Monodisperse Copper Chalcogenide Nanocrystals: Controllable Synthesis and the Pinning of Plasmonic Resonance Absorption

Heterostructures of Cu2-xS/Cu2-xTe plasmonic semiconductors: disappearing and reappearing LSPR with anion exchange

Localized surface plasmon resonance (LSPR) of Cu_2-xS nanorods is quenched during the initial Cu_2-xS/Cu_2-xTe core/shell stage of anion exchange then returns as Cu_2-xTe progresses into the nanorod. Phase change within the core accounts for this behaviour illustrating the complexity emergent from anion exchange.

Development of defective molybdenum oxides for photocatalysis, thermal catalysis, and photothermal catalysis

The localized surface plasmon resonance (LSPR) of noble metals has been investigated for decades for applications in various catalysis reactions and optical research studies, but its development has been hampered by inefficient light absorption and high costs. In comparison, the creation of less expensive semiconductors (metal oxides) with strong plasmonic absorption is an appealing option, particularly defective molybdenum oxide (H_xMoO_3-y) has received considerable attention and investigation as a promising plasmonic material for a variety of catalytic reactions (photocatalysis, thermocatalysis, photothermal catalysis, etc.).The LSPR effect of H_xMoO_3-y can be tuned throughout a broad spectrum range from visible to near-infrared (NIR) by altering the doping amount by electrochemical control, chemical reduction, or photochemical control. Notably, defects (oxygen vacancies) in H_xMoO_3-y arise in conjunction with the LSPR effect, resulting in the formation of unique and useful active sites in a range of catalytic processes. In this review, we explore the formation mechanism of H_xMoO_3-y with plasmonic features and discuss its applications in photocatalysis, thermocatalysis, and photothermal catalysis.

Synthesis of MnO2-Ag Nanojunctions with Plasmon-Enhanced Photocatalytic and Photothermal Effects for Constructing Rewritable Mono-/Multi-Color Fabrics

Semiconductor-mediated photoreversible color switching systems (PCSSs) have great potential to replace traditional photochromic materials, and the key is to obtain semiconductors with unique photocatalytic and photothermal features. Herein, we have developed MnO₂-Ag nanojunctions with plasmon-enhanced photocatalytic and photothermal effects for PCSSs. MnO₂-Ag nanojunctions are solvothermally synthesized with Mn(CH₃COO)₃, KMnO₄, and AgNO₃ in diethylene glycol as precursors, and they are composed of MnO₂ nanoparticles (∼30 nm) that are decorated by Ag nanodots (∼6 nm). The presence of Ag confers an enhanced visible photoabsorption with a narrow band gap for MnO₂ (E_g = 1.82 eV) and a weak/broad photoabsorption tail (∼875 nm) compared to that of pure MnO₂ (2.45 eV, ∼625 nm). By coupling MnO₂-Ag nanojunctions with various redox dyes, some PCSS inks can be obtained, and especially, the inks containing hydroxyethyl cellulose could be used to prepare rewritable fabrics. When inks and fabrics are irradiated by 475 nm light, rapid discoloration can occur, resulting from the photocatalytic reduction of the dye. Contrarily, the irradiation of 808 nm light promotes the rapid recoloration since Ag nanodots with plasmonic effects in the nanojunctions can absorb light to generate heat, which facilitates the oxidization of leuco dyes in air. Consequently, remote printing of figures was attained on the rewritable fabrics via 475 nm light illumination, and then, the erasure was performed by 808 nm light illumination in an O₂ atmosphere, with high reversibility and cycling stability. Therefore, MnO₂-Ag nanojunctions have tremendous promise for rewritable media, and the introduction of metal-semiconductor junctions as a nanophotocatalyst offers new insights for PCSSs.

Lenvatinib and Cu2-xS nanocrystals co-encapsulated in poly(D,L-lactide-co-glycolide) for synergistic chemo-photothermal therapy against advanced hepatocellular carcinoma

Lenvatinib (LT) is gradually replacing sorafenib as an alternative targeted drug against advanced hepatocellular carcinoma (HCC). However, the anticancer effects of LT are still limited because of its low cytotoxicity, multidrug resistance (MDR), and tumor relapse. Herein, we constructed a smart biophotonic nanoplatform to overcome the barriers preventing high performance. LT and copper sulfide nanocrystals (Cu_2-xS NCs) with excellent photothermal properties in the near-infrared-II (NIR-II) zone were co-encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) through nanoprecipitation. Both in vitro and in vivo evaluations demonstrated that Cu_2-xS NCs enhanced the anticancer efficacy of LT, without recurrence. In addition, the presence of copper ions could allow glutathione (GHS) to be consumed and oxygen to be produced, likely suppressing the expression of P-glycoprotein (P-gp) and overcoming the issue of MDR relating to LT. More importantly, synergistic chemo-photothermal therapy with LT and Cu_2-xS NCs was more effective than any single therapy or theoretical combination. This nanoplatform is promising for advancing future LT-based treatment strategies for HCC therapy.

