DNA-Mediated Excitonic Upconversion FRET Switching

Excitonics is a rapidly expanding field of nanophotonics in which the harvesting of photons, ensuing creation and transport of excitons via Förster resonant energy transfer (FRET), and subsequent charge separation or photon emission has led to the demonstration of excitonic wires, switches, Boolean logic and light harvesting antennas for many applications. FRET funnels excitons down an energy gradient resulting in energy loss with each step along the pathway. Conversely, excitonic energy upconversion via upconversion nanoparticles (UCNPs), although currently inefficient, serves as an energy ratchet to boost the exciton energy. Although FRET-based upconversion has been demonstrated, it suffers from low FRET efficiency and lacks the ability to modulate the FRET. We have engineered an upconversion FRET-based switch by combining lanthanide-doped UCNPs and fluorophores that demonstrates excitonic energy upconversion by nearly a factor of 2, an excited state donor to acceptor FRET efficiency of nearly 25%, and an acceptor fluorophore quantum efficiency that is close to unity. These findings offer a promising path for energy upconversion in nanophotonic applications including artificial light harvesting, excitonic circuits, photovoltaics, nanomedicine, and optoelectronics

Resurrecting “Poor Man’s Purple”: A Transdisciplinary Study of Color-Shifted Pigments Used in an Encaustic Fayum Mummy Portrait of Ancient Egypt

During the Coptic period in Fayum Egypt, encaustic (i.e. wax) mummy portraits were painted onto wooden panels or linen and attached to the mummy trappings of the deceased. One such portrait, “32.6: The Bearded Man” (c. 170-180 AD), features an unidentified Roman-Egyptian displaying a purple clavi. The trace swath of purple in the portrait provides evidence as to the origins of the painting and the identity of the man. Nanoscale analysis of the pigment suggests a red organic material was color shifted using a metal salt to produce a “poor man’s purple” as opposed to the expensive murex purple traditionally reserved for the elite. It is the goal of this project to reverse engineer the pigment using organic material and metal salts available to the Roman-Egyptians in order to fabricate a purple pigment possessing a similar chemical composition to that within the portrait. Analytical comparisons of the original pigment to our synthesized specimens will allow the identification of the original materials used. Ultimately, our aim is to have an in depth understanding of materials and processes used to create the purple clavi, thereby providing further detail as to the provenience of “The Bearded Man” Fayum portrait

Neuronal sensitivity to TDP-43 overexpression is dependent on timing of induction

Ubiquitin-immunoreactive neuronal inclusions composed of TAR DNA binding protein of 43 kDa (TDP-43) are a major pathological feature of frontotemporal lobar degeneration (FTLD-TDP). In vivo studies with TDP-43 knockout mice have suggested that TDP-43 plays a critical, although undefined role in development. In the current report, we generated transgenic mice that conditionally express wild-type human TDP-43 (hTDP-43) in the forebrain and established a paradigm to examine the sensitivity of neurons to TDP-43 overexpression at different developmental stages. Continuous TDP-43 expression during early neuronal development produced a complex phenotype, including aggregation of phospho-TDP-43, increased ubiquitin immunoreactivity, mitochondrial abnormalities, neurodegeneration and early lethality. In contrast, later induction of hTDP-43 in the forebrain of weaned mice prevented early death and mitochondrial abnormalities while yielding salient features of FTLD-TDP, including progressive neurodegeneration and ubiquitinated, phospho-TDP-43 neuronal cytoplasmic inclusions. These results suggest that neurons in the developing forebrain are extremely sensitive to TDP-43 overexpression and that timing of TDP-43 overexpression in transgenic mice must be considered when distinguishing normal roles of TDP-43, particularly as they relate to development, from its pathogenic role in FTLD-TDP and other TDP-43 proteinopathies. Finally, our adult induction of hTDP-43 strategy provides a mouse model that develops critical pathological features that are directly relevant for human TDP-43 proteinopathies

