to the in-plane isofrequency contours of α-MoO₃, which can be further tuned in the heterostructures based on α-MoO₃. This work demonstrates that natural vdW heterostructures can be used as a promising platform of reversed CR to design on-chip mid-infrared nano-light sources.

Bulk-Plasmon-Mediated Free-Electron Radiation Beyond the Conventional Formation Time

Free-electron radiation is a fundamental photon emission process that is induced by fast-moving electrons interacting with optical media. Historically, it has been understood that, just like any other photon emission process, free-electron radiation must be constrained within a finite time interval known as the "formation time," whose concept is applicable to both Cherenkov radiation and transition radiation, the two basic mechanisms describing radiation from a bulk medium and from an interface, respectively. Here, this work reveals an alternative mechanism of free-electron radiation far beyond the previously defined formation time. It occurs when a fast electron crosses the interface between vacuum and a plasmonic medium supporting bulk plasmons. While emitted continuously from the crossing point on the interface-thus consistent with the features of transition radiation-the extra radiation beyond the conventional formation time is supported by a long tail of bulk plasmons following the electron's trajectory deep into the plasmonic medium. Such a plasmonic tail mixes surface and bulk effects, and provides a sustained channel for electron-interface interaction. These results also settle the historical debate in Ferrell radiation, regarding whether it is a surface or bulk effect, from transition radiation or plasmonic oscillation.

2D Material Infrared Photonics and Plasmonics

Two-dimensional (2D) materials including graphene, transition metal dichalcogenides, black phosphorus, MXenes, and semimetals have attracted extensive and widespread interest over the past years for their many intriguing properties and phenomena, underlying physics, and great potential for applications. The vast library of 2D materials and their heterostructures provides a diverse range of electrical, photonic, mechanical, and chemical properties with boundless opportunities for photonics and plasmonic devices. The infrared (IR) regime, with wavelengths across 0.78 μm to 1000 μm, has particular technological significance in industrial, military, commercial, and medical settings while facing challenges especially in the limit of materials. Here, we present a comprehensive review of the varied approaches taken to leverage the properties of the 2D materials for IR applications in photodetection and sensing, light emission and modulation, surface plasmon and phonon polaritons, non-linear optics, and Smith-Purcell radiation, among others. The strategies examined include the growth and processing of 2D materials, the use of various 2D materials like semiconductors, semimetals, Weyl-semimetals and 2D heterostructures or mixed-dimensional hybrid structures, and the engineering of light-matter interactions through nanophotonics, metasurfaces, and 2D polaritons. Finally, we give an outlook on the challenges in realizing high-performance and ambient-stable devices and the prospects for future research and large-scale commercial applications.

Nanoparticles with ultrasound-induced afterglow luminescence for tumour-specific theranostics

Molecular imaging via afterglow luminescence minimizes tissue autofluorescence and increases the signal-to-noise ratio. However, the induction of afterglow requires the prior irradiation of light, which is attenuated by scattering and absorption in tissue. Here we report the development of organic nanoparticles producing ultrasound-induced afterglow, and their proof-of-concept application in cancer immunotheranostics. The 'sonoafterglow' nanoparticles comprise a sonosensitizer acting as an initiator to produce singlet oxygen and subsequently activate a substrate for the emission of afterglow luminescence, which is brighter and detectable at larger tissue depths (4 cm) than previously reported light-induced afterglow. We formulated sonoafterglow nanoparticles containing a singlet-oxygen-cleavable prodrug for the immune-response modifier imiquimod that specifically turn on in the presence of the inflammation biomarker peroxynitrite, which is overproduced by tumour-associated M1-like macrophages. Systemic delivery of the nanoparticles allowed for sonoafterglow-guided treatment of mice bearing subcutaneous breast cancer tumours. The high sensitivity and depth of molecular sonoafterglow imaging may offer advantages for the real-time in vivo monitoring of physiopathological processes.

Highly Bright Near-Infrared Chemiluminescent Probes for Cancer Imaging and Laparotomy

Near-infrared (NIR) chemiluminescence imaging holds potential for sensitive imaging of cancer due to its low background; however, few NIR chemiluminophores are available, which share the drawback of low chemiluminescence quantum yields (Φ_CL ). Herein, we report the synthesis of NIR chemiluminophores for cancer imaging and laparotomy. Molecular engineering of the electron-withdrawing group at the para-position of the phenol-dioxetane leads to a highly bright NIR chemiluminophore (DPT), showing the Φ_CL (4.6×10^-2  Einstein mol^-1 ) that is 3 to 5-fold higher than existing NIR chemiluminophores. By caging the phenol group of DPT with a cathepsin B (CatB) responsive moiety, an activatable chemiluminescence probe (DPT_CB ) is developed for real-time turn-on detection of deeply buried tumor tissues in living mice. Due to its high brightness, DPT_CB permits accurate chemiluminescence-guided laparotomy.

