Catalytic Nanoparticles in Biomedical Applications: Exploiting Advanced Nanozymes for Therapeutics and Diagnostics

Catalytic nanoparticles (CNPs) as heterogeneous catalyst reveals superior activity due to their physio-chemical features, such as high surface-to-volume ratio and unique optical, electric, and magnetic properties. The CNPs, based on their physio-chemical nature, can either increase the reactive oxygen species (ROS) level for tumor and antibacterial therapy or eliminate the ROS for cytoprotection, anti-inflammation, and anti-aging. In addition, the catalytic activity of nanozymes can specifically trigger a specific reaction accompanied by the optical feature change, presenting the feasibility of biosensor and bioimaging applications. Undoubtedly, CNPs play a pivotal role in pushing the evolution of technologies in medical and clinical fields, and advanced strategies and nanomaterials rely on the input of chemical experts to develop. Herein, a systematic and comprehensive review of the challenges and recent development of CNPs for biomedical applications is presented from the viewpoint of advanced nanomaterial with unique catalytic activity and additional functions. Furthermore, the biosafety issue of applying biodegradable and non-biodegradable nanozymes and future perspectives are critically discussed to guide a promising direction in developing span-new nanozymes and more intelligent strategies for overcoming the current clinical limitations.

pH/GSH dual responsive nanosystem for nitric oxide generation enhanced type I photodynamic therapy

Tumor hypoxia diminishes the effectiveness of traditional type II photodynamic therapy (PDT) due to oxygen consumption. Type I PDT, which can operate independently of oxygen, is a viable option for treating hypoxic tumors. In this study, we have designed and synthesized JSK@PEG-IR820 NPs that are responsive to the tumor microenvironment (TME) to enhance type I PDT through glutathione (GSH) depletion. Our approach aims to expand the sources of therapeutic benefits by promoting the generation of superoxide radicals (O2-.) while minimizing their consumption. The diisopropyl group within PEG-IR820 serves a dual purpose: it functions as a pH sensor for the disassembly of the NPs to release JSK and enhances intermolecular electron transfer to IR820, facilitating efficient O2-. generation. Simultaneously, the release of JSK leads to GSH depletion, resulting in the generation of nitric oxide (NO). This, in turn, contributes to the formation of highly cytotoxic peroxynitrite (ONOO-.), thereby enhancing the therapeutic efficacy of these NPs. NIR-II fluorescence imaging guided therapy has achieved successful tumor eradication with the assistance of laser therapy.

Nanomaterials-Induced Redox Imbalance: Challenged and Opportunities for Nanomaterials in Cancer Therapy

Cancer cells typically display redox imbalance compared with normal cells due to increased metabolic rate, accumulated mitochondrial dysfunction, elevated cell signaling, and accelerated peroxisomal activities. This redox imbalance may regulate gene expression, alter protein stability, and modulate existing cellular programs, resulting in inefficient treatment modalities. Therapeutic strategies targeting intra- or extracellular redox states of cancer cells at varying state of progression may trigger programmed cell death if exceeded a certain threshold, enabling therapeutic selectivity and overcoming cancer resistance to radiotherapy and chemotherapy. Nanotechnology provides new opportunities for modulating redox state in cancer cells due to their excellent designability and high reactivity. Various nanomaterials are widely researched to enhance highly reactive substances (free radicals) production, disrupt the endogenous antioxidant defense systems, or both. Here, the physiological features of redox imbalance in cancer cells are described and the challenges in modulating redox state in cancer cells are illustrated. Then, nanomaterials that regulate redox imbalance are classified and elaborated upon based on their ability to target redox regulations. Finally, the future perspectives in this field are proposed. It is hoped this review provides guidance for the design of nanomaterials-based approaches involving modulating intra- or extracellular redox states for cancer therapy, especially for cancers resistant to radiotherapy or chemotherapy, etc.

Core-shell structured carbon dots with up-conversion fluorescence and photo-triggered nitric oxide-releasing properties

Cancer-targeted nanotechnology has a new trend in the design and preparation of new materials with functions for imaging and therapeutic applications simultaneously. As a new type of carbon nanomaterial, the inherent core-shell structured carbon dots (CDs) can be designed to provide a modular nanoplatform for integration of bioimaging and therapeutic capabilities. Here, core-shell structured CDs are designed and synthesized from levofloxacin and arginine and named Arg-CDs, in which levofloxacin-derived chromophores with up-conversion fluorescence are densely packed into the carbon core while guanidine groups are located on the shell, providing nitric oxide (NO) for photodynamic therapy of tumors. Moreover, the chromophores in the carbon core irradiated by visible LED light generate large amounts of reactive oxygen species (ROSs) that will oxidize the guanidine groups located on the shell of the Arg-CDs and further increase the NO releasing capacity remarkably. The as-synthesized Arg-CDs show excellent biocompatibility, bright up-conversion fluorescence, and a light-controlled ROS & NO releasing ability, which can be a potential light-modulated nanoplatform to integrate bioimaging and therapeutic functionalities.

