Ben B. Y. Hsu

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.

Regioregular pyridal[2,1,3]thiadiazole π-conjugated copolymers

π-Conjugated, narrow band gap copolymers containing pyridal[2,1,3]thiadiazole (PT) were synthesized via starting materials that prevent random incorporation of the PT heterocycles relative to the backbone vector. Two regioregular structures could be obtained: in one the PTs are oriented in the same direction, and in the other the orientation of the PTs alternates every other repeat unit. Compared to their regiorandom counterparts, the regioregular polymers exhibit a 2 orders of magnitude increase of the hole mobilites, from 0.005 to 0.6 cm(2) V(-1) s(-1), as determined by field-effect transistor measurements.

A Porphyrin–Fullerene Dyad with a Supramolecular “Double‐Cable” Structure as a Novel Electron Acceptor for Bulk Heterojunction Polymer Solar Cells

Bulk heterojunction (BHJ) polymer solar cells (PSCs) offer a promising, low-cost, large-area, fl exible, light-weight, clean, and quiet alternative energy source for both indoor and outdoor applications. [ 1–4 ] Power conversion effi ciencies (PCEs) in response to solar AM1.5 radiation as high as 6–8% have been reported for BHJ PSCs. [ 5 , 6 ] In order to achieve PCEs over 10%, BHJ materials capable of generating higher short circuit current ( J sc ) and larger open circuit voltage ( V oc ) are required. [ 7 , 8 ]

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 thermal stability solution-processable narrow-band gap molecular semiconductors

A series of narrow-band gap conjugated molecules with specific fluorine substitution patterns has been synthesized in order to study the effect of fluorination on bulk thermal stability. As the number of fluorine substituents on the backbone increase, one finds more thermally robust bulk structures both under inert and ambient conditions as well as an increase in phase transition temperatures in the solid state. When integrated into field-effect transistor devices, the molecule with the highest degree of fluorination shows a hole mobility of 0.15 cm(2)/V·s and a device thermal stability of >300 °C. Generally, the enhancement in thermal robustness of bulk organization and device performance correlates with the level of C-H for C-F substitution. These findings are relevant for the design of molecular semiconductors that can be introduced into optoelectronic devices to be operated under a wide range of conditions.

Ordered Polymer Nanofibers Enhance Output Brightness in Bilayer Light-Emitting Field-Effect Transistors

Polymer light emitting field effect transistors are a class of light emitting devices that reveal interesting device physics. Device performance can be directly correlated to the most fundamental polymer science. Control over surface properties of the transistor dielectric can dramatically change the polymer morphology, introducing ordered phase. Electronic properties such as carrier mobility and injection efficiency on the interface can be promoted by ordered nanofibers in the polymer. Moreover, by controlling space charge in the polymer interface, the recombination zone can be spatially extended and thereby enhance the optical output.

Phosphorescent Light-Emitting Transistors: Harvesting Triplet Excitons

Phosphorescent light-emitting transistors, in which light emission from singlet and triplet energy levels is harvested using solution-processed materials, are presented. While a green phosphorescent dendrimer exhibits an external quantum efficiency of 0.45% at 480 cd m(-2) , a red polymer/phosphorescent small-molecule blend produces a brightness exceeding 30 cd m(-2) with a relatively high hole mobility of 2.5 × 10(-2)  cm(2) V(-1) s(-1) .

Insights into π-Conjugated Small Molecule Neat Films and Blends As Determined Through Photoconductivity

Spectrally dependent steady-state photoconductivity is a convenient method to gain insight into the charge generation and transport processes within a given material. In this work, we report on the photoconductive response of solution-processed neat films and blends of the fullerene, PC(71)BM, and the donor-acceptor small-molecule, p-DTS(PTTh(2))(2), as function of the processing additive, diiodooctance (DIO). The results, when considered in the context of their structural, optical, and electronic properties give insight into the dominant carrier generation and charge transport mechanisms in each of these molecular systems.

Split‐Gate Organic Field Effect Transistors: Control Over Charge Injection and Transport

A split-gate field effect transistor containing four electrodes, source, drain, two gates allows enhanced transport for specific carrier species and separate control of carrier polarity over two gate regimes. The device can be operated as a transistor or a diode by controlling gate biases.

Solution-processed cross-linkable hole selective layer for polymer solar cells in the inverted structure

Solution-processed cross-linkable tetraphenyldiamine-containing material (TPD-BVB) as a highly efficient hole selective transport layer was demonstrated. Polymer solar cells (PSCs) with an inverted structure fabricated with a thin cross-linked TPD-BVB film show comparable efficiency and superior long-term air stability when compared to devices fabricated with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). Thus, solution-processed TPD-BVB is an attractive alternative to PEDOT:PSS as a hole extraction layer in inverted structure PSCs.