Practical Guidance for Developing Small-Molecule Optical Probes for In Vivo Imaging

The WMIS Education Committee (2019-2022) reached a consensus that white papers on molecular imaging could be beneficial for practitioners of molecular imaging at their early career stages and other scientists who are interested in molecular imaging. With this consensus, the committee plans to publish a series of white papers on topics related to the daily practice of molecular imaging. In this white paper, we aim to provide practical guidance that could be helpful for optical molecular imaging, particularly for small molecule probe development and validation in vitro and in vivo. The focus of this paper is preclinical animal studies with small-molecule optical probes. Near-infrared fluorescence imaging, bioluminescence imaging, chemiluminescence imaging, image-guided surgery, and Cerenkov luminescence imaging are discussed in this white paper.

Theranostics through Utilizing Cherenkov Radiation of Radioisotope Zr-89 with a Nanocomposite Combination of TiO2 and MnO2

Cherenkov radiation (CR) derived from the decay of diagnostic and therapeutic radionuclides is currently being studied by the scientific community to determine if these emissions can be harnessed for cancer detection and therapy. While Cherenkov luminescence imaging (CLI) has been studied in the preclinical and clinical settings, Cherenkov radiation-induced cancer therapy (CRICT) is a relatively new area of research that harnesses the emitted photons to kill cancer cells through free radical generation and DNA damage. Nanoparticles seem well suited for developing a theranostic platform that would allow researchers to visualize therapy delivery and also generate the reactive oxygen species necessary to kill cancer cells. Herein, we report the preparation of an ⁸⁹Zr-TiO₂-MnO₂ nanocomposite that incorporates transferrin onto the nanoparticle surface to enhance cancer cell growth inhibition. The incorporation of the positron emission tomography (PET) radioisotope ⁸⁹Zr (half-life: 3.3 days) allowed for the detection of the nanoparticle using PET and for the creation of Cherenkov emissions that interacted with the nanoparticle surface to generate free radicals for therapy delivery. After preparation, these systems were observed to be stable in various media and provided excellent tumor growth control after being intratumorally injected into mice bearing CT-26 tumors. These results demonstrate that a therapeutically efficient CRICT platform can be generated using commercially available and affordable materials.

Radiances of Cerenkov-Emitting Isotopes on the IVIS

Cerenkov (or Cherenkov) luminescence occurs when charged particles exceed the phase velocity of a given medium. Cerenkov has gained interest in preclinical space as well as in clinical trials for optical visualization of numerous radionuclides. However, Cerenkov intensity has to be inferred from alternative databases with energy emission spectra, or theoretical fluence estimates. Here we present the largest experimental dataset of Cerenkov emitting isotopes recorded using the IVIS optical imaging system. We report Cerenkov measurements spanning orders of magnitude normalized to the activity concentration for 21 Cerenkov emitting isotopes, covering electron, alpha, beta minus, and positron emissions. Isotopes measured include Carbon-11, Fluorine-18, Phosphorous-32, Scandium-47, Copper-64, Copper-67, Gallium-68, Arsenic-72, Bromine-76, Yttrium-86, Zirconium-89, Yttrium-90, Iodine-124, Iodine-131, Cerium-134, Lutetium-177, Lead-203, Lead-212, Radium-223, Actinium-225, and Thorium-227. We hope this updating resource will serve as a rank ordering for comparing isotopes for Cerenkov luminescence in the visible window and serve as a rule of thumb for comparing Cerenkov intensities in vitro and in vivo.

Methods

All Cerenkov emitting radionuclides were either produced at Memorial Sloan Kettering Cancer Center (Carbon-11, ¹¹ C; Fluorine-18, ¹⁸ F; Iodine-124, ¹²⁴ I), from commercial sources such as Perkin Elmer (Phosphorous-32, ³² P; Yttrium-90, ⁹⁰ Y), Bayer (Radium-223, ²²³ Ra, Xofigo), 3D-Imaging (Zirconium-89, ⁸⁹ Zr), Nuclear Diagnostic Products (Iodine-131, ¹³¹ I), or from academic collaborators at Washington University at St. Louis (Copper-64, ⁶⁴ Cu), University of Wisconsin (Bromine-76, ⁷⁶ Br), MD Anderson Cancer Center (Yttrium-86, ⁸⁶ Y), Brookhaven National Laboratory (Arsenic-72, ⁷² As; Thorium-227, ²²⁷ Th), or Oak Ridge National Laboratory (Cerium-134, ¹³⁴ Ce, Actinium-225, ²²⁵ Ac), and Viewpoint Molecular Targeting (Lead-203, ²⁰³ Pb; Lead 212, ²¹² Pb). All isotopes were diluted in triplicate on a black bottomed corning 96 well plate to several activity concentrations ranging from 0.1-250 μCi in 100-200 μL of Phosphate Buffered Saline. Cerenkov imaging was acquired on a single Perkin-Elmer Spectrum In-Vivo Imaging System (IVIS) at field of view c with exposures ranging up to 15 minutes or lower provided no part of the image intensity was saturated, or that the activity significantly changed during the exposure. Experimental radiances on the IVIS were calculated from regions of interest drown over each 96 well, and then normalized for the activity present in the well, and the volume the isotope was diluted into.

