We report a low-cost compact diffuse speckle contrast flowmeter (DSCF) consisting of a small laser diode and a bare charge-coupled-device (CCD) chip, which can be used for contact measurements of blood flow variations in relatively deep tissues (up to ∼8 mm). Measurements of large flow variations by the contact DSCF probe are compared to a noncontact CCD-based diffuse speckle contrast spectroscopy and a standard contact diffuse correlation spectroscopy in tissue phantoms and a human forearm. Bland–Altman analysis shows no significant bias with good limits of agreement among these measurements: 96.5%±2.2% (94.4% to 100.0%) in phantom experiments and 92.8% in the forearm test. The relatively lower limit of agreement observed in the in vivo measurements (92.8%) is likely due to heterogeneous reactive responses of blood flow in different regions/volumes of the forearm tissues measured by different probes. The low-cost compact DSCF device holds great potential to be broadly used for continuous and longitudinal monitoring of blood flow alterations in ischemic/hypoxic tissues, which are usually associated with various vascular diseases.
This research numerically calculated the optical absorption of gold nanoparticles (AuNP) in the presence of metallic (Au) and dielectric (Si) AFM probes, illuminated by a surface plasmon polaritons on an infinite gold substrate. Nanoscale probes localize and enhance the field between the apex of the tip and the particle. However, the absorption of the nanoparticle is not always enhanced; in fact, under a gold tip, the absorption is suppressed for a 50 nm diameter AuNP. After fitting the numerical absorption data with the equation of a driven damped harmonic oscillator (HO), it was found that the AFM tip modifies both the driving force (F0), consisting of the free carrier charge (q) and the driving field (E), and the overall damping of the oscillator (β). The enhancement or suppression of absorption with different tips can be understood in terms of competition between β and F0. Introducing the metallic tip increases β and decreases F0, resulting in reduced absorption. Introducing the dielectric tip, although it increases β, it also increases F0, resulting in overall absorption enhancement. Therefore, one most consider both β and F0to control the absorption of nanoparticles under Surface Plasmon Polaritons.
Electron-beam-induced deposition (EBID) is a gas-phase direct-write technique capable of sub-10 nm resolution, with applications in micro- and nanoscale object manipulation, mask repair, and circuit edit. While several high purity materials can be deposited by EBID, the majority of deposits suffer from undesirable co-deposition of organic or inorganic ligands. As a result, impurity incorporation limits EBID application in processes requiring high purity. Recently, a complimentary technique known as liquid phase EBID (LP-EBID) has been shown to drastically improve deposit purity by utilizing precursors without carbon or phosphorous based architectures. Here we demonstrate direct-write deposition of silver nanostructure arrays, with tunable geometry for localized surface plasmon resonance (LSPR) control. Nanoparticle arrays with 55 – 100 nm diameters were obtained. Resonant wavelengths between 550 - 600 nm were achieved and correlated to the observed nanoparticle geometry. These results demonstrate how LP-EBID can be used to provide site-specific deposition for plasmonic devices and additionally open the door to fields inaccessible to traditional gas-phase EBID.
Noble metal nanoparticles supporting localized surface plasmon resonances (LSPR) have been extensively investigated
for label free detection of various biological and chemical interactions. When compared to traditional propagating
surface plasmon based sensors, LSPR sensors offer extensive wavelength tunability, greater electric field enhancement and sensing in reduced volumes. However, these sensors also suffer from a major disadvantage – LSPR sensors remain
highly susceptible to interference because they respond to both solution refractive index changes and non-specific
binding as well as specific binding of the target analyte. These interactions can compromise the measurement of the target analyte in a complex unknown media and hence limit the applicability and impact of the sensor. Despite the
extensive amount of work done in this field, there has been an absence of optical techniques that make these sensors
immune to interfering effects. Recently, our group experimentally demonstrated a multi-mode LSPR sensor that exploits
three resonances of a U-shaped gold nanostructure to differentiate the target interaction from bulk and surface interfering
effects. In this paper, we provide a comprehensive description of the electric field profiles of the three resonances of the U-shaped nanostructure. We will also evaluate the sensitivities of the nanostructure to the various bulk and surface interactions using numerical simulations.
Conference Committee Involvement (1)
Micro (MEMS) and Nanotechnologies for Defense and Security