Silicene: Wet-Chemical Exfoliation Synthesis and Biodegradable Tumor Nanomedicine

From Octahedron Crystals to 2D Silicon Nanosheets: Facet-Selective Cleavage and Biophotonic Applications

2D silicon nanosheets (SiNSs) are promising materials for biomedicine but facile synthesis of SiNSs remains a challenge. Herein, by means of a sulfur-iodine co-assisted chemical vapor transport method, octahedron silicon (oct-Si) crystals with fully exposed {111} planes are prepared as precursors for efficient synthesis of SiNSs by facet-selective exfoliation. The 13 nm thick SiNSs have good biocompatibility and the sharp Raman scattering signal facilitates intracellular Raman imaging upon exposure to a near-infrared (NIR) laser. Furthermore, the SiNSs have excellent NIR photothermal characteristics such as a large extinction coefficient of 11.3 L g^-1 cm^-1 and high photothermal conversion efficiency of 21.4% at 1064 nm. In vitro experiments demonstrate superior NIR-II photothermal therapeutic effects in killing cancer cells. Comparing to conventional methods, the novel facet-selective cleavage strategy is more controllable and environmentally friendly boding well for the fabrication of non-van der Waals 2D materials. The multimodal photonic behavior also suggests large potential of the SiNSs pertaining to integrated multi-NIR biophotonic techniques using single nanomaterials.

Engineering two-dimensional silicene composite nanosheets for dual-sensitized and photonic hyperthermia-augmented cancer radiotherapy

The rapid development of nanotechnology has triggered the emerging of tremendous theranostic nanoplatforms for combating cancers. Silicene, as an emerging two-dimensional (2D) material, has been recently explored as therapeutic agent due to their desirable biodegradation and strong photothermal-conversion performance. However, the rational design of silicene-based composites for further exerting multifunctional medical applications is still highly challenging. Herein, we report on the construction of silicene-based silicene@Pt composite nanosheets for computed tomography (CT)/photoacoustic (PA) imaging-guided dual-sensitized radiotherapy combined with photonic tumor hyperthermia, which has been achieved by a seed-growth approach to in situ grow Pt components onto silicene nanosheets' surface. Especially, by functionalization of Pt components, these nanosheets could act as both contrast agents for CT imaging and dual radio-sensitizing agents for radiotherapy, which could deposit Pt-involved radiation energy (sensitized therapeutic process I) and overcome hypoxia-associated radio-resistance by Pt-catalytic O₂ generation from overexpressed H₂O₂ within the tumor microenvironment (sensitized therapeutic process II). The strong photothermal-conversion performance of silicene nanosheets not only endowed silicene@Pt composite nanosheets with photoacoustic imaging property, but also realized the photonic tumor hyperthermia and achieved a combined therapeutic effect with radiotherapy. This work not only broadens the biomedical applications of silicene, but also develops functionalization strategies of silicene for versatile biomedical applications.

Potentiated cytosolic drug delivery and photonic hyperthermia by 2D free-standing silicene nanosheets for tumor nanomedicine

Silicene, as an emerging two-dimensional (2D) silicon allotrope, mainly serves in the field of electronics and energy devices but multidisciplinary studies on 2D silicene have been rarely carried out, especially the potential translational biomedical practice. In this study, we explore a high-performance photonic drug-delivery nanoplatform based on 2D ultrathin silicene nanosheets (DOX@silicene-BSA NSs) regarding effective chemotherapeutic drug loading (capacity amount of w/w%: 137.0%) while highlighting the potentiated cytosolic drug-delivery efficiency (spatiotemporally pH-/NIR-triggered drug-release) and NIR-II-activated photonic hyperthermia (η = 19.7%) performance, thus, enabling the potential synergistic chemotherapeutic and phototherapeutic outcomes. The cellular endocytotic mechanism of these nanosheets in cancer cells has been comprehensively studied and provides an essential understanding of the nano-bio interactions of silicene-based nanosheets or other emerging 2D nanostructures. Prominent suppression of tumor growth was achieved by synergistic chemotherapy and photonic hyperthermia with negligible adverse effects and expected degradability, thus addressing the several fundamental barriers of oncology-related nanotherapies. This work highlights silicene, which integrates the merits of high specific surface area endowed with 2D topology, intrinsic responsiveness toward physical/chemical stimuli, and biomedical necessity of biodegradation and biosafety, as a promising next-generation omnipotent alternative to subrogate traditional silicon-based biomaterials and non-biocompatible nanoagents in clinical translation nanomedicine.