Chlorin e6-loaded goat milk-derived extracellular vesicles for Cerenkov luminescence-induced photodynamic therapy

PURPOSE

Photodynamic therapy (PDT) is a promising cancer treatment strategy with rapid progress in preclinical and clinical settings. However, the limitations in penetration of external light and precise delivery of photosensitizers hamper its clinical translation. As such, the internal light source such as Cerenkov luminescence (CL) from decaying radioisotopes offers new opportunities. Herein, we show that goat milk-derived extracellular vesicles (GEV) can act as a carrier to deliver photosensitizer Chlorin e6 (Ce6) and tumor-avid 18F-FDG can activate CL-induced PDT for precision cancer theranostics.

METHODS

GEV was isolated via differential ultracentrifugation of commercial goat milk and photosensitizer Ce6 was loaded by co-incubation to obtain Ce6@GEV. Tumor uptake of Ce6@GEV was examined using confocal microscopy and flow cytometry. To demonstrate the ability of 18F-FDG to activate photodynamic effects against cancer cells, apoptosis rates were measured using flow cytometry, and the production of 1O2 was measured by reactive oxygen species (ROS) monitoring kit. Moreover, we used the IVIS device to detect Cherenkov radiation and Cerenkov radiation energy transfer (CRET). For animal experiments, a small-animal IVIS imaging system was used to visualize the accumulation of the GEV drug delivery system in tumors. PET/CT and CL images of the tumor site were performed at 0.5, 1, and 2 h. For in vivo antitumor therapy, changes of tumor volume, survival time, and body weight in six groups of tumor-bearing mice were monitored. Furthermore, the blood sample and organs of interest (heart, liver, spleen, lungs, kidneys, and tumor) were collected for hematological analysis, immunohistochemistry, and H&E staining.

RESULTS

Confocal microscopy of 4T1 cells incubated with Ce6@GEV for 4 h revealed strong red fluorescence signals in the cytoplasm, which demonstrated that Ce6 loaded in GEV could be efficiently delivered into tumor cells. When Ce6@GEV and 18F-FDG co-existed incubated with 4T1 cells, the cell viability plummeted from more than 88.02 ± 1.30% to 23.79 ± 1.59%, indicating excellent CL-induced PDT effects. In vivo fluorescence images showed a peak tumor/liver ratio of 1.36 ± 0.09 at 24 h after Ce6@GEV injection. For in vivo antitumor therapy, Ce6@GEV + 18F-FDG group had the best tumor inhibition rate (58.02%) compared with the other groups, with the longest survival rate (35 days, 40%). During the whole treatment process, neither blood biochemical analysis nor histological observation revealed vital organ damage, suggesting the biosafety of this treatment strategy.

CONCLUSIONS

The simultaneous accumulation of 18F-FDG and Ce6 in tumor tissues is expected to overcome the deficiency of traditional PDT. This strategy has the potential to extend PDT to a variety of tumors, including metastases, using targeted radiotracers to provide internal excitation of light-responsive therapeutics. We expect that our method will play a critical role in precision treatment of deep solid tumors.

Advanced techniques for performing photodynamic therapy in deep-seated tissues

Photodynamic therapy (PDT) is a promising localized cancer treatment modality. It has been used successfully to treat a range of dermatological conditions with comparable efficacy to conventional treatments. However, some drawbacks limit the clinical utility of PDT in treating deep-seated tumors. Notably, the penetration limitation of UV and visible light, commonly applied to activate photosensitizers, makes PDT incompetent in treating deep-seated tumors. Development in light delivery technologies, especially fiber optics, led to improved clinical strategies for accessing deep tissues for irradiation. However, PDT efficacy issues remained partly due to light penetration limitations. In this review, we first summarized the current PDT applications for deep-seated tumor treatment. Then, the most recent progress in advanced techniques to overcome the light penetration limitation in PDT, including using functional nanomaterials that can either self-illuminate or be activated by near-infrared (NIR) light and X-rays as transducers, and implantable light delivery devices were discussed. Finally, current challenges and future opportunities of these technologies were discussed, which we hope may inspire the development of more effective techniques to enhance PDT efficacy against deep-seated tumors.

