Bio


John is a postdoctoral scholar in the Department of Materials Science and Engineering at Stanford University in the group of Professor Jennifer A. Dionne. John completed his Ph.D. in June 2018 at the University of California, Los Angeles in the Department of Chemistry and Biochemistry where he was advised by Professor Paul S. Weiss and received his B.S. in Chemistry in 2011 from the University of Florida.

Honors & Awards


  • Physical Chemistry Dissertation Award, University of California Los Angeles (2018)
  • George Gregory Award for Research in Physical Chemistry, University of California Los Angeles (2018)
  • Dissertation Year Fellowship Award, University of California Los Angeles (2017)
  • Feinberg Graduate School Visiting Fellowship Award, Weizmann Institute of Science (2017)
  • Colloids and Surface Science Poster Award, 251st American Chemical Society National Meeting (2016)
  • Graduate Research Poster Award, Seaborg Symposium, University of California Los Angeles (2016)
  • Research Showcase Travel Award, University of California Los Angeles (2015)
  • Graduate Dean's Fellowship Award, University of California Los Angeles (2012)

Professional Education


  • Doctor of Philosophy, University of California Los Angeles (2018)
  • Master of Science, University of California Los Angeles (2013)
  • Bachelor of Science, University of Florida (2011)

Current Research and Scholarly Interests


John is a physical chemist researching chiral light–matter interactions, integrated dielectric nanophotonics for all-optical magnetic memory technologies, and chiral molecular spintronics.

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Chirality, the absence of mirror symmetry, is prominent across biological, chemical, and physical systems. Despite structural similarity, left- and right-handed mirror image molecules, or enantiomers, exhibit chiral-selective chemistries, optical properties, and emergent electronic and magnetic phenomena. In particular, differential electrical conductivity and absorption of left- vs right-handed circularly polarized light by enantiomers is related to spin states of electrons and photons, respectively. Understanding and enhancing this spin-dependent enantioselectivity is critical for widespread applications including information processing and memory technologies, pharmacology and drug development, and biochemical sensing.

John's Ph.D. research concentrated on elucidating spin-dependent electron transport through chiral molecular assemblies, measuring room-temperature electron spin filtering in DNA-mediated charge transfer, and spin-dependent energy barriers to photoelectron transmission through helical oligopeptides.

John's current postdoctoral research focuses on theoretical design and experimental implementation of nanophotonic platforms to amplify chiral light–matter interactions for advanced spectroscopies and spin- and valleytronic applications.

All Publications


  • Nanophotonic Platforms for Chiral Sensing and Separation. Accounts of chemical research Solomon, M. L., Saleh, A. A., Poulikakos, L. V., Abendroth, J. M., Tadesse, L. F., Dionne, J. A. 2020

    Abstract

    Chirality in Nature can be found across all length scales, from the subatomic to the galactic. At the molecular scale, the spatial dissymmetry in the atomic arrangements of pairs of mirror-image molecules, known as enantiomers, gives rise to fascinating and often critical differences in chemical and physical properties. With increasing hierarchical complexity, protein function, cell communication, and organism health rely on enantioselective interactions between molecules with selective handedness. For example, neurodegenerative and neuropsychiatric disorders including Alzheimer's and Parkinson's diseases have been linked to distortion of chiral-molecular structure. Moreover, d-amino acids have become increasingly recognized as potential biomarkers, necessitating comprehensive analytical methods for diagnosis that are capable of distinguishing l- from d-forms and quantifying trace concentrations of d-amino acids. Correspondingly, many pharmaceuticals and agrochemicals consist of chiral molecules that target particular enantioselective pathways. Yet, despite the importance of molecular chirality, it remains challenging to sense and to separate chiral compounds. Chiral-optical spectroscopies are designed to analyze the purity of chiral samples, but they are often insensitive to the trace enantiomeric excess that might be present in a patient sample, such as blood, urine, or sputum, or pharmaceutical product. Similarly, existing separation schemes to enable enantiopure solutions of chiral products are inefficient or costly. Consequently, most pharmaceuticals or agrochemicals are sold as racemic mixtures, with reduced efficacy and potential deleterious impacts. Recent advances in nanophotonics lay the foundation toward highly sensitive and efficient chiral detection and separation methods. In this Account, we highlight our group's effort to leverage nanoscale chiral light-matter interactions to detect, characterize, and separate enantiomers, potentially down to the single molecule level. Notably, certain resonant nanostructures can significantly enhance circular dichroism for improved chiral sensing and spectroscopy as well as high-yield enantioselective photochemistry. We first describe how achiral metallic and dielectric nanostructures can be utilized to increase the local optical chirality density by engineering the coupling between electric and magnetic optical resonances. While plasmonic nanoparticles locally enhance the optical chirality density, high-index dielectric nanoparticles can enable large-volume and uniform-sign enhancements in the optical chirality density. By overlapping these electric and magnetic resonances, local chiral fields can be enhanced by several orders of magnitude. We show how these design rules can enable high-yield enantioselective photochemistry and project a 2000-fold improvement in the yield of a photoionization reaction. Next, we discuss how optical forces can enable selective manipulation and separation of enantiomers. We describe the design of low-power enantioselective optical tweezers with the ability to trap sub-10 nm dielectric particles. We also characterize their chiral-optical forces with high spatial and force resolution using combined optical and atomic force microscopy. These optical tweezers exhibit an enantioselective optical force contrast exceeding 10 pN, enabling selective attraction or repulsion of enantiomers based on the illumination polarization. Finally, we discuss future challenges and opportunities spanning fundamental research to technology translation. Disease detection in the clinic as well as pharmaceutical and agrochemical industrial applications requiring large-scale, high-throughput production will gain particular benefit from the simplicity and relative low cost that nanophotonic platforms promise.