General Microwave Route to Single-Crystal Porous Transition Metal Nitrides for Highly Sensitive and Stable Raman Scattering Substrates

The synthesis of metallic transition metal nitrides (TMNs) has traditionally been performed under harsh conditions, which makes it difficult to prepare TMNs with high surface area and porosity due to the grain sintering. Herein, we report a general and rapid (30 s) microwave synthesis method for preparing TMNs with high specific surface area (122.6-141.7 m² g^-1) and porosity (0.29-0.34 cm³ g^-1). Novel single-crystal porous WN, Mo₂N, and V₂N are first prepared by this method, which exhibits strong surface plasmon resonance, photothermal conversion, and surface-enhanced Raman scattering effects. Different from the conventional low-temperature microwave absorbing media such as water and polymers, as new concept absorbing media, hydrated metal oxides and metallic metal oxides are found to have a remarkable high-temperature microwave heating effect and play key roles in the formation of TMNs. The current research results provide a new-concept microwave method for preparing high lattice energy compounds with high specific surface.

Cu-Sb-S Ternary Semiconductor Nanoparticle Plasmonics

Semiconductor plasmonics is a recently emerging field that expands the chemical and physical bandwidth of the hitherto well-established noble metallic nanoparticles. Achieving tunable plasmonics from colloidal semiconductor nanocrystals has drawn enormous interest and is promising for plasmon-related applications. However, realizing this goal of tunable semiconductor nanocrystals is currently still a synthetic challenge. Here, we report a colloidal synthesis strategy for highly dispersed, platelet-shaped, antimony-doped copper sulfide semiconductor nanocrystals (Sb_y-Cu_xS NCs) with a dominant localized surface plasmon resonance (LSPR) band tunable from the near-infrared into the midvisible spectral range. This work presents the synthesis and quantifies the resulting plasmonic features. It furthermore elucidates the underlying carrier concentration requirements to realize a continuum of LSPR spectra. Building on our previous work on binary plasmonics Cu_xS, Cu_xSe, and Cu_xTe NCs, the present method introduces a much wider and finer tunability with ternary semiconductor plasmonics.

CuGeO3 Nanoparticles: An Efficient Photothermal Theragnosis Agent for CT Imaging-Guided Photothermal Therapy of Cancers

The photothermal agents have been widely developed due to the minimally invasive treatment for targeted tumor photothermal therapy, which is considered to have great potential for antitumor bioapplications. The development of multifunctional photothermal agents is extremely challenging. This work presents a novel photothermal theragnosis agent, i.e., CuGeO3 nanoparticles (CGO NPs), showing intense absorption in the near-infrared (NIR) window and excellent ability of CT imaging. Due to the strong NIR absorption, CGO NPs exhibit excellent photothermal effect with a photothermal conversion efficiency of 59.4%. Moreover, because of the high X-ray attenuation coefficient of germanium, the CGO NPs have a great potential of CT imaging diagnosis in clinical application. Additionally, the CGO NPs show negligible cytotoxicity in vitro and in vivo, indicating that it can be served as an outstanding contrast and anticancer agent in a biosafe way. Our work opens the way for the development of bimetallic copper-based oxides used in photothermal diagnostic agents for cancer treatment.

Toxicity of nanomaterials due to photochemical degradation and the release of heavy metal ions