Cancer therapy by antibody-targeted Cerenkov light and metabolism-selective photosensitization

Photodynamic therapy (PDT) is an effective cancer treatment option, but it suffers from penetration limit of light, making it available only for superficial and endoscopically accessible cancers. Recently, there have been reports that Cerenkov luminescence originated from radioisotopes can be utilized as an excitation source for PDT without external light illumination. Here, cancer-selective agents, i.e., (1) clinically available 5-aminolevulinic acid (5-ALA), which promotes cancer metabolism-specific accumulation of protoporphyrin IX (PpIX), and (2) ⁶⁴Cu-DOTA-trastuzumab, which has HER2-expressing cancer selective uptake, are separately applied as a photosensitizer and an in situ radiator, respectively, to potentiate tumor-specific Cerenkov luminescence energy transfer (CLET) from ⁶⁴Cu to PpIX for high-precision PDT of cancer. It is shown that the combinational administration and tumor colocalization of 5-ALA and ⁶⁴Cu-DOTA-trastuzumab exert significant in vitro cytotoxicity (cell viability <9%) as well as in vivo antitumor effects (tumor volume ratio of 0.50 on 14 days post-injection) on HER2-expressing breast and gastric cancer models. This study proves that high-precision treatment regimen using dual-targeted CLET-based PDT is feasible for HER2-expressing cancers. Furthermore, the results offer great potential for clinical translation to the dual-targeted CLET-based PDT because the treatment regimen uses components, 5-ALA and ⁶⁴Cu-DOTA-trastuzumab, which are already in clinical uses.

Application of Cherenkov radiation in tumor imaging and treatment

Cherenkov radiation (CR) is the characteristic blue glow that is generated during radiotherapy or radioisotope decay. Its distribution and intensity naturally reflect the actual dose and field of radiotherapy and the location of radioisotope imaging agents in vivo. Therefore, CR can represent a potential in situ light source for radiotherapy monitoring and radioisotope-based tumor imaging. When used in combination with new imaging techniques, molecular probes or nanomedicine, CR imaging exhibits unique advantages (accuracy, low cost, convenience and fast) in tumor radiotherapy monitoring and imaging. Furthermore, photosensitive nanomaterials can be used for CR photodynamic therapy, providing new approaches for integrating tumor imaging and treatment. Here the authors review the latest developments in the use of CR in tumor research and discuss current challenges and new directions for future studies.

Activation of nano-photosensitizers by Y-90 microspheres to enhance oxidative stress and cell death in hepatocellular carcinoma

While radioembolization with yttrium-90 (Y-90) microspheres is a promising treatment for hepatocellular carcinoma (HCC), lower responses in advanced and high-grade tumors present an urgent need to augment its tumoricidal efficacy. The purpose of this study was to determine whether clinically used Y-90 microspheres activate light-responsive nano-photosensitizers to enhance hepatocellular carcinoma (HCC) cell oxidative stress and cytotoxicity over Y-90 alone in vitro. Singlet oxygen and hydroxyl radical production was enhanced when Y-90 microspheres were in the presence of several nano-photosensitizers compared to either alone in cell-free conditions. Both the SNU-387 and HepG2 human HCC cells demonstrated significantly lower viability when treated with low activity Y-90 microspheres (0.1-0.2 MBq/0.2 mL) and a nano-photosensitizer consisting of both titanium dioxide (TiO₂) and titanocene (TC) labelled with transferrin (TiO₂-Tf-TC) compared to Y-90 microspheres alone or untreated cells. Cellular oxidative stress and cell death demonstrated a linear dependence on Y-90 at higher activities (up to 0.75 MBq/0.2 mL), but was significantly more accentuated in the presence of increasing TiO₂-Tf-TC concentrations in the poorly differentiated SNU-387 HCC cell line (p < 0.0001 and p = 0.0002 respectively) but not the well-differentiated HepG2 cell line. Addition of TiO₂-Tf-TC to normal human hepatocyte THLE-2 cells did not increase cellular oxidative stress or cell death in the presence of Y-90. The enhanced tumoricidal activity of nano-photosensitizers with Y-90 microspheres is a potentially promising adjunctive treatment strategy for certain patient subsets. Applications in clinically relevant in vivo HCC models are underway.

Photoactivation of Chemotherapeutic Agents with Cerenkov Radiation for Chemo-Photodynamic Therapy

Cerenkov radiation (CR) can be used as an internal light source in photodynamic therapy (PDT). Methotrexate (MTX) and paclitaxel (PTX), chemotherapeutic agents with wide clinical use, have characteristics of photosensitizers (PS). This work evaluates the possibility of photoexciting MTX and PTX with CR from ¹⁸F-FDG to produce reactive oxygen species (ROS) capable of inducing cytotoxicity. PTX did not produce ROS when excited by CR from ¹⁸F-FDG, so it is not useful for PDT. In contrast, MTX produces ¹O₂ (detected by ABMA) in amounts sufficient to significantly decrease the viability of the T47D cells. MTX solutions of 100 nM combined with ¹⁸F-FDG activities of 50 (1.85 MBq) and 100 μCi (3.7 MBq) produced a significant decrease in cell viability to (50.09 ± 4.95) and (47.96 ± 11.19)%, respectively, compared to MTX (66.29 ± 5.92)% and ¹⁸F-FDG (91.35 ± 7.00% for 50 μCi and 99.43 ± 11.03% for 100 μCi) alone. Using the CellRox Green reagent, the intracellular production of ROS was confirmed as the main mechanism of cytotoxicity. The results confirm the therapeutic potential of photoactivation with CR and the synergy of the combined treatment with chemotherapy + photodynamic therapy (CMT + PDT). The combination of chemotherapeutic agents with PS properties and β-emitting radiopharmaceuticals, previously approved for clinical use, will make it possible to shorten the evaluation stages of new CMT + PDT systems.

