Karl A. Walczak

Quantum dot enhancement of bacteriorhodopsin-based electrodes

Nanoscale sensing arrays utilizing the unique properties of the optical protein bacteriorhodopsin and colloidal semiconductor quantum dots are being developed for toxin detection applications. This paper describes an innovative method to activate bacteriorhodopsin-based electrodes with the optical output of quantum dots, producing an enhanced electrical response from the protein. Results show that the photonic emission of CdSe/ZnS quantum dots is absorbed by the bacteriorhodopsin retinal and initiates the proton pumping sequence, resulting in an electrical output from a bacteriorhodopsin-based electrode. It is also shown that activated quantum dots in sub-10nm proximity to bacteriorhodopsin further amplify the photovoltaic response of the protein by approximately 23%, compared to without attached quantum dots, suggesting direct energy transfer mechanisms beyond photonic emission alone. The ability of quantum dots to activate nanoscale regions on bacteriorhodopsin-based electrodes could allow sub-micron sensing arrays to be created due to the ability to activate site-specific regions on the array.

Electronic Characteristics of Bacteriorhodopsin

To effectively integrate bacteriorhodopsin (bR) with micro electromechanical systems (MEMS) and nano electromechanical systems (NEMS) devices, it is critical to know the electrical properties of the material and to understand how it will affect the functionality of the device. Inductance, capacitance and resistance (LCR) measurements can be used to determine material characteristics, such as permittivity, film thickness, and capacitance. In this paper, LCR measurements of dried films of oriented and unoriented bR with both light-on and light-off conditions are presented. Tests were performed on dried films of bR to determine if there is a relationship between LCR measurements and orientation, light-on/off, frequency, and time. The results indicated that the LCR measurements depended on the thickness and area of the film, but not on the orientation, as with other biological materials such as muscle. However, there was a transient LCR response for both oriented and unoriented bR which depends on light intensity. The possible effect of integrating this material with a single electron transistor (SET) is also briefly discussed.

Chemical inertness of UV-cured optical elastomers within the printed circuit board manufacturing process for embedded waveguide applications

Embedding polymer optical waveguides (WGs) into printed circuit boards (PCBs) for intra-board or board-to-board high speed data communications requires polymer materials that are compatible and inert when exposed to common PCB manufacturing processes. Ensuring both WG functionality after chemical exposure and maintaining PCB manufacturing integrities within the production process is crucial for successful implementation. The PCB manufacturing flow is analyzed to expose major requirements that would be required for the successful implementation of polymer materials for embedded WG development. Chemical testing and analysis were performed on Dow Corning ® OE-4140 UV-Cured Optical Elastomer Core and Dow Corning® OE-4141 UV-Cured Optical Elastomer Cladding which are designed for low loss embedded optical WGs. Contamination testing was conducted to demonstrate polymer compatibility in both cured and uncured form. Various PCB chemicals were treated with uncured polymer material and tested for effective contamination. Fully polymerized multimode WGs were fabricated and exposed to PCB chemicals at temperatures and durations comparable to PCB manufacturing conditions. Chemical analysis shows that the chosen polymer is compatible and inert with most common PCB manufacturing processes.

Light Sensor Platform Based on the Integration of Bacteriorhodopsin with a Single Electron Transistor

This paper reports on the integration of an optical protein with single electron transistors to form a nano-bio-hybrid device for sensing. Bacteriorhodopsin (bR) is an optoelectric protein that translocates a proton across a distance of several nanometers in response to an absorbed photon of incident light. This charge gradient results in a measurable voltage in the dried state. Single electron transistors (SETs) have active regions consisting of one or more quantum islands with a size typically 10 nanometers or less. Integrating bacteriorhodopsin with the gate of a SET provides a device capable of a modulated electrical output in response to optical modulation at the device gate. Modulation of the optoelectric activity of the bR by chemical binding with a targeted environmental antigen can form a direct chemical-to-electrical sensor reducing the size and complexity of fluorescence-based systems. The work resulted in electrical resistance and capacitance characterization of purple membrane containing bR under variable illumination to ensure minimal impact on SET operation. Purple membrane containing bacteriorhodopsin was electrodeposited on the SET gates, and current throughput was well correlated with variable and cyclic illumination. It was confirmed that bR optoelectric activity is capable of driving SETs.

Optical loss characterization of polymer waveguides on halogen and halogen-free FR-4 substrates

In order to characterize and optimize the overall link budget for an optical communication channel, the absorption loss of the waveguides must be well known, stable, and minimized. Research and characterization has been performed to ascertain the impact of the use of halogen vs. halogen free FR-4 circuit boards. Halogen is utilized within glass resin epoxy circuit boards as a flame retardant. An analysis of rectangular multi-mode polymer waveguide structures, with a fixed core dimension of 50 μm × 50 μm, was done to characterize the effects of the halogen FR-4 on the absorption loss. Thermal cycling times were varied in order to determine the relationship between heating of the polymer material, halogen diffusion into the optical cladding and core layer, and optical losses.

Characterization of irradiance effects on curing of siloxane for embedded waveguide applications

In order to maintain the overall optical performance in a step index rectangular waveguide, the complex index of refraction of the core and cladding material must be maintained throughout the cycle of the lithographic fabrication process. The percentage of the core and cladding material that is cured and the irradiance that cure took place directly affects the complex index of refraction of these materials. Siloxanes produced by Dow Corning have been selected to meet the requirements for embedded waveguides for circuit board applications due to their optical performance characteristics and their compatibility with current manufacturing techniques. The required total dose for a 50 μm thick layer of siloxane is 1200 mJ at an irradiance of 30 mW/cm2. In order to utilize lower irradiance levels the total dose of the ultraviolet exposure must be characterized and calibrated. By measuring the changes in the absorption peaks of the materials using transmission data from ellipsometric techniques it is possible to define the percentage cure of the siloxane from different curing profiles. Ellipsometric techniques were also utilized to measure the complex refractive index of the materials cured using different profiles. It was found that the total dose required for a complete cure and the complex refractive index of these materials drastically changes with different irradiances and the profile for the total dose compared to the curing of the siloxane materials at all irradiances is logarithmic.