Colloidal CuFeS2 Nanocrystals: Intermediate Fe d-Band Leads to High Photothermal Conversion Efficiency

The Many "Facets" of Halide Ions in the Chemistry of Colloidal Inorganic Nanocrystals

Over the years, scientists have identified various synthetic "handles" while developing wet chemical protocols for achieving a high level of shape and compositional complexity in colloidal nanomaterials. Halide ions have emerged as one such handle which serve as important surface active species that regulate nanocrystal (NC) growth and concomitant physicochemical properties. Halide ions affect the NC growth kinetics through several means, including selective binding on crystal facets, complexation with the precursors, and oxidative etching. On the other hand, their presence on the surfaces of semiconducting NCs stimulates interesting changes in the intrinsic electronic structure and interparticle communication in the NC solids eventually assembled from them. Then again, halide ions also induce optoelectronic tunability in NCs where they form part of the core, through sheer composition variation. In this review, we describe these roles of halide ions in the growth of nanostructures and the physical changes introduced by them and thereafter demonstrate the commonality of these effects across different classes of nanomaterials.

Optical Transparency Enabled by Anomalous Stokes Shift in Visible Light-Emitting CuAlS2-Based Quantum Dots

We observe and study the anomalous Stokes shift of CuAlS₂/CdS quantum dots. While all known I-III-VI₂ semiconductor core/shell quantum dots show Stokes shifts in excess of 100 meV, the shift associated with CuAlS₂/CdS quantum dots is uniquely large, even exceeding 1.4 eV in some cases. CuAlS₂/CdS quantum dots are thus associated with cross sections less than 10^-17 cm² under the emission maximum. We investigate this anomaly using spectroscopic techniques and ascribe it to the existence of a strong type-II offset between CuAlS₂ and CdS layers. Besides their strong Stokes shift, CuAlS₂/CdS quantum dots also exhibit high quantum yields (63%) as well as long emission lifetimes (∼1500 ns). Because of the combined existence of these properties, CuAlS₂/CdS quantum dots can act as tunable, transparent emitters over the entire visible spectrum. As a demonstration of their potential, we describe the construction of a wide area transparent lighting device with waveguided optical excitation and a clear aperture of 7.5 cm².

The optical duality of tellurium nanoparticles for broadband solar energy harvesting and efficient photothermal conversion

Nanophotonic materials for solar energy harvesting and photothermal conversion are urgently needed to alleviate the global energy crisis. We demonstrate that a broadband absorber made of tellurium (Te) nanoparticles with a wide size distribution can absorb more than 85% solar radiation in the entire spectrum. Temperature of the absorber irradiated by sunlight can increase from 29° to 85°C within 100 s. By dispersing Te nanoparticles into water, the water evaporation rate is improved by three times under solar radiation of 78.9 mW/cm². This photothermal conversion surpasses that of plasmonic or all-dielectric nanoparticles reported before. We also establish that the unique permittivity of Te is responsible for the high performance. The real part of permittivity experiences a transition from negative to positive in the ultraviolet-visible-near-infrared region, which endows Te nanoparticles with the plasmonic-like and all-dielectric duality. The total absorption covers the entire spectrum of solar radiation due to the enhancement by both plasmonic-like and Mie-type resonances. It is the first reported material that simultaneously has plasmonic-like and all-dielectric properties in the solar radiation region. These findings suggest that the Te nanoparticle can be expected to be an advanced photothermal conversion material for solar-enabled water evaporation.

Vacancy engineering of Cu2-xSe nanoparticles with tunable LSPR and magnetism for dual-modal imaging guided photothermal therapy of cancer

The vacancies in the semiconductor nanocrystals not only induce unique properties, but also provide spaces for engineering them with multifunctions by the introduction of other elements. Herein, the vacancy of Cu_2-xSe nanoparticles was tuned by doping with magnetic ferric ions (Fe³⁺) at room temperature, and the position and intensity of the near-infrared localized surface plasmon resonance (LSPR) in the resultant nanostructure can be finely controlled by altering the feeding amount of Fe³⁺ ions. The results of the density-functional theory (DFT) calculations show that both doping and replacement reactions are favourable. Owing to its tunable near-infrared absorption and magnetic property, the obtained hybrid nanostructure was demonstrated to be a novel nanotheranostic agent for effective deep-tissue photoacoustic imaging, magnetic resonance imaging, and photothermal therapy of cancer.

Why Does CuFeS2 Resemble Gold?