Photonic hyperthermal and sonodynamic nanotherapy targeting oral squamous cell carcinoma

Nanomedicine that enables multiple synergetic treatments provides effective non-invasive treatment modalities for cancer therapy. Yet treatments for oral squamous cell carcinoma (OSCC) are rarely reported. Here, we designed OSCC-targeting multi-functional nanomedicines to overcome the therapeutic obstacles during OSCC treatments, including ineffective chemotherapy, and the traumatic surgery and radiotherapy. The urokinase plasminogen activator receptor (uPAR)-targeting ligand AE105 decorated dendritic mesoporous silica nanoparticles (DMSN) encapsulating photonic active ultrasmall Cu2-xS NPs and sonosensitizer Rose Bengal (RB) have been rationally designed and constructed (designated as Cu2-xS-RB@DMSN-AE105, abbreviated as CRDA). These CRDAs initially target the uPAR, which is overexpressed in the OSCC cell membrane, to increase the localized accumulation of CRDAs at tumor sites. Under the irradiation of both near-infrared laser and ultrasound, the in situ photonic-hyperthermal and sonodynamic effects are respectively enabled to induce the cell death of OSCC. Upon both in vitro/in vivo challenges, tumor cells/xenografts have been efficiently eradicated, achieving the targeting and synergetic treatment modality against the OSCC with satisfactory biocompatibility.

Two-dimensional silicene composite nanosheets enable exogenous/endogenous-responsive and synergistic hyperthermia-augmented catalytic tumor theranostics

Silicene as an emerging two-dimensional material (2DM) spurs the broad research interests due to its prominent electronic and physical properties, however, still lacking in exploitation for the biological and medical practices. Herein, we constructed a 2D silicene-based theranostic nanoplatform, MnO_x@silicene-BSA (MS-BSA), with tumor microenvironment (TME)-responsive and synergistic hyperthermia-augmented catalytic activity when irradiated by near infrared-II (NIR-II) laser because of the high photothermal-conversion efficiency of 2D silicene matrix. Such MS-BSA nanosheets possess the capability to react with glutathione (GSH) to generate Mn²⁺ and glutathione disulfide (GSSG) under acidity/reducing TME condition. With the presence/assistance of HCO₃^-, the released Mn²⁺ exhibited sensitive catalytic activity towards endogenous H₂O₂via Fenton-like reaction, enabling the generation of highly toxic hydroxyl radicals (•OH), which finally led to the enhanced nanocatalytic therapeutic efficacy followed by exogenous NIR-II laser exposure, originating from hyperthermia-augmented catalytic activity. Especially, these MS-BSA nanosheets accumulated into the tumor region to enable superb contrast enhancement of TME-responsive T₁-weighted magnetic resonance imaging (MRI) and photoacoustic imaging (PAI), and high-efficient in vivo synergistic tumor eradication. Therefore, such an intelligent photothermal-enhanced catalytic theranostic nanoplatform could realize the exogenous/endogenous-responsive and cooperative hyperthermia-augmented tumor treatment and accurate tumor positioning/monitoring.