Injectable cold atmospheric plasma-activated immunotherapeutic hydrogel for enhanced cancer treatment

Despite the promise of immune checkpoint blockade (ICB) for cancer treatment, challenges associated with this therapy still exist, including low response rates and severe side effects in patients. Here, we report a hydrogel-mediated combination therapy for enhanced ICB therapy. Specifically, cold atmospheric plasma (CAP), an ionized gas consisting of therapeutically effective reactive oxygen species (ROS) and reactive nitrogen species (RNS), can effectively induce cancer immunogenic cell death, releasing tumor-associated antigens in situ and initiating anti-tumor immune responses, which, therefore, can synergistically augment the efficacy of immune checkpoint inhibitors. To minimize the systemic toxicity of immune checkpoint inhibitors and improve the tissue penetration of CAP, an injectable Pluronic hydrogel was employed as a delivery method. Our results show that major long-lived ROS and RNS in CAP can be effectively persevered in Pluronic hydrogel and remain efficacious in inducing cancer immunogenic cell death after intratumoral injection. Our findings suggest that local hydrogel-mediated combination of CAP and ICB treatment can evoke both strong innate and adaptive, local and systemic anti-tumor immune responses, thereby inhibiting both tumor growth and potential metastatic spread.

Photocatalytic degradation of organic pollutants by carbon quantum dots functionalized g-C3N4: A review

Graphitic carbon nitride (g-C₃N₄) has received much attention due to its unique characteristics of stable physicochemical features, facile preparation, and inexpensive cost. However, the bulk g-C₃N₄ has a weak capacity for pollutant degradation and needs to be modified for real application. Therefore, extensive research has been done on g-C₃N₄, and the discovery of the novel zero-dimensional nanomaterials known as carbon quantum dots (CQDs) provided it with a unique modification option. In this review, the development for the removal of organic pollutants by g-C₃N₄/CQDs was discussed. Firstly, the preparation of g-C₃N₄/CQDs were introduced. Then, the application and the degradation mechanism of g-C₃N₄/CQDs were briefly described. And the discussion of the influencing factors on g-C₃N₄/CQDs' ability to degrade organic pollutants came in third. Finally, the conclusions of photocatalytic degradation of organic pollutants by g-C₃N₄/CQDs and future perspectives followed. This review will strengthen the understanding of the photocatalytic degradation of real organic wastewater by g-C₃N₄/CQDs, including their preparation, application, mechanism, and influencing factors.

A Supramolecular Nanoassembly of Lenvatinib and a Green Light-Activatable NO Releaser for Combined Chemo-Phototherapy

The chemotherapeutic Lenvatinib (LVB) and a nitric oxide (NO) photodonor based on a rhodamine antenna (RD-NO) activatable by the highly compatible green light are supramolecularly assembled by a β-cyclodextrin branched polymer (PolyCD). The poorly water-soluble LVB and RD-NO solubilize very well within the polymeric host leading to a ternary supramolecular nanoassembly with a diameter of ~55 nm. The efficiency of the NO photorelease and the typical red fluorescence of RD-NO significantly enhance within the polymer due to its active role in the photochemical and photophysical deactivation pathways. The co-presence of LVB within the same host does not affect either the nature or the efficiency of the photoinduced processes of RD-NO. Besides, irradiation of RD-NO does not lead to the decomposition of LVB, ruling out any intermolecular photoinduced process between the two guests despite sharing the same host. Ad-hoc devised Förster Resonance Energy Transfer experiments demonstrate this to be the result of the not close proximity of the two guests, which are confined in different compartments of the same polymeric host. The supramolecular complex is stable in a culture medium, and its biological activity has been evaluated against HEP-G2 hepatocarcinoma cell lines in the dark and under irradiation with visible green light, using LVB at a concentration well below the IC₅₀. Comparative experiments performed using the polymeric host encapsulating the individual LVB and RD-NO components under the same experimental conditions show that the moderate cell mortality induced by the ternary complex in the dark increases significantly upon irradiation with visible green light, more likely as the result of synergism between the NO photogenerated and the chemotherapeutic.

