(6ap) Electrochemical Biotechnology

Electrochemical Biotechnology

DNA has unique abilities of molecular recognition and self-assembly, which have fostered its widespread incorporation into devices for both science and medicine. In both my graduate and postdoctoral work, I have developed improved chemistries to form DNA monolayers on electrodes. Superior monolayer formation methods led to the direct electrochemical detection of DNMT1, a cancer biomarker, from human tissue samples. Using these chemistries, I have also made devices to pattern non-adherent cells and detect endocrine disrupting compounds. This work has significantly improved the field of DNA-based electrochemistry and broadened the potential applications of electrochemical detection with biomolecules. It has yielded fourteen publications, eleven of which are first authorships, as well as two patents. As I transition to an independent career, I plan to apply the methods developed in this work to improve the study and treatment of infectious disease.

Graduate Research with Prof. Jacqueline Barton at the California Institute of Technology.

Surface modification chemistries for diagnostics. Electrochemical nucleic acid sensors generally involve hybridization events, with DNA serving as a scaffold. I developed monolayers constructed from alkyne-modified DNA that was reacted with azide-terminated thiols on the electrode. The amount of azide in the underlying monolayer was tunable for the desired application. This monolayer assembly method yielded DNA helices with a high solvent accessibility, enabling the significantly more sensitive detection of proteins. The transcriptional activator TATA binding protein (TBP) was detected at 4 nM, its K_D. With this method, I also achieved extremely sensitive and specific monitoring of DNA lesions, mismatches, and hybridization events.

Detection of DNMT1 activity from patient tumor samples as a cancer diagnostic. With the sensitivity and selectivity of my surface-modification chemistries, I developed an electrochemical signal-on assay to measure the activity of the human methyltransferase DNMT1 using a methylation-specific restriction enzyme. Aberrant methylation has been linked to cancer. Prior to my platform, no methods existed to monitor methyltransferase activity in a clinically relevant setting. I successfully measured DNMT1 activity from crude human tumor lysate. In ten sets of tumor and healthy adjacent tissue, a direct correlation was observed between the high DNMT1 activity and tumorous tissue when activity was measured electrochemically. This activity does not correlate with either overexpression or total amount of DNMT1 within the sample.

This work has improved the sensitivity, selectivity and specificity of DNA-modified electrodes, especially for clinical applications. I trained three undergraduates, two of whom are currently pursuing Ph.D.s.

Postdoctoral Research with Prof. Matthew Francis at the University of California, Berkeley.

Reagentless DNA coupling to surfaces. I have developed a reagentless one-pot coupling method to tether biomolecules to surfaces. The reaction, between a catechol and an aniline installed on a biomolecule, proceeds rapidly in the presence of an applied electrical potential (in under four minutes) with the ability to tune the amount of DNA on the surface. I highlighted its application for diagnostics through the electrochemical sensing of the endocrine disruptor bisphenol A. Living, non-adherent cells were also captured on electrode surfaces by DNA hybridization. Both applications were found to be dependent on the surface coverage of DNA. Importantly, I have used this method to immobilize electron transfer-proficient cells and demonstrated efficient current generation on electrodes, which would significantly improve the construction of biofuel cells.

Engineered bacterial biosensor for pollutant detection. Endocrine disrupting compounds (EDCs) are ubiquitous, originating from pesticides, plasticizers, and pharmaceuticals. They have been implicated in diseases such as obesity, diabetes, and cancer. I developed a new detection strategy for EDCs that is both fast and portable. This system is based on an estrogen receptor construct expressed on the surface of E. coli, which enables the detection of many detrimental compounds with inherent signal amplification from impedance measurements. I detected sub-ppb levels of estradiol and ppm levels of bisphenol A in complex solutions. This system reports the total estrogenic activity of a sample. As an applied example, estrogenic chemicals released from a plastic baby bottle upon microwave heating were detectable with this technique.

I have trained an undergraduate who received the NSF GRFP fellowship, as well as four graduate students, one of whom also received the NSF GRFP based on our work. In the future, I will establish an independent research lab with a diverse and robust program making use of DNA-based methods to study, detect, and drug pathogenic bacteria.

Teaching Interests:

With interdisciplinary training, I am prepared and excited to teach a range of classes. My teaching program will ideally be centered on upper-level undergraduate and graduate courses, including Thermodynamics, Electrochemical Energy Systems, Device/Diagnostics Design, Biochemical Engineering, Molecular Bioengineering, and Biomaterials.