Dual Magnetic-/Temperature-Responsive Nanoparticles for Microfluidic Separations and Assays

Abstract

A stimuli-responsive magnetic nanoparticle system for diagnostic target capture and concentration has been developed for microfluidic lab card settings. Telechelic poly(N-isopropylacrylamide) (PNIPAAm) polymer chains were synthesized with dodecyl tails 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 magnetic nanoparticles. The resulting superparamagnetic nanoparticles exhibit a gamma-Fe2O3 core ( approximately 5 nm) with a layer of carboxylate-terminated PNIPAAm chains as a corona on the surface. The carboxylate group was used to functionalize the magnetic nanoparticles with biotin and subsequently with streptavidin. The functionalized magnetic nanoparticles can be reversibly aggregated in solution as the temperature is cycled through the PNIPAAm lower critical solution temperature (LCST). While the magnetophoretic mobility of the individual nanoparticles below the LCST is negligible, the aggregates formed above the LCST are large enough to respond to an applied magnetic field. The magnetic nanoparticles 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 redisperse into the channel flow stream for further downstream processing. The dual magnetic- and temperature-responsive nanoparticles can thus be used as soluble reagents to capture diagnostic targets at a controlled time point and channel position. They can then be isolated and released after the nanoparticles have captured target molecules, overcoming the problem of low magnetophoretic mobility of the individual particle while retaining the advantages of a high surface to volume ratio and faster diffusive properties during target capture.

Living Radical Polymerization by the RAFT Process - A Second Update

“…MMA [296] St [296] 128* [283] S S C 12 H 25 S CO 2 H AA [91] CA [297] tBA [298] MA [299] (BMA) [300] (BMA) [300] CMA [301] MMA [122,283] (MMA) [122] BAM [302] DEAM [302,303] DMAM [302,303] EMAM [302,303] NIPAM [302][303][304][305][306] PAM [302,306] MVK [307] PVK [307] 297 [308] tBS [276] CMS [309] HMS [309] St [91,300,309] (St) [300] 4VP [310] Ip [311] 320 [312] 325 [100] 327 [309] 331 [313] 332 [313] NVP [103] 331-b-St [313] tBA-b-Ip [298] tBA-b-St [298] tBA-b-IP-b-St …”

“…This approach has been used to make inorganic (TiO 2 , SnO 2 or ZnO) nanorods [102] or CdSe/ZnS quantum dots [538] with PAA-b-PSt, [539] P(AEME-co-328-co-342) [278] or semiconductor (P364 or P365) arms, gold nanoparticles with PSt, [476] PSt-b-P2VP, [198] PDMAEMA, PAA, or PSt, [91] P(340-co-AM) or P(341-co-AM), [239] PPEGA-b-PNIPAM, [217] PMMAb-PNIPAM, [189] or P(DEGMA-co-tBA), P(DEGMA-co-tBA)-b-PGMA, PGMA, PSt [398] grafts, magnetic iron with PNIPAM grafts, [305] silver nanoparticles with PSt grafts, [409] chitosan with PAA grafts, [487] and silicon wafers with NIPAM grafts. [273] Silicon wafers and silica particles have also been modified with multiple layers of an amine-functional polymer, polyethyleneimine or poly(allylamine hydrochloride), respectively, and PAA-bPSSO3Na in a layer-by-layer assembly process.…”

The Design of Temperature-Responsive Nanofiber Meshes for Cell Storage Applications

“…PNIPAAm is one of the most studied temperature-responsive polymers, which undergoes a transition from a hydrophilic state to a hydrophobic state in water at 32 • C (lower critical solution temperature; LCST) [20][21][22]. The high solubility of PNIPAAm in water below the LCST can be attributed to the ability of the macromolecule to form H-bonds to water molecules via the amide functional groups.…”

Surface design with self-heating smart polymers for on–off switchable traps

“…Their properties can be changed by external stimuli such as temperature [1,2], light [3,4], electric and magnetic fields [5][6][7], ionic strength [8], pH [9] and chemicals [10,11]. Therefore, smart polymers are used in biotechnology, medicine and engineering, in such applications as drug delivery systems [12][13][14], chemical separation [15,16], sensors [17] and actuators [18,19].…”