Recent advances in diverse nanosystems for nitric oxide delivery in cancer therapy

Gas therapy has been proven to be a promising and advantageous treatment option for cancers. Studies have shown that nitric oxide (NO) is one of the smallest structurally significant gas molecules with great potential to suppress cancer. However, there is controversy and concern about its use as it exhibits the opposite physiological effects based on its levels in the tumor. Therefore, the anti-cancer mechanism of NO is the key to cancer treatment, and rationally designed NO delivery systems are crucial to the success of NO biomedical applications. This review summarizes the endogenous production of NO, its physiological mechanisms of action, the application of NO in cancer treatment, and nano-delivery systems for delivering NO donors. Moreover, it briefly reviews challenges in delivering NO from different nanoparticles and the issues associated with its combination treatment strategies. The advantages and challenges of various NO delivery platforms are recapitulated for possible transformation into clinical applications.

A molecular dyad delivered by biodegradable polymeric nanoparticles for combined PDT and NO-PDT in cancer cells

The design, synthesis, photochemical properties, and biological evaluation of a novel molecular dyad with double photodynamic action and its formulation within biodegradable polymeric nanoparticles (NPs) are reported. A BODIPY-based singlet oxygen (¹O₂) photosensitizer (PS) and a nitric oxide (NO) photodonor (NOPD) based on an amino-nitro-benzofurazan moiety have been covalently joined in a new molecular dyad, through a flexible alkyl spacer. Excitation of the dyad with visible light in the range 400-570 nm leads to the concomitant generation of the cytotoxic ¹O₂ and NO with effective quantum yields, being Φ_Δ = 0.49 ± 0.05 and Φ_NO = 0.18 ± 0.01, respectively. Besides, the non-fluorescent NOPD unit becomes highly fluorescent after the NO release, acting as an optical reporter for the NO photogenerated. The dyad is not soluble in water medium but can be effectively entrapped in water-dispersible, biodegradable polymeric NPs made of mPEG-PCL, ca. 66 nm in diameter. The polymeric nano-environment affects in an opposite way the photochemical performances of the dyad, reducing Φ_Δ to 0.16 ± 0.02 and increasing Φ_NO to 0.92 ± 0.03, respectively. The NPs effectively deliver the photoactive cargo into the cytoplasm of HepG2 hepatocellular carcinoma cells. A remarkable level of cell mortality is observed for the loaded NPs at very low concentrations of the dyad (1-5 µM) and very low light doses (≤0.8 J cm^-2) more likely as the result of the combined photodynamic action of ¹O₂ and NO.

Folic Acid-Modified Cerium-Doped Carbon Dots as Photoluminescence Sensors for Cancer Cells Identification and Fe(III) Detection

Carbon dots (CDs) are a new class of carbon-based luminescence materials with fascinating properties. They have been given great expectations on superseding traditional semiconductor quantum dots due to their good dispersity and stability, relatively low toxicity, superior resistance to photobleaching, and excellent biocompatibility. The diversified luminescence properties of CDs are largely due to the synthetic strategies and precursors. In view of those described above, this study has explored the possibility to establish a facile one-step hydrothermal method for the one-pot synthesis of folic acid-modified cerium-doped CDs (Ce-CDs-FA), which could be further utilized as a sensitive fluorescent nanoprobe for biosensing. This investigation demonstrates that the Ce-CDs-FA nanocomposites have nice biocompatibility and bright fluorescent properties, which can be readily utilized to detect cancer cells through recognizing overexpressing folate receptors by virtue of folic acid. Meanwhile, it is noted that the Fe3+ ion can actualize a specific and hypersensitive quenching effect for these Ce-CDs-FA nanocomposites, which can be further explored for special ion recognition, including iron ions. It raises the possibility that the as-prepared Ce-CDs-FA nanocomposites could be extended as a dual fluorescence sensor for targeted cell imaging and Fe3+ ion detection.

Photoactivatable nanogenerators of reactive species for cancer therapy

In recent years, reactive species-based cancer therapies have attracted tremendous attention due to their simplicity, controllability, and effectiveness. Herein, we overviewed the state-of-art advance for photo-controlled generation of highly reactive radical species with nanomaterials for cancer therapy. First, we summarized the most widely explored reactive species, such as singlet oxygen, superoxide radical anion (O2 ●-), nitric oxide (●NO), carbon monoxide, alkyl radicals, and their corresponding secondary reactive species generated by interaction with other biological molecules. Then, we discussed the generating mechanisms of these highly reactive species stimulated by light irradiation, followed by their anticancer effect, and the synergetic principles with other therapeutic modalities. This review might unveil the advantages of reactive species-based therapeutic methodology and encourage the pre-clinical exploration of reactive species-mediated cancer treatments.

