Naziah Mohamad Latiff

Black Phosphorus Nanoparticle Labels for Immunoassays via Hydrogen Evolution Reaction Mediation

Black phosphorus is an emerging layered material. Its nanoparticles show an increased bandgap when compared to bulk materials and they are typically fabricated by ultrasonication of macroscopic black phosphorus crystals. Here we fabricate black phosphorus nanoparticles (BP NPs) by solution based electrochemical exfoliation with bipolar electrodes, which induces opposite potentials on the opposite ends of black phosphorus macroparticles thereby leading to its decomposition into nanoparticles. BP NPs have enhanced catalytic effect on the hydrogen evolution reaction (HER) relative to black phosphorus macroparticles. We utilize black phosphorus nanoparticles as electrocatalytic tags in a competitive immunoassay for rabbit immunoglobulin G (IgG) detection. The detection signal is produced via nanoimpacts of the BP NPs followed by HER catalysis.

The Cytotoxicity of Layered Black Phosphorus

Black phosphorus (BP), the latest addition to the family of 2D layered materials, has attracted much interest owing to potential optoelectronics, nanoelectronics, and biomedicine applications. Little is known about its toxicity, such as whether it could be as toxic as white phosphorus. In response to the possibility of BP employment into commercial products and biomedical devices, its cytotoxicity to human lung carcinoma epithelial cells (A549) was investigated. Following a 24 h exposure of the cells with different BP concentrations, cell viability assessments were conducted using water-soluble tetrazolium salt (WST-8) and methylthiazolyldiphenyltetrazolium bromide (MTT) assays. The toxicological effects were found to be dose-dependent, with BP reducing cell viabilities to 48% (WST-8) and 34% (MTT) at 50 μg mL(-1) exposure. This toxicity was observed to be generally intermediate between that of graphene oxides and exfoliated transition-metal dichalcogenides (MoS2, WS2, WSe2). The relatively low toxicity paves the way to utilization of black phosphorus.

Valence and oxide impurities in MoS2 and WS2 dramatically change their electrocatalytic activity towards proton reduction

Layered molybdenum disulfide (MoS2) and tungsten disulfide (WS2) have received renewed interest in recent years as they are catalytic towards the hydrogen evolution reaction (HER) and they are touted as future replacements of platinum in electrolyzers. There is a significant discrepancy in the found onset potentials of MoS2 and WS2 towards the hydrogen evolution reaction. Here we show that the presence of valence sulfide impurities, such as MoS3 and WS3, and their oxide counterparts, such as MoO2, MoO3 and WO2, WO3 can contribute to the catalytic activity towards hydronium reduction to hydrogen of MoS2 and WS2. Therefore, it is highly possible that the differences in the reported onset potentials and thus catalytic activities of the MoS2 and WS2 are due to the presence of catalytic impurities.

Toxicity of layered semiconductor chalcogenides: beware of interferences

The absence of bandgap in graphene has opened exploration in a new class of 2D nanomaterials: layered semiconductor chalcogenides. Research has found that they have promising properties which are advantageous for applications in a wide range of fields such as solar energy conversion, field effect transistors, optoelectronic devices, energy storage, and is expanding into biomedical applications. However, little is known about their toxicity effects. In view of the possibility of employing these materials into consumer products, we investigated the cytotoxicity of two common layered semiconductor chalcogenides, namely GaSe and GeS, based on cell viability assessments using water-soluble tetrazolium salt (WST-8) and methyl-thiazolyldiphenyl-tetrazolium bromide (MTT) assays after a 24 h exposure to varying concentrations of the nanomaterials on human lung carcinoma epithelial cells (A549). The cytotoxicity results indicated that GaSe is relatively more toxic than another group of 2D layered chalcogenide: transition metal dichalcogenides (MoS2, WS2, WSe2). On the other hand, GeS appeared to be non-toxic, with the concentration of GeS introduced having a positive correlation with the cell viability. Control experiments in cell-free conditions revealed that both GaSe and GeS interfered with the absorbance data gathered in the two assays, but the interference effect induced by GaSe could be minimized by additional washing steps to remove the nanomaterials prior to the cell viability assessments. In the case of GeS, however, the interference effect between GeS and both assay dyes were still significant despite the washing steps adopted, thereby giving rise to the false cytotoxicity results observed for GeS. Therein, we wish to highlight that control experiments should always be carried out to check for any possible interferences between the test specimen and cell viability markers when conducting cell viability assessments for cytotoxicity studies.

Cytotoxicity of Exfoliated Layered Vanadium Dichalcogenides

Transition-metal Group 5 vanadium dichalcogenides have shown promising properties for many applications, such as batteries, capacitors, electrocatalysts for hydrogen production and many more. However, their toxicological effects have not yet been well understood. Here, we studied the cytotoxicity of exfoliated VS2 , VSe2 and VTe2 by incubating various concentrations of the materials with human lung carcinoma (A549) cells for 24 h and measuring the remaining cell viabilities after the treatment. We found that these vanadium dichalcogenides are relatively more toxic compared to Group 6 transition-metal dichalcogenides (TMDs), namely MoS2 , WS2 and WSe2 . This study is important for a better understanding of the toxicity of TMDs in preparation for their actual commercialisation in the future.