The increased production of semiconductor nanomaterials such as heavy metal quantum dots and perovskites for applications such as in energy harvesting, optoelectronic devices, bioanalysis, phototherapy and consumer health products raises concerns regarding nanotoxicity. After disposal, these materials degrade upon interaction with the environment, such as rain and surface waters, soil and oxygen, and solar irradiation, leading to the release of heavy metal ions in the environment with exposure to aquatic and terrestrial animals and plants, and humans. Researchers are in the early stages of understanding the potential toxicity of such nanomaterials by quantifying the amount of heavy metal ions released due to environmental or biological transformation. Here, we evaluate the toxicity of environmentally transformed nanomaterials by considering PbS quantum dots as a model system. Using metal ion sensors and steady-state fluorescence spectroscopy, we quantify the amount of Pb2+ released by the photochemical etching of quantum dots. Furthermore, with the help of cytotoxicity and comet assays, and DNA gel electrophoresis, we evaluate the adverse effects of the released metal ions into the cultured lung epithelial (H1650), and neuronal (PC12) cells. These studies reveal higher levels of cell proliferation and DNA damage to PC12 cells, suggesting the neurotoxicity of lead due to not only the downregulation of glutathione, elevated levels of reactive oxygen and nitrogen species, and a calcium influx but also the proactivation of activator protein 1 that is correlated with protein kinase c. This research shows the significance of molecular biology studies on different cells and animals to critically understand the health and environmental costs of heavy metal-based engineered nanomaterials.

Hollow Octahedral Cu2-xS/CdS/Bi2S3 p-n-p Type Tandem Heterojunctions for Efficient Photothermal Effect and Robust Visible-Light-Driven Photocatalytic Performance

Reasonable design of the nanostructure of heterogeneous photocatalysts is of great significance for improving their performance and stability. We report the design and fabrication of hollow sandwich-layered octahedral Cu_2-xS/CdS/Bi₂S₃ p-n-p type tandem heterojunctions constructed via the continuous growth deposition method on the surface of hollow octahedral Cu_2-xS with well-defined structures and interfaces. The unique hollow sandwich nanostructure has a large specific surface area and abundant reaction sites and enhances the separation and transfer of photogenerated carriers. In addition, the formation of a p-n-p heterojunction coupled with the surface plasmon resonance effect of Cu_2-xS could also aid in photocatalytic H₂ evolution performance and photocatalytic degradation efficiency. Under vis-NIR light irradiation, the optimized Cu_2-xS/CdS/Bi₂S₃ photocatalyst displays a notable H₂ production rate of 8012 μmol h^-1 g^-1, and 2,4-dichlorophenol is almost completely photocatalytically degraded in 150 min. This strategy and rational design offer a new path toward the design of specific nanocatalysts with enhanced activity and stability and challenging reactions.

Properties, fabrication and applications of plasmonic semiconductor nanocrystals

We highlight three widely explored oxide-based plasmonic materials, including H_xMoO_3−y, H_xWO_3−y, and Mo_xW_1−xO_3−y, and their applications in catalysis.

Peptide Nanotube-Templated Biomineralization of Cu2-x S Nanoparticles for Combination Treatment of Metastatic Tumor

1D peptide nanostructures (i.e., peptide nanotubes, PNTs) exhibit tunable chemo-physical properties and functions such as improved tissue adhesion, increased cellular uptake, and elongated blood circulation. In this study, the application of PNTs as a desirable 1D template for biomineralization of Cu_2-x S nanoparticles (Cu_2-x S NPs, x = 1-2) is reported. Monodisperse Cu_2-x S NPs are uniformly coated on the peptide nanotubes owing to the specific high binding affinity of Cu ions to the imidazole groups exposed on the surface of nanotubes. The Cu_2-x S NP-coated PNTs are further covalently grafted with an oxaliplatin prodrug (Pt-CuS-PNTs) to construct a versatile nanoplatform for combination cancer therapy. Upon 808 nm laser illumination, the nanoplatform induces significant hyperthermia effect and elicits reactive oxygen species generation through electron transfer and Fenton-like reaction. It is demonstrated that the versatile nanoplatform dramatically inhibits tumor growth and lung metastasis of melanoma in a B16-F10 melanoma tumor-bearing mouse model by combined photo- and chemotherapy. This study highlights the ability of PNTs for biomineralization of metal ions and the promising potential of such nanoplatforms for cancer treatment.

Controllable Synthesis of Monodispersed Fe1- xS2 Nanocrystals for High-Performance Optoelectronic Devices

The optical properties of stoichiometric iron pyrite (FeS₂) nanocrystals (NCs) are characterized by strong UV-Visible (UV-Vis) absorption within the cutoff while negligible absorption beyond the cutoff in near-infrared and longer wavelengths. Herein, we show this bandgap limitation can be broken through controllable synthesis of nonstoichiometric Fe_{1- x}S₂ NCs ( x = 0.01-0.107) to induce localized surface plasmonic resonance (LSPR) absorption beyond the cutoff to short-wave infrared spectrum (SWIR, 1-3 μm) with remarkably enhanced broadband absorption across UV-Vis-SWIR spectra. To illustrate the benefit of the broadband absorption, colloidal LSPR Fe_{1- x}S₂ NCs were printed on graphene to form LSPR Fe_{1- x}S₂ NCs/graphene heterostructure photodetectors. Extraordinary photoresponsivity in exceeding 4.32 × 10⁶ A/W and figure-of-merit detectivity D* > 7.50 × 10¹² Jones have been demonstrated in the broadband of UV-Vis-SWIR at room temperature. These Fe_{1- x}S₂ NCs/graphene heterostructures are printable and flexible and therefore promising for practical optical and optoelectronic applications.