While several potential applications of CuFeS₂ quantum dots have already been reported, doubts regarding their optical and physical properties persist. In particular, it is unclear if the quantum dot material is metallic, a degenerately doped semiconductor, or else an intrinsic semiconductor material. Here we examine the physical properties of CuFeS₂ quantum dots in order to address this issue. Specifically, we study the bump that is observed in the optical spectra of these quantum dots at ∼500 nm. Using a combination of structural and optical characterization methods, ultrafast spectroscopy, as well as electronic structure calculations, we ascertain that the unusual purple color of CuFeS₂ quantum dots as well the golden luster of CuFeS₂ films arise from the existence of a plasmon resonance in these materials. While the presence of free carriers causes this material to resemble gold, surface treatments are also described to suppress the plasmon resonance altogether.

Layered tin monoselenide as advanced photothermal conversion materials for efficient solar energy-driven water evaporation

Solar energy-driven water evaporation lays a solid foundation for important photothermal applications such as sterilization, seawater desalination, and electricity generation. Due to the strong light-matter coupling, broad absorption wavelength range, and prominent quantum confinement effect, layered tin monoselenide (SnSe) holds a great potential to effectively harness solar irradiation and convert it to heat energy. In this study, SnSe is successfully deposited on a centimeter-scale nickel foam using a facile one-step pulsed-laser deposition approach. Importantly, the maximum evaporation rate of SnSe-coated nickel foam (SnSe@NF) reaches 0.85 kg m^-2 h^-1, which is even 21% larger than that obtained with the commercial super blue coating (0.7 kg m^-2 h^-1) under the same condition. A systematic analysis reveals that its good photothermal conversion capability is attributed to the synergetic effect of multi-scattering-induced light trapping and the optimal trade-off between light absorption and phonon emission. Finally, the SnSe@NF device is further used for seawater evaporation, demonstrating a comparable evaporation rate (0.8 kg m^-2 h^-1) to that of fresh water and good stability over many cycles of usage. In summary, the current contribution depicts a facile one-step scenario for the economical and efficient solar-enabled SnSe@NF evaporation devices. More importantly, an in-depth analysis of the photothermal conversion mechanism underneath the layered materials depicts a fundamental paradigm for the design and application of photothermal devices based on them in the future.

Synthesis of Cisplatin(IV) Prodrug-Tethered CuFeS2 Nanoparticles in Tumor-Targeted Chemotherapy and Photothermal Therapy

In this study, for the first time, CuFeS₂ nanocrystals were successfully prepared through a facile noninjection-based synthetic strategy, by reacting Cu and Fe precursors with dodecanethiol in a 1-octadecene solvent. This one-pot noninjection strategy features easy handling, large-scale production, and high synthetic reproducibility. Following hyaluronic acid (HA) encapsulation, CuFeS₂ nanocrystals coated with HA (CuFeS₂@HA) not only readily dispersed in water and showed improved biocompatibility but also possessed a tumor-specific targeting ability of cancer cells bearing the cluster determinant 44 (CD44) receptors. The encapsulated CuFeS₂@HA showed broad optical absorbance from the visible to the near-infrared (NIR) region and high photothermal conversion efficiencies of about 74.2%. They can, therefore, be utilized for the photothermal ablation of cancer cells with NIR light irradiation. In addition, toxicity studies in vitro (B16F1 and HeLa) and in vivo (zebrafish embryos), as well as in vitro blood compatibility studies, indicated that CuFeS₂@HA show low cytotoxicity at the doses required for photothermal therapy. More importantly, CuFeS₂@HA can be used as delivery vehicles for chemotherapy cisplatin(IV) prodrug forming CuFeS₂@HA-Pt(IV). Their release profile revealed pH- and glutathione-mediated drug release from CuFeS₂@HA-Pt(IV), which may minimize the side effects of the drug to normal tissues during therapy. Subsequent in vitro experiments confirmed that the use of CuFeS₂@HA-Pt(IV) provides an enhanced and synergistic therapeutic effect compared to that from the use of either chemotherapy or photothermal therapy alone.

