Adam Hughes

Questions and Answers (79) View all

• Answer added in Nanophotonics
  1 SERS without laser
  By Adam Hughes · George Washington University
  Adam Hughes · George Washington University

  And also, if I tried to capture raman signal through light transmitted through a 1m silica fiber, is there going to be huge loss from this? Or in oth... [more]

  And also, if I tried to capture raman signal through light transmitted through a 1m silica fiber, is there going to be huge loss from this? Or in other words, how much background raman signal would I expect from light going through a 1m glass fiber vs. signal from a strong collection of nanoparticles? What other fibers would you recommend?
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• Question asked in Nanophotonics
  1 SERS without laser
  Hi all, I'm new to SERS, but have a nice fiber optic sensor that uses visible light on gold nanopaticle monolayers to measure biomolecular interactio... [more]
  Hi all, I'm new to SERS, but have a nice fiber optic sensor that uses visible light on gold nanopaticle monolayers to measure biomolecular interactions. I am very interested in measuring SERS signals with the setup, but must admit I'm new to the field. I have a few questions to should be easy to answer for anyone with SERS experience, but aren't so obvious to me from some of my readings. Thanks in advance. 1. Instead of using a green or red laser, would it make a difference if measured SERS from a concentrated white light source (lets say in principle, ignoring power issues). 2. In regard to power, I know that nanoparticles enhance SERS signals a great deal, so that comparatively weak light sources should still induce the scattering processes. Does anyone have any feel for the numbers at work here? A friend of mine said he only uses a mW laser. I have a 1 Watt LED that gets focused on an optical fiber endface. I'd expect that maybe 10-20% of the power interacts with the sample, but it's hard to tell. Can anyone give me a ballpark estimate here for the power ranges needed to get SERS signals measurable from, say, a benchtop Raman spectrometer. 3. I know that various nanoparticle morphologies and compositions have different Raman enhancement factors. I was thinking of looking at gold nanorods, since we're pretty sold on the gold, and I know the rods can be designed for SERS. Are there any other particles (eg silver nanoprisms) that you'd recommend over others for SERS consideration? How much better, for example, are silver nanorods?
  By Adam Hughes · George Washington University
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• Question asked in Fiber Optics
  Open Light reflectance from tapered/nanofocused optical fibers
  I am very interested in using optical fibers with sharpened tips for detection in biochemical systems. We are coating the tips with metallic films or... [more]
  I am very interested in using optical fibers with sharpened tips for detection in biochemical systems. We are coating the tips with metallic films or nanoparticles. I've noticed that groups that make these types of sensors always detect the transmitted light from the tip of the fiber. I am curious whether or not the reflected light could be harnessed to do the same sorts of measurements. I know the relationship between the light transmittance and reflectance of a metallic-coated tapered optical fiber is not trivial, but is there any reason to believe the light reflectance would not be usable in measuring environmental changes? Any info on the subject is tremendously helpful, even if it does not directly resolve my question. Thanks.
  By Adam Hughes · George Washington University
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• Answer added in Nanoparticles
  3 Surface plasmon resonance of Gold Nanoparticles. Anyone knows if it goes to IR region?
  By Oommen Oommen · Uppsala University
  Adam Hughes · George Washington University

  Well, the images will probably tell the story. If you look at manufactures of AuNanoRods they have specsheets that show how the plasmon resonance lon... [more]

  Well, the images will probably tell the story. If you look at manufactures of AuNanoRods they have specsheets that show how the plasmon resonance longitudinal peak shifts to long wavelengths as the aspect ratio of the rod increases. Like I said before, it's more likely that your resonances are mostly due to the shape of the particles, with slight deviations from bare particles induced by the coating.
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• Answer added in Nanoparticles
  3 Surface plasmon resonance of Gold Nanoparticles. Anyone knows if it goes to IR region?
  By Oommen Oommen · Uppsala University
  Adam Hughes · George Washington University

  Have you imaged your particles? If you know their shapes, it might explain why you have 4 resonances. I wouldn't expect the resonances to be from th... [more]

  Have you imaged your particles? If you know their shapes, it might explain why you have 4 resonances. I wouldn't expect the resonances to be from the biopolymer, as the SPR usually shifts slightly in the presence of biomolecules; however, these molecules don't induce NEW resonance peaks that aren't otherwise there. Depending on your application, do you need a laser? A diffuse lightsource such as a common light bulb emits at these wavelengths and could be used for spectroscopy.
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