Mohammad Yusuf Mulla

Electrolyte‐Gated Organic Field‐Effect Transistor Sensors Based on Supported Biotinylated Phospholipid Bilayer

Anchored, biotinylated phospholipids forming the capturing layers in an electrolyte-gated organic field-effect transistor (EGOFET) allow label-free electronic specific detection at a concentration level of 10 nM in a high ionic strength solution. The sensing mechanism is based on a clear capacitive effect across the PL layers involving the charges of the target molecules.

Capacitance-modulated transistor detects odorant binding protein chiral interactions

Peripheral events in olfaction involve odorant binding proteins (OBPs) whose role in the recognition of different volatile chemicals is yet unclear. Here we report on the sensitive and quantitative measurement of the weak interactions associated with neutral enantiomers differentially binding to OBPs immobilized through a self-assembled monolayer to the gate of an organic bio-electronic transistor. The transduction is remarkably sensitive as the transistor output current is governed by the small capacitance of the protein layer undergoing minute changes as the ligand–protein complex is formed. Accurate determination of the free-energy balances and of the capacitance changes associated with the binding process allows derivation of the free-energy components as well as of the occurrence of conformational events associated with OBP ligand binding. Capacitance-modulated transistors open a new pathway for the study of ultra-weak molecular interactions in surface-bound protein–ligand complexes through an approach that combines bio-chemical and electronic thermodynamic parameters.

Detection beyond Debye's length with an electrolyte-gated organic field-effect transistor.

Electrolyte-gated organic field-effect transistors are successfully used as biosensors to detect binding events occurring at distances from the transistor electronic channel that are much larger than the Debye length in highly concentrated solutions. The sensing mechanism is mainly capacitive and is due to the formation of Donnans equilibria within the protein layer, leading to an extra capacitance (CDON) in series to the gating system.

Printable Bioelectronics To Investigate Functional Biological Interfaces

Thin-film transistors can be used as high-performance bioelectronic devices to accomplish tasks such as sensing or controlling the release of biological species as well as transducing the electrical activity of cells or even organs, such as the brain. Organic, graphene, or zinc oxide are used as convenient printable semiconducting layers and can lead to high-performance low-cost bioelectronic sensing devices that are potentially very useful for point-of-care applications. Among others, electrolyte-gated transistors are of interest as they can be operated as capacitance-modulated devices, because of the high capacitance of their charge double layers. Specifically, it is the capacitance of the biolayer, being lowest in a series of capacitors, which controls the output current of the device. Such an occurrence allows for extremely high sensitivity towards very weak interactions. All the aspects governing these processes are reviewed here.

Printable and flexible electronics: From TFTs to bioelectronic devices

Printable and flexible thin-film transistors (TFTs) have gained significant attention over the last few years thanks to their implementation in many different sectors. Beside applications in large-area electronics such as flat displays, sensors and radio frequency identification tags, these devices have been widely investigated for life sciences applications too, including label-free biosensors, systems for drug delivery and implantable platforms. This review highlights the recent advances in the field of highly performing low-cost TFT devices realized by printing or printing compatible technologies and suitable for bioelectronics applications. Novel printable materials used as semiconductors, dielectrics and electrodes as well as printing technologies useful for the realization of the elicited devices are discussed as well. Particularly attention is given to printing techniques employed for the deposition of biological materials and to methods for realizing label-free electronic biosensors.

A comparative study of the gas sensing behavior in P3HT- and PBTTT-based OTFTs: the influence of film morphology and contact electrode position.

Bottom- and top-contact organic thin film transistors (OTFTs) were fabricated, using poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C16) as p-type channel semiconductors. Four different types of OTFTs were fabricated and investigated as gas sensors against three volatile organic compounds, with different associated dipole moments. The OTFT-based sensor responses were evaluated with static and transient current measurements. A comparison between the different architectures and the relative organic semiconductor was made.

UV crosslinked poly(acrylic acid): a simple method to bio-functionalize electrolyte-gated OFET biosensors

A simple and time-saving wet method to endow the surface of organic semiconductor films with carboxyl functional groups is presented. A thin layer of poly(acrylic acid) (pAA) is spin-coated directly on the electronic channel of an electrolyte-gated organic FET (EGOFET) device and cross-linked by UV exposure without the need for any photo-initiator. The carboxyl functionalities are used to anchor phospholipid bilayers through the reaction with the amino-groups of phosphatidyl-ethanolamine (PE). By loading the membranes with phospholipids carrying specific functionalities, such a platform can be easily implemented with recognition elements. Here the case of biotinylated phospholipids that allow selective streptavidin electronic detection is described. The surface morphology and chemical composition are monitored using SEM and XPS, respectively, during the whole process of bio-functionalization. The electronic and sensing performance level of the EGOFET biosensing platform is also evaluated. Selective analyte (streptavidin) detection in the low pM range is achieved, this being orders of magnitude lower than the performance level obtained by the well assessed surface plasmon resonance assay reaching the nM level, at most.

Effect of the gate metal work function on water-gated ZnO thin-film transistor performance

ZnO thin films, prepared using a printing-compatible sol–gel method involving a thermal treatment below 400 °C, are proposed as active layers in water-gated thin-film transistors (WG-TFTs). The thin-film structure and surface morphology reveal the presence of contiguous ZnO crystalline (hexagonal wurtzite) with isotropic nano-grains as large as 10 nm characterized by a preferential orientation along the a-axis. The TFT devices are gated through a droplet of deionized water by means of electrodes characterized by different work functions. The high capacitance of the electrolyte allowed operation below 0.5 V. While the Ni, Pd, Au and Pt gate electrodes are electrochemically stable in the inspected potential range, electrochemical activity is revealed for the W one. Such an occurrence leads to an increase of capacitance (and current), which is ascribed to a high output current from the dissolution of a lower capacitance W-oxide layer. The environmental stability of the ZnO WG-TFTs is quite good over a period of five months.

Correction: Printable and flexible electronics: from TFTs to bioelectronic devices

Correction for ‘Printable and flexible electronics: from TFTs to bioelectronic devices’ by M. Magliulo et al., J. Mater. Chem. C, 2015, 3, 12347–12363.

Bio-functionalization of ZnO water gated thin-film transistors

ZnO based thin-film transistors are very promising to be used as electronic biosensors due to their very good electronic performances and inherent biocompatibility. Herein, we report on the use of a solution processed ZnO water gated thin-film transistor (WG-TFT) whose channel surface is bio-functionalized with a streptavidin protein layer. This is a very critical process as it endows the device with bio-recognition capabilities. The bio-functionalization process is carried out by attaching an organosilane self-assembled monolayer to the ZnO surface that is coupled to the biomolecule afterwards. A systematic X-Ray Photoelectron Spectroscopy surface characterization allows assessing that the immobilization of the streptavidin proteins on the ZnO surface has been successfully accomplished. Upon deposition of the protein layer, a decrease in the ZnO WG-TFT source-drain current is observed. Such an occurrence is ascribable to the electrostatic effect of the negatively charged protein molecules lying on the ZnO semiconductor layer in contact with the transistor 2D-channel. The deposited streptavidin layer can be prospectively further used for the immobilization and orientation of biotinylated recognition elements in view of the use of ZnO TFTs as electronic biosensors for real-life applications.