Monitoring photosynthetic microorganism activity with an electrolyte-gated organic field effect transistor

An Electrolyte-Gated Graphene Field-Effect Transistor for Detection of Gadolinium(III) in Aqueous Media

In this work, an electrolyte-gated graphene field-effect transistor is developed for Gd³⁺ ion detection in water. The source and drain electrodes of the transistor are fabricated by photolithography on polyimide, while the graphene channel is obtained by inkjet-printing a graphene oxide ink subsequently electro-reduced to give reduced graphene oxide. The Gd³⁺-selective ligand DOTA is functionalized by an alkyne linker to be grafted by click chemistry on a gold electrode without losing its affinity for Gd³⁺. The synthesis route is fully described, and the ligand, the linker and the functionalized surface are characterized by electrochemical analysis and spectroscopy. The as functionalized electrode is used as gate in the graphene transistor so to modulate the source-drain current as a function of its potential, which is itself modulated by the concentration of Gd³⁺captured on the gate surface. The obtained sensor is able to quantify Gd³⁺ even in a sample containing several other potentially interfering ions such as Ni²⁺, Ca²⁺, Na⁺ and In³⁺. The quantification range is from 1 pM to 10 mM, with a sensitivity of 20 mV dec^-1 expected for a trivalent ion. This paves the way for Gd³⁺ quantification in hospital or industrial wastewater.

Glyphosate Sensor Based on Nanostructured Water-Gated CuO Field-Effect Transistor

This research presents a comparative analysis of water-gated thin film transistors based on a copper oxide (CuO) semiconductor in the form of a smooth film and a nanostructured surface. A smooth CuO film was deposited through reactive magnetron sputtering followed by annealing in atmosphere at a temperature of 280 ∘C. Copper oxide nanostructures were obtained by hydrothermal synthesis on a preliminary magnetron sputtered 2 nm thick CuO precursor followed by annealing at 280 ∘C. An X-ray diffraction (XRD) analysis of the samples revealed the presence of a tenorite (CuO) phase with a predominant orientation of (002). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies of the samples revealed a highly developed surface with crystallites having a monoclinic syngony and dimensions of 15-20 nm in thickness, 150 nm in length, and 100 nm in height relative to a 2.5 nm height for the CuO crystallites of the smooth film. Electric measurements of the studied devices revealed typical current-voltage characteristics of semiconductors with predominant hole conductivity. The maximum ON/OFF ratio at a rain-source voltage of 0.4 volts and -1.2 volts on the gate for a smooth film was 102, and for a nanostructured transistor, it was 103. However, a much stronger saturation of the channel was observed for the nanostructured channel than for the smooth film. A test solution containing glyphosate dissolved in deionized water in three different concentrations of 5, 10, and 15 μmol/L was used during the experiments. The principle of operation was based on the preliminary saturation of the solution with Cu ions, followed by the formation of a metal-organic complex alongside glyphate. The glyphosate contents in the analyte led to a decrease in the conductivity of the transistor on the axis of the smooth film. In turn, the opposite effect was observed on the nanostructured surface, i.e., an increase in conductivity was noted upon the introduction of an analyte. Despite this, the overall sensitivity of the nanostructured device was twice as high as that of the device with a thin film channel. The relative changes in the field-effect transistor (FET) conductivity at maximum glyphosate concentrations of 15 μmol/L reached 19.42% for the nanostructured CuO film and 3.3% for the smooth film.

Interplay between Electrolyte-Gated Organic Field-Effect Transistors and Surfactants: A Surface Aggregation Tool and Protecting Semiconducting Layer

Molecular surfactants, which are based on a water-insoluble tail and a water-soluble head, are widely employed in many areas, such as surface coatings or for drug delivery, thanks to their capability to form micelles in solution or supramolecular structures at the solid/liquid interface. Electrolyte-gated organic field-effect transistors (EGOFETs) are highly sensitive to changes occurring at their electrolyte/gate electrode and electrolyte/organic semiconductor interfaces, and hence, they have been much explored in biosensing due to their inherent amplification properties. Here, we demonstrate that the EGOFETs and surfactants can provide mutual benefits to each other. EGOFETs can be a simple and complementary tool to study the aggregation behavior of cationic and anionic surfactants at low concentrations on a polarized metal surface. In this way, we have monitored the monolayer formation of cationic and anionic surfactants at the water/electrode interface with p-type and n-type devices, respectively. On the other hand, the operational stability of EGOFETs has been dramatically enhanced, thanks to the formation of a protective layer on top of the organic semiconductor by exposing it to a high concentration of a surfactant solution (above the critical micelle concentration). Stable performances were achieved for more than 10 and 2 h of continuous operation for p-type and n-type devices, respectively. Accordingly, this work points not only that EGOFETs can be applied to a wider range of applications beyond biosensing but also that these devices can effectively improve their long-term stability by simply treating them with a suitable surfactant.

Electrochemical Stability Investigations and Drug Toxicity Tests of Electrolyte-Gated Organic Field-Effect Transistors

Electrolyte-gated organic field-effect transistors (EGOFETs) are emerging as a new frontier of organic bioelectronics, with promising applications in biosensing, pharmaceutical testing, and neuroscience. However, the limited charge carriers' mobility and well-known environmental instability of conjugated polymers constrain the real applications of organic bioelectronics. Here, we comparatively studied the electrochemical stability of p-type conjugated polymer films in the EGOFET configuration. By combining electrochemical stability tests, morphology characterization, and EQCM-D monitoring, we find that a donor-acceptor copolymer, poly(N-alkyldiketopyrrolo-pyrrole-dithienylthieno[3,2-b]thiophene) (DPP-DTT) shows improved mobility and electrochemical stability under an electrolyte, which may benefit from the ordered morphology and close alkyl side-chains' interdigitation preventing water diffusion and ion doping during long-term operation under an electrolyte. Based on the DPP-DTT EGOFETs, we have demonstrated a low-cost drug toxicity test platform that is sensitive enough to distinguish the cytotoxicity of different chemicals. This study overall pushes forward the development of organic bioelectronics with enhanced stability and sensitivity and presents successful exploitation of EGOFET in pharmaceutical research.