Optimization of Printed Polyaniline Composites for Gas Sensing Applications.

Polyaniline (PANI) films are promising candidates for electronic nose-based IoT applications, but device performances are influenced by fabrication parameters and ambient conditions. Affinities of different PANI composites to analytes for gas sensing applications remain elusive. In this study, we investigate the material properties in detail for two different dopant systems: F4TCNQ and carbon black. Using a reproducibility-driven approach, we investigate different dopant concentrations in regard to their sensitivity and specificity towards five relevant markers for breath cancer diagnosis. We benchmark the system using ammonia measurements and evaluate limits of detection. Furthermore, we provide statistical analysis on reproducibility and pave the way towards machine learning discrimination via principal component analysis. The influence of relative humidity on sensor hysteresis is also investigated. We find that F4TCNQ-doped PANI films show improved reproducibility compared to carbon black-doped films. We establish and quantify a tradeoff between sensitivity, reproducibility, and environmental stability by the choice of dopant and concentrations ratios.

Field-Effect Transistor with a Plasmonic Fiber Optic Gate Electrode as a Multivariable Biosensor Device.

A novel multivariable system, combining a transistor with fiber optic-based surface plasmon resonance spectroscopy with the gate electrode simultaneously acting as the fiber optic sensor surface, is reported. The dual-mode sensor allows for discrimination of mass and charge contributions for binding assays on the same sensor surface. Furthermore, we optimize the sensor geometry by investigating the influence of the fiber area to transistor channel area ratio and distance. We show that larger fiber optic tip diameters are favorable for electronic and optical signals and demonstrate the reversibility of plasmon resonance wavelength shifts after electric field application. As a proof of principle, a layer-by-layer assembly of polyelectrolytes is performed to benchmark the system against multivariable sensing platforms with planar surface plasmon resonance configurations. Furthermore, the biosensing performance is assessed using a thrombin binding assay with surface-immobilized aptamers as receptors, allowing for the detection of medically relevant thrombin concentrations.

Controlled covalent functionalization of a graphene-channel of a field effect transistor as an ideal platform for (bio)sensing applications.

The controlled covalent functionalization of the graphene channel of a field effect transistor, based on interdigitated gold electrodes (source and drain), via electrochemical grafting, using specifically designed aryl diazonium species is demonstrated to allow the simple fabrication of a general platform for (bio)sensing applications. The electrochemical grafting of a protected ethynylphenyl diazonium salt leads to the deposition of only a monolayer on the graphene channel. This controlled covalent functionalization of the graphene channel results in a charge mobility of the GFET of 1739 ± 376 cm2 V-1 s-1 and 1698 ± 536 cm2 V-1 s-1 for the holes and electrons, respectively, allowing their utilization as (bio)sensors. After deprotection, a dense and compact ethynylphenyl monolayer is obtained and allows the immobilization of a wide range of (bio)molecules by a "click" chemistry coupling reaction (Huisgen 1,3-dipolar cycloaddition). This finding opens promising options for graphene-based (bio)sensing applications.

Reduced graphene oxide-based field effect transistors for the detection of E7 protein of human papillomavirus in saliva.

Several challenging biological sensing concepts have been realized using electrolyte-gated reduced graphene oxide field effect transistors (rGO-FETs). In this work, we demonstrate the interest of rGO-FET for the sensing of human papillomavirus (HPV), one of the most common sexually transmitted viruses and a necessary factor for cervical carcinogenesis. The highly sensitive and selective detection of the HPV-16 E7 protein relies on the attractive semiconducting characteristics of pyrene-modified rGO functionalized with RNA aptamer Sc5-c3. The aptamer-functionalized rGO-FET allows for monitoring the aptamer-HPV-16 E7 protein binding in real time with a detection limit of about 100 pg mL-1 (1.75 nM) for HPV-16 E7 from five blank noise signals (95% confidence level). The feasibility of this method for clinical application in point-of-care technology is evaluated using HPV-16 E7 protein suspended in saliva and demonstrates the successful fabrication of a promising field effect transistor biosensor for HPV diagnosis.Graphical abstract.

Dual Monitoring of Surface Reactions in Real Time by Combined Surface-Plasmon Resonance and Field-Effect Transistor Interrogation.

By combining surface plasmon resonance (SPR) and electrolyte gated field-effect transistor (EG-FET) methods in a single analytical device we introduce a novel tool for surface investigations, enabling simultaneous measurements of the surface mass and charge density changes in real time. This is realized using a gold sensor surface that simultaneously serves as a gate electrode of the EG-FET and as the SPR active interface. This novel platform has the potential to provide new insights into (bio)adsorption processes on planar solid surfaces by directly relating complementary measurement principles based on (i) detuning of SPR as a result of the modification of the interfacial refractive index profile by surface adsorption processes and (ii) change of output current as a result of the emanating effective gate voltage modulations. Furthermore, combination of the two complementary sensing concepts allows for the comparison and respective validation of both analytical techniques. A theoretical model is derived describing the mass uptake and evolution of surface charge density during polyelectrolyte multilayer formation. We demonstrate the potential of this combined platform through the observation of layer-by-layer assembly of PDADMAC and PSS. These simultaneous label-free and real-time measurements allow new insights into complex processes at the solid-liquid interface (like non-Fickian ion diffusion), which are beyond the scope of each individual tool.

Color Fine-Tuning of Optical Materials Through Rational Design.

We report on the feasibility for color fine-tuning of optical materials using rational design principles based on chemical reasoning. For this purpose, a modular framework for the construction of symmetrical cap-linker-cap compounds, using triarylamine caps and oligothiophene linkers, is applied. The chosen structural scaffolds are heavily used in recent industrial applications and provide five possibilities for altering their electronic and steric properties: electron donor/acceptor groups, planarization/deplanarization, and modulation of the π-conjugation length. Permutation of the used building blocks leads to a set of 54 different molecules, out of which 32 are synthesized and characterized in solution as well as in example fabricated OLED devices. This setup allows for color fine-tuning in the range of 412 nm to 540 nm with typical steps of 4 nm. In addition, to further benefit from the large experimental data set the spectroscopic results are used to benchmark quantum chemical computations, which show excellent agreement thus highlighting the potential of these calculations to guide future syntheses.

Green and highly efficient synthesis of perylene and naphthalene bisimides in nothing but water.

High-purity, symmetrically substituted perylene and naphthalene bisimides were obtained by hydrothermal condensation of monoamines with the corresponding bisanhydride. The hydrothermal imidization proceeds quantitatively, without the need for organic solvents, catalysts or excess of the amines.