Localized Surface Plasmon Resonance in Semiconductor Nanocrystals

Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals (NCs) that results in resonant absorption, scattering, and near field enhancement around the NC can be tuned across a wide optical spectral range from visible to far-infrared by synthetically varying doping level, and post synthetically via chemical oxidation and reduction, photochemical control, and electrochemical control. In this review, we will discuss the fundamental electromagnetic dynamics governing light matter interaction in plasmonic semiconductor NCs and the realization of various distinctive physical properties made possible by the advancement of colloidal synthesis routes to such NCs. Here, we will illustrate how free carrier dielectric properties are induced in various semiconductor materials including metal oxides, metal chalcogenides, metal nitrides, silicon, and other materials. We will highlight the applicability and limitations of the Drude model as applied to semiconductors considering the complex band structures and crystal structures that predominate and quantum effects that emerge at nonclassical sizes. We will also emphasize the impact of dopant hybridization with bands of the host lattice as well as the interplay of shape and crystal structure in determining the LSPR characteristics of semiconductor NCs. To illustrate the discussion regarding both physical and synthetic aspects of LSPR-active NCs, we will focus on metal oxides with substantial consideration also of copper chalcogenide NCs, with select examples drawn from the literature on other doped semiconductor materials. Furthermore, we will discuss the promise that LSPR in doped semiconductor NCs holds for a wide range of applications such as infrared spectroscopy, energy-saving technologies like smart windows and waste heat management, biomedical applications including therapy and imaging, and optical applications like two photon upconversion, enhanced luminesence, and infrared metasurfaces.

Switching between Plasmonic and Fluorescent Copper Sulfide Nanocrystals

Control over the doping density in copper sulfide nanocrystals is of great importance and determines its use in optoelectronic applications such as NIR optical switches and photovoltaic devices. Here, we demonstrate that we can reversibly control the hole carrier density (varying from >10²² cm^–3 to intrinsic) in copper sulfide nanocrystals by electrochemical methods. We can control the type of charge injection, i.e., capacitive charging or ion intercalation, via the choice of the charge compensating cation (e.g., ammonium salts vs Li⁺). Further, the type of intercalating ion determines whether the charge injection is fully reversible (for Li⁺) or leads to permanent changes in doping density (for Cu⁺). Using fully reversible lithium intercalation allows us to switch between thin films of covellite CuS NCs (E_g = 2.0 eV, hole density 10²² cm^–3, strong localized surface plasmon resonance) and low-chalcocite CuLiS NCs (E_g = 1.2 eV, intrinsic, no localized surface plasmon resonance), and back. Electrochemical Cu⁺ ion intercalation leads to a permanent phase transition to intrinsic low-chalcocite Cu₂S nanocrystals that display air stable fluorescence, centered around 1050 nm (fwhm ∼145 meV, PLQY ca. 1.8%), which is the first observation of narrow near-infrared fluorescence for copper sulfide nanocrystals. The dynamic control over the hole doping density and fluorescence of copper sulfide nanocrystals presented in this work and the ability to switch between plasmonic and fluorescent semiconductor nanocrystals might lead to their successful implementation into photovoltaic devices, NIR optical switches and smart windows.

Emerging Low-Dimensional Materials for Nonlinear Optics and Ultrafast Photonics

Low-dimensional (LD) materials demonstrate intriguing optical properties, which lead to applications in diverse fields, such as photonics, biomedicine and energy. Due to modulation of electronic structure by the reduced structural dimensionality, LD versions of metal, semiconductor and topological insulators (TIs) at the same time bear distinct nonlinear optical (NLO) properties as compared with their bulk counterparts. Their interaction with short pulse laser excitation exhibits a strong nonlinear character manifested by NLO absorption, giving rise to optical limiting or saturated absorption associated with excited state absorption and Pauli blocking in different materials. In particular, the saturable absorption of these emerging LD materials including two-dimensional semiconductors as well as colloidal TI nanoparticles has recently been utilized for Q-switching and mode-locking ultra-short pulse generation across the visible, near infrared and middle infrared wavelength regions. Beside the large operation bandwidth, these ultrafast photonics applications are especially benefit from the high recovery rate as well as the facile processibility of these LD materials. The prominent NLO response of these LD materials have also provided new avenues for the development of novel NLO and photonics devices for all-optical control as well as optical circuits beyond ultrafast lasers.

