Publications by Year: 2019

2019
Phenylalanine Monitoring via Aptamer-Field-Effect Transistor Sensors
Cheung, K. M. ; Yang, K. - A. ; Nakatsuka, N. ; Zhao, C. ; Ye, M. ; Jung, M. E. ; Yang, H. ; Weiss, P. S. ; Stojanović, M. N. ; Andrews, A. M. Phenylalanine Monitoring via Aptamer-Field-Effect Transistor Sensors. ACS Sensors 2019, 4 3308-3317. Publisher's VersionAbstract

 

Determination of the amino acid phenylalanine is important for lifelong disease management in patients with phenylketonuria, a genetic disorder in which phenylalanine accumulates and persists at levels that alter brain development and cause permanent neurological damage and cognitive dysfunction. Recent approaches for treating phenylketonuria focus on injectable medications that efficiently break down phenylalanine but sometimes result in detrimentally low phenylalanine levels. We have identified new DNA aptamers for phenylalanine in two formats, initially as fluorescent sensors and then, incorporated with field-effect transistors (FETs). Aptamer-FET sensors detected phenylalanine over a wide range of concentrations (fM to mM). para-Chlorophenylalanine, which inhibits the enzyme that converts phenylalanine to tyrosine, was used to induce hyperphenylalaninemia during brain development in mice. Aptamer-FET sensors were specific for phenylalanine versus para-chlorophenylalanine and differentiated changes in mouse serum phenylalanine at levels expected in patients. Aptamer-FETs can be used to investigate models of hyperphenylalanemia in the presence of structurally related enzyme inhibitors, as well as naturally occurring amino acids. Nucleic acid-based receptors that discriminate phenylalanine analogs, some that differ by a single substituent, indicate a refined ability to identify aptamers with binding pockets tailored for high affinity and specificity. Aptamers of this type integrated into FETs enable rapid, electronic, label-free phenylalanine sensing.

Lau, J. ; Trojniak, A. E. ; Maraugha, M. J. ; VanZanten, A. J. ; Osterbaan, A. J. ; Serino, A. C. ; Ohnsorg, M. L. ; Cheung, K. M. ; Ashby, D. S. ; Weiss, P. S. ; et al. Conformal Ultrathin Film Metal–Organic Framework Analogues: Characterization of Growth, Porosity, and Electronic Transport. Chemistry of Materials 2019, 31, 8977-8986. Publisher's VersionAbstract

Thin-film formation and transport properties of two copper-paddlewheel metal–organic framework (MOF)-based systems (MOF-14 and MOF-399) are investigated for their potential integration into electrochemical device architectures. Thin-film analogues of these two systems are fabricated by the sequential, alternating, solution-phase deposition of the inorganic and organic ligand precursors that result in conformal films via van der Merwe-like growth. Atomic force microscopy reveals smooth film morphologies with surface roughnesses determined by the underlying substrates and linear film growth of 1.4 and 2.2 nm per layer for the MOF-14 and MOF-399 systems, respectively. Electrochemical impedance spectroscopy is used to evaluate the electronic transport properties of the thin films, finding that the MOF-14 analogue films demonstrate low electronic conductivity, while MOF-399 analogue films are electronically insulating. The intrinsic porosities of these ultrathin MOF analogue films are confirmed by cyclic voltammetry redox probe characterization using ferrocene. Larger peak currents are observed for MOF-399 analogue films compared to MOF-14 analogue films, which is consistent with the larger pores of MOF-399. The layer-by-layer deposition of these systems provides a promising route to incorporate MOFs as thin films with nanoscale thickness control and low surface roughness for electrochemical devices.

Thin-film formation and transport properties of two copper-paddlewheel metal–organic framework (MOF)-based systems (MOF-14 and MOF-399) are investigated for their potential integration into electrochemical device architectures. Thin-film analogues of these two systems are fabricated by the sequential, alternating, solution-phase deposition of the inorganic and organic ligand precursors that result in conformal films via van der Merwe-like growth. Atomic force microscopy reveals smooth film morphologies with surface roughnesses determined by the underlying substrates and linear film growth of 1.4 and 2.2 nm per layer for the MOF-14 and MOF-399 systems, respectively. Electrochemical impedance spectroscopy is used to evaluate the electronic transport properties of the thin films, finding that the MOF-14 analogue films demonstrate low electronic conductivity, while MOF-399 analogue films are electronically insulating. The intrinsic porosities of these ultrathin MOF analogue films are confirmed by cyclic voltammetry redox probe characterization using ferrocene. Larger peak currents are observed for MOF-399 analogue films compared to MOF-14 analogue films, which is consistent with the larger pores of MOF-399. The layer-by-layer deposition of these systems provides a promising route to incorporate MOFs as thin films with nanoscale thickness control and low surface roughness for electrochemical devices.

Abendroth, J. M. ; Cheung, K. M. ; Stemer, D. M. ; Hadri, M. S. E. ; Zhao, C. ; Fullerton, E. E. ; Weiss, P. S. Spin-Dependent Ionization of Chiral Molecular Films. Journal of the American Chemical Society 2019, 141, 3863-3874. Publisher's VersionAbstract

Spin selectivity in photo-emission from ferromagnetic substrates functionalized with chiral organic films was analyzed by ultraviolet photoelectron spectroscopy at room temperature. Using radiation with photon energy greater than the ionization potential of the adsorbed molecules, photoelectrons were collected that originated from both underlying ferromagnetic substrates and the organic films, with kinetic energies in the range of ca. 0–18 eV. We investigated chiral organic films composed of self-assembled monolayers of α-helical peptides and electrostatically adsorbed films of the protein, bovine serum albumin, with different α-helix and β-sheet contents. Ultraviolet photoelectron spectral widths were found to depend on substrate magnetization orientation and polarization, which we attribute to helicity-dependent molecular ionization cross sections arising from photoelectron impact, possibly resulting in spin-polarized holes. These interactions between spin-polarized photoelectrons and chiral molecules are physically manifested as differences in the measured photoionization energies of the chiral molecular films. Substrate magnetization-dependent ionization energies and work function values were deconvoluted using surface charge neutralization techniques, permitting the measurement of relative spin-dependent energy barriers to transmission through chiral organic films.