Dual-Mode Tumor Imaging Using Probes That Are Responsive to Hypoxia-Induced Pathological Conditions

Hypoxia in solid tumors is associated with poor prognosis, increased aggressiveness, and strong resistance to therapeutics, making accurate monitoring of hypoxia important. Several imaging modalities have been used to study hypoxia, but each modality has inherent limitations. The use of a second modality can compensate for the limitations and validate the results of any single imaging modality. In this review, we describe dual-mode imaging systems for the detection of hypoxia that have been reported since the start of the 21st century. First, we provide a brief overview of the hallmarks of hypoxia used for imaging and the imaging modalities used to detect hypoxia, including optical imaging, ultrasound imaging, photoacoustic imaging, single-photon emission tomography, X-ray computed tomography, positron emission tomography, Cerenkov radiation energy transfer imaging, magnetic resonance imaging, electron paramagnetic resonance imaging, magnetic particle imaging, and surface-enhanced Raman spectroscopy, and mass spectrometric imaging. These overviews are followed by examples of hypoxia-relevant imaging using a mixture of probes for complementary single-mode imaging techniques. Then, we describe dual-mode molecular switches that are responsive in multiple imaging modalities to at least one hypoxia-induced pathological change. Finally, we offer future perspectives toward dual-mode imaging of hypoxia and hypoxia-induced pathophysiological changes in tumor microenvironments.

Generation of Airy beams in Smith-Purcell radiation

The metasurface has recently emerged as a powerful platform to engineer wave packets of free electron radiation at the mesoscale. Here, we propose that Airy beams can be generated when moving electrons interact with bianisotropic metasurfaces. By changing the intrinsic coupling strength, full amplitude coverage and 0-to-π phase switching of Smith-Purcell radiation can be realized from the meta-atoms. This unusual property shifts the wave front of the assembled Airy beam toward a parabolic trajectory. Experimental implementation displays that evanescent fields bounded at slotted waveguides can be coupled into Airy beams via Smith-Purcell radiation from a designed bianisotropic metasurface. Our method and design strategy offer an alternative route toward free-electron lasers with diffraction-free, self-accelerating, and self-healing beam properties.

Cherenkov Luminescence in Tumor Diagnosis and Treatment: A Review

Malignant tumors rank as a leading cause of death worldwide. Accurate diagnosis and advanced treatment options are crucial to win battle against tumors. In recent years, Cherenkov luminescence (CL) has shown its technical advantages and clinical transformation potential in many important fields, particularly in tumor diagnosis and treatment, such as tumor detection in vivo, surgical navigation, radiotherapy, photodynamic therapy, and the evaluation of therapeutic effect. In this review, we summarize the advances in CL for tumor diagnosis and treatment. We first describe the physical principles of CL and discuss the imaging techniques used in tumor diagnosis, including CL imaging, CL endoscope, and CL tomography. Then we present a broad overview of the current status of surgical resection, radiotherapy, photodynamic therapy, and tumor microenvironment monitoring using CL. Finally, we shed light on the challenges and possible solutions for tumor diagnosis and therapy using CL.

Research progress and applications of silica-based aerogels - a bibliometric analysis

Silica aerogels are three-dimensional porous materials that were initially produced in 1931. During the past nearly 90 years, silica aerogels have been applied extensively in many fields. In order to grasp the progress of silica-based aerogels, we utilize bibliometrics and visualization methods to analyze the research hotspots and the application of this important field. Firstly, we collect all the publications on silica-based aerogels and then analyze their research trends and performances by a bibliometric method regarding publication year/citation, country/institute, journals, and keywords. Following this, the major research hotspots of this area with a focus on synthesis, mechanical property regulation, and the applications for thermal insulation, adsorption, and Cherenkov detector radiators are identified and reviewed. Finally, current challenges and directions in the future regarding silica-based aerogels are also proposed.

Silica aerogels are three-dimensional porous materials that were initially produced in 1931. During the past nearly 90 years, silica aerogels have been applied extensively in many fields.

