title: Magnetic vs. non-magnetic colloids - A comparative adsorption study to quantify the effect of dye-induced aggregation on the binding affinity of an organic dye.
abstract: OBJECTIVE
  Due to attractive magnetic forces, magnetic particles (MPs) can exhibit colloidal instability upon molecular adsorption. Thus, by comparing the dye adsorption isotherms of MPs and non-magnetic particles of the same size, shape and functional group it should be possible to characterize the influence of magnetic attraction on MP aggregation.
  
  
  METHODS
  For a range of particle densities, a comparative adsorption study of malachite green (MG(+)) onto magnetic and non-magnetic colloids was carried out using a combination of a separation technique coupled with UV-vis spectroscopy, optical microscopy, and polarization dependent second harmonic generation (SHG) spectroscopy.
  
  
  RESULTS
  Significant MP aggregation occurs in aqueous solution due to MG(+) adsorption. This alters the adsorption isotherm and challenges the determination of the adsorption equilibrium constant, Kads. The dye-induced aggregation is directly related to the MG(+) concentration, [MG(+)]. A modified Langmuir equation, which incorporates loss of surface sites due to this aggregation, accurately describes the resulting adsorption isotherms. The Kads of 1.1 (±0.3)×10(7) and a loss of maximum MP surface capacity of 2.8 (±0.7)×10(3)M(-1) per [MG(+)] has been obtained. Additionally, SHG has been established as an effective tool to detect aggregation in nanoparticles.
authors.affiliation: Department of Chemistry, Ball State University, 2000 W. University Avenue, Muncie, IN 47306, USA. Electronic address: tawilliams5@bsu.edu.
authors.forename: Tyler A
authors.initials: TA
authors.lastname: Williams
authors.affiliation: Department of Chemistry, Ball State University, 2000 W. University Avenue, Muncie, IN 47306, USA. Electronic address: jlee8@bsu.edu.
authors.forename: Jenny
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Chemistry, Ball State University, 2000 W. University Avenue, Muncie, IN 47306, USA. Electronic address: cadiemler@bsu.edu.
authors.forename: Cory A
authors.initials: CA
authors.lastname: Diemler
authors.affiliation: Department of Chemistry, Ball State University, 2000 W. University Avenue, Muncie, IN 47306, USA. Electronic address: msubir@bsu.edu.
authors.forename: Mahamud
authors.initials: M
authors.lastname: Subir
keywords: Adsorption isotherm; Aggregation detection; Magnetic nanoparticle; Nanotechnology; Pollution remediation; SHG spectroscopy