Minh-Chau Pham

A Water‐Gate Organic Field‐Effect Transistor

High-dielectric-constant insulators, organic monolayers, and electrolytes have been successfully used to generate organic field-effect transistors operating at low voltages. Here, we report on a de ...

Advances in organic transistor-based biosensors: from organic electrochemical transistors to electrolyte-gated organic field-effect transistors.

AbstractOrganic electronics have, over the past two decades, developed into an exciting area of research and technology to replace classic inorganic semiconductors. Organic photovoltaics, light-emitting diodes, and thin-film transistors are already well developed and are currently being commercialized for a variety of applications. More recently, organic transistors have found new applications in the field of biosensors. The progress made in this direction is the topic of this review. Various configurations are presented, with their detection principle, and illustrated by examples from the literature.n FigureElectrolyte-Gated OFET (EGOFET) architecture. EGOFETs differ from OFETs, as in OECTs, in that the gate is separated from the semiconductor by an electrolyte. This allows low voltage operation compared with OFETs gated via solid dielectrics. The red circle indicates the interface involved in the detection of biomolecules, when water is used as electrolyte.

Label-free and reagentless electrochemical detection of microRNAs using a conducting polymer nanostructured by carbon nanotubes: application to prostate cancer biomarker miR-141.

In this paper, a label-free and reagentless microRNA sensor based on an interpenetrated network of carbon nanotubes and electroactive polymer is described. The nanostructured polymer film presents very well-defined electroactivity in neutral aqueous medium in the cathodic potential domain from the quinone group embedded in the polymer backbone. Addition of microRNA miR-141 target (prostate cancer biomarker) gives a signal-on response, i.e. a current increase due to enhancement of the polymer electroactivity. On the contrary, non-complementary miRNAs such as miR-103 and miR-29b-1 do not lead to any significant current change. A very low detection limit of ca. 8 fM is achieved with this sensor.

Detection of Glutamate and Acetylcholine with Organic Electrochemical Transistors Based on Conducting Polymer/Platinum Nanoparticle Composites

The aim of the study is to open a new scope for organic electrochemical transistors based on PEDOT:PSS, a material blend known for its stability and reliability. These devices can leverage molecular electrocatalysis by incorporating small amounts of nano-catalyst during the transistor manufacturing (spin coating). This methodology is very simple to implement using the know-how of nanochemistry and results in efficient enzymatic activity transduction, in this case utilizing choline oxidase and glutamate oxidase.

Poly(5‐amino‐1,4‐naphthoquinone), a Novel Lithium‐Inserting Electroactive Polymer with High Specific Charge

The monomer 5‐amino‐1,4‐naphthoquinone can be polymerized electrochemically or chemically to form a redox polymer in which the quinone/hydroquinone redox couple can be electrochemically oxidized and reduced in aqueous and organic electrolytes. The polymer exchanges cations for the charge‐compensating process. In electrolyte lithium ions can be inserted and expelled reversibly. Cyclic voltammograms and galvanostatic experiments show that the charge storage capacity of this polymer is very close to its theoretical value of 290 Ah/kg. The redox potential is about 2.6 V more positive than that of the couple. If the electrode potential is kept within the window from −1.25 to −0.20 V vs. Ag/AgCl the stability of poly(5‐amino‐1,4‐naphthoquinone) (PANQ) is reasonable, and an acceptable cycle life can be reached. However, at lower potentials irreversible electrochemical reactions proceed, and the cycle life of PANQ is shortened. Hence, PANQ is an interesting electrode material for lithium metal or lithium‐ion batteries. From potential‐jump experiments on porous composite PANQ electrodes an overall diffusion coefficient at least was estimated for the lithium deinsertion. Assuming a thin‐layer cell with a negative and a PANQ positive electrode (using common dimensions for the current collectors and battery housing, and accounting for the electrolyte necessary to fill the pores in the electrode and separator), we estimated that a battery having a specific energy of up to 125 Wh/kg at very low charge/discharge rates could be realized. For the 1 h discharge rate about 100 Wh/kg should be possible.

An electrochemical ELISA-like immunosensor for miRNAs detection based on screen-printed gold electrodes modified with reduced graphene oxide and carbon nanotubes.

