Microfluidic-based continuous self-assembly, alignment, and printing of oligopeptides with π-conjugated cores accompanied by advanced single molecule characterization

Organic semiconducting materials exist in an immense and complex space that,despite decades of extensive exploration, still has unexplored regions with exciting potential. The mysteries of this science lie in the myriad combinations in which organic building blocks can be arranged and how these geometric conditions impact the bulk electronic properties of materials. Furthermore, the ability to physically manipulate reactants via intelligently engineered extensional flows has presented interesting avenues for control in directed assembly of biomimetic materials. Several years ago,we began to apply these new microfluidic techniques to a new class of functionalized peptides. Soon after its inception, I took over that work and have continued efforts to optimize devices and hone the techniques of their use in order to create a platform for high-throughput production of exceptionally aligned oligomer fibers. Early efforts have suggested that the optoelectronic properties of these aligned materials differ significantly and advantageously from their quiescently assembled analogs. Having developed a method for continuous assembly of oligopeptide, I sought collaboration with members of the Mechanical Engineering department to investigate the next step toward using these aligned materials in advanced functional devices, continuous printing and aligned deposition.We have achieved preliminary results with both continuous-line and dot printing with microscopic resolution that demonstrate the potential for optimizing printing techniques once specific device applications for these materials are determined. In collaboration with peers in both the Materials Science and Engineering and Chemical Engineering departments, I simultaneously turned to characterizing three aspects of these materials with the goal of ultimately comparing quiescently assembled material to its aligned counterparts assembled in flow. One project was geared toward understanding the kinetics of the material’s self-assembly reaction through the use of fluorescence correlation microscopy. I measured fluctuations in fluorescence of a stimulated femtovolume to calculate diffusion constants, and thus particle size as a function of time during reaction.We correlated these findings with molecular dynamics simulations to gain surprising insight into the early timescales of these reactions.In short, it was discovered that the hitherto used method of acid-mediated self-assembly for creating functional peptide fibers operates in a pre-nucleated regime and, in fact, the early stages of assembly begin independent of protonation at concentrations as low as 100 nM, but no lower than10 nM. Second, I utilized a recently developed nearfield optical microscopy system to conductnanoFourier transform infrared spectroscopyat sub-diffraction-limited spatial resolution, probing structural details and optoelectronic properties of several biohybrid materials at the single fibril level. We can identify infrared absorption features corresponding molecular secondary structure, and the calculation of complex indices of refraction and dielectric constants for these materials should be a facile operation with the collected data. Third, I used conductive probe atomic force microscopy techniques in conjunction with lithographic techniques for single-molecule transistor architectures to characterize charge carrier transport and other optoeletronic properties.Finally, through collaboration with peers conducting tangential research on the same biomimetic materials, I used optical fluorescence microscopy to characterize fluorescence spectra and polarization macroscopically aligned peptide fibers.This body of work on microfluidic device and printer fabrication along with detailed characterizations can help to inform the suitable applications for these materials in semiconductor devices.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2018

Author dc:creator

• Valverde, Lawrence Rene

Contributors dc:contributor

• Wilson, William L
• Shim, Moonsub
• Toussaint, Kimani C.
• Leal, Cecilia
• Evans, Christopher

• directed assembly
• optoelectronic materials
• biomimetic materials
• microfluidics
• peptide aggregation
• self-assembly
• molecular dynamics
• fluorescence correlation spectroscopy
• nano Fourier transform infrared spectroscopy
• apertureless scanning near field optical microscopy
• conductive probe atomic force microscopy

Statement dc:rights

• Copyright 2018 Lawrence Valverde

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/100893

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/100893