Seung Soo Oh

The development of a biosensor system capable of continuous, real-time measurement of small-molecule analytes directly in complex, unprocessed aqueous samples has been a significant challenge, and successful implementation has been achieved for only a limited number of targets. Toward a general solution to this problem, we report here the Microfluidic Electrochemical Aptamer-based Sensor (MECAS) chip wherein we integrate target-specific DNA aptamers that fold, and thus generate an electrochemica

This review provides insight into how current problems of biosensors can be solved by the use of nucleic acid aptamers.

The ability to obtain sequence-specific genetic information about rare target organisms directly from complex biological samples at the point-of-care would transform many areas of biotechnology. Microfluidics technology offers compelling tools for integrating multiple biochemical processes in a single device, but despite significant progress, only limited examples have shown specific, genetic analysis of clinical samples within the context of a fully integrated, portable platform. Herein we pres

We report here an electrochemical approach that offers, for the first time, single-step, room-temperature single nucleotide polymorphism (SNP) detection directly in complex samples (such as blood serum) without the need for target modification, postwashing, or the addition of exogenous reagents. This sensor, which is sensitive, stable, and reusable, is comprised of a single, self-complementary, methylene blue-labeled DNA probe possessing a triple-stem structure. This probe takes advantage of the

Aptamers are nucleic acid-based reagents that bind to target molecules with high affinity and specificity. However, methods for generating aptamers from random combinatorial libraries (e.g., systematic evolution of ligands by exponential enrichment (SELEX)) are often labor-intensive and time-consuming. Recent studies suggest that microfluidic SELEX (M-SELEX) technology can accelerate aptamer isolation by enabling highly stringent selection conditions through the use of very small amounts of targ

Singled out for its singularity: In a single-step, single-component, fluorescence-based method for the detection of single-nucleotide polymorphisms at room temperature, the sensor is comprised of a single, self-complementary DNA strand that forms a triple-stem structure. The large conformational change that occurs upon binding to perfectly matched (PM) targets results in a significant increase in fluorescence (see picture; F = fluorophore, Q = quencher).

We describe an innovative selection approach to generate self-reporting aptamers (SRAs) capable of converting target-binding events into fluorescence readout without requiring additional modification, optimization, or the use of DNA helper strands. These aptamers contain a DNAzyme moiety that is initially maintained in an inactive conformation. Upon binding to their target, the aptamers undergo a structural switch that activates the DNAzyme, such that the binding event can be reported through si

Viruses have evolved specialized mechanisms to efficiently transport nucleic acids and other biomolecules into specific host cells. They achieve this by performing a coordinated series of complex functions, resulting in delivery that is far more efficient than existing synthetic delivery mechanisms. Inspired by these natural systems, we describe a process for synthesizing chemically defined molecular constructs that likewise achieve targeted delivery through a series of coordinated functions. We

Multivalent molecular interactions can be exploited to dramatically enhance the performance of an affinity reagent. The enhancement in affinity and specificity achieved with a multivalent construct depends critically on the effectiveness of the scaffold that joins the ligands, as this determines their positions and orientations with respect to the target molecule. Currently, no generalizable design rules exist for construction of an optimal multivalent ligand for targets with known structures, a

We report a single-step, single-reagent, label-free, isothermal electrochemical DNA sensor based on the phenomenon of target recycling. The sensor exploits strand-specific exonuclease activity to achieve the selective enzymatic digestion of target/probe duplexes. This results in a permanent change in the probe structure that yields an increased faradaic current and liberates the intact target molecule to interact with additional detection probes to achieve further signal amplification. Using thi

The generation of nucleic acid aptamers with high affinity typically entails a time-consuming, iterative process of binding, separation, and amplification. It would therefore be beneficial to develop an efficient selection strategy that can generate these high-quality aptamers rapidly, economically, and reproducibly. Toward this goal, we have developed a method that efficiently generates DNA aptamers with slow off-rates. This methodology, called VDC-MSELEX, pairs the volume dilution challenge pr

We report the utilization of microfluidic technology to phage selection and demonstrate that accurate control of washing stringency in our microfluidic magnetic separator (MMS) directly impacts the diversity of isolated peptide sequences. Reproducible generation of magnetic and fluidic forces allows controlled washing conditions that enable rapid convergence of selected peptide sequences. These findings may provide a foundation for the development of automated microsystems for rapid in vitro dir

Getting a response: A surface-bound and redox-modified (methylene blue) DNA probe architecture is at the heart of a sensor for detecting single-nucleotide mismatched targets with a “polarity-switching” response. It outputs a decreased Faradaic current when hybridized to a perfectly matched (PM) target, and an increased Faradaic current when hybridized to a single-base mismatched (SM) target (see scheme).

Microbial production of many lipophilic compounds is often limited by product toxicity to host cells. Engineering cell walls can help mitigate the damage caused by lipophilic compounds by increasing tolerance to those compounds. To determine if the cell wall engineering would be effective in enhancing lipophilic compound production, we used a previously constructed squalene-overproducing yeast strain (SQ) that produces over 600 mg/L of squalene, a model membrane-damaging lipophilic compound. Thi