Polystyrene microspheres with ultra-rough surfaces engineered using RIE technique and applied using SERS

In this study, we successfully fabricated two ultra-rough surfaces based on polystyrene (PS) microspheres by employing the reactive ion etching (RIE) technique. Elemental analysis confirmed a stable AlF3 composition of the structures of these surfaces. We proposed the mechanism of the formation of these surfaces and performed SERS-related tests; the prepared substrates exhibited excellent SERS performance.

Ultrasensitive SERS detection of exhaled biomarkers of lung cancer using a multifunctional solid phase extraction membrane

The construction and clinical application of a surface-enhanced Raman scattering (SERS) platform for the early diagnosis of lung cancer could improve the survival rate of patients and would be of great significance. Nevertheless, a sensitive and reusable method for the detection of aldehydes, as biomarkers of lung cancer, in exhaled breath is still an enormous challenge. Aldehydes generally have a low cross section in Raman scattering and have a weak specific affinity to plasmonic nanoparticle surfaces, meaning that sensing them at low concentrations is incredibly difficult. Herein, an ultrasensitive SERS strategy, that can be recycled for further use, for the detection of lung cancer biomarkers in the form of aldehydes was realized by fabrication of a multifunctional Ag NPs@ZIF-67/g-C₃N₄ solid phase extraction (SPE) membrane. Based on the change in the vibrational fingerprints of 4-ATP before and after reaction with the aldehydes, the SPE membrane was successfully used for the ultrasensitive detection of aldehydes with a detection limit of 1.35 nM. The excellent SERS performance was attributed to the synergistic effect of the densely and closely distributed Ag NPs (providing SERS "hot spots"), ZIF-67 (concentrating the analyte molecules) and g-C₃N₄ (forming a membrane to prolong the contact time between the aldehydes and the substrate). In addition, recycling of the SPE membrane was achieved by utilizing the self-cleaning ability of the Ag NPs@ZIF-67/g-C₃N₄ membrane originating from the photocatalytic properties of g-C₃N₄. The proposed SERS membrane was easy to operate, rapid and portable, thus providing a potential tool for a point-of-care test in clinical and diagnostic practice.

Atomic Layer Deposition of Inorganic Films for the Synthesis of Vertically Aligned Carbon Nanotube Arrays and Their Hybrids

Vertically aligned carbon nanotube arrays (VACNTs) have many excellent properties and show great potential for various applications. Recently, there has been a desire to grow VACNTs on nonplanar surfaces and synthesize core-sheath-structured VACNT–inorganic hybrids. To achieve this aim, atomic layer deposition (ALD) has been extensively applied, especially due to its atomic-scale thickness controllability and excellent conformality of films on three-dimensional (3D) structures with high aspect ratios. In this paper, the ALD of catalyst thin films for the growth of VACNTs, such as Co3O4, Al2O3, and Fe2O3, was first mentioned. After that, the ALD of thin films for the synthesis of VACNT–inorganic hybrids was also discussed. To highlight the importance of these hybrids, their potential applications in supercapacitors, solar cells, fuel cells, and sensors have also been reviewed.

Single-step ambient-air synthesis of graphene from renewable precursors as electrochemical genosensor

Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are necessary for creating a highly controlled environment, isolated from ambient air, to enable the growth of graphene films. Here we exploit the ambient-air environment to enable the growth of graphene films, without the need for compressed gases. A renewable natural precursor, soybean oil, is transformed into continuous graphene films, composed of single-to-few layers, in a single step. The enabling parameters for controlled synthesis and tailored properties of the graphene film are discussed, and a mechanism for the ambient-air growth is proposed. Furthermore, the functionality of the graphene is demonstrated through direct utilization as an electrode to realize an effective electrochemical genosensor. Our method is applicable to other types of renewable precursors and may open a new avenue for low-cost synthesis of graphene films.

Graphene films are commonly produced by thermal chemical vapour deposition, which is capable of producing high-quality films but still limited by factors such as high cost. Here, the authors report the growth of single-to-few-layer continuous graphene films under ambient-air conditions.

Electronic structure characterization of an individual single-walled carbon nanotube by in situ electrochemical surface-enhanced Raman scattering spectroscopy

We present an electronic structural analysis of an individual single-walled carbon nanotube (SWNT) by employing electrochemical surface-enhanced Raman scattering (SERS). An isolated SWNT was supported on a well-defined Au nanodimer structure, which possesses a localized surface plasmon resonance (LSPR) field at the nanogap, and highly intense SERS spectra were obtained for the SWNT at the gap region. The absolute potential of the Fermi level of the isolated SWNT in an ionic liquid was determined from the electrochemical potential dependence of the SERS intensity showing the dependence on the chirality of SWNTs. The electronic structural change in an isolated SWNT by ozone oxidation treatment was also analyzed. The results indicate that the electrochemical SERS technique is a powerful tool for detailed analysis of the electronic structure of isolated SWNTs.

Sustainable Life Cycles of Natural-Precursor-Derived Nanocarbons

Sustainable societal and economic development relies on novel nanotechnologies that offer maximum efficiency at minimal environmental cost. Yet, it is very challenging to apply green chemistry approaches across the entire life cycle of nanotech products, from design and nanomaterial synthesis to utilization and disposal. Recently, novel, efficient methods based on nonequilibrium reactive plasma chemistries that minimize the process steps and dramatically reduce the use of expensive and hazardous reagents have been applied to low-cost natural and waste sources to produce value-added nanomaterials with a wide range of applications. This review discusses the distinctive effects of nonequilibrium reactive chemistries and how these effects can aid and advance the integration of sustainable chemistry into each stage of nanotech product life. Examples of the use of enabling plasma-based technologies in sustainable production and degradation of nanotech products are discussed-from selection of precursors derived from natural resources and their conversion into functional building units, to methods for green synthesis of useful naturally degradable carbon-based nanomaterials, to device operation and eventual disintegration into naturally degradable yet potentially reusable byproducts.

