Black phosphorus-based nanoplatforms for cancer therapy: chemistry, design, biological and therapeutic behaviors

Cancer, a significant threat to human lives, has been the target of research for several decades. Although conventional therapies have drawbacks, such as side effects, low efficacy, and weak targeting, they have been applied extensively due to a lack of effective alternatives. The emergence of nanotechnology in medicine has opened up new possibilities and offered promising solutions for cancer therapy. In recent years, 2D nanomaterials have attracted enormous attention in nanomedicine due to their large surface-to-volume ratio, photo-responsivity, excellent electrical conductivity, etc. Among them, black phosphorus (BP) is a 2D nanomaterial consisting of multiple layers weakly bonded together through van der Waals forces. Its distinct structure makes BP suitable for biomedical applications, such as drug/gene carriers, PTT/PDT, and imaging agents. BP has demonstrated remarkable potential since its introduction in cancer therapy in 2015, particularly due to its selective anticancer activity even without the aid of near-infrared (NIR) or anticancer drugs. The present review makes efforts to cover and discuss studies published on the anticancer activity of BP. Based on the type of cancer, the subcategories are organized to shed light on the potential of BP nanosheets and BP quantum dots (BPQDs) against breast, brain, skin, prostate, and bone cancers, and a section is devoted to other cancer types. Since extensive attention has been paid to breast cancer cells and in vivo models, various subsections, including mono-, dual, and triple therapeutic approaches are established for this cancer type. Furthermore, the review outlines various synthesis approaches employed to produce BP nanomaterials, providing insights into key synthesis parameters. This review provides an up-to-date platform for the potential reader to understand what has been done about BP cancer therapy based on each disease, and the conclusions and outlook cover the directions in which this approach is going to proceed in the future.

Tribology of 2D black phosphorus - Current state-of-the-art and future potential

Since the first mechanical exfoliation of graphene in 2004, the interest in 2D materials has significantly risen due to their outstanding property combination. Multiple 2D materials have been synthesized until today, while black phosphorus (BP) resembles one of their latest additions. The unique properties of BP, especially for electronic and optical devices (i.e., high carrier mobility and electrical conduction, field-effect transistor, layer-dependent bandgap, anisotropic transport), have gained notable attention. However, its layered structure, similar to those of graphene and MoS2, is also advantageous to optimize the friction and wear performance. Moreover, the strong in-plane covalent bonds and weak interlayer van-der-Waals forces favour the formation of low-friction and wear-resistant films. Although BP holds a great tribological potential, the literature to date on this topic is rather scarce. Therefore, it is a timely moment to holistically summarize the synthesis approaches and properties of BP thus guiding interested researchers to use it in mechanical/tribological applications. The existing state-of-the-art regarding tribological research is critically discussed and compared to other 2D materials thus highlighting existing research gaps and paving the way for future research activities.

Production of high-quality and large lateral-size black phosphorus nanoparticles/nanosheets by liquid-phase exfoliation

The liquid phase exfoliation (LPE) of layered black phosphorus (BP) material is essential in the field of electronics. N-Methyl-2-pyrrolidone (NMP) is one of the most promising precursors for obtaining BP nanosheets/nanoparticles, but the longer sonication time leads to smaller production of phosphorene. Herein, for the first time, the large lateral size fabrication of phosphorene was attained through NMP solvent by optimizing the process parameters. The resultant dispersions were characterized by atomic force microscopy, X-ray powder diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and ultraviolet-visible spectroscopy. The characterization results revealed that the average lateral sizes of BP nanoparticles were found to be 67.8 ± 18.6 nm and the lateral size of fabricated BP nanosheets was found to be 5.37 μm. Moreover, this research provides a strategic approach for the mass production of phosphorene for photodetection applications.

Black Phosphorous Aptamer-based Platform for Biomarker Detection

Black phosphorus nanostructures (nano-BPs) mainly include BP nanosheets (BP NSs), BP quantum dots (BPQDs), and other nano-BPs-based particles at nanoscale. Firstly discovered in 2014, nano-BPs are one of the most popular nanomaterials. Different synthesis methods are discussed in short to understand the basic concepts and developments in synthesis. Exfoliated nano-BPs, i.e. nano-BPs possess high surface area, high photothermal conversion efficacy, excellent biocompatibility, high charge carrier mobility (~1000 cm^-2V^-1s^-1), thermal conductivity of 86 Wm^-1K^-1; and these properties make it a highly potential candidate for fabrication of biosensing platform. These properties enable nano-BPs to be promising photothermal/drug delivery agents as well as in electrochemical data storage devices and sensing devices; and in super capacitors, photodetectors, photovoltaics and solar cells, LEDs, super-conductors, etc. Early diagnosis is very critical in the health sector scenarios. This review attempts to highlight the attempts made towards attaining stable BP, BP-aptamer conjugates for successful biosensing applications. BP-aptamer- based platforms are reviewed to highlight the significance of BP in detecting biological and physiological markers of cardiovascular diseases and cancer; to be useful in disease diagnosis and management.

Crystallization kinetics of amorphous red phosphorus to black phosphorus by chemical vapor transport

The aRP–P4-HP–BP three-stage phase transition revealed the crystallization kinetics and nucleation mechanism of the high-quality BP crystal synthesized by the CVT reaction in the aRP–Sn–I system.

Controllable preparation of crystalline red phosphorus and its photocatalytic properties

Single-element phosphorus has received extensive attention in recent years because of its remarkable photocatalytic properties. In the present experiment, amorphous red phosphorus was controllably transformed into [P12(4)]P2[and Hittorf's phosphorus structures by performing bismuth catalysis. The temperature-controllable chemical vapor transport reaction realized the conversion of more than 90% of amorphous red phosphorus to single-phase crystalline red phosphorus. Under very mild ultrasonic treatment, the high-quality [P12(4)]P2[microbelts and Hittorf's phosphorus microrods were stripped into a few layers of nanobelts and sheet-like structures, respectively. As non-metallic catalysts, their rapid photocatalytic degradations of pollutants (methyl orange) and high hydrogen evolution rates revealed the rapid charge transfer and application potential of the crystalline red phosphorus catalyst. The results of this work could provide new ideas for the development of phosphorus-based crystalline photocatalytic systems.

Synthesis and stabilization of black phosphorus and phosphorene: recent progress and perspectives

Two-dimensional black phosphorus (BP) has triggered tremendous research interest owing to its unique crystal structure, high carrier mobility, and tunable direct bandgap. Preparation of few-layer BP with high quality and stability is very important for its related research and applications in biomedicine, electronics, and optoelectronics. In this review, the synthesis methods of BP, including the preparation of bulk BP crystal which is an important raw material for preparing few-layer BP, the popular top-down methods, and some direct growth strategies of few-layer BP are comprehensively overviewed. Then chemical ways to enhance the stability of few-layer BP are concretely introduced. Finally, we propose a selection rule of preparation methods of few-layer BP according to the requirement of specific BP properties for different applications. We hope this review would bring some insight for future researches on BP and contributes to the acceleration of BP's commercial progress.

2D ternary vanadium phosphorous chalcogenide with strong in-plane optical anisotropy

2D ternary vanadium phosphorous chalcogenide V₂P₄S₁₃, with novel porous structure, ultra-low crystallographic symmetry, and highly optical anisotropy, was introduced as a new member of 2D anisotropic materials.