This presentation concerns two developments in nanoparticle technologies. First, the development and physical characterization of monodisperse 30 nm iron oxide-core, gold-shell nanoparticles will be described. These nanoparticles combine the potential for magnetic manipulation and plasmonic sensing in a single entity for eventual use as an intracellular probe. This part of the presentation will focus on surface chemical modifications that were necessary to perform the synthesis and to stabilize the resulting particles. Transmission electron microscope (TEM) images obtained at various stages reveal the development of the core-shell morphology. Completion of the gold shell produces an intensification and pronounced shift of the surface plasmon resonance peak in the optical absorbance spectrum, a requirement for biosensing. TEM and absorbance spectra together indicate that both the magnetic cores and the gold shells are monodisperse in size. All particles are core-shell, with no non-magnetic gold particle byproducts. The particles are superparamagnetic at room temperature. Darkfield microscopy shows the feasibility of detecting single nanoparticles undergoing Brownian motion. Magnetophoretic calculations indicate the suitability for manipulating the particles in micropatterned high magnetic field gradient devices. The remainder of the presentation will focus on the development of block copolymers as surface modifiers for nanoscale zero valent iron (NZVI) particles that have good potential for the remediation of groundwater contamination by chlorinated organic compounds. NZVI has poor colloidal stability and a tendency to adhere to mineral surfaces. These limit their effectiveness as in situ treatment agents. Here we describe the design of adsorbed polymer coatings to enhance NZVI source zone targeting in groundwater environments. Using atom transfer radical polymerization (ATRP), we have synthesized a family of poly(methacrylic acid)-block-poly(methyl or butyl methacrylate)-block-poly(styrene sulfonate) triblock copolymers with varying compositions. Quartz crystal microgravimetry and ellipsometry show that the polymers effectively eliminate adhesion to silica and to natural organic matter surfaces under representative groundwater electrolyte conditions. The benefit is attributed to repulsive electrosteric forces.