A plasmon-assisted fluoro-immunoassay using gold nanoparticle-decorated carbon nanotubes for monitoring the influenza virus

A plasmon-assisted fluoro-immunoassay (PAFI) was developed for the detection of the influenza virus by using Au nanoparticle (Au NP)-decorated carbon nanotubes (AuCNTs) that were synthesized using phytochemical composites at room temperature in deionized water. Specific antibodies (Abs) against the influenza virus were conjugated onto the surface of AuCNTs and cadmium telluride quantum dots (QDs), which had a photoluminescence intensity that varied as a function of virus concentration and a detection limit of 0.1 pg/mL for all three types of influenza viruses examined. The clinically isolated influenza viruses (A/Yokohama/110/2009 (H3N2)) were detected in the range of 50-10,000 PFU/mL, with a detection limit of 50 PFU/mL. From a series of proof-of-concept and clinical experiments, the developed PAFI biosensing system provided robust signal production and enhancement, as well as an excellent selectivity and sensitivity for influenza viruses. This nanoparticle-based technique could be potentially developed as an efficient detection platform for the influenza virus.

Synergistic fusion of vertical graphene nanosheets and carbon nanotubes for high-performance supercapacitor electrodes

Graphene and carbon nanotubes (CNTs) are attractive electrode materials for supercapacitors. However, challenges such as the substrate-limited growth of CNTs, nanotube bundling in liquid electrolytes, under-utilized basal planes, and stacking of graphene sheets have so far impeded their widespread application. Here we present a hybrid structure formed by the direct growth of CNTs onto vertical graphene nanosheets (VGNS). VGNS are fabricated by a green plasma-assisted method to break down and reconstruct a natural precursor into an ordered graphitic structure. The synergistic combination of CNTs and VGNS overcomes the challenges intrinsic to both materials. The resulting VGNS/CNTs hybrids show a high specific capacitance with good cycling stability. The charge storage is based mainly on the non-Faradaic mechanism. In addition, a series of optimization experiments were conducted to reveal the critical factors that are required to achieve the demonstrated high supercapacitor performance.

Plasma-Enabled Carbon Nanostructures for Early Diagnosis of Neurodegenerative Diseases

Carbon nanostructures (CNs) are amongst the most promising biorecognition nanomaterials due to their unprecedented optical, electrical and structural properties. As such, CNs may be harnessed to tackle the detrimental public health and socio-economic adversities associated with neurodegenerative diseases (NDs). In particular, CNs may be tailored for a specific determination of biomarkers indicative of NDs. However, the realization of such a biosensor represents a significant technological challenge in the uniform fabrication of CNs with outstanding qualities in order to facilitate a highly-sensitive detection of biomarkers suspended in complex biological environments. Notably, the versatility of plasma-based techniques for the synthesis and surface modification of CNs may be embraced to optimize the biorecognition performance and capabilities. This review surveys the recent advances in CN-based biosensors, and highlights the benefits of plasma-processing techniques to enable, enhance, and tailor the performance and optimize the fabrication of CNs, towards the construction of biosensors with unparalleled performance for the early diagnosis of NDs, via a plethora of energy-efficient, environmentally-benign, and inexpensive approaches.

Carbon nanotube membranes with ultrahigh specific adsorption capacity for water desalination and purification

Development of technologies for water desalination and purification is critical to meet the global challenges of insufficient water supply and inadequate sanitation, especially for point-of-use applications. Conventional desalination methods are energy and operationally intensive, whereas adsorption-based techniques are simple and easy to use for point-of-use water purification, yet their capacity to remove salts is limited. Here we report that plasma-modified ultralong carbon nanotubes exhibit ultrahigh specific adsorption capacity for salt (exceeding 400% by weight) that is two orders of magnitude higher than that found in the current state-of-the-art activated carbon-based water treatment systems. We exploit this adsorption capacity in ultralong carbon nanotube-based membranes that can remove salt, as well as organic and metal contaminants. These ultralong carbon nanotube-based membranes may lead to next-generation rechargeable, point-of-use potable water purification appliances with superior desalination, disinfection and filtration properties.

Selective decoration of Au nanoparticles on monolayer MoS2 single crystals

We report a controllable wet method for effective decoration of 2-dimensional (2D) molybdenum disulfide (MoS₂) layers with Au nanoparticles (NPs). Au NPs can be selectively formed on the edge sites or defective sites of MoS₂ layers. The Au-MoS₂ nano-composites are formed by non-covalent bond. The size distribution, morphology and density of the metal nanoparticles can be tuned by changing the defect density in MoS₂ layers. Field effect transistors were directly fabricated by placing ion gel gate dielectrics on Au-decorated MoS₂ layers without the need to transfer these MoS₂ layers to SiO₂/Si substrates for bottom gate devices. The ion gel method allows probing the intrinsic electrical properties of the as-grown and Au-decorated MoS₂ layers. This study shows that Au NPs impose remarkable p-doping effects to the MoS₂ transistors without degrading their electrical characteristics.

Plasma break-down and re-build: same functional vertical graphenes from diverse natural precursors

Plasmas, the 4(th) state of matter, uniformly transform natural precursors with different chemical composition in solid, liquid, and gas states into the same functional vertical graphenes in a single-step process within a few minutes. Functional vertical graphenes show reliable biosensing properties, strong binding with proteins, and improved adhesion to substrates.