Prospective testing of clinical Cerenkov luminescence imaging against standard-of-care nuclear imaging for tumour location

In oncology, the feasibility of Cerenkov luminescence imaging (CLI) has been assessed by imaging superficial lymph nodes in a few patients undergoing diagnostic ¹⁸F-fluoro-2-deoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT). However, the weak luminescence signal requires the removal of ambient light. Here we report the development of a clinical CLI fiberscope with a lightproof enclosure, and the clinical testing of the setup using five different radiotracers. In an observational prospective trial (ClinicalTrials.gov identifier NCT03484884 ) involving 96 patients with existing or suspected tumours, scheduled for routine clinical FDG PET or ¹³¹I therapy, the level of agreement of CLI with standard-of-care imaging (PET or planar single-photon emission CT) for tumour location was 'acceptable' or higher (≥3 in the 1-5 Likert scale) for 90% of the patients. CLI correlated with the concentration of radioactive activity, and captured therapeutically relevant information from patients undergoing targeted radiotherapy or receiving the alpha emitter ²²³Ra, which cannot be feasibly imaged clinically. CLI could supplement radiological scans, especially when scanner capacity is limited.

Minimizing adverse effects of Cerenkov radiation induced photodynamic therapy with transformable photosensitizer-loaded nanovesicles

Background

Photodynamic therapy (PDT) is a promising antitumor strategy with fewer adverse effects and higher selectivity than conventional therapies. Recently, a series of reports have suggested that PDT induced by Cerenkov radiation (CR) (CR-PDT) has deeper tissue penetration than traditional PDT; however, the strategy of coupling radionuclides with photosensitizers may cause severe side effects.

Methods

We designed tumor-targeting nanoparticles (¹³¹I-EM@ALA) by loading 5-aminolevulinic acid (ALA) into an ¹³¹I-labeled exosome mimetic (EM) to achieve combined antitumor therapy. In addition to playing a radiotherapeutic role, ¹³¹I served as an internal light source for the Cerenkov radiation (CR).

Results

The drug-loaded nanoparticles effectively targeted tumors as confirmed by confocal imaging, flow cytometry, and small animal fluorescence imaging. In vitro and in vivo experiments demonstrated that ¹³¹I-EM@ALA produced a promising antitumor effect through the synergy of radiotherapy and CR-PDT. The nanoparticles killed tumor cells by inducing DNA damage and activating the lysosome-mitochondrial pathways. No obvious abnormalities in the hematology analyses, blood biochemistry, or histological examinations were observed during the treatment.

Conclusions

We successfully engineered a nanocarrier coloaded with the radionuclide ¹³¹I and a photosensitizer precursor for combined radiotherapy and PDT for the treatment of breast cancer.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01401-0.

Transforming Nuclear Medicine with Nanoradiopharmaceuticals

Nuclear medicine is expected to make major advances in cancer diagnosis and therapy; tumor-targeted radiopharmaceuticals preferentially eradicate tumors while causing minimal damage to healthy tissues. The current scope of nuclear medicine can be significantly expanded by integration with nanomedicine, which utilizes nanoparticles for cancer diagnosis and therapy by capitalizing on the increased surface area-to-volume ratio, the passive/active targeting ability and high loading capacity, the greater interaction cross section with biological tissues, the rich surface properties of nanomaterials, the facile decoration of nanomaterials with a plethora of functionalities, and the potential for multiplexing several functionalities within one construct. This review provides a comprehensive discussion of nuclear nanomedicine using tumor-targeted nanoparticles for cancer radiation therapy with either pre-embedded radionuclides or nonradioactive materials which can be extrinsically triggered using various external nuclear particle sources to produce in situ radioactivity. In addition, it describes the prospect of combining nuclear nanomedicine with other modalities to enable synergistically enhanced combination therapies. The review also discusses advances in the fabrication of radionuclides as well as describes laser ablation technologies for producing nanoradiopharmaceuticals, which combine the ease of production with exceptional purity and rapid biodegradability, along with additional imaging or therapeutic functionalities. From a practical standpoint, these attributes of nanoradiopharmaceuticals may provide distinct advantages in diagnostic/therapeutic sensitivity and specificity, imaging resolution, and scalability of turnkey platforms. Coupling image-guided targeted radiation therapy with the possibility of in situ activation of nanomaterials as well as combining with other therapeutic modalities using a multifunctional nanoplatform could herald an era of exciting technological and therapeutic advances to radically transform the landscape of nuclear medicine. The review concludes with a discussion of current challenges and presents the authors' views on future opportunities to stimulate further research in this rewarding field of high societal impact.