A bifunctional scaffold with CuFeSe2 nanocrystals for tumor therapy and bone reconstruction

Bone tumor is one of major challenging issues clinically. After surgical intervention, a few bone tumor cells still remain around bone defects and then proliferate over days. Fabrication of specific biomaterials with dual functions of bone tumor therapy and bone regeneration is of great significance. In order to achieve this aim, we managed to prepare bioactive glass (BG) scaffolds functionalized by the CuFeSe₂ nanocrystals (BG-CFS) by combining 3D printing technique with solvothermal method. During the solvothermal reaction process, CuFeSe₂ nanocrystals could in situ grow on the strut surface of BG scaffolds and thus endow BG scaffolds excellent photothermal performance. The photothermal performance of BG-CFS scaffolds could be well regulated through altering the content of CuFeSe₂ nanocrystals and laser power density when exposed to the near infrared laser (808 nm). The BG-CFS scaffolds could not only effectively ablate the bone tumor cells (Saos-2 cells) in vitro, but also significantly inhibit bone tumor growth in vivo. Moreover, BG-CFS scaffolds could stimulate osteogenic gene expressions of rabbit bone marrow stromal cells (rBMSCs) and finally facilitate the formation of new bone in the bone defects. Our study, for the first time, combined the photothermal performance of semiconductor CuFeSe₂ nanocrystals with the bone-forming activity of bioactive glass scaffolds, which can offer a more extensive horizon for developing novel biomaterials with dual functions of bone tumor therapy and bone regeneration.

Co-delivery of cisplatin and CJM-126 via photothermal conversion nanoparticles for enhanced synergistic antitumor efficacy

Polymeric biomaterials that can be smartly disassembled through the cleavage of the covalent bonds in a controllable way upon an environmental stimulus such as pH change, redox, special enzymes, temperature, or ultrasound, as well as light irradiation, but are otherwise stable under normal physiological conditions have attracted great attention in recent decades. The 2-(4-aminophenyl) benzothiazole molecule (CJM-126), as one of the benzothiazole derivatives, has exhibited a synergistic effect with cisplatin (CDDP) and restrains the bioactivities of a series of human breast cancer cell lines. In our study, novel NIR-responsive targeted binary-drug-loaded nanoparticles encapsulating indocyanine green (ICG) dye were prepared as a new co-delivery and combined therapeutic vehicle. The prepared drug-loaded polymeric nanoparticles (TNPs/CDDP-ICG) are stable under normal physiological conditions, while burst drugs release upon NIR laser irradiation in a mild acidic environment. The results further confirmed that the designed co-delivery platform showed higher cytotoxicity than the single free CDDP due to the synergistic treatment of CJM-126 and CDDP in vitro. Taken together, the work might provide a promising approach for effective site-specific antitumor therapy.

Facile preparation of ion-doped poly(p-phenylenediamine) nanoparticles for photothermal therapy

Ion-doped poly(p-phenylenediamine) nanoparticles were synthesized and used as a photothermal agent for photothermal therapy for the first time.

Hydrophilic K2Mn4O8 nanoflowers as a sensitive photothermal theragnosis synergistic platform for the ablation of cancer

Hydrophilic flower-like K₂Mn₄O₈ is fabricated and works simultaneously as an effective photothermal agent and an ultrasensitive T₁-weighted MRI enhancing agent.

Quasi-Static Resonances in the Visible Spectrum from All-Dielectric Intermediate Band Semiconductor Nanocrystals

The quest for materials with metal-like properties as alternatives to noble metals is an intense area of research that is set to lead to dramatic improvements in technologies based on plasmonics. Here, we present intermediate band (IB) semiconductor nanocrystals (NCs) as a class of all-dielectric nanomaterials providing quasi-static optical resonances. We show that IB NCs can display a negative permittivity in a broad range of visible wavelengths, enabling a metal-like optical response despite the absence of free carriers in the NC ground state. Using a combination of spectroscopy measurements and ab initio calculations, we hereby provide a theoretical model for both the linear and nonlinear optical properties of chalcopyrite CuFeS₂ NCs, as a case study of IB semiconductor nanomaterials. Our results rationalize the high performance of IB nanomaterials as photothermal agents and suggest the use of IB semiconductors as alternatives to noble metals for technologies based on plasmonic materials.

cis-Platinum pro-drug-attached CuFeS2 nanoplates for in vivo photothermal/photoacoustic imaging and chemotherapy/photothermal therapy of cancer

