Microbial Nanocellulose Printed Circuit Boards for Medical Sensing.

We demonstrate the viability of using ultra-thin sheets of microbially grown nanocellulose to build functional medical sensors. Microbially grown nanocellulose is an interesting alternative to plastics, as it is hydrophilic, biocompatible, porous, and hydrogen bonding, thereby allowing the potential development of new application routes. Exploiting the distinguishing properties of this material enables us to develop solution-based processes to create nanocellulose printed circuit boards, allowing a variety of electronics to be mounted onto our nanocellulose. As proofs of concept, we have demonstrated applications in medical sensing such as heart rate monitoring and temperature sensing-potential applications fitting the wide-ranging paradigm of a future where the Internet of Things is dominant.

A Fully-Flexible Solution-Processed Autonomous Glucose Indicator.

We present the first demonstration of a fully-flexible, self-powered glucose indicator system that synergizes two flexible electronic technologies: a flexible self-powering unit in the form of a biofuel cell, with a flexible electronic device - a circuit-board decal fabricated with biocompatible microbial nanocellulose. Our proof-of-concept device, comprising an enzymatic glucose fuel cell, glucose sensor and a LED indicator, does not require additional electronic equipment for detection or verification; and the entire structure collapses into a microns-thin, self-adhering, single-centimeter-square decal, weighing less than 40 mg. The flexible glucose indicator system continuously operates a light emitting diode (LED) through a capacitive charge/discharge cycle, which is directly correlated to the glucose concentration. Our indicator was shown to operate at high sensitivity within a linear glucose concentration range of 1 mM-45 mM glucose continuously, achieving a 1.8 VDC output from a flexible indicator system that deliver sufficient power to drive an LED circuit. Importantly, the results presented provide a basis upon which further development of indicator systems with biocompatible diffusing polymers to act as buffering diffusion barriers, thereby allowing them to be potentially useful for low-cost, direct-line-of-sight applications in medicine, husbandry, agriculture, and the food and beverage industries.

Electrolyte-Sensing Transistor Decals Enabled by Ultrathin Microbial Nanocellulose.

We report an ultra-thin electronic decal that can simultaneously collect, transmit and interrogate a bio-fluid. The described technology effectively integrates a thin-film organic electrochemical transistor (sensing component) with an ultrathin microbial nanocellulose wicking membrane (sample handling component). As far as we are aware, OECTs have not been integrated in thin, permeable membrane substrates for epidermal electronics. The design of the biocompatible decal allows for the physical isolation of the electronics from the human body while enabling efficient bio-fluid delivery to the transistor via vertical wicking. High currents and ON-OFF ratios were achieved, with sensitivity as low as 1 mg·L-1.

Ambient method for the production of an ionically gated carbon nanotube common cathode in tandem organic solar cells.

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two solution-processed polymeric cells connected in parallel by a transparent carbon nanotubes (CNT) interlayer. This structure includes improvements in fabrication techniques for tandem OPV devices. First the need for ambient-processed cathodes is considered. The CNT anode in the tandem device is tuned via ionic gating to become a common cathode. Ionic gating employs electric double layer charging to lower the work function of the CNT electrode. Secondly, the difficulty of sequentially stacking tandem layers by solution-processing is addressed. The devices are fabricated via solution and dry-lamination in ambient conditions with parallel processing steps. The method of fabricating the individual polymeric cells, the steps needed to laminate them together with a common CNT cathode, and then provide some representative results are described. These results demonstrate ionic gating of the CNT electrode to create a common cathode and addition of current and efficiency as a result of the lamination procedure.

N-alkyldinaphthocarbazoles, azaheptacenes, for solution-processed organic field-effect transistors.

Substituted N-alkyldinaphthocarbazoles were synthesized using a key double Diels-Alder reaction. The angular nature of the dinaphthocarbazole system allows for increased stability of the conjugated system relative to linear analogues. The N-alkyldinaphthocarbazoles were characterized by UV-vis absorption and fluorescence spectroscopy as well as cyclic voltammetry. X-ray structure analysis based on synchrotron X-ray powder diffraction revealed that the N-dodecyl-substituted compound was oriented in an intimate herringbone packing motif, which allowed for p-type mobilities of 0.055 cm(2) V(-1) s(-1) from solution-processed organic field-effect transistors.

High-hole-mobility field-effect transistors based on co-benzobisthiadiazole-quaterthiophene.

High-mobility organic thin film transistors based on a benzobisthiadiazole-containing polymer are presented together with their morphological and optical properties. A very tight packing pattern of "edge-on" orientated polymer chains is observed in their thin films after annealing, and the hole mobility of this polymer is up to 2.5 cm(2) V(-1) s(-1) .

High-performance ambipolar transistors and inverters from an ultralow bandgap polymer.

High mobility ambipolor organic thin-film transistors based on an ultralow bandgap polymer are presented together with their morphological and optical properties. Hole and electron mobilities of this polymer are of 1.0 cm(2) V(-1) s(-1) and 0.7 cm(2) V(-1) s(-1), respectively. The inverter based on two identical ambipolar transistors exhibits a gain around 35.

Control of efficiency, brightness, and recombination zone in light-emitting field effect transistors.

The split-gate light emitting field effect transistors (SG-LEFETs) demonstrate a new strategy for ambipolar LEFETs to achieve high brightness and efficiency simultaneously. The SG architecture forces largest quantity of opposite charges on Gate 1 and Gate 2 area to meet in the center of the channel. By actively and independently controlling current injection from separated gate electrodes within transporting channel, high brightness can be obtained in the largest injection current regime with highest efficiency.

