NQPI Seminar 11/05/2026 - Umar Umaru

About

The Nanoscale and Quantum Phenomena Institute (NQPI) Seminar Series is pleased to welcome Umar Umaru, Ohio University, as our featured speaker on Thursday, November 5 at 4:10 p.m. All seminars take place in Walter 145 and are also accessible virtually via Teams.

Title: Minimizing Non-Specific Binding of Oligonucleotides to Glass Surface via PEGylation

Abstract: My project aims to develop a single-molecule strategy to obtain optical maps of stretched DNA molecules. A central challenge in single-molecule measurements is non-specifically bound biomolecules on the imaging surface, which are difficult to distinguish from genuine target interactions. Nonspecific binding can distort kinetic parameters and complicate data analysis consequently inaccurate results. NHS-functionalized polyethylene glycol (PEG) is standardly employed for surface passivation to minimize nonspecific binding. However, the method relies on treating the surface with 3-Aminopropyltriethoxysilane (APTES), which deposits amine groups onto the surface, to which the PEG molecules are attached via covalent coupling to the APTES-functionalized amine groups. Because grafted PEG chains sterically hinder access, a significant fraction of primary surface amines remains unreacted. These residual, unneutralized amine sites introduce localized positive charges that readily attract negatively charged biomolecules like DNA, particularly under low-ionic-strength buffer conditions.

Standard monofunctional PEG-NHS coupling frequently leaves a significant fraction of surface amines unneutralized. To address this challenge, we evaluated the passivation efficiency of a novel polyethylene glycol derivative featuring two amine-reactive anchoring ends (2E-PEG), designed to crosslink and neutralize two surface amine groups per molecule. We directly compared its performance with conventional single-NHS linear (L-PEG) and branched (B-PEG) architectures. We prepared quartz surfaces by sequentially sonicating them in ultrapure water and potassium hydroxide (KOH), followed by acid-base piranha cleaning, silanization with APTES, and subsequent PEGylation. Passivated surfaces were evaluated using fluorescence microscopy and contact angle goniometry using an Atto 633-labeled single-stranded DNA probe (5'-GGTGTG-3') as a model target. Our results show that 2E-PEG provides superior passivation against non-specific ssDNA binding compared with conventional single-NHS PEGs, likely due to higher-density amine neutralization and enhanced surface crosslinking.

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