Selective Manipulation of Molecules by Electrostatic Force and Detection of Single Molecules in Aqueous Solution

Manipulation of biomolecules in aqueous solution has been a critical issue for the development of many biosensing techniques and biomedical devices. Electrostatic force is an effective method for increasing both sensitivity and selectivity of various biosensing techniques. In this study, we employed surface-enhanced Raman spectroscopy (SERS) as an <i>in situ</i> label-free method to monitor the motion of biomolecules driven by this manipulation technique. We present the results of a combined experimental and simulation study to demonstrate that electrostatic force could enhance SERS detection of molecules in aqueous solutions with respect to sensitivity and selectivity. In regards to sensitivity, we successfully observed the signature of single molecule addition to individual SERS hot spots, in the form of the stepwise increase of Raman signal with time. With regard to selectivity, we obtained discernible SERS signature of selected families of molecules from a mixture of other molecular families of higher concentration by driving the specifically charged or polarized molecules toward or away from the electrodes/SERS surface based on their charge state, polarizability, mass, and environment pH value. We further report the experimental results on how the key factors affect the selective attraction and repulsion motion of biomolecules

Giant Optical Response from Graphene–Plasmonic System

The unique properties of graphene when coupled to plasmonic surfaces render a very interesting physical system with intriguing responses to stimuli such as photons. It promises exciting application potentials such as photodetectors as well as biosensing. With its semimetallic band structure, graphene in the vicinity of metallic nanostructures is expected to lead to non-negligible perturbation of the local distribution of electromagnetic field intensity, an interesting plasmonic resonance process that has not been studied to a sufficient extent. Efforts to enhance optoelectronic responses of graphene using plasmonic structures have been demonstrated with rather modest Raman enhancement factors of less than 100. Here, we examine a novel cooperative graphene–Au nanopyramid system with a remarkable graphene Raman enhancement factor of up to 10⁷. Experimental evidence including polarization-dependent Raman spectroscopy and scanning electron microscopy points to a new origin of a drastically enhanced D-band from sharp folds of graphene near the extremities of the nanostructure that is free of broken carbon bonds. These observations indicate a new approach for obtaining detailed structural and vibrational information on graphene from an extremely localized region. The new physical origin of the D-band offers a realistic possibility of defining active devices in the form of, for example, graphene nanoribbons by engineered graphene folds (also known as wrinkles) to realize edge-disorder-free transport. Furthermore, the addition of graphene made it possible to tailor the biochemical properties of plasmonic surfaces from conventional metallic ones to biocompatible carbon surfaces

Copper Ion Binding Site in β‑Amyloid Peptide

β-Amyloid aggregates in the brain play critical roles in Alzheimer’s disease, a chronic neurodegenerative condition. Amyloid-associated metal ions, particularly zinc and copper ions, have been implicated in disease pathogenesis. Despite the importance of such ions, the binding sites on the β-amyloid peptide remain poorly understood. In this study, we use scanning tunneling microscopy, circular dichroism, and surface-enhanced Raman spectroscopy to probe the interactions between Cu²⁺ ions and a key β-amyloid peptide fragment, consisting of the first 16 amino acids, and define the copper–peptide binding site. We observe that in the presence of Cu²⁺, this peptide fragment forms β-sheets, not seen without the metal ion. By imaging with scanning tunneling microscopy, we are able to identify the binding site, which involves two histidine residues, His13 and His14. We conclude that the binding of copper to these residues creates an interstrand histidine brace, which enables the formation of β-sheets

Imaging Structure and Composition Homogeneity of 300 mm SiGe Virtual Substrates for Advanced CMOS Applications by Scanning X‑ray Diffraction Microscopy

Advanced semiconductor heterostructures are at the very heart of many modern technologies, including aggressively scaled complementary metal oxide semiconductor transistors for high performance computing and laser diodes for low power solid state lighting applications. The control of structural and compositional homogeneity of these semiconductor heterostructures is the key to success to further develop these state-of-the-art technologies. In this article, we report on the lateral distribution of tilt, composition, and strain across step-graded SiGe strain relaxed buffer layers on 300 mm Si(001) wafers treated with and without chemical–mechanical polishing. By using the advanced synchrotron based scanning X-ray diffraction microscopy technique K-Map together with micro-Raman spectroscopy and Atomic Force Microscopy, we are able to establish a partial correlation between real space morphology and structural properties of the sample resolved at the micrometer scale. In particular, we demonstrate that the lattice plane bending of the commonly observed cross-hatch pattern is caused by dislocations. Our results show a strong local correlation between the strain field and composition distribution, indicating that the adatom surface diffusion during growth is driven by strain field fluctuations induced by the underlying dislocation network. Finally, it is revealed that a superficial chemical–mechanical polishing of cross-hatched surfaces does not lead to any significant change of tilt, composition, and strain variation compared to that of as-grown samples