We design an electrochemical immunosensor for miRNA detection, based on screen-printed gold electrodes modified with reduced graphene oxide and carbon nanotubes. An original immunological approach is followed, using antibodies directed to DNA.RNA hybrids. An electrochemical ELISA-like amplification strategy was set up using a secondary antibody conjugated to horseradish peroxidase (HRP). Hydroquinone is oxidized into benzoquinone by the HRP/H2O2 catalytic system. In turn, benzoquinone is electroreduced into hydroquinone at the electrode. The catalytic reduction current is related to HRP amount immobilized on the surface, which itself is related to miRNA.DNA surface density on the electrode. This architecture, compared to classical optical detection, lowers the detection limit down to 10 fM. Two miRNAs were studied: miR-141 (a prostate biomarker) and miR-29b-1 (a lung cancer biomarker).

Antibodies directed to RNA/DNA hybrids: an electrochemical immunosensor for microRNAs detection using graphene-composite electrodes.

We report a simple and sensitive label-free immunosensor for detection of microRNAs (miRNA) based on a conducting polymer/reduced graphene oxide-modified electrode to detect miR-29b-1 and miR-141. Square wave voltammetry is used to record the redox signal. Current increases upon hybridization (signal on) from 1 fM to 1 nM of target miRNA. The limit of quantification is ca. 5 fM. The sensor exhibits high selectivity as it distinguishes mismatch. To double-check its selectivity, two specific RNA-DNA antibodies recognizing miRNA-DNA heteroduplexes, antipoly(A)-poly(dT) and anti-S9.6, were used. The antibody complexation with the hybrid leads to a current decrease that confirms the presence of miRNA, down to a concentration of 8 fM. The antibody-hybrid complex can be then dissociated by adding miRNA-DNA hybrids in solution, causing a shift-back on the signal, i.e., an increase in the current density (signal-on). This On-Off-On detection sequence was used as a triple verification to increase the reliability of the results.

Nanometric layers for direct, signal-on, selective, and sensitive electrochemical detection of oligonucleotides hybridization.

We report a signal-on, reagentless electrochemical DNA biosensor, based on an electroactive self-assembled naphthoquinone derivative (JUG(thio)) monolayer. This system achieves highly sensitive (approximately 300 pM) and selective signal-on detection. Before hybridization, the single strand can interact with JUG(thio) and slow down the redox reaction. When the complementary target is added, the formation of the double helix eliminates the single strand/JUG(thio) interactions and the JUG(thio) redox rate, and hence the current increase.

A label-free electrochemical immunosensor for direct, signal-on and sensitive pesticide detection

A new electropolymerizable monomer, [N-(6-(4-hydroxy-6-isopropylamino-1,3,5-triazin-2-ylamino)hexyl) 5-hydroxy-1,4-naphthoquinone-3-propionamide], has been designed for use in a label-free electrochemical immunosensor when polymerized on an electrode and coupled with a monoclonal anti-atrazine antibody. This monomer contains three functional groups: hydroxyl group for electropolymerization, quinone group for its transduction capability, and hydroxyatrazine as bioreceptor element. Square wave voltammetry shows that the polymer film, poly[N-(6-(4-hydroxy-6-isopropylamino-1,3,5-triazin-2-ylamino)hexyl) 5-hydroxy-1,4-naphthoquinone-3-propionamide], presents negative current change following anti-atrazine antibody complexation and positive current change after atrazine addition in solution. This constitutes a direct, label-free and signal-on electrochemical immunosensor, with a very low detection limit of ca. 1 pM, i.e. 0.2 ng L(-1), one of the lowest reported for such immunosensors. This is far lower than the detection limit required by the European Union directives for drinkable water and food samples (0.1 μg L(-1)). The strategy described has great promise for the development of simple, cost-effective and reagentless on-site environmental monitors.

Label-free electrochemical detection of prostate-specific antigen based on nucleic acid aptamer.

We report a label-free aptasensor to make direct detection of prostate specific antigen (PSA, a biomarker of prostate cancer) using a quinone-containing conducting copolymer acting as redox transducer and grafting matrix for immobilization of the short aptamer strands. It is shown that capture of PSA generates a current decrease (signal-off) measured by Square Wave Voltammetry. This current decrease is specific for PSA above a limit of quantification in the ng mL(-1) range. The change in current is used to determine the PSA-aptamer dissociation constant K(D), of ca. 2.6 nM. To consolidate the proof of concept, a heterogeneous competitive exchange with a complementary DNA strand which breaks PSA-aptamer interactions is studied. This double-check followed by a current increase provides full assurance of a perfectly specific recognition.