Graphene is a breakthrough 2D material due to its unique mechanical, electrical, and thermal properties, with considerable responsiveness in real applications. However, the coverage of large areas with pristine graphene is a challenge and graphene derivatives have been alternatively exploited to produce hybrid and composite materials that allow for new developments, considering also the handling of large areas using distinct methodologies. For electronic applications there is significant interest in the investigation of the electrical properties of graphene derivatives and related composites to determine whether the characteristic 2D charge transport of pristine graphene is preserved. Here, we report a systematic study of the charge transport mechanisms of reduced graphene oxide chemically functionalized with sodium polystyrene sulfonate (PSS), named as GPSS. GPSS was produced either as quantum dots (QDs) or nanoplatelets (NPLs), being further nanostructured with poly(diallyldimethylammonium chloride) through the layer-by-layer (LbL) assembly to produce graphene nanocomposites with molecular level control. Current-voltage (I-V) measurements indicated a meticulous growth of the LbL nanostructures onto gold interdigitated electrodes (IDEs), with a space-charge-limited current dominated by a Mott-variable range hopping mechanism. A 2D intra-planar conduction within the GPSS nanostructure was observed, which resulted in effective charge carrier mobility (μ) of 4.7 cm V s for the QDs and 34.7 cm V s for the NPLs. The LbL assemblies together with the dimension of the materials (QDs or NPLs) were favorably used for the fine tuning and control of the charge carrier mobility inside the LbL nanostructures. Such 2D charge conduction mechanism and high μ values inside an interlocked multilayered assembly containing graphene-based nanocomposites are of great interest for organic devices and functionalization of interfaces.

Precision agriculture is crucial for increasing food output without expanding the cultivable area, which requires sensors to be deployed for controlling the level of nutrients in the soil. In this paper, we report on a microfluidic electronic tongue (e-tongue) based on impedance measurements which is capable of distinguishing soil samples enriched with plant macronutrients. The e-tongue setup consisted of an array of sensing units made with layer-by-layer films deposited onto gold interdigitated electrodes. Significantly, the sensing units could be reused with adequate reproducibility after a simple washing procedure, thus indicating that there is no cross-contamination in three independent sets of measurements. A high performance was achieved by treating the capacitance data with the multidimensional projection techniques Principal Component Analysis (PCA), Interactive Document Map (IDMAP), and Sammon's Mapping. While an optimized performance was demonstrated with IDMAP and feature selection, during which data of a limited frequency range were used, the distinction of all soil samples was also possible with the well-established PCA analysis for measurements at a single frequency. The successful use of a simple microfluidic e-tongue for soil analysis paves the way for enhanced tools to support precision agriculture.

Reduced graphene oxide (rGO) layers are known to be significantly conductive along the basal plane throughout delocalized sp2 domains. Defects present in rGO implies in disordered systems with numerous localized sites, resulting in a charge transport governed mainly by a 2D variable range hopping (VRH) mechanism. These characteristics are observed even in multilayered rGO since the through-plane conduction is expected to be insubstantial. Here, we report on the multilayer assembly of functionalized rGO quantum dots (GQDs) presenting 3D VRH transport that endows elevated charge carrier mobility, ca ∼ 236 cm2 V−1 s−1. Polyelectrolyte-wrapped GQDs were assembled by layer-by-layer technique (LbL), ensuring molecular level thickness control for the formed nanostructures, along with the adjustment of the film transparency (up to 92% in the visible region). The small size and the random distribution of GQDs in the LbL structure are believed to overcome the translational disorder in multilayered films, contributing to a 3D interlayer conduction that enhances the electronic properties. Such high-mobility, transparency-tunable films assembled by a cost-effective method possess interesting features and wide applicability in optoelectronics.

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The unique electronic, mechanical and optical properties of graphene make it a remarkable 2D material, widely explored in a plethora of applications. However, graphene zero-bandgap and the production of defect-free pristine graphene in large areas still limit some applications. To circumvent these issues, graphene-derived 2D materials have arisen as attractive candidates for low-dimensional systems, which requires a better comprehension of their properties. Here, we report a detailed investigation of the conduction mechanisms of two functionalized reduced graphene oxides (rGOs) nanoplatelets, named GPAH and GPSS. The functionalized rGO nanoplatelets were bottom-up assembled via the layer-by-layer technique, enabling molecular-level thickness control of nanostructures with well-defined composition and structure. For the reported multilayered GPAH/GPSS films the charge carriers followed Mott's law, presenting a typical conduction behavior of 2D systems described by the Poole-Frenkel model. The multilayered GPAH/GPSS nanostructure presented a conductivity of 10 S cm, optical bandgap of ∼3.3 eV and a relative dielectric permittivity (ε ) of 6.4. Temperature-dependent I-V measurements indicated a strong variation of ε below the critical temperature (T = 237 K), associated with a high dipole reorientation in the formed GPAH/GPSS nanostructure. All these characteristics make the GPAH/GPSS nanocomposite attractive for graphene-oriented applications, such as electronic devices.