Total Variation Constrained Graph Manifold Learning Strategy for Cerenkov Luminescence Tomography

Harnessing the power and flexibility of radiolabeled molecules, Cerenkov luminescence tomography (CLT) provides a novel technique for non-invasive visualisation and quantification of viable tumour cells in a living organism. However, owing to the photon scattering effect and the ill-posed inverse problem, CLT still suffers from insufficient spatial resolution and shape recovery in various preclinical applications. In this study, we proposed a total variation constrained graph manifold learning (TV-GML) strategy for achieving accurate spatial location, dual-source resolution, and tumour morphology. TV-GML integrates the isotropic total variation term and dynamic graph Laplacian constraint to make a trade-off between edge preservation and piecewise smooth region reconstruction. Meanwhile, the tetrahedral mesh-Cartesian grid pair method based on the k-nearest neighbour, and the adaptive and composite Barzilai-Borwein method, were proposed to ensure global super linear convergence of the solution of TV-GML. The comparison results of both simulation experiments and in vivo experiments further indicated that TV-GML achieved superior reconstruction performance in terms of location accuracy, dual-source resolution, shape recovery capability, robustness, and in vivo practicability. Significance: We believe that this novel method will be beneficial to the application of CLT for quantitative analysis and morphological observation of various preclinical applications and facilitate the development of the theory of solving inverse problem.

Sensitivity improved Cerenkov luminescence endoscopy using optimal system parameters

Background

The challenges of clinical translation of optical imaging, including the limited availability of clinically used imaging probes and the restricted penetration depth of light propagation in tissues can be avoided using Cerenkov luminescence endoscopy (CLE). However, the clinical applications of CLE are limited due to the low signal level of Cerenkov luminescence and the large transmission loss caused by the endoscope, which results in a relatively low detection sensitivity of current CLE. The aim of this study was to enhance the detection sensitivity of the CLE system and thus improve the system for clinical application in the detection of gastrointestinal diseases.

Methods

Four optical fiber endoscopes were customized with different system parameters, including monofilament (MF) diameter of imaging fiber bundles, fiber material, probe coating, etc. The endoscopes were connected to the detector via a specifically designed straight connection device to form the CLE system. The β-2-[¹⁸F]-Fluoro-2-deoxy-D-glucose (¹⁸F-FDG) solution and the radionuclide of Gallium-68 (⁶⁸Ga) were used to evaluate the performance of the CLE system. The images of the ¹⁸F-FDG solution acquired by the CLE were used to optimize imaging parameters of the system. By using the endoscope with optimized parameters, including the MF diameter of imaging fiber bundles, fiber materials, etc., the resolution and sensitivity of the assembled CLE system were measured by imaging the radionuclide of ⁶⁸Ga.

Results

The results of ¹⁸F-FDG experiments showed that larger MF diameter led to higher collection efficiency. The fiber material and probe coating with high transmission ratios in the range of 400-900 nm also increased signal collection and transmission efficiency. The results of ⁶⁸Ga evaluations showed that a minimum radioactive activity of radionuclides as low as 0.03 µCi was detected in vitro within 5 minutes, while that of 0.68 µCi can be detected within 1 minute. In vivo experiments also demonstrated that the developed CLE system achieved a high sensitivity at a submicrocurie level; that is, 0.44 µCi within 5 minutes, and 0.83 µCi within 1 minute. The weaker in vivo sensitivity was due to the attenuation of the signal by the mouse tissue skin and the autofluorescence interference produced by biological tissues.

Conclusions

By optimizing the structural parameters of fiber endoscope and imaging parameters for data acquisition, we developed a CLE system with a sensitivity at submicrocurie level. These results support the possibility that this technology can clinically detect early tumors within 1 minute.

Ligand Engineering of Titanium-Oxo Nanoclusters for Cerenkov Radiation-Reinforced Photo/Chemodynamic Tumor Therapy

The therapeutic effect of general photodynamic therapy (PDT) is gravely limited by the poor penetration depth of exogenous light radiation. In recent years, Cerenkov radiation (CR) has been exploringly applied to overcome this critical defect. However, the currently reported type I photosensitizers for CR-induced PDT (CRIT) are only TiO₂ nanoparticle-based agents with numerous fatally intrinsic drawbacks. Herein, we developed NH₂-Ti₃₂O₁₆ nanocluster (NTOC)-derived ultrasmall nanophotosensitizers (NPSs, denoted as TDPs) via innovate ligand engineering. The introduced dopamine (DA) ligands not only facilitate the water solubility and photocatalytic properties of NPSs but also involve the tumor-targeting behavior through the binding affinity with DA receptors on cancer cells. Under CR irradiation, TDPs enable efficient hydroxyl radical (·OH) generation benefiting from the enhanced separation of hole (h⁺)-electron (e^-) pairs, where the h⁺ will react with H₂O to execute type I PDT and the transferred e^- can realize the augmentation of Ti³⁺ to substantially promote the therapeutic index of chemodynamic therapy. This study provides an easy but feasible strategy for constructing versatile NPSs with an ultrasmall framework structure, propounding a refreshing paradigm for implementing efficient CR-induced combined therapy (CRICT) and spurring the development of CR and titanium-familial nanoplatforms in the fields of photocatalysis and nanocatalytic medicine.