High performance weak donor-acceptor polymers in thin film transistors: effect of the acceptor on electronic properties, ambipolar conductivity, mobility, and thermal stability.

We have studied the electronic, physical, and transistor properties of a family of donor-acceptor polymers consisting of diketopyrrolopyrrole (DPP) coupled with different accepting companion units in order to determine the effects of donor-acceptor interaction. Using the electronically neutral benzene (B), the weakly accepting benzothiadiazole (BT), and the strongly accepting benzobisthiadiazole (BBT), the accepting strength of the companion unit was systematically modulated. All polymers exhibited excellent transistor performance, with mobilities above 0.1 cm(2)V(-1)s(-1), even exceeding 1 cm(2)V(-1)s(-1) for one of the BBT-containing polymers. We find that the BBT is the strongest acceptor, enabling the BBT-containing polymers to be strongly ambipolar. The BBT moiety also strengthens interchain interactions, which provides higher thermal stability and performance for transistors with BBT-containing polymers as the active layer.

Observations of PDDTT subject to thermal treatment: correlation between performance and order.

We show that polybis(thienyl)thienodia-thiazolethiophene (PDDTT), a high-performance semiconducting polymer for photodetectors and field-effect transistors, has strong performance dependence on annealing temperature. An unprecedented increase of 3 orders of magnitude is observed in both transistor and photoconductive properties. XRD and AFM evidence points to increased ordering in PDDTT films with annealing. This correlation highlights the importance that order has in determining performance in PDDTT and has possible implications in the design of polymers.

Ambipolarity in benzobisthiadiazole-based donor-acceptor conjugated polymers.

A family of four new DA polymers, in which the acceptor moiety benzobisthiadiazole was paired with four different donor moieties, has been synthesized. Surpri-singly, all members of the family exhibit balanced ambipolar behavior, despite polymer to polymer mobilities varying from 10(-4) cm(2) V(-1) s(-1) to 10(-1) cm(2) V(-1) s(-1). Applications in single component CMOS integrated circuits are envisioned.

Colorimetric detection of DNA, small molecules, proteins, and ions using unmodified gold nanoparticles and conjugated polyelectrolytes.

We have demonstrated a novel sensing strategy employing single-stranded probe DNA, unmodified gold nanoparticles, and a positively charged, water-soluble conjugated polyelectrolyte to detect a broad range of targets including nucleic acid (DNA) sequences, proteins, small molecules, and inorganic ions. This nearly "universal" biosensor approach is based on the observation that, while the conjugated polyelectrolyte specifically inhibits the ability of single-stranded DNA to prevent the aggregation of gold-nanoparticles, no such inhibition is observed with double-stranded or otherwise "folded" DNA structures. Colorimetric assays employing this mechanism for the detection of hybridization are sensitive and convenient--picomolar concentrations of target DNA are readily detected with the naked eye, and the sensor works even when challenged with complex sample matrices such as blood serum. Likewise, by employing the binding-induced folding or association of aptamers we have generalized the approach to the specific and convenient detection of proteins, small molecules, and inorganic ions. Finally, this new biosensor approach is quite straightforward and can be completed in minutes without significant equipment or training overhead.

Label-free, dual-analyte electrochemical biosensors: a new class of molecular-electronic logic gates.

An "XOR" gate built using label-free, dual-analyte electrochemical sensors and the activation of this logic gate via changing concentrations of cocaine and the relevant cDNA as inputs are described.

Nonlinear transport in semiconducting polymers at high carrier densities.

Conducting and semiconducting polymers are important materials in the development of printed, flexible, large-area electronics such as flat-panel displays and photovoltaic cells. There has been rapid progress in developing conjugated polymers with high transport mobility required for high-performance field-effect transistors (FETs), beginning with mobilities around 10(-4) cm(2) V(-1) s(-1) to a recent report of 1 cm(2) V(-1) s(-1) for poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). Here, the electrical properties of PBTTT are studied at high charge densities both as the semiconductor layer in FETs and in electrochemically doped films to determine the transport mechanism. We show that data obtained using a wide range of parameters (temperature, gate-induced carrier density, source-drain voltage and doping level) scale onto the universal curve predicted for transport in the Luttinger liquid description of the one-dimensional 'metal'.

Electrochemical doping in electrolyte-gated polymer transistors.

By comparing the changes in pi-pi* absorption with the transconductance in PEO-LiClO4 electrolyte-gated FETs, we have demonstrated that the high channel currents obtained at low gate voltages result from reversible electrochemical doping of the semiconducting polymer film. At low temperatures, the conductivity of the electrochemically doped poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT-C14, is nonlinear with a crossover from dsigma(T)/dT > 0 to dsigma(T)/dT approximately 0 as a function of the source-drain voltage. High current densities, up to 10(6) A/cm2 at 4.2 K, can be sustained in the electrochemically doped PBTTT-C14 films.

Beyond the metal-insulator transition in polymer electrolyte gated polymer field-effect transistors.

We have studied the carrier transport in poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) field-effect transistors (FETs) at very high field-induced carrier densities (10(15) cm(-2)) using a polymer electrolyte as gate and gate dielectric. At room temperature, we find high current densities, 2 x 10(6) A/cm(2), and high metallic conductivities, 10(4) S/cm, in the FET channel; at 4.2 K, the current density is sustained at 10(7) A/cm(2). Thus, metallic conductivity persists to low temperatures. The carrier mobility in these devices is approximately 3.5 cm(2).V(-1).s(-1) at 297 K, comparable with that found in fully crystalline organic devices.