    View details for DOI 10.1021/acs.accounts.9b00460

    View details for PubMedID 31913015

  • Spin-Dependent Ionization of Chiral Molecular Films Journal of the American Chemical Society Abendroth, J. M., Cheung, K. M., Stemer, D. M., El Hadri, M. S., Zhao, C., Fullerton, E. E., Weiss, P. S. 2019; 141 (9): 3863–74

    View details for DOI 10.1021/jacs.8b08421

  • Spin Selectivity in Photoinduced Charge-Transfer Mediated by Chiral Molecules. ACS nano Abendroth, J. M., Stemer, D. M., Bloom, B. P., Roy, P., Naaman, R., Waldeck, D. H., Weiss, P. S., Mondal, P. C. 2019; 13 (5): 4928–46

    Abstract

    Optical control and readout of electron spin and spin currents in thin films and nanostructures have remained attractive yet challenging goals for emerging technologies designed for applications in information processing and storage. Recent advances in room-temperature spin polarization using nanometric chiral molecular assemblies suggest that chemically modified surfaces or interfaces can be used for optical spin conversion by exploiting photoinduced charge separation and injection from well-coupled organic chromophores or quantum dots. Using light to drive photoexcited charge-transfer processes mediated by molecules with central or helical chirality enables indirect measurements of spin polarization attributed to the chiral-induced spin selectivity effect and of the efficiency of spin-dependent electron transfer relative to competitive relaxation pathways. Herein, we highlight recent approaches used to detect and to analyze spin selectivity in photoinduced charge transfer including spin-transfer torque for local magnetization, nanoscale charge separation and polarization, and soft ferromagnetic substrate magnetization- and chirality-dependent photoluminescence. Building on these methods through systematic investigation of molecular and environmental parameters that influence spin filtering should elucidate means to manipulate electron spins and photoexcited states for room-temperature optoelectronic and photospintronic applications.

    View details for DOI 10.1021/acsnano.9b01876

    View details for PubMedID 31016968

  • Small-Molecule Patterning via Prefunctionalized Alkanethiols CHEMISTRY OF MATERIALS Cao, H. H., Nakatsuka, N., Deshayes, S., Abendroth, J. M., Yang, H., Weiss, P. S., Kasko, A. M., Andrews, A. M. 2018; 30 (12): 4017–30
  • Aptamer-Field-Effect Transistors Overcome Debye Length Limitations for Small-Molecule Sensing Science Nakatsuka, N., Yang, K., Abendroth, J. M., Cheung, K. M., Xu, X., Yang, H., Zhao, C., Zhu, B., Rim, Y., Yang, Y., Weiss, P. S., Stojanović, M. N., Andrews, A. M. 2018; 362 (6412): 319-24

    View details for DOI 10.1126/science.aao6750

  • Analyzing Spin Selectivity in DNA-Mediated Charge Transfer via Fluorescence Microscopy ACS NANO Abendroth, J. M., Nakatsuka, N., Ye, M., Kim, D., Fullertor, E. E., Andrews, A. M., Weiss, P. S. 2017; 11 (7): 7516–26

    Abstract

    Understanding spin-selective interactions between electrons and chiral molecules is critical to elucidating the significance of electron spin in biological processes and to assessing the potential of chiral assemblies for organic spintronics applications. Here, we use fluorescence microscopy to visualize the effects of spin-dependent charge transport in self-assembled monolayers of double-stranded DNA on ferromagnetic substrates. Patterned DNA arrays provide background regions for every measurement to enable quantification of substrate magnetization-dependent fluorescence due to the chiral-induced spin selectivity effect. Fluorescence quenching of photoexcited dye molecules bound within DNA duplexes is dependent upon the rate of charge separation/recombination upon photoexcitation and the efficiency of DNA-mediated charge transfer to the surface. The latter process is modulated using an external magnetic field to switch the magnetization orientation of the underlying ferromagnetic substrates. We discuss our results in the context of the current literature on the chiral-induced spin selectivity effect across various systems.

