Gregory A. Sotzing

Designing nanomaterial-enhanced electrochemical immunosensors for cancer biomarker proteins

Detection of multiple cancer biomarker proteins in human serum and tissue at point-of-care is a viable approach for early cancer detection, but presents a major challenge to bioanalytical device development. This article reviews recent approaches developed in our laboratories combining nanoparticle decorated electrodes and multilabeled secondary antibody labeled particles to achieve high sensitivity for the detection of cancer biomarker proteins. Two nanomaterial-based sensor platforms were used: (a) upright single wall carbon nanotube forests and (b) layers of densely packed 5 nm gold nanoparticles. Both platforms feature pendant carboxylate groups for easy attachment of enzymes or antibodies by amidization. In quality performance tests, the biocatalytic responses for determination of hydrogen peroxide of AuNP layers with attached horseradish peroxidase (HRP) on electrodes gave somewhat better detection limit and sensitivity than single wall carbon nanotube (SWNT) forest platforms with HRP attached. Evaluation of these sensors as platforms for sandwich immunoassays for cancer biomarker prostate specific antigen (PSA) in serum showed that both approaches gave accurate results for human serum samples from cancer patients. The best detection limit (0.5 pg mL(-1)) and sensitivity were obtained by combining the AuNP immunosensors with binding of 1 mum diameter magnetic particles decorated with secondary antibodies and 7500 HRP labels.

Inkjet-printed gold nanoparticle electrochemical arrays on plastic. Application to immunodetection of a cancer biomarker protein

Electrochemical detection combined with nanostructured sensor surfaces offers potentially low-cost, high-throughput solutions for detection of clinically significant proteins. Inkjet printing offers an inexpensive non-contact fabrication method for microelectronics that is easily adapted for incorporating into protein immunosensor devices. Herein we report the first direct fabrication of inkjet-printed gold nanoparticle arrays, and apply them to electrochemical detection of the cancer biomarker interleukin-6 (IL-6) in serum. The gold nanoparticle ink was printed on a flexible, heat resistant polyimide Kapton substrate and subsequently sintered to create eight-electrode arrays costing <0.2 euro per array. The inkjet-printed working electrodes had reproducible surface areas with RSD <3%. Capture antibodies for IL-6 were linked onto the eight-electrode array, and used in sandwich immunoassays. A biotinylated secondary antibody with 16-18 horseradish peroxidase labels was used, and detection was achieved by hydroquinone-mediated amperometry. The arrays provided a clinically relevant detection limit of 20 pg mL(-1) in calf serum, sensitivity of 11.4 nA pg(-1) cm(-2), and a linear dynamic range of 20-400 pg mL(-1).

White Luminescence from Multiple‐Dye‐Doped Electrospun DNA Nanofibers by Fluorescence Resonance Energy Transfer

A DNA spin-off: Electrospinning of DNA complexes gives nanofibers with a highly ordered morphology that allows homogeneous distribution of encapsulated multiple chromophores. The emission color can be controlled by suitable choice of the donor-acceptor pair and the doping ratio. Pure white-light emission from nanofibers is demonstrated (see picture).

A simple, low waste and versatile procedure to make polymer electrochromic devices

Herein we present a simple and elegant method for the creation of solid-state conjugated polymer devices. Their electrochromic properties were fully explored in this study, but one could envision the extension of this method to displays, solar cells, OLEDs, transistors, or many other applications. We prepared conductive polymer composites or blends within a polymer electrolyte using electrochemical polymerization of these monomers inside an assembled solid-state device. This method will work for any monomer that can be dissolved in the gel electrolyte. This technique offers simplicity in device construction, is easily adapted to patterned systems and comprises a low-waste assembly process. Our novel approach of assembling polymer electrochromic devices avoids the tedious cleaning process of the substrates, produces almost no waste, and by inkjetting insulating materials to mask the substrates, letters and high-resolution images could be achieved inside the converted polymer devices. Electrochromic devices utilizing PEDOT assembled by our method showed compatible switching speed and durability with a slightly higher contrast ratio.

Gold Nanoparticles with Externally Controlled, Reversible Shifts of Local Surface Plasmon Resonance Bands

We have achieved reversible tunability of local surface plasmon resonance in conjugated polymer functionalized gold nanoparticles. This property was facilitated by the preparation of 3,4-ethylenedioxythiophene (EDOT) containing polynorbornene brushes on gold nanoparticles via surface-initiated ring-opening metathesis polymerization. Reversible tuning of the surface plasmon band was achieved by electrochemically switching the EDOT polymer between its reduced and oxidized states.