Carbon Dots: Classification, Properties, Synthesis, Characterization, and Applications in Health Care-An Updated Review (2018-2021)

Carbon dots (CDs) are usually smaller than 10 nm in size, and are meticulously formulated and recently introduced nanomaterials, among the other types of carbon-based nanomaterials. They have gained significant attention and an incredible interest in the field of nanotechnology and biomedical science, which is merely due to their considerable and exclusive attributes; including their enhanced electron transferability, photobleaching and photo-blinking effects, high photoluminescent quantum yield, fluorescence property, resistance to photo-decomposition, increased electrocatalytic activity, good aqueous solubility, excellent biocompatibility, long-term chemical stability, cost-effectiveness, negligible toxicity, and acquaintance of large effective surface area-to-volume ratio. CDs can be readily functionalized owing to the abundant functional groups on their surfaces, and they also exhibit remarkable sensing features such as specific, selective, and multiplex detectability. In addition, the physico-chemical characteristics of CDs can be easily tunable based on their intended usage or application. In this comprehensive review article, we mainly discuss the classification of CDs, their ideal properties, their general synthesis approaches, and primary characterization techniques. More importantly, we update the readers about the recent trends of CDs in health care applications (viz., their substantial and prominent role in the area of electrochemical and optical biosensing, bioimaging, drug/gene delivery, as well as in photodynamic/photothermal therapy).

Nitric Oxide Photoreleasers with Fluorescent Reporting

Nitric oxide (NO) plays a multifaceted role in human physiology and pathophysiology, and its controlled delivery has great prospects in therapeutic applications. The light-activated uncaging of NO from NO caging compounds allows this free radical to be released with accurate control of site and dosage, which strictly determine its biological effects. Molecular constructs able to activate fluorescence concomitantly to NO release offer the important advantage of easy and real-time tracking of the amount of NO uncaged in a non-invasive fashion even in the cell environment. This contribution provides an overview of the advances in photoactivatable NO releasers bearing fluorescent reporting functionalities achieved in our and other laboratories, highlighting the rationale design and their potential therapeutic applications.

Advanced nitric oxide donors: chemical structure of NO drugs, NO nanomedicines and biomedical applications

Nitric oxide (NO), as an endogenous diatomic molecule, plays a key regulatory role in many physiological and pathological processes. This diatomic free radical has been shown to affect different physiological and cellular functions and participates in many regulatory functions ranging from changing the cardiovascular system to regulating neuronal functions. Thus, NO gas therapy as an emerging and promising treatment method has attracted increasing attention in the treatment of various pathological diseases. As is known, the physiological and pathological regulation of NO depends mainly on its location, exposure time and released dosage. However, NO gas lacks effective accumulation and controlled long-term gas releasing capacity at specific sites, resulting in limited therapeutic efficacy and potential side effects. Thus, researchers have developed various NO donors, but eventually found that it is still difficult to control the long-term release of NO. Inspired by the self-assembly properties of nanomaterials, researchers have realized that nanomaterials can be used to support NO donors to form nanomedicine to achieve spatial and temporal controlled release of NO. In this review, according to the history of the medicinal development of NO, we first summarize the chemical design of NO donors, NO prodrugs, and NO-conjugated drugs. Then, NO nanomedicines formed by various nanomaterials and NO donors depending on nanotechnology are highlighted. Finally, the biomedical applications of NO nanomedicine with optimized properties are summarized.

Theranostic Activity of Nitric Oxide-Releasing Carbon Quantum Dots

The synthesis and anticancer cell activity of nitric oxide (NO)-releasing carbon quantum dots (CQDs) are described as potential theranostics. A series of secondary amine-modified CQDs were prepared using a hydrothermal method to modify β-cyclodextrin with hydroxyl and primary amine terminal functional groups. Subsequent reaction of the CQDs with NO gas under alkaline conditions yielded N-diazeniumdiolate NO donor-modified CQDs with adjustable NO payloads (0.2-1.1 μmol/mg) and release kinetics (half-lives from 29 to 79 min) depending on the level of secondary amines and surface functional groups. The anticancer activity of the NO-releasing CQDs against Pa14c, A549, and SW480 cancer cell lines proved to be dependent on both NO payloads and surface functionalizations. Primary amine-modified CQDs with NO payloads ∼1.11 μmol/mg exhibited the greatest anticancer action. A fluorescence microscopy study demonstrated the utility of these NO-releasing CQDs as dual NO-releasing and bioimaging probes.

