Ye Gan

Screen-printed microfluidic device for electrochemical immunoassay.

In this paper, a new microfluidic array device has been fabricated with screen printing technology. In contrast to traditional microfabrication processes, our method is simple, inexpensive and also suitable for mass production. The device is used for sandwich-type electrochemical immunoassay, in which probes are covalently attached to the electrode surface via electropolymerized polypyrrole propylic acid (PPA) film. This novel microfluidic system enables the whole array preparation and detection processes, including the probe immobilization, sample injection, enzyme incubation and electrochemical detection, to be conducted in the sealed microchannels. For a demonstration, mouse IgG is selected as the target analyte and its detection is realized by sandwich ELISA with goat anti-mouse IgG, rat anti-mouse IgG (conjugated to alkaline phosphatase) and p-aminophenyl phosphate (PAPP) as the primary antibody, second antibody, and enzyme substrate, respectively. A detection limit of 10 ng mL(-1) (67 pM) is achieved with a dynamic range of 100 ng mL(-1)-10 microg mL(-1). In addition, anti-goat IgG is also immobilized as an alternative probe to test mouse IgG in the solution, in order to demonstrate the multiplexing capability as well as the specificity of the device. As expected, the electrochemical responses are much lower than that using anti-mouse IgG as the probe, indicating good selectivity of the immunoassay device. These results indicate a great promise toward the development of miniaturized, low-cost protein biochips for clinical, forensics, environmental, and pharmaceutical applications.

Evidence of Harvesting Electricity by Exciton Recombination in an n−n Type Solar Cell

Free electrons and holes bounded by weak interactions in organic molecules must be generated from excitons to produce photocurrent in organic solar cells. Free charge carriers, in either small molecule- or polymer-based solar cells, are generated so far by dissociation of excitons at the donor-acceptor interface through injecting electrons (holes) from a donor (acceptor) into an acceptor (donor) while leaving holes (electrons) in the donor (acceptor). Here we report a new way, intermolecular exciton recombination, to generate free carriers from organic semiconductors. Unlike the exciton dissociation between donor and acceptor, the recombination of electrons from perfluorinated hexadecafluorophthalo-cyaninatozinc (F16ZnPc) with holes from fullerene (C(60)) frees their counterpart carriers. A new organic solar cell based on this intermolecular exciton recombination at the interface is fabricated to clearly demonstrate this new way to produce free carriers and then harvest electricity from sunlight.

High-performance UV-curable epoxy resin-based microarray and microfluidic immunoassay devices.

Immunoassay devices including microarray and microfluidic systems were fabricated with an UV-curable resin by a new economic approach, which can not only simply produce a 3-dimensional (3D) patterned structure, but also simultaneously introduce functional epoxide groups for efficient protein immobilization. The performance of the epoxy resin-based microarray was improved by optimization of printing buffer, probe concentration, and immobilization time, showing a detection dynamic range of 5 orders of magnitude and a limit of detection (LOD) of 10 pg mL(-1) for immunoglobulin G (IgG). The developed microfluidic immunoassay device demonstrates a LOD of 100 pg mL(-1) for IL-5 detection. The device can also be used to colorimetrically detect proteins via naked human eyes for immunoassays. This work provides a simple and inexpensive method to fabricate a sensitive immunoassay device, especially a 3D microfluidic system, which has great potential to develop a portable immunoassay device via human eye detection for point-of-care service and/or high throughput screening of infectious diseases.

Solution-processable organic-capped titanium oxide nanoparticle dielectrics for organic thin-film transistors

Oleic acid-capped titanium dioxide (OA-TiO2) nanoparticles were solution-processed to form homogeneous dielectrics for organic thin-film transistors (TFTs) of top-gate and bottom-gate configurations. The OA-TiO2 nanoparticles were well-dispersed into the organic solvent and spin-coated to give homogeneous films. These nanoparticle films showed a dielectric constant of about 5.3 and low leakage current density of ∼3×10−8 A/cm2 under an electric field of 1 MV/cm. Poly(3,3‴-didodecylquaterthiophene) and pentacene TFTs with OA-TiO2 dielectrics exhibited mobilities of 0.05±0.02 and 0.2±0.05 cm2 V−1 s−1, respectively, with on/off ratios of 103–105. This material appears to be useful for applications in printable organic TFTs.

Fabrication of thin-film organic transistor on flexible substrate via ultraviolet transfer embossing

Organic field-effect transistors with large-area coverage on flexible plastic substrates are fabricated by ultraviolet transfer embossing printing method. The source and drain electrodes are formed on the plastic substrate with gold by means of transfer embossing. The active layer is spin coated from 5wt% poly(3-hexylthiophene)-chloroform solution. Poly(4-vinylphenol) is used as the dielectric layer and a thin layer of silver paste is applied to cover the channel area as the gate electrode. The device shows good saturation behavior and gives an on/off ratio of 102 and the extracted field-effect mobility of the transistor is 0.0016cm2∕Vs.

Spark plasma sintering-fabricated one-dimensional nanoscale “crystalline-amorphous” carbon heterojunction

One-dimensional (1D) nanoscale “crystalline-amorphous” carbon heterojunction is fabricated by post-treatment of an amorphous carbon nanofiber in a spark plasma sintering (SPS) system. It is proposed that the unique SPS process is responsible for the heterojunction formation. Studies of the electrical transport property show that the nanoscale heterojunction exhibits a typical rectification behavior. The heterojunctions may have broad potential applications in nanoelectronics and optoelectronics and the SPS technique could be a distinctive approach to construct 1D functional nanomaterials with high throughput.

Bidirectional mediation of TiO2 nanowires field effect transistor by dipole moment from purple membrane

Bacteriorhodopsin-embedded purple membrane (bR-PM) is one of the most promising biomaterials for various bioelectronics applications. In this work, we demonstrate that a dipole bio-originated from bR-PM can bidirectionally mediate the performance of a bottom-contact TiO(2) nanowire field effect transistor (FET) for performance improvement. When negative gate voltage is applied, both transfer and output characteristics of the TiO(2) nanowire FET are enhanced by the bR-PM modification, resulting in a hole mobility increased by a factor of 2. The effect of the number of the deposited bR-PM layers on the normalized DeltaI(D) of the FET suggests that the additional electric field generated by the dipole moment natively existing in bR-PM actually boosts the performance of the TiO(2) nanowires FET.

AFM study of adsorption of protein A on a poly(dimethylsiloxane) surface.

In this paper, the morphology and kinetics of adsorption of protein A on a PDMS surface is studied by AFM. The results of effects of pH, protein concentration and contact time of the adsorption reveal that the morphology of adsorbed protein A is significantly affected by pH and adsorbed surface concentration, in which the pH away from the isoelectric point (IEP) of protein A could produce electrical repulsion to change the protein conformation, while the high adsorbed surface protein volume results in molecular networks. Protein A can form an adsorbed protein film on PDMS with a maximum volume of 2.45 x 10(-3) microm(3). This work enhances our fundamental understanding of protein A adsorption on PDMS, a frequently used substrate component in miniaturized immunoassay devices.

Organic Thin-Film Transistors Based On Conjugated Polymer and Carbon Nanotube Composites

In this paper we report on thin film transistors based on poly(3-hexylthiophene) (P3HT) and carbon nanotubes (CNTs) composite active materials. Single walled CNTs were dispersed into P3HT chloroform solution. By drop casting, the composite solution was deposited onto the pre-fabricated device and formed thin active layer. The effect of different concentrations of CNTs to the charge carrier mobility of the composite was studied. Very little amount of CNT added into the active material can improve the carrier mobility while the on/off ratio is not reduced.