Michael T.Y. Paul

Platinum Ordered Porous Electrodes: Developing a Platform for Fundamental Electrochemical Characterization

High surface area platinum electrodes with an ordered porous structure (Pt-OP electrodes) have been prepared and characterized by electrochemical methods. This study builds a foundation upon which we can seek an in-depth understanding of the limitations and design considerations to make efficient and stable Pt-OP electrodes for use in electrochemical applications. A set of Pt-OP electrodes were prepared by controlled electrodeposition of Pt through a self-assembled array of spherical particles and subsequent removal of the spherical templates by solvent extraction. The preparation method was shown to be reproducible and the resulting electrodes were found to have clean Pt surfaces and a large electrochemical surface area (Aecsa) resulting from both the porous structure, as well as the nano- and micro-scale surface roughness. Additionally, the Pt-OP electrodes exhibit a surface area enhancement comparable to commercially available electrocatalysts. In summary, the Pt-OP electrodes prepared herein show properties of interest for both gaining fundamental insights into electrocatalytic processes and for use in applications that would benefit from enhanced electrochemical response.

Self-assembly of nanoparticles onto the surfaces of polystyrene spheres with a tunable composition and loading.

Functional colloidal materials were prepared by design through the self-assembly of nanoparticles (NPs) on the surfaces of polystyrene (PS) spheres with control over NP surface coverage, NP-to-NP spacing, and NP composition. The ability to control and fine tune the coating was extended to the first demonstration of the co-assembly of NPs of dissimilar composition onto the same PS sphere, forming a multi-component coating. A broad range of NP decorated PS (PS@NPs) spheres were prepared with uniform coatings attributed to electrostatic and hydrogen bonding interactions between stabilizing groups on the NPs and the functionalized surfaces of the PS spheres. This versatile two-step method provides more fine control than methods previously demonstrated in the literature. These decorated PS spheres are of interest for a number of applications, such as catalytic reactions where the PS spheres provide a support for the dispersion, stabilization, and recovery of NP catalysts. The catalytic properties of these PS@NPs spheres were assessed by studying the catalytic degradation of azo dyes, an environmental contaminant detrimental to eye health. The PS@NPs spheres were used in multiple, sequential catalytic reactions while largely retaining the NP coating.

Hexagonal Arrays of Cylindrical Nickel Microstructures for Improved Oxygen Evolution Reaction

Fuel-cell systems are of interest for a wide range of applications, in part for their utility in power generation from nonfossil-fuel sources. However, the generation of these alternative fuels, through electrochemical means, is a relatively inefficient process due to gas passivation of the electrode surfaces. Uniform microstructured nickel surfaces were prepared by photolithographic techniques as a systematic approach to correlating surface morphologies to their performance in the electrochemically driven oxygen evolution reaction (OER) in alkaline media. Hexagonal arrays of microstructured Ni cylinders were prepared with features of proportional dimensions to the oxygen bubbles generated during the OER process. Recessed and pillared features were investigated relative to planar Ni electrodes for their influence on OER performance and, potentially, bubble release. The arrays of cylindrical recesses were found to exhibit an enhanced OER efficiency relative to planar nickel electrodes. These microstructured electrodes had twice the current density of the planar electrodes at an overpotential of 100 mV. The results of these studies have important implications to guide the preparation of more-efficient fuel generation by water electrolysis and related processes.

Revealing 3D Information of Porous Catalytic Structures Prepared by Template Methods

Nanostructures of diverse materials prepared by using monodispersed colloidal spheres as templates have found potential applications in many fields such as photonic crystals, sensors, and catalysts. Such nanostructured materials include polymers, oxides, metals, semiconductor compounds, as well as composites. Polystyrene (PS) beads are commonly used as the templates since the removal of the templates can be achieved by both calcination and dissolution [1,2]. Templates fabricated from a colloidal PS solution consist of many close-packed regions, where 26% void space can be used for filling up with functional materials [2]. After the removal of the PS spheres, the remaining nanostructures have high surface area and 74% spherical void volume, which allow efficient mass transport and further materials modification. These templated nanostructures incorporated with catalytic nanoparticles (NPs) attract a wide range of research interests, due to their potential in reducing and tuning the loading of precious catalytic metals, improving catalytic performance, as well as the scalability for mass production.

Verifying the Structure and Composition of Prepared Porous Catalytic Supports

The incorporation of catalytic nanoparticles (NPs) within nanostructured materials have been popular in recent years due to the excellent surface area to volume ratios that can be achieved for these materials and their ability to reduce the required loading of precious metal catalysts. The use of Pt and Pd NPs is especially attractive for power generating systems, such as proton exchange membrane and methanol oxidation fuel cells . Further studies on these nanoparticle incorporated materials have revealed the underlying support materials can enhance catalytic properties and stabilities of the NPs [4, . However, due to processing constraints, loading of functional NPs is often limited to 2-D supports [7, . The incorporation of NPs into 3-D porous supports can be performed by sophisticated systems, such as physical vapor and atomic layer depositions . In this study, we demonstrate a relatively simple and cost effective method, which was developed previously in our research group, for preparing various combinations of NPs loaded into 3-D structured materials . The NP loading and spatial distribution were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDS). Our technique could be used to prepare novel electrochemical and photochemical porous materials for increased catalytic efficiency and stability.