Organic dots (O-dots) for theranostic applications: preparation and surface engineering

Organic dots is a term used to represent materials including graphene quantum dots and carbon quantum dots because they rely on the presence of other atoms (O, H, and N) for their photoluminescence or fluorescence properties. They generally have a small size (as low as 2.5 nm), and show good photostability under prolonged irradiation. The excitation and emission wavelengths of O-dots can be tailored according to their synthetic procedure, where although their quantum yield is quite low compared with organic dyes, this is partly compensated by their large absorption coefficients. A wide range of strategies have been used to modify the surface of O-dots for passivation, improving their solubility and biocompatibility, and allowing the attachment of targeting moieties and therapeutic cargos. Hybrid nanostructures based on O-dots have been used for theranostic applications, particularly for cancer imaging and therapy. This review covers the synthesis, physics, chemistry, and characterization of O-dots. Their applications cover the prevention of protein fibril formation, and both controlled and targeted drug and gene delivery. Multifunctional therapeutic and imaging platforms have been reported, which combine four or more separate modalities, frequently including photothermal or photodynamic therapy and imaging and drug release.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Advances in inorganic-based colloidal nanovehicles functionalized for nitric oxide delivery

Nitric oxide (NO) is an important pharmaceutical agent of considerable therapeutic interest ascribed to its vasodilative, tumoricidal and antibacterial effects. Rapid development of functional nanomaterials has provided opportunities for us to achieve controllable exogenous delivery of NO. In the current review, a variety of functionalized colloidal nanovehicles that have been developed to date for nitric oxide delivery are reported. Specifically, we focus on inorganic nanomaterials such as semiconductor quantum dots, silica nanoparticles, upconversion nanomaterials, carbon/graphene nanodots, gold nanoparticles, iron oxide nanoparticles as the functional or/and supporting materials to carry NO donors. N-diazeniumdiolates, S-nitrosothiols, nitrosyl metal complexes and organic nitrates as main types of NO donors have their own unique properties and molecular structures. Conjugating the NO donors of different forms with appropriate nanomaterials results in NO delivery nanovehicles capable of releasing NO in a dose-controllable or/and on-demand manner. We also consider the therapeutic applications of those NO delivery nanovehicles, especially their applications for cancer therapy. In the end, we discuss possible future directions for developing exogenous NO delivery systems with more desired structure and improved performance. This review aims to offer the readers an overall view of the advances in functionalized colloidal nanovehicles for NO delivery. It will be attractive to scientists and researchers in the areas of material science, nanotechnology, biomedical engineering, chemical biology, etc.

Activation Strategies in Image-Guided Nanotherapeutic Delivery

Therapeutic nanomaterials serve as an important platform for drug delivery under image guidance. Despite significant growth and broad applications, their design specifics remain a subject of continued interest primarily due to multifunctional factors involved, ranging from nanomaterial properties, imaging modalities, and therapeutic agents to activation strategies. This review article summarizes key findings on their design characteristics with a particular interest in strategies developed for therapeutic activation (release). First, their activation can be controlled using either an endogenous factor including low pH and glutathione or an external stimulation by light, ultrasound, or electromagnetic field. The former is passively controlled from a spatiotemporal aspect compared to the latter, which is otherwise actively controlled through drug linker photolysis, nanomaterial disassembly, or gate opening. Second, light stimulation serves a most notable strategy due to its essential role in controlled drug release, photothermal activation (hyperthermia), and photodynamic production of reactive oxygen species (ROS). Third, some of those activation strategies that rely on ultrasound, photothermal, photoacoustic, magnetic field, or X-ray radiation are dually functional due to their role in imaging modalities. In summary, this review article presents recent advances and new insights that pertain to nanotherapeutic delivery systems. It also addresses their technical limitations associated with tissue penetration (light), spatial resolution (ultrasound, hyperthermia), and occurrence of cellular resistance (ROS).

A turn-on and lysosome-targeted fluorescent NO releaser in water media and its application in living cells and zebrafishes

Due to the high activity and difficult to transport of nitric oxide, the controlled release of nitric oxide has been a new trend in the research on the biological effect of nitric oxide. In this paper, a water-soluble and turn-on fluorescent NO donor Rh-NO was synthesized. Upon 525 nm irradiation, the fluorescence of the Rh-NO at 568 nm enhanced with the quantum yield (Φ_F) of Rh-NO changing from 5.08% to 35.96%. The mechanism of NO releasing was proved by HRMS and the Dan. The releasing time of 6 min and the releasing yield of 0.61 proved the superiority of Rh-NO. Excellent cell activity above 80% of Rh-NO and Rh guaranteed that nitric oxide was released from Rh-NO in lysosome and zebrafishes successfully, which provided a good platform to understand the biological effects of nitric oxide in lysosomes.

