Water-gated Organic Field-effect Transistor Research Articles

Real-Time Detection of Glyphosate by a Water-Gated Organic Field-Effect Transistor with a Microfluidic Chamber.

This paper reports the development of a real-time monitoring system utilizing the combination of a water-gated organic field-effect transistor (WG-OFET) and a microfluidic chamber for the detection of the herbicide glyphosate (GlyP). For the realization of the real-time sensing with the WG-OFET, the surface of a polymer semiconductor was utilized as a sensing unit. The aqueous solution including the target analyte, which is employed as a gate dielectric of the WG-OFET, flows into a designed microfluidic chamber on the semiconductor layer and the gate electrode. As the sensing mechanism, the WG-OFET-based sensor utilizes the competitive complexation among carboxylate-functionalized polythiophene, a copper(II) (Cu2+) ion, and GlyP. The reversible accumulation and desorption of the positively charged Cu2+ ion on the semiconductor surface induced a change in the electrical double-layer capacitance (EDLC). The optimization of the microfluidic chamber enables a uniform water flow and contributes to real-time quantitative sensing of GlyP at a micromolar level. Thus, this study would lead to practical real-time sensing in water for various fields including environmental assessment.

Sensitive Detection of Glyphosate by a Water-Gated Organic Transistor

In this study, we developed a glyphosate (GlyP) sensor based on a water-gated organic field-effect transistor (WG-OFET). The WG-OFET has a side-gated structure, which is easier to fabricate compared to the conventional multi-stacked OFET structure. A carboxylate-functionalized polythiophene (PT) was employed as the organic semiconductor and receptor, which enabled a competitive assay among PT, Cu2+, and GlyP in water. The WG-OFET sensor achieved highly sensitive and selective detection (i.e. limit of detection = 0.26 ppm), which was lower than the maximum approved GlyP level (0.7 ppm) in drinking water in the United States. This study demonstrates the promising potential of WG-OFET as an electronic sensor device for the detection of analytes in aqueous media.

Facile and cost-effective liver cancer diagnosis by water-gated organic field-effect transistors

The rise of mortality rate caused by hepatocellular carcinoma accelerates requirements of biosensors for early liver cancer diagnosis and treatment to improve the clinical prognosis and prolong the survival of patients. However, how to realize label-free, low-cost, easy and fast-detection is the major challenge in the design of biosensors. Water-gated organic field-effect transistors efficiently bridge the gap between semiconductor devices and biological systems, leading to an organic device suitable for health or body signal monitoring. Herein, a kind of high-performance water-gated organic field-effect transistor is developed through the optimization process. This method provides a label-free general sensing platform for the determination of liver cancer biomarker alpha-fetoprotein in 45 minutes, much quicker than traditional methods such as the enzyme-linked immunosorbent assay for several hours. In addition, with the detection limit lower than the cut-off value as well as the ability to achieve quantitative detection, this novel water-gated organic field-effect transistor enables a much broader analysis of other biomarkers in cancer patient samples.

Stable operation of water-gated organic field-effect transistor depending on channel flatness, electrode metals and surface treatment

The main purpose of this study is to clarify the factors for the stable operation of a poly(3-hexylthiophene) (P3HT)-based water gated organic field effect transistor (WG-OFET). To this end, the influence of the surface morphologies and electrode metals on the transistor properties were investigated. The experimental results indicated that a flat surface improved the on/off ratio and switching repeatability. Treating the surface with a lipid membrane was found to reduce hysteresis loops in the transfer curves probably due to the reduced number of carrier traps. The Au gate electrode effectively lowered the threshold voltage. Consequently, stable transistor operation with a low threshold voltage of 35 mV was achieved by employing a gold gate electrode and lipid membrane treatment. These results suggest that WG-OFETs with an ultra-thin lipid membrane have great potential for sensor applications, and in particular for sensing water-soluble analytes.

Design and synthesis of stable indigo polymer semiconductors for organic field-effect transistors with high fluoride sensitivity and selectivity.