Molecular Probes for Autofluorescence-Free Optical Imaging

Optical imaging is an indispensable tool in clinical diagnostics and fundamental biomedical research. Autofluorescence-free optical imaging, which eliminates real-time optical excitation to minimize background noise, enables clear visualization of biological architecture and physiopathological events deep within living subjects. Molecular probes especially developed for autofluorescence-free optical imaging have been proven to remarkably improve the imaging sensitivity, penetration depth, target specificity, and multiplexing capability. In this Review, we focus on the advancements of autofluorescence-free molecular probes through the lens of particular molecular or photophysical mechanisms that produce long-lasting luminescence after the cessation of light excitation. The versatile design strategies of these molecular probes are discussed along with a broad range of biological applications. Finally, challenges and perspectives are discussed to further advance the next-generation autofluorescence-free molecular probes for in vivo imaging and in vitro biosensors.

Smart 131 I-Labeled Self-Illuminating Photosensitizers for Deep Tumor Therapy

Stimulating photosensitizers (PS) by Cerenkov radiation (CR) can overcome the light penetration limitation in traditional photodynamic therapy. However, separate injection of radiopharmaceuticals and PS cannot guarantee their efficient interaction in tumor areas, while co-delivery of radionuclides and PS face the problem of nonnegligible phototoxicity in normal tissues. Here, we describe a ¹³¹ I-labeled smart photosensitizer, composed of pyropheophorbide-a (photosensitizer), a diisopropylamino group (pH-sensitive group), an ¹³¹ I-labeled tyrosine group (CR donor), and polyethylene glycol, which can self-assemble into nanoparticles (¹³¹ I-sPS NPs). The ¹³¹ I-sPS NPs showed low phototoxicity in normal tissues due to aggregation-caused quenching effect, but could self-produce reactive oxygen species in tumor sites upon disassembly. Upon intravenous injection, ¹³¹ I-sPS NPs showed great tumor inhibition capability in subcutaneous 4T1-tumor-bearing Balb/c mice and orthotopic VX2 liver tumor bearing rabbits. We believed ¹³¹ I-sPS NPs could expand the application of CR and provide an effective strategy for deep tumor theranostics.

A review of recent and emerging approaches for the clinical application of Cerenkov luminescence imaging

Cerenkov luminescence (CL) is a blue-weighted emission of light produced by a vast array of clinically approved radioisotopes and LINAC accelerators. When β particles (emitted during the decay of radioisotopes) are present in a medium such as water or tissue, they are able to travel faster than the speed of light in that medium and in doing so polarize the molecules around them. Once the particle has left the local area, the polarized molecules relax and return to their baseline state releasing the additional energy as light (luminescence). This blue glow has commonly been used to determine the output of nuclear power plant cores and, in recent years, has found traction in the preclinical and clinical imaging field. This brief review will discuss the technology which has enabled the emergence of the biomedical Cerenkov imaging field, recent pre-clinical studies with potential clinical translation of Cerenkov luminescence imaging (CLI) and the current clinical implementations of the method. Finally, an outlook is given as to the direction in which the field is heading.

Utilization of nanotechnology in targeted radionuclide cancer therapy: monotherapy, combined therapy and radiosensitization

The rapid progress of nanomedicine field has a great influence on the different tumor therapeutic trends. It achieves a potential targeting of the therapeutic agent to the tumor site with neglectable exposure of the normal tissue. In nuclear medicine, nanocarriers have been employed for targeted delivery of therapeutic radioisotopes to the malignant tissues. This systemic radiotherapy is employed to overcome the external radiation therapy drawbacks. This review overviews studies concerned with investigation of different nanoparticles as promising carriers for targeted radiotherapy. It discusses the employment of different nanovehicles for achievement of the synergistic effect of targeted radiotherapy with other tumor therapeutic modalities such as hyperthermia and photodynamic therapy. Radiosensitization utilizing different nanosensitizer loaded nanoparticles has also been discussed briefly as one of the nanomedicine approach in radiotherapy.

Ultrasmall Downconverting Nanoparticle for Enhanced Cerenkov Imaging

Cerenkov imaging provides an opportunity to expand the application of approved radiotracers and therapeutic agents by utilizing them for optical approaches, which opens new avenues for nuclear imaging. The dominating Cerenkov radiation is in the UV/blue region, where it is readily absorbed by human tissue, reducing its utility in vivo. To solve this problem, we propose a strategy to shift Cerenkov light to the more penetrative red-light region through the use of a fluorescent down-conversion technique, based upon europium oxide nanoparticles. We synthesized square-shape ultrasmall Eu₂O₃ nanoparticles, functionalized with polyethylene glycol and chelate-free radiolabeled for intravenous injection into mice to visualize the lymph node and tumor. By adding trimethylamine N-oxide during the synthesis, we significantly increased the brightness of the particle and synthesized the (to-date) smallest radiolabeled europium-based nanoparticle. These features allow for the exploration of Eu₂O₃ nanoparticles as a preclinical cancer diagnosis platform with multimodal imaging capability.