Enhancing doxorubicin anticancer activity with a novel polymeric platform photoreleasing nitric oxide

Combination of Doxorubicin with light-regulated NO release achieved through formulation strategy of tailored polymeric conjugate nanoparticles may open new treatment modalities to improve cancer therapies.

Quinoline H2S donor decorated fluorescent carbon dots: visible light responsive H2S nanocarriers

Fluorescent carbon dots decorated by quinoline H₂S donor have been demonstrated as a photoresponsive nanocarrier for the effective release of H₂S.

Carbon Dots as a New Class of Diamagnetic Chemical Exchange Saturation Transfer (diaCEST) MRI Contrast Agents

While carbon dots (C-dots) have been extensively investigated pertaining to their fluorescent, phosphorescent, electrochemiluminescent, optoelectronic, and catalytic features, their inherent chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) properties are unknown. By virtue of their hydrophilicity and abundant exchangeable protons of hydroxyl, amine, and amide anchored on the surface, we report here that C-dots can be adapted as effective diamagnetic CEST (diaCEST) MRI contrast agents. As a proof-of-concept demonstration, human glioma cells were labeled with liposomes with or without encapsulated C-dots and implanted in mouse brain. In vivo CEST MRI was able to clearly differentiate labeled cells from non-labeled cells. The present findings may encourage new applications of C-dots for in vivo imaging in deep tissues, which is currently not possible using conventional fluorescent (near-infrared) C-dots.

"Three-Bullets" Loaded Mesoporous Silica Nanoparticles for Combined Photo/Chemotherapy

This contribution reports the design, preparation, photophysical and photochemical characterization, as well as a preliminary biological evaluation of mesoporous silica nanoparticles (MSNs) covalently integrating a nitric oxide (NO) photodonor (NOPD) and a singlet oxygen (¹O₂) photosensitizer (PS) and encapsulating the anticancer doxorubicin (DOX) in a noncovalent fashion. These MSNs bind the NOPD mainly in their inner part and the PS in their outer part in order to judiciously exploit the different diffusion radius of the cytotoxic NO and ¹O₂. Furthermore this silica nanoconstruct has been devised in such a way to permit the selective excitation of the NOPD and the PS with light sources of different energy in the visible window. We demonstrate that the individual photochemical performances of the photoactive components of the MSNs are not mutually affected, and remain unaltered even in the presence of DOX. As a result, the complete nanoconstruct is able to deliver NO and ¹O₂ under blue and green light, respectively, and to release DOX under physiological conditions. Preliminary biological results performed using A375 cancer cells show a good tolerability of the functionalized MSNs in the dark and a potentiated activity of DOX upon irradiation, due to the effect of the NO photoreleased.

Precise ricin A-chain delivery by Golgi-targeting carbon dots

The as-prepared CDs–RTA conjugates exhibit enhanced internalization, improved stability against enzymatic digestion and an increased location rate of RTA to the ER, and thus much more RTA could translocate to the cytosol and ribosome to exert toxic effects.

Visible light-activatable multicargo microemulsions with bimodal photobactericidal action and dual colour fluorescence

A microemulsion co-solubilizing a photosensitizer and a NO photodonor in the oily phase can be excited with visible light stimuli resulting in the photogeneration of cytotoxic ¹O₂ and NO together with red and green fluorescence emission.

A molecular hybrid producing simultaneously singlet oxygen and nitric oxide by single photon excitation with green light

Combination of photosensitizers (PS) for photodynamic therapy with NO photodonors (NOPD) is opening intriguing horizons towards new and still underexplored multimodal anticancer and antibacterial treatments not based on "conventional" drugs and entirely controlled by light stimuli. In this contribution, we report an intriguing molecular hybrid based on a BODIPY light-harvesting antenna that acts simultaneously as PS and NOPD upon single photon excitation with the highly biocompatible green light. The presented hybrid offers a combination of superior advantages with respect to the other rare cases reported to date, meeting most of the key criteria for both PSs and NOPDs in the same molecular entity such as: (i) capability to generate ¹O₂ and NO with single photon excitation of biocompatible visible light, (ii) excellent ¹O₂ quantum yield and NO quantum efficiency, (iii) photogeneration of NO independent from the presence of oxygen, (iv) large light harvesting properties in the green region. Furthermore, this compound together with its stable photoproduct, is well tolerated by both normal and cancer cells in the dark and exhibits bimodal photomortality of cancer cells under green light excitation due to the combined action of the cytotoxic ¹O₂ and NO.