Photothermal therapy (PTT) has attracted considerable attention in cancer treatment. Herein, the facile synthesis of copper iron sulfide (chalcopyrite, CuFeS₂) nanoplates (NPs) with well-defined shape was achieved by a template-mediated method. Chitosan (CS), a linear cationic polysaccharide, was used to improve the physiological stability and biocompatibility. CuFeS₂ NPs with strong near-infrared (NIR) absorbance enabled contrasts in photothermal and photoacoustic (PA) imaging. In vitro and in vivo tumor ablation studies further demonstrated that CS-functionalized CuFeS₂ (CuFeS₂-CS) NPs could convert 808 nm NIR light into heat for PTT with a photothermal conversion efficiency up to 30.5%, which was clearly higher than that of CuS NPs (only 21.4%). Furthermore, CuFeS₂-CS NPs could also load cis-platinum pro-drug (CuFeS₂-CS-Pt), and CuFeS₂-CS-Pt showed a better synergistic therapeutic effect with respect to either chemotherapy or PTT.

Self-quenched ferrocenyl diketopyrrolopyrrole organic nanoparticles with amplifying photothermal effect for cancer therapy

Organic nanoparticles (NPs) with near-infrared absorbance possess high photothermal conversion (PTC) efficiency and an excellent photoacoustic signal, presenting a great prospect for photoacoustic imaging (PAI)-guided photothermal therapy (PTT). Herein, a novel diketopyrrolopyrrole derivative (DPPCN-Fc) is synthesized for use as a PTT agent with PAI performance. Due to photo-induced electron transfer (PET), the two flanked ferrocene moieties significantly quench the radiative decay and intersystem crossing process, resulting in an enhanced nonradiative transition, and an amplifying photothermal effect is observed. Exposing the DPPCN-Fc NP aqueous dispersion (100 μg mL-1) to 730 nm (1.0 W cm-2) laser radiation results in a temperature elevation of 33.4 °C within 10 min and the PTC efficiency reaches up to 59.1%, which is higher than most reported photothermal therapeutic agents. Furthermore, under irradiation from 730 nm lasers, cancer cells could be completely killed in vivo due to the amplifying photothermal effects. Therefore, the as-prepared DPPCN-Fc NPs are a promising cancer theranostic agent for photoacoustic imaging-guided cancer photothermal therapy.

One-pot solution synthesis of shape-controlled copper selenide nanostructures and their potential applications in photocatalysis and photothermal therapy

Developing a facile and reliable method for the fabrication of transition metal chalcogenides is a vital and endless pursuit of scientific and technological disciplines. In this work, we develop a one-pot solution approach to obtain copper selenide nanostructures with different morphologies and crystal structures (Cu₂Se nanoparticles, CuSe nanoplates and CuSe₂ nanosheets). In comparison to previously reported methods, our method did not use expensive and very toxic raw materials. After detailed studies of reaction conditions, including temperature, reaction time, and feeding amount of surfactants and precursors, we found that the feeding ratio of precursors played a key role in the crystal structures and morphologies of the final products. Moreover, as a proof-of-concept study, the potential applications of the as-prepared copper selenide nanostructures in the photocatalytic discoloration of aqueous methylene blue (MB) under visible light irradiation and near-infrared (NIR) light induced photothermal therapy for cancer treatment were investigated. Encouraged by their strong photocatalytic activities and high photothermal conversion efficiencies (calculated to be 51.0%, 49.5% and 48.9% for Cu₂Se nanoparticles, CuSe nanoplates and CuSe₂ nanosheets, respectively), we believe that copper selenide nanostructures fabricated from the one-pot solution approach developed in this work would be promising candidates for a wide variety of emerging applications.

Ultra-small pH-responsive Nd-doped NaDyF4 Nanoagents for Enhanced Cancer Theranostic by in situ Aggregation

To achieve accurate tumor location and highly efficient cancer therapy effect, the properties of cancer theranostic agents should be optimized and enhanced. In this work, ultra-small Nd doped NaDyF₄ were firstly reported as novel contrast agents for near-infrared second window downconversion luminescence (NIR II DCL) and magnetic resonance imaging. Based on the optimization strategy, gallic acid-Fe(III) complex modified NaDyF₄:10%Nd (NaDyF₄:10%Nd-GA-Fe) was selected as the optimal agent with high transversal relaxivity, strong NIR II DCL, high photothermal conversion efficiency, and low toxicity. In vitro experiment found that it can be aggregated rapidly in low pH condition, leading to the particle size increasing. Due to the theranostic properties coupled in NaDyF₄:10%Nd-GA-Fe are size dependent, properties enhancement was observed within the pH responsive aggregation progress. Further study in small animal model bearing tumor demonstrated the enhanced cancer theranostic by in situ aggregation. The optimized nanoagents have potential applications in medical and also provide a novel strategy for future study of cancer theranostic enhancement.