Recent advances in the rational design of copper chalcogenide to enhance the photothermal conversion efficiency for the photothermal ablation of cancer cells

Three rational designs and the mechanism for copper chalcogenide to enhance the heat conversion efficiency were discussed.

Universal Near-Infrared and Mid-Infrared Optical Modulation for Ultrafast Pulse Generation Enabled by Colloidal Plasmonic Semiconductor Nanocrystals

Field effect relies on the nonlinear current-voltage relation in semiconductors; analogously, materials that respond nonlinearly to an optical field can be utilized for optical modulation. For instance, nonlinear optical (NLO) materials bearing a saturable absorption (SA) feature an on-off switching behavior at the critical pumping power, thus enabling ultrafast laser pulse generation with high peak power. SA has been observed in diverse materials preferably in its nanoscale form, including both gaped semiconductor nanostructures and gapless materials like graphene; while the presence of optical bandgap and small carrier density have limited the active spectral range and intensity. We show here that solution-processed plasmonic semiconductor nanocrystals exhibit superbroadband (over 400 THz) SA, meanwhile with large modulation depth (∼7 dB) and ultrafast recovery (∼315 fs). Optical modulators fabricated using these plasmonic nanocrystals enable mode-locking and Q-switching operation across the near-infrared and mid-infrared spectral region, as exemplified here by the pulsed lasers realized at 1.0, 1.5, and 2.8 μm bands with minimal pulse duration down to a few hundreds of femtoseconds. The facile accessibility and superbroadband optical nonlinearity offered by these nonconventional plasmonic nanocrystals may stimulate a growing interest in the exploiting of relevant NLO and photonic applications.

Photothermal-enhanced catalysis in core-shell plasmonic hierarchical Cu7S4 microsphere@zeolitic imidazole framework-8

A strategy to improve reaction activity via the photothermal effect of plasmonic semiconductor nanomaterials is demonstrated in a core–shell structured catalyst.

Conventional semiconductor photocatalysis based on band-edge absorption remains inefficient due to the limited harvesting of solar irradiation and the complicated surface/interface chemistry. Herein, novel photothermal-enhanced catalysis was achieved in a core–shell hierarchical Cu₇S₄ nano-heater@ZIF-8 heterostructures via near-infrared localized surface plasmon resonance. Our results demonstrated that both the high surface temperature of the photothermal Cu₇S₄ core and the close-adjacency of catalytic ZIF-8 shell contributed to the extremely enhanced catalytic activity. Under laser irradiation (1450 nm, 500 mW), the cyclocondensation reaction rate increased 4.5–5.4 fold compared to that of the process at room temperature, in which the 1.6–1.8 fold enhancement was due to the localized heating effect. The simulated sunlight experiments showed a photothermal activation efficiency (PTAE) of 0.07%, further indicating the validity of photothermal catalysis based on the plasmonic semiconductor nanomaterials. More generally, this approach provides a platform to improve reaction activity with efficient utilization of solar energy, which can be readily extended to other green-chemistry processes.

Copper-Based Nanomaterials for Cancer Imaging and Therapy

Copper based nanoparticles (NPs) have attracted increased attention for biomedical applications. Copper chalcogenide NPs exhibit strong absorption in near-infrared region, demonstrate highly efficient light-to-heat transformation under near-infrared laser irradiation, and cause selective thermal destruction to the tumor. Smaller copper NPs display fluorescence signal and capability for optical imaging. Copper based NPs also serve as a versatile vehicle for drug delivery and image-guided therapy. This review covers recent advances related to the biomedical application of copper based NPs, with a focus on cancer imaging and therapy. We also discuss challenges to their successful clinical translation.

Synthetic methods of CuS nanoparticles and their applications for imaging and cancer therapy

A comprehensive survey of basic concepts and up-to-date literature results concerning the potential use of CuS nanoparticles for biomedical applications.

Structural evolution from CuS nanoflowers to Cu9S5 nanosheets and their applications in environmental pollution removal and photothermal conversion

The influence of crystal phase and morphologies from 3D CuS nanoflowers to Cu₉S₅ nanosheets with hexagonal holes on their photothermal conversion and photocatalytic activity were systemically investigated.