A light-induced nitric oxide controllable release nano-platform based on diketopyrrolopyrrole derivatives for pH-responsive photodynamic/photothermal synergistic cancer therapy

Emerging treatment approaches, such as gas therapy (GT), photodynamic therapy (PDT) and photothermal therapy (PTT), have received widespread attention. The development of an intelligent multifunctional nano-platform responding to tumor microenvironments for multimodal therapy is highly desirable. Herein, a near-infrared (NIR) light-responsive nitric oxide (NO) photodonor (4-nitro-3-trifluoromethylaniline, NF) and a pH-sensitive group (dimethylaminophenyl) have been introduced into a diketopyrrolopyrrole core (denoted as DPP-NF). The DPP-NF nanoparticles (NPs) can be activated under weakly acidic conditions of lysosomes (pH 4.5-5.0) to generate reactive oxygen species (ROS) and enhance photothermal efficiency. The fluorescence detection demonstrated that NO controllable release can be realized by "on-off" switching of the NF unit under NIR light irradiation or dark conditions. The controllable NO release of DPP-NF NPs can not only trigger tumor cell death by DNA damage, but also overcome PDT inefficiencies caused by hypoxia in tumors. Additionally, DPP-NF NPs displayed 45.6% photothermal conversion efficiency, making them superior to other reported DPP derivatives. In vitro studies showed that DPP-NF NPs possessed low dark toxicity and high phototoxicity with a half-maximal inhibitory concentration of about 38 μg mL-1. In vivo phototherapy indicated that DPP-NF NPs exhibited excellent tumor phototherapeutic efficacy with passive targeting of the tumor site via the enhanced permeability and retention (EPR) effect. These results highlight that the nano-platform has promising potential for NO-mediated multimodal synergistic phototherapy in clinical settings.

Photoelectron Transfer at ZnTPyP Self-Assembly/TiO2 Interfaces for Enhanced Two-Photon Photodynamic Therapy

Two-photon (TP) absorption nanomaterials are highly desirable for deep-tissue clinical diagnostics and orthotopic disease treatment. Here, a well-designed core/shell nanostructure was successfully synthesized with a ZnTPyP self-assembly nanocrystal (ZSN) inner core coated by a homogeneous TiO₂ layer outside (ZSN-TO). The ZSN is a good photosemiconductor, showing both one-photon (OP) and TP absorption properties for red fluorescence emission and electron-hole pair generation; TiO₂ with good biocompatibility acts as the electron acceptor, which can transfer photoelectron from ZSN to TiO₂ for highly effective electron-hole separation, favoring the production of long-life superoxide anion (O₂^•-) by electrons and oxygen and strong oxidizing hydroxyl radical (•OH) by holes and surrounding H₂O. Once pretreated with ZSN-TO, the simultaneous OP-405 nm or TP-800 nm laser stimulation and fluorescent imaging of reactive oxygen species (ROS) showed dynamical and continuous generation of ROS in HeLa cells, with cytotoxicity significantly increasing via the type-1-like photodynamic therapy process. The results demonstrated that the combination of organic ZSN with inorganic TiO₂ has great applications as an excellent photosensitizer for deep-tissue fluorescent imaging and noninvasive disease treatment via TP photodynamic therapy.

NIR fluorescent organic nanoparticles for photoinduced nitric oxide delivery with self monitoring and real time reporting abilities

Nitric oxide photodonor (NOD) conjugated perylene tetracarboxylate ester (TPT) based fluorescent organic TPT(NOD)₄ nanoparticles (NPs) with aggregation induced NIR emission have shown photoinduced nitric oxide delivery along with a red to green emission transition.

Nanoparticle-triggered in situ catalytic chemical reactions for tumour-specific therapy

This tutorial review highlights the progress and future development of nanoparticle-triggered in situ catalytic chemical reactions for tumour-specific therapy.

Simultaneous supramolecular activation of NO photodonor/photosensitizer ensembles by a calix[4]arene nanoreactor

A calix[4]arene-based micellar nanoscaffold allows the co-encapsulation of photosensitizers with a NO photodonor, activating their response to light, otherwise precluded/limited in water medium, resulting in the simultaneous photogeneration of cytotoxic ¹O₂ and NO.

Novel Sigma Receptor Ligand-Nitric Oxide Photodonors: Molecular Hybrids for Double-Targeted Antiproliferative Effect

This contribution reports the synthesis and evaluation of novel hybrid compounds that conjugate a sigma (σ) receptor pharmacophore and a nitric oxide (NO) photodonor. All compounds preserve their capability to generate NO under visible light and possess overall σ receptor nanomolar affinity, with one of them (8b) exhibiting remarkable σ₂ receptor selectivity. Compounds 8b, 11a, and 11b were tested on tumorigenic MCF-7 and A2058 cells expressing high levels of σ₂ and σ₁ receptor, respectively. Considerable loss of cell viability was detected under light excitation, while negligible effects in the dark were detected. Moreover, they did not show any significant cytotoxicity in the dark or under irradiation on nontumorigenic NCTC-2544 keratinocytes. NO-induced reduction of cellular viability was demonstrated by in-cell NO detection and total nitrite estimation. For the first time, a combination of σ receptor moieties and a NO photodonor is reported, providing distinctive ligands potentially useful for cancer management.

