Presentation by Prof Ashutosh Chilkoti of Duke University

Prof. Ashutosh Chilkoti visited the LBSA on 14^th December 2010 to meet with members of the group and he presented a talk entitled “Nanostructures of Macromolecules to Direct Biological Function“. Ashutosh Chilkoti is holder of the Theo Pilkington Chair for Biomedical Engineering and Director of the Center for Biologically Inspired Materials and Material Systems at Duke University.

Nanostructures of Macromolecules to Direct Biological Function

I will present some recent examples of work from my laboratory on the fabrication of nanoscale polymer structures that can modulate biological events. In the first example, the in situ synthesis of nanometer thick brushes of a PEG-like polymer, poly(oligo(ethylene glycol) methyl ether methacrylate) (poly(OEGMA)), by surface-initiated atom-transfer radical polymerization (ATRP)  will be described. These oligoethyleneglycol-functionalized polymer brushes are useful for the fabrication of protein microarrays, as their resistance to adventitious adsorption of proteins allows us to assay for analytes from serum and whole blood down to the femtomolar level. I will then describe the consequences of scaling down the surface –from the macroscopic surface of a chip to the molecular surface of a protein– on which the same polymer is grown by in situ polymerization, and its consequences on the in vivo behavior of a protein-polymer conjugate.  I will discuss two new and general routes to grow poly(OEGMA) with low polydispersity and high yield solely from the N-terminus or C-terminus of a protein by in situ ATRP under aqueous conditions, to yield site-specific (N- or C-terminal) and stoichiometric conjugates (1:1).  Notably, both the myoglobin-poly(OEGMA) conjugate (N-terminal conjugate) and green fluorescent protein conjugate (C-terminal conjugate) showed a 40-50 fold increase in their blood exposure compared to the unmodified protein after intravenous administration to mice, thereby demonstrating that comb polymers that present short oligo(ethylene glycol) side-chains are a new class of PEG-like polymers that can significantly improve the pharmacological properties of proteins. Finally, I will summarize recent work in my laboratory on the development of a new isothermal fluorescence signal amplification and detection scheme –termed surface-initiated enzymatic polymerization (SIEP)– that exploits the ability of terminal deoxynucleotidyl transferase (TdTase) to add up to 100 fluorescent nucleotides to the end of a short DNA tag with an exposed 3’-OH.  I will show how DNA microarrays that are printed on the nonfouling polymer brush exhibit low background signal, yet allow on-chip fluorescence signal amplification by SIEP, leading to DNA microarrays that exhibit a picomolar LOD.  Finally, I will report on recent results where we have extended this approach to the on-chip detection of microRNA