A simple approach to making electrochemical biosensors

H we report a nano-enabled electronic biosensor for direct detection of biomarkers e.g. insulin down to 10 femtoMolar levels in human serum and saliva samples. First we present a design and fabrication of silicon nanowire field effect transistor (SiNW-FET) as biosensor. We use top-down strategy to fabricate silicon nanowire devices by the combination of photolithography and e-beam lithography on silicon on insulator wafers (SOI). The number of nanowires has shown a significant impact on the device performance, with better performance for larger number of nanowires used. We then test this type of sensor for medical diagnostic applications, such as insulin detection. Insulin is a diabetes related hormones and the quick detection of its level in blood is important for diagnosis of diabetes mellitus and also guiding its treatment. The traditional approaches for insulin quantification with mass spectra, ELISA or Western Blot etc are lack of sensitivity, time-consuming and/or requiring expensive equipments. Here we are using the SiNW FET devices to quantify the insulin level in human serum samples. Our preliminary sensing work has demonstrated repeatable detection of insulin directly from diluted patient serum without purification. The sensing experiments have repeatedly shown well correlated sensing of insulin with concentration from 10 femtoMolar (fM) to 1nM in pure PBS buffer and in human serum samples. We will demonstrate detailed sensing results related to diabetes disease in the meeting.C diseases, including hypertension, coronary heart disease, stroke, congenital cardiovascular defects, congestive heart failure, and peripheral vascular disease, is the leading cause of morbidity and mortality in the industrialized world. These conditions affect more than 60 million people and are responsible for the death of almost 1 million Americans per year. Imaging represents an important component of the diagnosis and evaluation of cardiovascular disease. Modalities to image the heart and vasculature include radiography, echocardiography, nuclear imaging, cineangiography, and computed tomography. Magnetic resonance imaging (MRI) has recently emerged as a growing means of cardiovascular imaging. The goal of our work is to develop an advanced MRI active nanoparticle (NP) platform with an excellent pharmacokinetic (PK) profile and plaque targeting properties to allow apoptosis sensing in atherosclerosis and locally release therapy. Conventional statin therapies show residual risk of coronary artery disease. Development of cardiovascular sensing and treatment strategies has stagnated in recent years. This can be ascribed to limited improvements in targeting and discriminating between atherosclerotic lesions and establishing robust endpoints for a given sensing is difficult due to the complex vasculature network. Our approach have potential in visualizing, quantifying, and characterizing atherosclerosis, and can be used to determine valid endpoints to address the current limitations. This MRI active NP platform specifically designed for atherosclerosis, when shown effective, can be used as the basis for novel therapeutics for their clinical transition. This talk will be focused to summarize some of our preliminary results based on nanotechnologies for cardiovascular diagnosis and therapy.R photonic biosensing is a powerful technique for label-free detection of biomolecules and viruses. Specifically during the past 5 years photonic biosensning using high quality factor (high-Q) optical microresonators has been the subject of intensive research and development. High-Q optical resonance in micron and sub-micron scale provides a sensitive transduction mechanism for generating a detectable signal proportional to the molecular binding events in label-free affinity based assays. A plethora of microresonator based photonic biosensors have been demonstrated that translate the surface density of bound molecules to measurable changes in optical transmission spectrum using resonant frequency shift. Although a large volume of research has been dedicated to different designs, sensitivity improvement in specific configurations and in few cases simple analysis of the performance, less effort has been spent on developing a comprehensive framework for comparing the practical performance of resonant photonic biosensors as an important class of biosensors. Here after a brief review of the fundamental principles of photonic biosensing using microresonators and related devices, we present a framework for a fair comparison of different devices and sensor configurations. Specifically we explore the detection limit,\ dynamic range and noise in resonant photonic biosensors. This analysis covers Whispering-Gallery microresonators, monolithic microring cavities, gratings, photonic crystals and microcapillaries. The proposed approach also lays the ground for the development of a universal framework that also includes microelectronic and micromechanical biosensors.A number of emerging areas are being driven by a fusion of ideas and techniques from a variety of disciplines. In particular, a fusion of ideas from the physical, chemical, and even biological sciences is being utilized to develop novel materials for new technology and applications. Of the various materials under investigation, none have received more attention than graphenebased materials --carbon nanotubes, fullerenes, and, more recently graphene sheets. These materials have a wealth of interesting and useful properties --they raise a number of fascinating questions in the fundamental