Acrylated Poly(3,4-propylenedioxythiophene) for Enhancement of Lifetime and Optical Properties for Single-Layer Electrochromic Devices

We utilized our in situ method for the one-step assembly of single-layer electrochromic devices (ECDs) with a 3,4-propylenedioxythiophene (ProDOT) acrylate derivative, and long-term stability was achieved. By coupling the electroactive monomer to the cross-linkable polymer matrix, preparation of the electrochromic ProDOT polymer can occur followed by UV cross-linking. Thus, we achieve immobilization of the unreacted monomer, which prevents any degradative processes from occurring at the counter electrode. This approach eliminated spot formation in the device and increased stability to over 10 000 cycles when compared to 500 cycles with conventional ProDOT devices wherein the monomer is not immobilized. The acrylated electrochromic polymer exhibits similar electrochromic properties as conventional ProDOT devices, such as photopic contrast (48% compared to 46%) and switch speed (both 2 s). This method can be applied to any one-layer electrochromic system where improved stability is desired.

Solid-state electrochromic devices: relationship of contrast as a function of device preparation parameters

The establishment of a relationship between device performance parameters such as switch speed and photopic contrast with device composition, electrochromic polymer thickness, and gel electrolyte composition is reported here for a versatile one-step preparation method of relatively large area, 105 cm2, solid-state electrochromic devices. The electrochromic polymer, hereby, generated from a monomer after device construction, i.e. in situ, is a way to simplify the fabrication of electrochromic devices by reducing waste generation and assembly time as well as by increasing the versatility of device manufacturing in an open atmosphere. Photopic contrast is a critical property for electrochromic displays, windows, and lenses necessitating the study of how changing the selected material and device properties such as monomer diffusion, thickness of the electrochromic polymer layer, and ionic conductivity of the electrolyte impact electrochromic device functionality. More specifically photopic contrast performance is evaluated as a function of polymerization time, effective electrochromic polymer layer thickness, monomer loading, salt loading, thickness of the gel electrolyte, and in situ conversion temperature. Photopic contrasts of 47% for polybiphenylmethyloxymethyl-3,4-propylenedioxythiophene (BPMOM-ProDOT), 46% for poly2,2-dimethyl-3,4-propylenedioxythiophene (PProDOT-Me2), and 40% for poly(3,4-ethylenedioxythiophene) (PEDOT) without background correction were achieved.

Rationally designed polyimides for high-energy density capacitor applications.

Development of new dielectric materials is of great importance for a wide range of applications for modern electronics and electrical power systems. The state-of-the-art polymer dielectric is a biaxially oriented polypropylene (BOPP) film having a maximal energy density of 5 J/cm(3) and a high breakdown field of 700 MV/m, but with a limited dielectric constant (∼2.2) and a reduced breakdown strength above 85 °C. Great effort has been put into exploring other materials to fulfill the demand of continuous miniaturization and improved functionality. In this work, a series of polyimides were investigated as potential polymer materials for this application. Polyimide with high dielectric constants of up to 7.8 that exhibits low dissipation factors (<1%) and high energy density around 15 J/cm(3), which is 3 times that of BOPP, was prepared. Our syntheses were guided by high-throughput density functional theory calculations for rational design in terms of a high dielectric constant and band gap. Correlations of experimental and theoretical results through judicious variations of polyimide structures allowed for a clear demonstration of the relationship between chemical functionalities and dielectric properties.

Poly(dimethyltin glutarate) as a Prospective Material for High Dielectric Applications

Poly(dimethyltin glutarate) is presented as the first organometallic polymer, a high dielectric constant, and low dielectric loss material. Theoretical results correspond well in terms of the dielectric constant. More importantly, the dielectric constant can be tuned depending on the solvent a film of the polymer is cast from. The breakdown strength is increased through blending with a second organometallic polymer.

New Group IV Chemical Motifs for Improved Dielectric Permittivity of Polyethylene

An enhanced dielectric permittivity of polyethylene and related polymers, while not overly sacrificing their excellent insulating properties, is highly desirable for various electrical energy storage applications. In this computational study, we use density functional theory (DFT) in combination with modified group additivity based high throughput techniques to identify promising chemical motifs that can increase the dielectric permittivity of polyethylene. We consider isolated polyethylene chains and allow the CH2 units in the backbone to be replaced by a number of Group IV halides (viz., SiF2, SiCl2, GeF2, GeCl2, SnF2, or SnCl2 units) in a systematic, progressive, and exhaustive manner. The dielectric permittivity of the chemically modified polyethylene chains is determined by employing DFT computations in combination with the effective medium theory for a limited set of compositions and configurations. The underlying chemical trends in the DFT data are first rationalized in terms of various tabulated atomic properties of the constituent atoms. Next, by parametrizing a modified group contribution expansion using the DFT data set, we are able to predict the dielectric permittivity and bandgap of nearly 30,000 systems spanning a much larger part of the configurational and compositional space. Promising motifs which lead to simultaneously large dielectric constant and band gap in the modified polyethylene chains have been identified. Our theoretical work is expected to serve as a possible motivation for future experimental efforts.