We report the design and synthesis of two novel indigo donor–acceptor (D–A) polymers, PIDG-T-C20 and PIDG-BT-C20, comprising an indigo moiety that has intramolecular hydrogen-bonds as the acceptor building block and thiophene (T) and bithiophene (BT) as the donor building block, respectively. PIDG-T-C20 and PIDG-BT-C20 exhibited characteristic p-type semiconductor performance, achieving hole mobilities of up to 0.016 and 0.028 cm2 V−1 s−1, respectively, which are highest values reported for indigo-based polymers. The better performing PIDG-BT-C20 was used for the fabrication of water-gated organic field-effect transistors (WGOFETs), which showed excellent stability at ambient conditions. The PIDG-BT-C20-based WGOFETs exhibited rapid response when fluoride ions were introduced to the water gate dielectric, achieving a limit of detection (LOD) of 0.40 mM. On the other hand, the devices showed much lower sensitivities towards other halide ions with the order of relative response: F− ≫ Cl− > Br− > I−. The high sensitivity and selectivity of PIDG-BT-C20 to fluoride over other halides is considered to be realized through the strong interaction of the hydrogen atoms of the N–H groups in the indigo unit with fluoride ions, which alters the intramolecular hydrogen-bonding arrangement, the electronic structures, and thus the charge transport properties of the polymer.

Spectroscopic Study of Charge Transport at Organic Solid–Water Interface

Charge transport in an organic solid and its coupling with the neighboring aqueous biological environment dictates the performance of many organic bioelectronic devices. Understanding how the transport property at the solid–water interface is influenced by the surface structure characteristics of the organic solid is essential for rational design of organic bioelectronics and chemical sensors. However, in situ probing such structure–property relationships has been difficult due to lack of experimental techniques with sufficient sensitivity to the water-buried interface. Here, we demonstrate a charge accumulation spectroscopy (CAS)-based protocol, exploiting water-gated organic field-effect transistor as the testing platform, to investigate the structure-dependent localization of polaronic charge carriers at the organic semiconductor–liquid interface. Our results reveal that the degree of charge delocalization is reduced drastically when the charge carriers are moved from the bulk semiconductor to the semiconductor–water interface, suggesting the existence of a highly disordered surface layer in contact with water. It is also found that the charge delocalization could be further reduced by intercalation of chloride ions (from salt water) in the semiconductor surface layer. This study suggests that the spectroscopic signatures of polaronic charge carriers could be a sensitive probe to detect the structure-dependent charge localization at organic solid–liquid interfaces.

Water-Gated n-Type Organic Field-Effect Transistors for Complementary Integrated Circuits Operating in an Aqueous Environment.

The first demonstration of an n-type water-gated organic field-effect transistor (WGOFET) is here reported, along with simple water-gated complementary integrated circuits, in the form of inverting logic gates. For the n-type WGOFET active layer, high-electron-affinity organic semiconductors, including naphthalene diimide co-polymers and a soluble fullerene derivative, have been compared, with the latter enabling a high electric double layer capacitance in the range of 1 μF cm–2 in full accumulation and a mobility–capacitance product of 7 × 10–3 μF/V s. Short-term stability measurements indicate promising cycling robustness, despite operating the device in an environment typically considered harsh, especially for electron-transporting organic molecules. This work paves the way toward advanced circuitry design for signal conditioning and actuation in an aqueous environment and opens new perspectives in the implementation of active bio-organic interfaces for biosensing and neuromodulation.

Field-effect and capacitive properties of water-gated transistors based on polythiophene derivatives

Recently, water-gated organic field-effect transistors (WGOFET) have been intensively studied for their application in the biological field. Surprisingly, a very limited number of conjugated polymers have been reported so far. Here, we systematically explore a series of polythiophene derivatives, presenting different alkyl side chains lengths and orientation, and characterized by various morphologies: comparative evaluation of their performances allows highlighting the critical role played by alkyl side chains, which significantly affects the polymer/water interface capacitance. Reported results provide useful guidelines towards further development of WGOFETs and represent a step forward in the understanding of the polymer/water interface phenomena.