Ultrasmall Magnetic CuFeSe2 Ternary Nanocrystals for Multimodal Imaging Guided Photothermal Therapy of Cancer

Nanoscale ternary chalcogenides have attracted intense research interest due to their wealth of tunable properties and diverse applications in energy and environmental and biomedical fields. In this article, ultrasmall magnetic CuFeSe₂ ternary nanocrystals (<5.0 nm) were fabricated in the presence of thiol-functionalized poly(methacrylic acid) by an environmentally friendly aqueous method under ambient conditions. The small band gap and the existence of intermediate bands lead to a broad NIR absorbance in the range of 500-1100 nm and high photothermal conversion efficiency (82%) of CuFeSe₂ nanocrystals. The resultant CuFeSe₂ nanocrystals show superparamagnetism and effective attenuation for X-rays. In addition, they also exhibit excellent water solubility, colloidal stability, biocompatibility, and multifunctional groups. These properties enable them to be an ideal nanotheranostic agent for multimodal imaging [e.g., photoacoustic imaging (PAI), magnetic resonance imaging (MRI), computed tomography (CT) imaging] guided photothermal therapy of cancer.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.

CuCo2S4 nanocrystals: a new platform for multimodal imaging guided photothermal therapy

Multifunctional nanomaterials open an avenue for the integration of cancer treatment and diagnosis, trending towards the clinical application of nanomedicines in future. Herein, we synthesized biocompatible CuCo₂S₄ nanocrystals (NCs) via a simple reflux method and unitized them as a new theranostic platform, where an intense near-infrared (NIR) absorption offers the CuCo₂S₄ NCs a perfect photothermal performance and photoacoustic (PA) imaging ability; the magnetic characteristic of Co allows them to serve as an enhanced magnetic resonance (MR) contrast agent. The in vitro and in vivo experiments demonstrated their good biocompatibility, non-toxicity and perfect photothermal conversion performance and further confirmed that HeLa tumors could be effectively thermal-ablated upon the assistance of the CuCo₂S₄ NCs. This work introduces the first bioapplication of the CuCo₂S₄ NCs and promotes theranostics based on other ternary compounds.

Synthetic strategies and biomedical applications of I–III–VI ternary quantum dots

In this review, we discuss recent advances of I–III–VI QDs with a major focus on synthesis and biomedical applications; advantages include low toxicity and fluorescent tuning in the biological window.

Layered structure of the near-surface region of oxidized chalcopyrite (CuFeS2): hard X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and DFT+U studies

Metal-depleted layers with different S species are found, and mechanisms for their formation and metal sulfide ‘passivation’ are proposed.

Construction of flexible and stable near-infrared absorbing polymer films containing nickel-bis(dithiolene) moieties via ligand-exchange post-polymerization modification

The expected combinational merits of polymeric materials and nickel-bis(dithiolene) complexes are successfully achieved by a ligand-exchange post-polymerization modification method.

A Porphyrin-Based Conjugated Polymer for Highly Efficient In Vitro and In Vivo Photothermal Therapy

Conjugated polymers have been increasingly studied for photothermal therapy (PTT) because of their merits including large absorption coefficient, facile tuning of exciton energy dissipation through nonradiative decay, and good therapeutic efficacy. The high photothermal conversion efficiency (PCE) is the key to realize efficient PTT. Herein, a donor-acceptor (D-A) structured porphyrin-containing conjugated polymer (PorCP) is reported for efficient PTT in vitro and in vivo. The D-A structure introduces intramolecular charge transfer along the backbone, resulting in redshifted Q band, broadened absorption, and increased extinction coefficient as compared to the state-of-art porphyrin-based photothermal reagent. Through nanoencapsulation, the dense packing of a large number of PorCP molecules in a single nanoparticle (NP) leads to favorable nonradiative decay, good photostability, and high extinction coefficient of 4.23 × 10⁴ m^-1 cm^-1 at 800 nm based on porphyrin molar concentration and the highest PCE of 63.8% among conjugated polymer NPs. With the aid of coloaded fluorescent conjugated polymer, the cellular uptake and distribution of the PorCP in vitro can be clearly visualized, which also shows effective photothermal tumor ablation in vitro and in vivo. This research indicates a new design route of conjugated polymer-based photothermal therapeutic materials for potential personalized theranostic nanomedicine.