    View details for DOI 10.1021/acsnano.7b04165

    View details for Web of Science ID 000406649700102

    View details for PubMedID 28672111

  • Polymer-Pen Chemical Lift-Off Lithography NANO LETTERS Xu, X., Yang, Q., Cheung, K. M., Zhao, C., Wattanatorn, N., Belling, J. N., Abendroth, J. M., Slaughter, L. S., Mirkin, C. A., Andrews, A. M., Weiss, P. S. 2017; 17 (5): 3302–11

    Abstract

    We designed and fabricated large arrays of polymer pens having sub-20 nm tips to perform chemical lift-off lithography (CLL). As such, we developed a hybrid patterning strategy called polymer-pen chemical lift-off lithography (PPCLL). We demonstrated PPCLL patterning using pyramidal and v-shaped polymer-pen arrays. Associated simulations revealed a nanometer-scale quadratic relationship between contact line widths of the polymer pens and two other variables: polymer-pen base line widths and vertical compression distances. We devised a stamp support system consisting of interspersed arrays of flat-tipped polymer pens that are taller than all other sharp-tipped polymer pens. These supports partially or fully offset stamp weights thereby also serving as a leveling system. We investigated a series of v-shaped polymer pens with known height differences to control relative vertical positions of each polymer pen precisely at the sub-20 nm scale mimicking a high-precision scanning stage. In doing so, we obtained linear-array patterns of alkanethiols with sub-50 nm to sub-500 nm line widths and minimum sub-20 nm line width tunable increments. The CLL pattern line widths were in agreement with those predicted by simulations. Our results suggest that through informed design of a stamp support system and tuning of polymer-pen base widths, throughput can be increased by eliminating the need for a scanning stage system in PPCLL without sacrificing precision. To demonstrate functional microarrays patterned by PPCLL, we inserted probe DNA into PPCLL patterns and observed hybridization by complementary target sequences.

    View details for DOI 10.1021/acs.nanolett.7b01236

    View details for Web of Science ID 000401307300082

    View details for PubMedID 28409640

  • Surface Structure and Electron Transfer Dynamics of the Self-Assembly of Cyanide on Au{111} Journal of Physical Chemistry C Guttentag, A. I., Waechter, T., Barr, K. K., Abendroth, J. M., Song, T., Sullivan, N. F., Yang, Y., Allara, D. L., Zharnikov, M., Weiss, P. S. 2016; 120 (47): 26736–46
  • Controlling Motion at the Nanoscale: Rise of the Molecular Machines ACS NANO Abendroth, J. M., Bushuyev, O. S., Weiss, P. S., Barrett, C. J. 2015; 9 (8): 7746–68

    Abstract

    As our understanding and control of intra- and intermolecular interactions evolve, ever more complex molecular systems are synthesized and assembled that are capable of performing work or completing sophisticated tasks at the molecular scale. Commonly referred to as molecular machines, these dynamic systems comprise an astonishingly diverse class of motifs and are designed to respond to a plethora of actuation stimuli. In this Review, we outline the conditions that distinguish simple switches and rotors from machines and draw from a variety of fields to highlight some of the most exciting recent examples of opportunities for driven molecular mechanics. Emphasis is placed on the need for controllable and hierarchical assembly of these molecular components to display measurable effects at the micro-, meso-, and macroscales. As in Nature, this strategy will lead to dramatic amplification of the work performed via the collective action of many machines organized in linear chains, on functionalized surfaces, or in three-dimensional assemblies.

    View details for DOI 10.1021/acsnano.5b03367

    View details for Web of Science ID 000360323300004

    View details for PubMedID 26172380

  • Halide Anions as Shape-Directing Agents for Obtaining High-Quality Anisotropic Gold Nanostructures CHEMISTRY OF MATERIALS DuChene, J. S., Niu, W., Abendroth, J. M., Sun, Q., Zhao, W., Huo, F., Wei, W. 2013; 25 (8): 1392–99

    View details for DOI 10.1021/cm3020397

    View details for Web of Science ID 000318144000023