Melanie M. Tomczak

Bio-based approaches to inorganic material synthesis

Nature is an exquisite designer of inorganic materials using biomolecules as templates. Diatoms create intricate silica wall structures with fine features using the protein family of silaffins as templates. Marine sponges create silica spicules also using proteins, termed silicateins. In recent years, our group and others have used biomolecules as templates for the deposition of inorganic materials. In contrast with the traditional materials science approach, which requires high heat, extreme pH and non-aqueous solutions, the bio-based approaches allow the reactions to proceed usually at near ambient conditions. Additionally, the biological templates allow for the control of the inorganic nanoparticle morphology. The use of peptides and biomolecules for templating and assembling inorganics will be discussed here.

Entrapment of enzymes and nanoparticles using biomimetically synthesized silica

Entrapment of enzymes and nanoparticles using biosilicification reactions.

Nondestructive In Situ Identification of Crystal Orientation of Anisotropic ZnO Nanostructures

We present a novel method for direct, fast, nonambiguous, and nondestructive identification of the growth direction and orientation of individual ZnO nanostructures in the device-ready environment by exploiting high-resolution confocal Raman mapping. Various features of the Raman spectrum of ZnO nanostructures, vapor deposition grown nanobelts and peptide-assisted vertical nanorods, were found to be sensitive to the relative orientation of the crystal plane. Furthermore, we discovered that the waveguiding property of the ZnO nanobelt is also orientation dependent and results in either apparent enhancement or suppression of Raman scattering from the underlying substrate. We demonstrate that various features of Raman spectrum of ZnO and the modulation of the substrate signal can be employed for the rapid and nondestructive identification of the crystal growth direction and orientation of these nanostructures even after integration into devices, which is impossible with current electron microscopy and diffraction techniques. We believe that the general features observed here are equally applicable to other wurtzite nanostructures (ZnS, GaN) which are critical in optoelectronics, lasing, and piezotronic applications.

Development of an all-DNA-surfactant electro-optic modulator

Marine-based deoxyribonucleic acid (DNA), purified from waste products of the Japanese fishing industry, has recently become a new material of interest in photonics applications. The water soluble DNA is precipitated with a surfactant complex, cetyltrimethl-ammonium chloride (CTMA), to form a water insoluble complex, DNA-CTMA, for application as a nonlinear optical material. It is possible to fabricate an all-DNA-CTMA waveguide by crosslinking the DNA-CTMA. Crosslinking causes the material to become resistant to its initial solvents upon curing; this allows a core layer of crosslinked DNA-CTMA-chromophore to be spin coated directly on top of a cladding layer of crosslinked DNA-CTMA. The chromophore dye provides for the electro-optic effect to be induced through contact poling. The chromophore also raises the index of refraction of the core layer above that of the cladding needed for waveguiding. Progress on the development of this all-DNA-CTMA electro-optic modulator is presented.

Detection of orexin A neuropeptide in biological fluids using a zinc oxide field effect transistor.

Biomarkers which are indicative of acute physiological and emotional states are studied in a number of different areas in cognitive neuroscience. Currently, many cognitive studies are conducted based on programmed tasks followed by timed biofluid sampling, central laboratory processing, and followed by data analysis. In this work, we present a sensor platform capable of rapid biomarker detection specific for detecting neuropeptide orexin A, found in blood and saliva and known as an indicator of fatigue and cognitive performance. A peptide recognition element that selectively binds to orexin A was designed, characterized, and functionalized onto a zinc oxide field effect transistor to enable rapid detection. The detection limit using the sensor platform was sub-picomolar in water, and picomolar to nanomolar levels in saliva and serum. The transistor and recognition element sensor platform can be easily expanded, allowing for multiple biomarkers to be detected simultaneously, lending itself to complex biomarker analysis applicable to rapid feedback for neuroscience research and physiological monitoring.