Application of Soxhlet Extractor for Ultra-clean Graphene Transfer.

Surface contamination experienced during polymer-assisted transfer is detrimental for optical and electrical properties of 2D materials. This contamination is usually due to incomplete polymer removal and also due to impurities present in organic solvents. Here, we report a simple, economical, and highly efficient approach for obtaining pristine graphene on a suitable substrate (e.g., SiO2/Si) by utilizing Soxhlet extraction apparatus for delicate removal of the polymer with a freshly distilled ultrapure solvent (acetone) in a continuous fashion. Excellent structural and morphological qualities of the material thus produced were confirmed using optical microscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. Compared to the conventional protocol, graphene produced by the current approach has a lower residual polymer content, leading to a root mean square roughness of only 1.26 nm. The amount of strain and doping was found to be similar, but the D-band, which is indicative of the defects, was less pronounced in the samples prepared by Soxhlet-assisted transfer. The new procedure is virtually effortless from the experimental point of view, utilizes much less solvent compared to the conventional washing procedure, and allows for easy scale-up. Extension of this process to other 2D materials would not only provide samples with superior intrinsic properties but also enhance their suitability for advanced technological applications.

Multidimensional Imaging Reveals Mechanisms Controlling Multimodal Label-Free Biosensing in Vertical 2DM-Heterostructures.

Two-dimensional materials and their van der Waals heterostructures enable a large range of applications, including label-free biosensing. Lattice mismatch and work function difference in the heterostructure material result in strain and charge transfer, often varying at a nanometer scale, that influence device performance. In this work, a multidimensional optical imaging technique is developed in order to map subdiffractional distributions for doping and strain and understand the role of those for modulation of the electronic properties of the material. As an example, vertical heterostructures comprised of monolayer graphene and single-layer flakes of transition metal dichalcogenide MoS2 were fabricated and used for biosensing. Herein, the optical label-free detection of doxorubicin, a common cancer drug, is reported via three independent optical detection channels (photoluminescence shift, Raman shift, and graphene enhanced Raman scattering). Non-uniform broadening of components of multimodal signal correlates with the statistical distribution of local optical properties of the heterostructure. Multidimensional nanoscale imaging allows one to reveal the physical origin for such a local response and propose the best strategy for the mitigation of materials variability and future device fabrication, enabling multiplexed biosensing.

Recent Advances in Nanomaterial-Based Aptasensors in Medical Diagnosis and Therapy.

Rapid and accurate diagnosis of various biomarkers associated with medical conditions including early detection of viruses and bacteria with highly sensitive biosensors is currently a research priority. Aptamer is a chemically derived recognition molecule capable of detecting and binding small molecules with high specificity and its fast preparation time, cost effectiveness, ease of modification, stability at high temperature and pH are some of the advantages it has over traditional detection methods such as High Performance Liquid Chromatography (HPLC), Enzyme-linked Immunosorbent Assay (ELISA), Polymerase Chain Reaction (PCR). Higher sensitivity and selectivity can further be achieved via coupling of aptamers with nanomaterials and these conjugates called "aptasensors" are receiving greater attention in early diagnosis and therapy. This review will highlight the selection protocol of aptamers based on Traditional Systematic Evolution of Ligands by EXponential enrichment (SELEX) and the various types of modified SELEX. We further identify both the advantages and drawbacks associated with the modified version of SELEX. Furthermore, we describe the current advances in aptasensor development and the quality of signal types, which are dependent on surface area and other specific properties of the selected nanomaterials, are also reviewed.

Bandgap recovery of monolayer MoS2 using defect engineering and chemical doping.

Two-dimensional transition metal dichalcogenide materials have created avenues for exciting physics with unique electronic and photonic applications. Among these materials, molybdenum disulfide is the most known due to extensive research in understanding its electronic and optical properties. In this paper, we report on the successful growth and modification of monolayer MoS2 (1L MoS2) by controlling carrier concentration and manipulating bandgap in order to improve the efficiency of light emission. Atomic size MoS2 vacancies were created using a Helium Ion Microscope, then the defect sites were doped with 2,3,5,6-tetrafluro7,7,8,8-tetracyanoquinodimethane (F4TCNQ). The carrier concentration in intrinsic (as-grown) and engineered 1L MoS2 was calculated using Mass Action model. The results are in a good agreement with Raman and photoluminescence spectroscopy as well as Kelvin probe force microscopy characterizations.

Stabilization of anaerobic co-digestion of biowaste using activated carbon of coffee ground biomass.

Process instability commonly encountered in anaerobic co-digestion (AcoD) of organic fractions of municipal solid wastes (OFMSWs) is addressed by utilizing hydrochar (CB-HTC) and activated hydrochar (ACB-HTC) derived from coffee ground biomass. Addition of CB-HTC or ACB-HTC shortened the lag phase resulting in high biogas yield of 68.57 Nl/kg oTS or 102.86 Nl/kg oTS, respectively within the first week. Improvement in biogas yield (~5% higher than the control) was due to unique properties which prevented washout of consortia of bacteria useful for AcoD and subsequently led to a more stable process. An increase in either OLR [1.0 kg oTS/(m3*d) to 1.5 kg oTS/(m3*d)] or temperature (36.5 °C to 42.5 °C) did not lead to increase in ammonium-nitrogen or TKN in reactors amended with hydrochars. Likewise, ratio of VFA/TA was within 0.2-0.3 after the fourth week in ACB-HTC treated reactor. Addition of ACB-HTC greatly improved nutrient retention in the digestate.