| AVS 54th International Symposium | |
| Biomaterial Interfaces | Friday Sessions |
| Session BI-FrM |
| Session: | Microbioanalytical Systems |
| Presenter: | J.I. Lai, University of Washington |
| Authors: | J.I. Lai, University of Washington J.M. Hoffman, University of Washington M. Ebara, University of Washington A.S. Hoffman, University of Washington P. Stayton, University of Washington |
| Correspondent: | Click to Email |
Magnetic nanoparticle (mNP) technologies have attracted attention for diagnostic applications because mNPs display potential advantages in their diffusive and superparamagnetic properties. However, their small particle size reduces the magnetic capture efficiency. Therefore, there is a need to design mNPs that can be effectively separated without compromising their diffusive properties. Here we have developed an approach that addresses this challenge in the microfluidic channel setting by using mNPs synthesized from temperature-responsive polymeric micelles. Telechelic poly(N-isopropylacrylamide) (PNIPAAm) polymer chains were synthesized with a dodecyl tail at one end and a reactive carboxylate at the opposite end by the reversible addition fragmentation transfer technique. These PNIPAAm chains self-associate into nanoscale micelles that were used as dimensional confinements to synthesize the mNPs. The Mössbauer spectrum of the resulting mNPs shows two broad quadrupolar doublets with chemical shifts of 0.38 and 0.21 mm/s suggesting that the mNPs contain only Fe3+. The X-ray diffraction spectrum confirms the mNP is γ-Fe2O3. The mNPs exhibit a layer of carboxylate-terminated PNIPAAm chains as a corona on the surface. The carboxylate group was used to functionalize the mNPs with biotin which was subsequently bound to streptavidin. The biotinylation increases the mNP size from 7 to 11 nm. The functionalized mNPs can be reversibly aggregated in solution as the temperature is cycled through the PNIPAAm lower critical solution temperature (LCST). The LCST of the mNP is ~ 32 oC before and after the biotinylation. While the magnetophoretic mobility of the individual mNPs below the LCST is negligible, the aggregates formed above the LCST are large enough to respond to an applied magnetic field. The mNPs can associate with biotinylated targets as individual particles, and then subsequent application of a combined temperature increase and magnetic field can be used to magnetically separate the aggregated particles onto the poly(ethylene glycol)-modified polydimethylsiloxane channel walls of a microfluidic device. When the magnetic field is turned off and the temperature is reversed, the captured aggregates re-disperse into the channel flow stream. The dual magnetic- and temperature-responsive nanoparticles can thus be used as soluble reagents to capture diagnostic targets at a specific channel position with temporal control.