Molybdenum Disulfide Quantum Dots Prepared by Bipolar-Electrode Electrochemical Scissoring

Gum arabic-assisted green synthesis of biocompatible MoS2 nanoparticles for methylene blue photodegradation

The current work reports the gum arabic-mediated greener synthesis of MoS2 nanoparticles (NPs) and its utilization for the solar light-assisted degradation of methylene blue. Furthermore, the safety analyses were performed on human-beneficial gut bacterium, L. delbrueckii, and human blood cells to confirm the biocompatibility of NPs synthesized. Antioxidant and antimicrobial activities were done to explore their usefulness for biological applications. Sonication and microwave treatment were used to obtain spherical 10-12 nm MoS2 NPs as characterized using high-resolution transmission electron microscopy. FT-IR characterization revealed the occurrence of gum arabic on the NPs surface. The MoS2 NPs exhibited ~ 98% MB degradation within 8 h under direct sunlight exposure. Moreover, the reusability studies have also been evaluated and free radical trapping experiments indicated that superoxide (•O2-) is the dominant active species of the reaction system. Furthermore, 98.89% MB degradation efficiency was observed within 150 min in the case of real textile industry MB effluent samples. Untreated MB inhibited the growth of L. delbrueckii on MRS agar plates, while growth was observed in the case of MoS2 NPs-treated MB samples indicating safety of current MB degradation approach. MoS2 NPs inhibited the growth of E. coli MTCC1698 and S. aureus MTCC 3160 with 26 mm and 21 mm zone of inhibition, respectively. Furthermore, MoS2 NPs have shown antioxidant properties, resulting in 82.3 ± 0.43% of DPPH scavenging activity which was comparable to ascorbic acid (81.6 ± 0.6%), a standard antioxidant molecule. The NPs have not shown any hemolytic activity at 0.0625 and 0.125 mg/mL doses to human blood proving their biocompatible nature. Gum arabic-synthesized biocompatible MoS2 NPs have good potential to treat MB released as waste from the textile industry and other biological applications.

Selective and Sensitive Electrochemical Sensor for Aflatoxin M1 with a Molybdenum Disulfide Quantum Dot/Metal-Organic Framework Nanocomposite

Aflatoxins are the hepatotoxic secondary metabolites which are highly carcinogenic and known to cause several adverse effects on human health. The present study reports a simple, sensitive, and novel electrochemical sensor for aflatoxin M1 (AFM1). The sensor has been fabricated by modifying the screen-printed carbon electrodes with a functional nanocomposite of molybdenum disulfide (MoS₂) quantum dots (QDs) and a zirconium-based metal-organic framework (MOF), that is, UiO-66-NH₂. The MoS₂/UiO-66-modified electrodes were decorated with the AFM1-specific monoclonal antibodies and then investigated for the electrochemical detection of AFM1. Based on the electrochemical impedance spectroscopy analysis, it was possible to detect AFM1 in the concentration range of 0.2-10 ng mL^-1 with a limit of detection of 0.06 ng mL^-1. The realization of an excellent sensing performance can be attributed to the electroactivity of MoS₂ QDs and the large surface to volume area achieved by the addition of the MOF. The presence of UiO-66-NH₂ is also useful to attain readily available amine functionality for the robust interfacing of antibodies. The performance of the developed sensor has also been validated by detecting AFM1 in the spiked milk samples.

Single-Layer MoS2-MoO3-x Heterojunction Nanosheets with Simultaneous Photoluminescence and Co-Photocatalytic Features

Single-layer MoS2-MoO3-x heterojunction nanosheets with visible-light-sensitive band gap energy and average lateral dimensions of ~70 nm were synthesized by using a two-step combined exfoliation method. The exfoliation was initiated from pristine MoS2, while some sulfur sites in expanded MoS2 sheets during exfoliating were substituted by ambient non-thermal oxygen, resulting in formation of α-MoO3-x crystalline domains. The morphological features, crystalline structure, phase formation, number of layers, and optical properties of the MoS2-MoO3-x nanosheets were determined by atomic force microscopy; X-ray diffraction; field emission electron microscopy; transmission electron microscopy; and Raman, UV–visible–NIR, diffuse transmittance, and photoluminescence spectroscopies. The produced α-MoO3-x domains displayed a narrower indirect band gap energy (~1.95 eV) than that of stoichiometric MoO3 (~3 eV), and a broad light absorption range from visible to near-infrared region can act as a plasmonic material facilitating the separation of the photoinduced carriers and enhancing the photocatalytic activity of the MoS2 domain, having ~1.75(2.16) eV indirect (direct) band gap energy. In this regard, the MoS2-MoO3-x heterojunction nanosheets showed single-layer-based excitation-dependent luminescence emissions and visible-light-induced photocatalytic features, at the same time. This study can contribute to promising applications of sheet-like nanomaterials for purposes requiring simultaneous photoluminescence and photocatalytic features, such as in-vivo monitoring and targeting.

A study of microbially fabricated bio-conjugated quantum dots for pico-molar sensing of H2O2 and glucose

Quantum dots (QDs) as bio-detectors have been intensively explored owing to their size dependent optical properties and are still envisioned to be used in a plethora of biomedical and healthcare areas. However, the medical application of the biosensors demands the ultrasensitive detection of the analytes, which is usually limited for the conventional methods of colorimetric and fluorescence detection. The Fluorescence Resonance Energy Transfer (FRET) process, exploited by QDs, translates the close association between the analyte and the detector into optical properties and thus promises the effective detection of biomolecules. FRET based detection systems for biomolecules utilize surface-functionalized QDs which are usually modified post production using different organic groups. In this work, a novel protocol was formulated to produce bio-functionalized QDs with controlled chemical and optical characteristics. Here, we demonstrate the first-ever biological green synthesis of MoS2 QDs using Pseudomonas aeruginosa. The bio-functionalized QDs show green luminescence with a quantum yield of 42%, supporting their application as an optical sensor. These QDs are utilized to detect the pico-molar concentration of glucose, which makes them ideal for early diabetes detection and many biomedical applications. Also, the ability to sense pico-molar levels of H2O2 opens the path for its utilization in apprehending the plant signaling pathways under stress conditions.