An active structure preservation method for developing functional graphitic carbon dots as an effective antibacterial agent and a sensitive pH and Al(iii) nanosensor

Functional engineering is a crucial prerequisite for specific and wide applications of optical probes. In this study, we proposed a facile active structure preservation (ASP) method to directly develop new self-functional graphitic carbon dots (g-CDs) through a hydrothermal synthesis route by taking ciprofloxacin hydrochloride, an antibiotic belonging to a group of fluoroquinolone drugs, as an example. To retain the functional structures of the starting materials, the reaction temperature is intentionally controlled below the decomposition temperature of the reactants that hold the functional groups. As a proof of concept, we successfully prepared g-CDs with ciprofloxacin-like structures on its surface, as identified by mass spectrometric (MS) analysis. The as-prepared g-CDs not only exhibit effective antibacterial activity towards the bacteria Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative), but can also optically sense pH in the range from 5.02 to 9.91. Furthermore, the g-CDs can coordinate with aluminum ions to show a chelation-enhanced photoluminescence (CHEP) effect. These results indicate that the ASP method can be promising for engineering CDs with various properties.

Multivalent mesoporous silica nanoparticles photo-delivering nitric oxide with carbon dots as fluorescence reporters

Amino-terminated mesoporous silica nanoparticles embedding carbon dots (MSCD) formed by calcination were functionalized with a nitric oxide (NO) photodonor (1) to give a robust MSCD-1 conjugate. The intense fluorescence of MSCDs was strongly quenched in MSCD-1 by effective energy transfer. Visible light excitation of MSCD-1 liberates NO, suppresses the energy transfer mechanism and leads to concomitant fluorescence restoration of the MSCD scaffold, which acts as an optical reporter for the released NO. The MSCD-1 hybrid is also able to encapsulate the highly hydrophobic photosensitizer temoporfin, preserving the fluorescence reporting function.

Carbon Nanodot-Sensitized Modulation of Alzheimer's β-Amyloid Self-Assembly, Disassembly, and Toxicity

The self-assembly of amyloidogenic peptides into β-sheet-rich aggregates is a general feature of many neurodegenerative diseases, including Alzheimer's disease, which signifies the need for the effective attenuation of amyloid aggregation toward alleviating amyloid-associated neurotoxicity. This study reports that photoluminescent carbon nanodots (CDs) can effectively suppress Alzheimer's β-amyloid (Aβ) self-assembly and function as a β-sheet breaker disintegrating preformed Aβ aggregates. This study synthesizes CDs using ammonium citrate through one-pot hydrothermal treatment and passivates their surface with branched polyethylenimine (bPEI). The bPEI-coated CDs (bPEI@CDs) exhibit hydrophilic and cationic surface characteristics, which interact with the negatively charged residues of Aβ peptides, suppressing the aggregation of Aβ peptides. Under light illumination, bPEI@CDs display a more pronounced effect on Aβ aggregation and on the dissociation of β-sheet-rich assemblies through the generation of reactive oxygen species from photoactivated bPEI@CDs. The light-triggered attenuation effect of Aβ aggregation using a series of experiments, including photochemical and microscopic analysis, is verified. Furthermore, the cell viability test confirms the ability of photoactivated bPEI@CDs for the suppression of Aβ-mediated cytotoxicity, indicating bPEI@CDs' potency as an effective anti-Aβ neurotoxin agent.

Carbon dots: materials, synthesis, properties and approaches to long-wavelength and multicolor emission

Herein, we summarize recent research developments and progress of carbon dots (CDs), which have been attracting considerable attention as a new type of photoluminescent material. Raw materials, from single carbonaceous compounds to colorful natural substances, for the synthesis of CDs are discussed. A range of diverse synthetic methodologies to achieve better photoluminescence performance and more advanced functions are summarized, and these are basically divided into two classes: top-down and bottom-up. The inspiring properties, mainly including composites, optical properties and cytotoxicity, are listed. In particular, the luminescence mechanism and surface functionalization of the CDs are briefly discussed. Moreover, on the basis of the above, the long-wavelength and multicolor emission properties of CDs and ways to achieve these goals including surface state and size controlled by synthesis strategies, proper precursors, chemical doping and modification, solvatochromic effects and energy transfer are reviewed in detail.