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October 12th, 2021 Webinar Speakers

Our next webinar will take place via the internet on Tuesday October 12th at 8 PM EDT/ 1 AM GMT. Sign up on our mailing list to receive the Zoom link!

We hope to see/hear from you all at one of our sessions or as one of the next speakers. If you are an early career scientist and would like to present your research, don't hesitate to submit an abstract today! For now, please learn more about our current speakers and their research below. We also thank the generous support from Cell Reports Physical Science, Merck, and the Royal Society of Chemistry.

Our featured speakers this week are Siew Ting Melissa Tan (graduate student, Stanford University, USA), and Dr. Johannes Karges (postdoctoral researcher, University of California, San Diego, USA). The seminar will be guest-moderated by Prof. Jessica Lamb from the University of Minnesota.


SIEW TING MELISSA TAN (on Twitter @Melterialsgal)

Biography: Melissa earned her Bachelor’s in Materials Science and Engineering with a specialization in Nanotechnology from Nanyang Technological University, Singapore where she was an Agency for Science, Technology and Research Scholar, CN Yang Scholar, and Koh Boon Hwee Scholar. She is currently pursuing a PhD in Materials Science and Engineering at Stanford University with Prof. Alberto Salleo, supported by the Stanford Graduate Fellowship and the National University of Singapore Development Grant. Her research interests include organic mixed conductors, electrochemical transistors, biosensors, sustainable energy storage devices, electronic-skins, and soft haptics. She is a Biodesign NEXT Fellow, Dorm Room Fund PhD Founder, and Co-founder of SWell, a platform that aims to reverse the mental health crisis in higher education. Beyond the lab and startup scene, she can be found swimming, biking, and running around the Bay Area.

Title of Talk: High–Gain Chemically–Gated Organic Electrochemical Transistor

Abstract: There is intense interest in utilizing the redox activity of Organic Mixed Ionic Electronic Conductors for faradaic chemical sensing. In particular, the investigation of organic electrochemical transistors (OECTs) as biosensors due to their low operational potentials, ease of fabrication (e.g. by inkjet printing), biocompatibility, and large transconductance. OECT performance in aqueous electrolytes as well as the OMIECs’ redox activity has spurred myriad studies employing OECTs as chemical transducers e.g. for detection of metabolites in biomedical sensors. However, the OECT’s large (potentiometrically derived) transconductance is not fully leveraged in common approaches that directly conduct chemical reactions amperometrically within the OECT electrolyte with direct charge transfer between the analyte and the OMIEC, which results in sub–unity transduction of gate to drain current. Hence, amperometric OECTs do not truly display current gains in the traditional sense, falling short of the expected transistor performance. We demonstrate an alternative device architecture that separates chemical transduction and amplification processes on two distinct electrochemical cells, thus fully utilizing the OECT’s large transconductance to achieve current gains of 10^3 and current modulations of four orders of magnitude. This transduction mechanism represents a general approach enabling high–gain amplification in chemical OECT transducers.

In a follow up work, we further investigate the operation mechanism of various OECT architectures to deduce the design principles required to achieve reliable chemical detection and signal amplification. We further demonstrate that systematic and rational design of OECT chemical sensors requires understanding the electrochemical processes that result in changes in the potential (charge density) of the channel, the underlying phenomenon behind amplification. Finally, we elucidate the basic principles on how to further optimize the RC-OECT.

We believe that our findings will be of great interest to researchers in the fields of bioelectronics as a call to action to re-evaluate present approaches of utilizing OECTs for chemical detection and to help practitioners select materials and designs to optimize redox sensors based on organic semiconductors.

DR JOHANNES KARGES (on Twitter @Johannes_Karges)

Biography: Johannes Karges undertook his undergraduate studies at the Philipps-University Marburg (Germany) and the Imperial College London (United Kingdom) thanks to an Erasmus scholarship. He then joined the lab of Prof. Gilles Gasser at the Paris Sciences et Lettres University (France) and in part in the lab of Prof. Hui Chao at Sun Yat-Sen University (China) to undertake a PhD thesis in the development of metal complexes as photosensitizers for photodynamic therapy and their selective delivery to the cancer tissue. Currently, Johannes is a postdoctoral fellow in the lab of Prof. Seth Cohen at the University of California, San Diego (USA) where he is working on the development of metal complexes as enzyme inhibitors.

Title of Talk: Ruthenium(II) Polypyridine Complexes as Photosensitizers for Photodynamic Therapy

Abstract: During the last decades, cancer has emerged as one of the deadliest diseases worldwide. Photodynamic Therapy (PDT) has expanded the range of treatment opportunities for various types of cancer. In PDT, a preferably non-toxic photosensitiser (PS) is activated at a specific wavelength to generate reactive oxygen species. As these are highly reactive, they can rapidly interact with essential biomolecules present in cells to trigger their death. The first clinically approved PS was Photofrin®, which is used to treat various types of cancers (e.g. non-small lung, bladder, oesophageal or brain cancer). As the majority of clinically accepted and investigated PSs are based on the same structural scaffold, these compounds are usually associated with similar drawbacks including poor water solubility, tedious synthesis and purification, photodegradation and slow clearance from the body causing photosensitivity. To overcome these limitations, there is a need for modification of existing PSs or the development of new classes of PSs. As an emerging class of compounds, Ru(II) polypyridine complexes have gained much attention due to their attractive chemical and photophysical properties (e.g., high water solubility, high ROS production, chemical stability and photostability). Despite recent research efforts, the majority of investigated Ru(II) polypyridyl complexes lack absorption in the biological spectral window (600-900 nm). This aim could be achieved by a red-shift of the 1-Photon (1P) absorption or the use of a 2-Photon (2P) process, in which the compound absorbs two photons of low energy simultaneously. Herein, we present the systematic investigation of novel Ru(II) polypyridyl complexes as PSs for long wavelength PDT.

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