Lysine demethylase KDM3A regulates nanophotonic hyperthermia resistance generated by 2D silicene in breast cancer

Breast cancer (BC) is the most common malignant disease affecting women's health worldwide. The benefits from conventional therapeutic modalities are severely limited. An increasing number of promising photothermal materials have been recently developed and introduced into the therapeutic regimens of BC, but the underlying biological mechanism remains unclear. Silicon-based materials have enjoyed many popularities in the biomedical field owing to their desirable biocompatibility, biodegradability and versatility. Herein, we introduced two dimensional (2D) silicene nanosheets (SNSs) into the BC treatment and achieved profound photothermal-ablation efficacy. Importantly, this work reveals the underlying biological mechanism and regulation factors of photonic hyperthermia in BC. The RNA sequencing and immunoblot demonstrated that photothermia enhanced apoptosis in BC by activating caspase 3 and caspase 7. Importantly, knockdown of lysine demethylase KDM3A sensitized BC to photothermia epigenetically. It has been revealed that KDM3A could erase p53K372me1 and suppress the anti-cancer functions of p53, leading to the downregulation of pro-apoptotic proteins-PUMA and NOXA verified by Co-IP and ChIP-qPCR assays. Therefore, our results not only import near infrared light (NIR) induced photothermal ablation generated by SNSs-BSA into the BC treatment, but also clarify the underlying mechanism and regulation factors for further photothermal performance optimization and clinical translation.

Nanoengineering Microstructure of Hybrid C-S-H/Silicene Gel

Two-dimensional (2D) materials have been incorporated into calcium silicate hydrate (C-S-H) gel to enhance its mechanical performance for decades, while the modified C-S-H gel exhibits poor toughness, tensile strength, and ductility. In this work, we report a new design strategy and synthesis route to strengthen C-S-H interface by intercalating a silicene sheet of one atom thickness. The hybrid C-S-H/Silicene gel shows superb mechanical properties, with a remarkable enhancement in strength and other functional properties. By using density functional theory (DFT) and molecular dynamics (MD) simulations, we have demonstrated that Si-O bonds between silicene and C-S-H are stable and covalent, and the interaction energy of this bilayer gel nearly doubles by forming a 3D covalent network with a strong bridging effect. Owing to its better crystallinity enrichment and its induced dislocation dissipation mechanism, the hybrid C-S-H/Silicene gel possesses a higher tensile ductility (∼118% average enhancement and ∼228% in the c direction) and a much smaller elastic stiffness (59.04 GPa for average Young's modulus). This work offers an ingenuous route in turning brittle C-S-H gel into a soft gel, which provides opportunities for fabricating ultrahigh performance cementitious materials.

Graphene and other 2D materials: a multidisciplinary analysis to uncover the hidden potential as cancer theranostics

Cancer represents one of the main causes of death in the world; hence the development of more specific approaches for its diagnosis and treatment is urgently needed in clinical practice. Here we aim at providing a comprehensive review on the use of 2-dimensional materials (2DMs) in cancer theranostics. In particular, we focus on graphene-related materials (GRMs), graphene hybrids, and graphdiyne (GDY), as well as other emerging 2DMs, such as MXene, tungsten disulfide (WS2), molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN), black phosphorus (BP), silicene, antimonene (AM), germanene, biotite (black mica), metal organic frameworks (MOFs), and others. The results reported in the scientific literature in the last ten years (>200 papers) are dissected here with respect to the wide variety of combinations of imaging methodologies and therapeutic approaches, including drug/gene delivery, photothermal/photodynamic therapy, sonodynamic therapy, and immunotherapy. We provide a unique multidisciplinary approach in discussing the literature, which also includes a detailed section on the characterization methods used to analyze the material properties, highlighting the merits and limitations of the different approaches. The aim of this review is to show the strong potential of 2DMs for use as cancer theranostics, as well as to highlight issues that prevent the clinical translation of these materials. Overall, we hope to shed light on the hidden potential of the vast panorama of new and emerging 2DMs as clinical cancer theranostics.

Ultrasonic-Ball Milling: A Novel Strategy to Prepare Large-Size Ultrathin 2D Materials

Large-size ultrathin 2D materials, with extensive applications in optics, medicine, biology, and semiconductor fields, can be prepared through an existing common physical and chemical process. However, the current exfoliation technologies still need to be improved upon with urgency. Herein, a novel and simple "ultrasonic-ball milling" strategy is reported to effectively obtain high quality and large size ultrathin 2D materials with complete lattice structure through the introduction of moderate sapphire (Al₂ O₃ ) abrasives in a liquid phase system. Ultimately numerous high-quality ultrathin h-BN, graphene, MoS₂ , WS₂ , and BCN nanosheets are obtained with large sizes ranging from 1-20 µm, small thickness of ≈1-3 nm and a high yield of over 20%. Utilizing shear and friction force synergistically, this strategy provides a new method and alternative for preparing and optimizing large size ultrathin 2D materials.