sciences, and they hold promise for countless applications. In this talk, I will describe some of our recent investigations of the electronic properties of graphene-based materials; I will discuss phenomena/applications which derive from their unique electronic properties, ranging from scanning tunneling microscopy, to molecular electronics, and also terahertz photonics.M noncovalent bonds are the foundation for many key processes in the life sciences and medical diagnostics, such as DNA replication, enzyme catalysis, and cellular uptake. Magnetic labeling with nanoparticles and optical labeling with fluorescent dyes are major avenues to probe the molecules involved in noncovalent bonds. Compared to optical sensing which uses a wavelength parameter to achieve molecular and cellular specificity, magnetic detection has no analogous parameter. To solve this problem, we develop a spectroscopic technique based on the binding force between the probe molecules labeled with magnetic nanoparticles and the receptor molecules on cell surface. This force-induced remnant magnetization spectroscopy (FIRMS) measures the magnetization of the magnetic nanoparticles as a function of the binding force between the magneticallylabeled probe molecules and the target molecules. Molecular specificity is achieved from the spectrum of magnetization vs. binding force. We will demonstrate this novel concept by investigating the reversible binding between biotin and streptavidin, and between biotin and avidin, using various forms of forces. Because magnetic labeling, unlike optical labeling, can be employed under opaque conditions, the addition of molecular specificity afforded by the FIRMS technique will lead to quantitative molecular and cellular imaging for diagnostics at practical settings.N acids, whether designed or selected in vitro, play important roles in biosensing, medical diagnostics, and therapy. Specifically, the conjugation of functional nucleic acid based probe molecules and nanomaterials has resulted in an unprecedented improvement in the field of molecular recognition. With their unique physical and chemical properties, nanomaterials facilitate the sensing process and amplify the signal of recognition events. Thus, the coupling of nucleic acids with various nanomaterials opens up a promising future for molecular recognition. We report herein the recent study of our group on how to combine DNA molecular design and nanoparticle materials as new approaches for to achieving efficient molecular recognition[1],[2], which includes: 1) non-covalent assembly of single-walled carbon nanotubes and fluorescent single-stranded DNA for fluorescent assays of DNA hybridization,[3],[4] thrombin,[5],[6] and time-resolved luminescent detection of lysozyme,[7] 2) combination of gold nanoparticle-quenched fluorescent oligonucleotides with metal-DNA ligation or DNA ligase reaction for fluorescent assayings of metal ion and SNP, [8],[9] and 3) nucleic acid conjugated quantum dot to separate molecular recognition element and signal reporter for nucleic acid probe.[10]I this study, we present a fully integrated and portable Rotary Genetic Analyzer for detecting the gene expression of influenza A virus with high speed and sensitivity. The Rotary Genetic Analyzer is made up of four parts including a disposable microchip, thermal blocks for temperature control, a stepper motor for precise spinning of the chip, and a miniaturized optical fluorescence detector. A disposable RT-PCR microchip (50 × 20 × 2 mm) consists of a solid-phase extraction based sample pretreatment unit and 1 μL of the PCR chamber. A thermal block made from duralumin is integrated with a film heater at the bottom and a resistance temperature detector (RTD) in the middle. For the efficient performance of RT-PCR, three thermal blocks were placed on the Rotary stage and the temperature of each block was corresponded to the thermal cycling, namely 95 °C (denature), 58 °C (annealing), and 72 °C (extension). With an optimized microchannel dimension and surface treatment, we could dispense a RNA sample, a washing buffer, and an elution buffer subsequently by controlling the RPM into the 3D silica monolith enabling efficient RNA purification. Then, the extracted target RNA was moved into the PCR chamber and a Rotary RT-PCR reaction was performed with high speed. This novel Rotary Genetic Analyzer could analyze influenza A virus subtype H1N1, H5N1 and H3N2 simultaneously in 30 min.R spectroscopy can provide molecular information via inelastic light scattering without physical contact. Coupled with microscopic imaging, Raman microspectroscopy is a powerful technique for sensing and material analysis. With the coupling of light into localized surface plasmons, surface-enhanced Raman scattering (SERS) of near-surface molecules can be boost by many orders of magnitude. Existing designs of microspectroscopy imaging system is, however, significantly limiting the throughput. Here we present a novel parallel Raman microspectroscopysystem which enables the acquisition of full Raman spectra from many spots simultaneous without scanning. This scheme is realized by projecting a multiple-point laser illumination pattern using a spatial light modulator (SLM) coupled with wide-field Raman imaging collection. We demonstrate the performance of this scheme by measuring normal spectra from uniform samples and microparticles, within a ~ 1000 x 100 μm2 field of view. We also demonstrate the rapid collection of SERS spectra from different substrates, allowing the fast characterization of these substrates, as well as the film properties of the surface monolayer coating.