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Project Title
Direct Functionalization of Patterned Arrays
 

Research Program
Nanoscale Materials
 
Project #
NM3
 

Participating Faculty:             D. Y. Sogah, B. Baird, D. Holowka

NBTC Students/Postdocs:     Sean Ramirez

Other Students/Postdocs:     

 

Objectives
(1) Biofunctionalization of patterned arrays. (2) Incorporation of water-stable, water-soluble functionality at ambient temperature. (3) Extension to nanoparticles and carbon nanotubes and development of techniques for introducing a single bioactive group per particle.

Methods
(1) Biofunctionalization of carbon nanotubes (CNTs) and e-beam patterned silicon wafers with biocompatible poly(N,N-dimethylacrylamide) (PDMA) containing chain end biotin and dinitrophenyl (DNP). (2) Binding and detection of IgE and streptavidin using fluorescence microscopy. (3) Ambient temperature in situ photopolymerization from nanoparticles (grafting-from method) and a grafting-to approach utilizing preformed novel copolymers carrying anchoring sites uniformly distributed throughout the chain. (4) NMR, SEM, GPC, TGA, fluorescence microscopy, and DSC.

Summary
We have successfully functionalized CNTs with nitroxide mediated living free radical polymerization (NMP) initiator and polymerized DMA, known to prevent non-specific binding (NSB), leading to water soluble CNTs. The ends of the attached polymer chains were then functionalized with biotin and DNP using nitroxide exchange and radical crossover reactions developed in our lab. Binding of streptavidin to the biotin and IgE to the DNP were demonstrated (Fig.1). Our approach offers an advantage over the most often used non-covalent adsorption by having a protecting polymer layer covalently bound to the nanotube surface, forming a more permanent water soluble structure, capable of preventing NSB.

Because NMP and nitroxide exchange chemistry take place at elevated temperatures (120-125°C), thiocarbamate-mediated photopolymerization, which works well at ambient temperature and for a broader monomer scope, is being investigated. Thus, by attaching the thiocarbamate initiators to nanoparticles using a metal-phosphine oxide interaction, we demonstrated feasibility of growing polymer chains from nanoparticles to yield soluble materials. We have also demonstrated that using preformed novel copolymers containing varying amounts of phosphine oxide groups per chain, large quantities of nanoparticles (ZnO, CuO, and TiO2 up to 65 wt%) could readily be incorporated (Fig. 2).

As part of our ongoing effort to better understand the factors that govern biointeractions on surfaces we have initiated biofunctionalization of three different model surfaces of biocompatible polymer brushes patterned by e-beam using the thiocarbamate-mediated polymerization. The first one has the bioactive groups concentrated in a top layer formed by a block copolymer segment, the second one contains one functional group per chain, and the third one has the groups uniformly distributed throughout random copolymer brushes (Fig. 3). The homo, random and block copolymers are formed from DMA and appropriate macromonomers containing exchangeable nitroxide or thiocarbamate end groups. The protein loading on these substrates will be quantified and compared to the protein loadings on previously made homopolymer brushes. The resulting diagnostic arrays will be used in fundamental studies to resolve such critical challenges as surface functional group density and nonspecific protein absorption.

Accomplishments

  • Functionalized carbon nanotubes with water-soluble polymers carrying bioactive groups specific for IgE and streptavidin (Figure 1).
  • Developed methods for functionalizing various nanoparticles through “grafting-from” and “grafting-to” approaches (Figure 2).
  • Fabricated model surfaces of biocompatible polymer brushes using ambient temperature and water-compatible thiocarbamate-mediated polymerization and demonstrated utility in probing biological materials (Figure 3).

 

Fig.1: (a) Fluorescence of Alexa 546 anti-DNP IgE bound to DNP functionalized CNT. (b) Fluorescence of Alexa 488 labeled streptavidin bound to biotin functionalized CNT on Si wafer. Individual CNTs are spread out over the surface.  Scale bars = 5 mm.

Fig.2:  Nanoparticle functionalization with polymers (blue lines) using a “grafting from” and “grafting to” approach.

Fig. 3. Three models of DNP functionalized patterned surfaces prepared by exchanging thiocarbamate end groups of the living polymer brushes with DNP functionalized nitroxyl.

Insert: Red fluorescence of Alexa 546 anti-DNP IgE bound to DNP functionalized PDMA brushes.

This material is based upon work supported in part by the STC Program of the National Science Foundation under Agreement No. ECS-9876771. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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