The development of sensitive graphene-based surface acoustic wave sensors for NO2 detection at room temperature.

Bilayer graphene (Bl-Gr) and sulphur-doped graphene (S-Gr) have been integrated with LiTaO3 surface acustic wave (SAW) sensors to enhance the performance of NO2 detection at room temperature. The sensitivity of the Bl-Gr SAW sensors toward NO2, measured at room temperature, was 0.29º/ppm, with a limit of detection of 0.068 ppm. The S-Gr SAW sensors showed 0.19º/ppm sensitivity and a limit of detection of 0.140 ppm. The origin of these high sensitivities was attributed to the mass loading and elastic effects of the graphene-based sensing materials, with surface changes caused by the absorption of the NO2 molecules on the sensing films. Although there are no significant differences regarding the sensitivity and detection limit of the two types of sensors, the measurements in the presence of interferent gases and various humidity conditions outlined much better selectivity and sensing performances towards NO2 gas for the Bl-Gr SAW sensors.

Field-Effect Transistors Based on Single-Layer Graphene and Graphene-Derived Materials.

The progress of advanced materials has invoked great interest in promising novel biosensing applications. Field-effect transistors (FETs) are excellent options for biosensing devices due to the variability of the utilized materials and the self-amplifying role of electrical signals. The focus on nanoelectronics and high-performance biosensors has also generated an increasing demand for easy fabrication methods, as well as for economical and revolutionary materials. One of the innovative materials used in biosensing applications is graphene, on account of its remarkable properties, such as high thermal and electrical conductivity, potent mechanical properties, and high surface area to immobilize the receptors in biosensors. Besides graphene, other competing graphene-derived materials (GDMs) have emerged in this field, with comparable properties and improved cost-efficiency and ease of fabrication. In this paper, a comparative experimental study is presented for the first time, for FETs having a channel fabricated from three different graphenic materials: single-layer graphene (SLG), graphene/graphite nanowalls (GNW), and bulk nanocrystalline graphite (bulk-NCG). The devices are investigated by scanning electron microscopy (SEM), Raman spectroscopy, and I-V measurements. An increased electrical conductance is observed for the bulk-NCG-based FET, despite its higher defect density, the channel displaying a transconductance of up to ≊4.9×10-3 A V-1, and a charge carrier mobility of ≊2.86×10-4 cm2 V-1 s-1, at a source-drain potential of 3 V. An improvement in sensitivity due to Au nanoparticle functionalization is also acknowledged, with an increase of the ON/OFF current ratio of over four times, from ≊178.95 to ≊746.43, for the bulk-NCG FETs.

Multilayer Smart Holographic Label with Integrated RFID for Product Security and Monitoring.

Counterfeiting presents a major economic problem and an important risk for the public health and safety of individuals and countries. To make the counterfeiting process more difficult, and to ensure efficient authentication, a solution would be to attach anti-counterfeit labels that include a radio frequency identification (RFID) element to the products. This can allow real-time quality check along the entire supply chain. In this paper we present the technology optimized to obtain a multilayer holographic label with a high degree of security, patterned on a thin zinc sulfide film of a semi-transparent holographic foil rather than on the standard substrate for diffractive optical elements (metallized foil). The label is applied onto the product surface or packaging for anti-counterfeit protection. The developed multilayer structure contains various elements such as: a holographic background, nanotext-type elements, holographic elements, and an RFID antenna. The employed semi-transparent holographic foil offers the RFID antenna the possibility to transmit the electromagnetic signal through the label and thus to maximize the antenna footprint, achieving up to 10 m reading distance, with a 6 cm × 6 cm label, much smaller than the commercial standard (minimum 10 cm × 10 cm).

Influence of Random Plasmonic Metasurfaces on Fluorescence Enhancement.

One of the strategies employed to increase the sensitivity of the fluorescence-based biosensors is to deposit chromophores on plasmonic metasurfaces which are periodic arrays of resonating nano-antennas that allow the control of the electromagnetic field leading to fluorescence enhancement. While artificially engineered metasurfaces realized by micro/nano-fabrication techniques lead to a precise tailoring of the excitation field and resonant cavity properties, the technological overhead, small areas, and high manufacturing cost renders them unsuitable for mass production. A method to circumvent these challenges is to use random distribution of metallic nanoparticles sustaining plasmonic resonances, which present the properties required to significantly enhance the fluorescence. We investigate metasurfaces composed of random aggregates of metal nanoparticles deposited on a silicon and glass substrates. The finite difference time domain simulations of the interaction of the incident electromagnetic wave with the structures reveals a significant enhancement of the excitation field, which is due to the resonant plasmonic modes sustained by the nanoparticles aggregates. We experimentally investigated the role of these structures in the fluorescent behaviour of Rhodamine 6G dispersed in polymethylmethacrylate finding an enhancement that is 423-fold. This suggests that nanoparticle aggregates have the potential to constitute a suitable platform for low-cost, mass-produced fluorescent biosensors.

Optimized Technologies for Cointegration of MOS Transistor and Glucose Oxidase Enzyme on a Si-Wafer.

The biosensors that work with field effect transistors as transducers and enzymes as bio-receptors are called ENFET devices. In the actual paper, a traditional MOS-FET transistor is cointegrated with a glucose oxidase enzyme, offering a glucose biosensor. The manufacturing process of the proposed ENFET is optimized in the second iteration. Above the MOS gate oxide, the enzymatic bioreceptor as the glucose oxidase is entrapped onto the nano-structured TiO2 compound. This paper proposes multiple details for cointegration between MOS devices with enzymatic biosensors. The Ti conversion into a nanostructured layer occurs by anodization. Two cross-linkers are experimentally studied for a better enzyme immobilization. The final part of the paper combines experimental data with analytical models and extracts the calibration curve of this ENFET transistor, prescribing at the same time a design methodology.

Manufacture of a nothing on insulator nano-structure with two Cr/Au nanowires separated by 18 nm air gap.

Despite the huge number of previous studies of vacuum devices, nanoscale technologies open new paradigms. Vacuum nanodevices bring multiple advantages, such as air instead of a vacuum for the nanometric gap, strong non-linear characteristics, and a metal oxide semiconductor co-integration facility. This paper presents the manufacturing process and measured characteristics of a nano-device that uses a sub-36 nm gap between two Cr/Au nano-wires. In this way, the metal nano-wires replace the semiconductor nano-islands, while an air gap stands for the 'nothing' region of a first-time fabricated variant for a nothing on insulator device. The electron beam lithography mask-less technology is pushed to its technical limit to define a minimum 18 nm-wide gap between two Cr/Au nanowires. The main current-voltage curves are measured for this first real device called a nothing on insulator in the variant metal-air-metal, indicating 10 nA at 10 V as the optimal variant. The main connections between the measurements and technology are emphasized.