Facile maskless fabrication of organic field effect transistors on biodegradable substrates

Fabrication of a test pattern with interdigitated gold electrodes (channel length 12 μm) on a biodegradable substrate is achieved by direct laser ablation of a Au film using a high-precision multifunction infrared-laser scan marker. The whole process involves two solvent-free steps: Au film deposition by sublimation followed by maskless ablation. The approach is suited for fast prototyping of a variety of materials. We demonstrate the fabrication of a water-gated organic field effect transistor on the biodegradable poly(lactic-co-glycolic acid) scaffold and its operations in water.

Water-gated organic field effect transistors - opportunities for biochemical sensing and extracellular signal transduction.

There is a quest for electronic biosensors operated in water for biomedical applications and environmental monitoring. Water is an aggressive medium for standard electronics materials and devices due to its strong polarizability and electrochemical activity. Thick dielectric encapsulation provides necessary stability while it damps the sensitivity of the device to sensing events occurring in the aqueous environment. Organic electronics provides materials that exhibit stable electronic conduction in direct contact with water combined with other desirable properties like mechanical softness, biocompatibility and processability onto flexible substrates. In this review, we introduce an emerging class of organic transistors, in which the current across the organic film is gated by the electric field of the Debye-Helmholtz layer. We discuss the device physics, the sensing mechanism and the relevant electrochemical processes. Applications of water-gated transistors range from the sensing of biologically relevant molecules like DNA, proteins or hormones to non-invasive recording and stimulation of electrical activity of neurons. Materials chemistry is crucial to control properties of electrically active films and to allow the introduction of specific chemical functionalities and receptors at sensing interfaces of the device.

Copolythiophene-based water-gated organic field-effect transistors for biosensing.

This paper reports on the sensing of proteins using water-gated organic field-effect transistors. As a proof-of-concept, streptavidin and avidin were used, with a biotinylated polymer as the active sensing material. The latter is a copolythiophene modified to graft biotin by peptidic coupling. After characterization of its structure, it was integrated as the channel material into transistors and its interactions with several proteins were investigated. Non-specific interactions were reduced when the polymer surface was pretreated with 1-octanol. In this case, human serum albumin had no effect on the transistor characteristics whereas avidin and streptavidin led to a decrease of the drain current.

DNA detection with a water-gated organic field-effect transistor

A DNA sensor based on a water-gated organic field-effect transistor is described. The semiconductor is poly [3-(5-carboxypentyl)thiophene-2,5-diyl] onto which DNA probes are covalently grafted via NHS/EDC chemistry. Clear changes in the output characteristic of the device are observed upon DNA immobilization and after DNA hybridization. Experimental data point out the importance of the electrolyte Debye length that can screen negative DNA charges and impede transduction. For this reason, deionized water was used in order to increase the Debye length up to several hundreds of nanometers. In this case, a decrease in the off current was observed upon hybridization, whereas no significant change occurred when using saline solutions.

Use of poly(3-hexylthiophene)/poly(methyl methacrylate) (P3HT/PMMA) blends to improve the performance of water-gated organic field-effect transistors

Poly(3-hexylthiophene)/poly(methyl methacrylate) (P3HT/PMMA) blends were used as the semiconducting layer in water-gated organic field-effect transistors (OFETs), which resulted in improving the electrical performance of the previously reported devices with pure P3HT. Topographic investigations by atomic force microscopy carried out on blends with various PMMA to P3HT ratio reveal a lateral phase separation of the two components. All transistors operate at very low voltage (below 1 V), with a threshold voltage ranging form 0.3 to 0.5 V. An optimum of the composition of the blend is found with 70% of PMMA, leading to a maximum on/off current ratio and a mobility comparable to that of pure P3HT.