Anti-Infective Application of Graphene-Like Silicon Nanosheets via Membrane Destruction

The increasing problem of bacterial resistance to the currently effective antibiotics has resulted in the need for increasingly potent therapeutics to eradicate pathogenic microorganisms. 2D nanomaterials (2D NMs) have unique physical and chemical properties that make them attractive candidates for biomedical applications. Recently, the application of 2D NMs as antibacterial agents has attracted significant attention. Herein, a novel 2D graphene-like silicon nanosheet (GS NS) antimicrobial agent is fabricated from pristine silicon crystals by ultrasonication, which results in a highly exfoliated planar morphology and a significantly larger surface area as compared with bulk silicon. The GS NSs exhibit remarkable in vitro broad-spectrum bactericidal activity against Gram (-) Escherichia coli and Gram (+) Staphylococcus aureus because of a close interaction with the bacteria, which leads to highly efficient membrane destruction. The in vivo studies demonstrate that the local administration of GS NSs effectively mitigates implant-related infection by reducing the bacterial burden of the extracted samples and accelerating the remission of local inflammation. Based on these encouraging results, GS NSs are expected to be a useful new member of the 2D NMs family, with the potential of effectively killing pathogenic bacteria in clinical applications.

Anti‐Infective Application of Graphene‐Like Silicon Nanosheets via Membrane Destruction

The increasing problem of bacterial resistance to the currently effective antibiotics has resulted in the need for increasingly potent therapeutics to eradicate pathogenic microorganisms. 2D nanomaterials (2D NMs) have unique physical and chemical properties that make them attractive candidates for biomedical applications. Recently, the application of 2D NMs as antibacterial agents has attracted significant attention. Herein, a novel 2D graphene‐like silicon nanosheet (GS NS) antimicrobial agent is fabricated from pristine silicon crystals by ultrasonication, which results in a highly exfoliated planar morphology and a significantly larger surface area as compared with bulk silicon. The GS NSs exhibit remarkable in vitro broad‐spectrum bactericidal activity against Gram (−) Escherichia coli and Gram (+) Staphylococcus aureus because of a close interaction with the bacteria, which leads to highly efficient membrane destruction. The in vivo studies demonstrate that the local administration of GS NSs effectively mitigates implant‐related infection by reducing the bacterial burden of the extracted samples and accelerating the remission of local inflammation. Based on these encouraging results, GS NSs are expected to be a useful new member of the 2D NMs family, with the potential of effectively killing pathogenic bacteria in clinical applications.

Phototherapy with layered materials derived quantum dots

Quantum dots (QDs) originating from two-dimensional (2D) sheets of graphitic carbon nitride (g-C₃N₄), graphene, hexagonal boron nitride (h-BN), monoatomic buckled crystals (phosphorene), germanene, silicene and transition metal dichalcogenides (TMDCs) are emerging zero-dimensional materials. These QDs possess diverse optical properties, are chemically stable, have surprisingly excellent biocompatibility and are relatively amenable to surface modifications. It is therefore not difficult to see that these QDs have potential in a variety of bioapplications, including biosensing, bioimaging and anticancer and antimicrobial therapy. In this review, we briefly summarize the recent progress of these exciting QD based nanoagents and strategies for phototherapy. In addition, we will discuss about the current limitations, challenges and future prospects of QDs in biomedical applications.

2D nanostructures beyond graphene: preparation, biocompatibility and biodegradation behaviors

The research advances of the preparation, biocompatibility and biodegradation of 2D nanomaterials are introduced. The prospects and challenges of the biomedical applications of 2D nanomaterials are summarized.