ASU Scholarship Showcase

Molecule-plasmon interactions have been shown to have a definite role in light propagation through optical microcavities due to strong coupling between molecular excitations and surface plasmons. This coupling can lead to macroscopic extended coherent states exhibiting increment in temporal and spatial coherency and a large Rabi splitting. Here, we demonstrate spatial modulation of light transmission through a single microcavity patterned on a freestanding Au film, strongly coupled to one of the most efficient energy transfer photosynthetic proteins in nature, photosystem I. Here we observe a clear correlation between the appearance of spatial modulation of light and molecular photon absorption, accompanied by a 13-fold enhancement in light transmission and the emergence of a distinct electromagnetic standing wave pattern in the cavity. This study provides the path for engineering various types of bio-photonic devices based on the vast diversity of biological molecules in nature.

The broad recognition specificity exhibited by integrin α_Mβ₂ (Mac-1, CD11b/CD18) has allowed this adhesion receptor to play innumerable roles in leukocyte biology, yet we know little about how and why α_Mβ₂ binds its multiple ligands. Within α_Mβ₂, the α_MI-domain is responsible for integrin’s multiligand binding properties. To identify its recognition motif, we screened peptide libraries spanning sequences of many known protein ligands for α_MI-domain binding and also selected the α_M I-domain recognition sequences by phage display. Analyses of >1400 binding and nonbinding peptides derived from peptide libraries showed that a key feature of the α_MI-domain recognition motif is a small core consisting of basic amino acids flanked by hydrophobic residues. Furthermore, the peptides selected by phage display conformed to a similar pattern. Identification of the recognition motif allowed the construction of an algorithm that reliably predicts the α_MI-domain binding sites in the α_Mβ₂ ligands. The recognition specificity of the α_MI-domain resembles that of some chaperones, which allows it to bind segments exposed in unfolded proteins. The disclosure of the α_Mβ₂ binding preferences allowed the prediction that cationic host defense peptides, which are strikingly enriched in the α_MI-domain recognition motifs, represent a new class of α_Mβ₂ ligands. This prediction has been tested by examining the interaction of α_Mβ₂ with the human cathelicidin peptide LL-37. LL-37 induced a potent α_Mβ₂-dependent cell migratory response and caused activation of α_Mβ₂ on neutrophils. The newly revealed recognition specificity of α_Mβ₂ toward unfolded protein segments and cationic proteins and peptides suggests that α_Mβ₂ may serve as a previously proposed “alarmin” receptor with important roles in innate host defense.

The aim of this article was to study sound source localization by cochlear implant (CI) listeners with low-frequency (LF) acoustic hearing in both the operated ear and in the contralateral ear. Eight CI listeners had symmetrical LF acoustic hearing and 4 had asymmetrical LF acoustic hearing. The effects of two variables were assessed: (i) the symmetry of the LF thresholds in the two ears and (ii) the presence/absence of bilateral acoustic amplification. Stimuli consisted of low-pass, high-pass, and wideband noise bursts presented in the frontal horizontal plane. Localization accuracy was 23° of error for the symmetrical listeners and 76° of error for the asymmetrical listeners. The presence of a unilateral CI used in conjunction with bilateral LF acoustic hearing does not impair sound source localization accuracy, but amplification for acoustic hearing can be detrimental to sound source localization accuracy.

New and important separations capabilities are being enabled by utilizing other electric field-induced forces besides electrophoresis, among these is dielectrophoresis. Recent works have used experimentally simple insulator-based systems that induce field gradients creating dielectrophoretic force in useful formats. Among these, juxtaposing forces can generate gradient-based steady-state separations schemes globally similar to isoelectric focusing. The system of interest is termed gradient insulator-based dielectrophoresis and can create extremely high resolution steady-state separations for particles four nanometers to ten micrometers in diameter, including nearly all important bioparticles (large proteins, protein aggregates, polynucleotides viruses, organelles, cells, bacteria, etc.). A theoretical underpinning is developed here to understand the relationship between experimental parameters and resolution and to identify the best expected resolution possible. According to the results, differences in particles (and bioparticles) as small as one part in 10⁴ for diameter (subnanometer resolution for a one micrometer particle), one part in 10⁸ for dielectrophoretic parameters (dielectrophoretic mobility, Clausius-Mossotti factor), and one part in 10⁵ for electrophoretic mobility can be resolved. These figures of merit are generally better than any competing technique, in some cases by orders of magnitude. This performance is enabled by very strong focusing forces associated with localized gradients.

To achieve improved sensitivity in cardiac biomarker detection, a batch incubation magnetic microbead immunoassay was developed and tested on three separate human protein targets: myoglobin, heart-type fatty acid binding protein, and cardiac troponin I. A sandwich immunoassay was performed in a simple micro-centrifuge tube allowing full dispersal of the solid capture surface during incubations. Following magnetic bead capture and wash steps, samples were analyzed in the presence of a manipulated magnetic field utilizing a modified microscope slide and fluorescent inverted microscope to collect video data files. Analysis of the video data allowed for the quantitation of myoglobin, heart-type fatty acid binding protein and cardiac troponin I to levels of 360 aM, 67 fM, and 42 fM, respectively. Compared to the previous detection limit of 50 pM for myoglobin, this offers a five-fold improvement in sensitivity. This improvement in sensitivity and incorporation of additional markers, along with the small sample volumes required, suggest the potential of this platform for incorporation as a detection method in a total sample analysis device enabling multiplexed detection for the analysis of clinical samples.

Electrophoretic and dielectrophoretic approaches to separations can provide unique capabilities. In the past, capillary and microchip-based approaches to electrophoresis have demonstrated extremely high-resolution separations. More recently, dielectrophoretic systems have shown excellent results for the separation of bioparticles. Here we demonstrate resolution of a difficult pair of targets: gentamicin resistant and susceptible strains of Staphylococcus epidermidis. This separation has significant potential implications for healthcare. This establishes a foundation for biophysical separations as a direct diagnostic tool, potentially improving nearly every figure of merit for diagnostics and antibiotic stewardship. The separations are performed on a modified gradient insulator-based dielectrophoresis (g-iDEP) system and demonstrate that the presence of antibiotic resistance enzymes (or secondary effects) produces a sufficient degree of electrophysical difference to allow separation. The differentiating factor is the ratio of electrophoretic to dielectrophoretic mobilities. This factor is 4.6 ± 0.6 × 109 V m−2 for the resistant strain, versus 9.2 ± 0.4 × 109 V m−2 for the susceptible strain. Using g-iDEP separation, this difference produces clear and easily discerned differentiation of the two strains.