Reversible Meso-Scale Smart Polymer−Protein Particles of Controlled Sizes

Abstract

Functionalized beads and particles in the size range of tens to hundreds of nanometers (nano- to meso-scale) are finding increased applications in the bioanalytical field. We show here that conjugates of streptavidin and the temperature-responsive polymer poly(N-isopropylacrylamide) (PNIPAAm), synthesized with low polydispersities by reversible addition--fragmentation chain transfer (RAFT) polymerization, rapidly formed mesoscale polymer--protein particles above the lower critical solution temperature (LCST). The average hydrodynamic diameters of these particles could be controlled between 250 nm to 900 nm by the choice of conjugate concentration and polymer molecular weight, and/or through control of the rate of temperature change. Once formed, the biohybrid particles were found to be stable for >16 h at the controlled size, unlike the free PNIPAAm which continued to aggregate and grow over time into very large and polydisperse aggregates. The reversibility between the smart polymer--protein particles and the free polymer--protein conjugates opens potential uses in traditional diagnostic formats and in microfluidic formats where the differential diffusive and physical properties might be exploited for separations, analyte concentration, and signal generation.

Responsive Polymer‐Protein Bioconjugates Prepared by RAFT Polymerization and Copper‐Catalyzed Azide‐Alkyne Click Chemistry

“…While we cannot be certain of the aggregate morphology, it is likely the conjugates form polymerprotein particles composed of hydrophobic PNIPAM stabilized by hydrophilic BSA. [13] The BSA red -PNIPAM conjugate demonstrated a bimodal size distribution at ; M w =M n ¼ 1.06). ; M w =M n ¼ 1.06).…”

“…[7] While the former has proven highly successful for the synthesis of polymerprotein conjugates, [8][9][10] the adoption of RAFT has been considerably more gradual, [11][12][13] despite the absence of a metal catalyst and facile amenability to aqueous, nondenaturing media. [14] For the grafting reaction, a wide variety of coupling strategies has been considered including reductive alkylation, [15] thiol-maleimide Michael addition, [16] and oxime formation.…”

Living Radical Polymerization by the RAFT Process

“…Other applications of thiol functional polymers relate to the property of thiols to complex metals and to form conjugates with biological polymers, such as proteins. [95,196] …”

“…[242] RAFT-synthesized thiols have also been used to make protein conjugates. [95,196] Summary RAFT polymerization has emerged as one of the most important methods for living radical polymerization. The method is robust and versatile and can be applied to the majority of polymers prepared by radical polymerization.…”

Smart Reactivity in Gelatine/PNIPAM Mixtures: Control of the Cross‐Linking and Microheterogeneities

“…At the LCST (32 8C) the polymer chain undergoes a coil-to-globule transition and this thermo-sensitive behaviour is of interest for the development of stimuli responsive aqueous formulations, surfaces and gels. [4][5][6][7][8] The properties of gelatine and PNIPAM have been combined in graft copolymers [9,10] and interpenetrating networks. [2,3] In this work we explore the possibility to control the chemical cross-linking and properties (local heterogeneity) of gelatine gels by using a NIPAM-based copolymer as a thermo-sensitive cross-linker.…”