DNA-Based Excitonic AND Logic Gate

Scaffolded DNA Origami1 has been utilized as a ‘nanobreadboard,’ and decorated with nanoparticles (e.g. organic dyes, inorganic quantum dots and metallic nanoparticles) to engineer near-field optoelectronic devices. Successfully fabricated DNA origami-based excitonic devices include waveguides2-5, switches6, and logic gates7-9. Recently, an alternative approach to scaffolded DNA origami, termed ‘molecular canvases’, has been introduced that uses short single-stranded DNA motifs (~16-42 bps) to fabricate two- and three-dimensional nanostructures10-12. DNA motifs can be viewed as ‘molecular pixels/voxels’ and constituently selected to reconfigure the shape and size of the canvas. Similar to DNA origami, molecular canvas self-assembly is a one-step process that offers programmability afforded by DNA, however, without the aid of a long single-stranded scaffold. Molecular canvas structures can be utilized as nanobreadboards with programmable sub-diffraction resolution positioning of nanoparticles. Augmenting certain single-stranded DNA motifs with strand extensions, called ‘sticky-ends’ (~20-25 bps), enables nanoparticle attachment to occur via strand hybridization13 and allows dynamic device operations to be performed. Though the molecular canvas offers reconfigurability and modularity, it has yet to be utilized as a nanobreadboard for device applications. Constructing single-module devices utilizing molecular canvases is the first step towards developing self-ordering modular devices. In Figure 1(a), we present a 16 nm X 28 nm two-dimensional molecular canvas composed of 28 short DNA strands used as a nanobreadboard for the attachment of fluorescent dyes (FAM, TAMRA, and Cy5)11. Figure 1(b,c) demonstrates programmable reconfigurability of the structure shape and size as provided by the molecular canvas. AND logic operations and excitonic waveguides (e.g. photonic wires) are demonstrated through proximate positioning of four dyes onto nanobreadboards. The input and output dyes (named F and C, respectively) are attached directly onto nanobreadboards. Two intermediary dyes (T1 and T2) are attached to independent strands such that logic operations can be performed via strand hybridization. Attachment of all four dyes yields an energy waveguide resulting in photonic emission that is easily detected. As depicted in the truth table in Fig. 1(d), a ‘1’ truth value corresponds only to the attachment of both T1 and T2 in which the ON-OFF threshold is surpassed. Spectral data, such as that shown in Fig. 1(e), is obtained by exciting the input dye (F) with 450 nm wavelength photons and monitoring fluorescent emission over a range of wavelengths. Excitonic energy transfer from F to T1 & T2 and from T1 & T2 to C corresponds to spectral peaks at 579 nm and 661 nm, respectively. Logic operations are expressed by exciting F with 450 nm wavelength photons and examining fluorescent emission wavelengths from C at only 668 nm. Figure 1(f, g) demonstrates the attachment of T1 and T2 independently to define an ON-OFF threshold. Hence, we have validated the use of a molecular canvas as a nanobreadboard and demonstrated a near-field AND logic device that can be extended to fabricate near-field logic devices of greater complexity via a modular approach. Acknowledgment This project was supported in part by: (1) NSF Grant No. CCF 0855212, (2) NSF IDR No. 1014922, (3) NIH Grant No. P20 RR016454, (4) NIH Grant No. K25GM093233, (5) W.M. Keck Foundation Award, (6) DARPA Contract No. N66001-01-C-80345, and (6) Micron MSE PhD Fellowship. We also thank the students and staff within the Nanoscale Materials & Device Research Group (nano.boisestate.edu). References [1] Rothemund, P. W. K., Nature 2006, 440, 297-302. [2] Vyawahare, S.; et al. Nano Letters 2004, 4, 1035-1039. [3] Hannestad, J. K.; et al. Small 2011, 7, 3178-3185. [4] Dutta, P. K.; et al. Journal of the American Chemical Society 2011, 133, 11985-11993. [5] Stein, I. H.; et al. Journal of the American Chemical Society 2011, 133, 4193-4195. [6] Graugnard, E.; et al. Nano Letters 2012, 12, 2117-2122. [7] Okamoto, A.; et al. Journal of the American Chemical Society 2004, 126, 9458-9463. [8] Douglas, S. M.; et al. Science 2012, 335, 831-834. [9] Zhang, X. C.; et al. Journal of Computational and Theoretical Nanoscience 2012, 9, 1680-1685. [10] Lin, C. X.; et al. ChemPhysChem 2006, 7, 1641-1647. [11] Wei, B.; et al. Nature 2012, 485, 623. [12] Ke, Y. G.; et al. Science 2012, 338, 1177-1183. [13] Zhang, D. Y.; et al. Nature Chemistry 2011, 3, 103-13

An All-Optical Excitonic Switch Operated in the Liquid and Solid Phases

The excitonic circuitry found in photosynthetic organisms suggests an alternative to electronic circuits, but the assembly of optically active molecules to fabricate even simple excitonic devices has been hampered by the limited availability of suitable molecular scale assembly technologies. Here we have designed and operated a hybrid all-optical excitonic switch comprised of donor/ acceptor chromophores and photochromic nucleotide modulators assembled with nanometer scale precision using DNA nanotechnology. The all-optical excitonic switch was operated successfully in both liquid and solid phases, exhibiting high ON/OFF switching contrast with no apparent cyclic fatigue through nearly 200 cycles. These findings, combined with the switch’s small footprint and volume, estimated low energy requirement, and potential ability to switch at speeds in the 10s of picoseconds, establish a prospective pathway forward for all-optical excitonic circuits

Large Davydov Splitting and Strong Fluorescence Suppression: An Investigation of Exciton Delocalization in DNA-Templated Holliday Junction Dye Aggregates

Exciton delocalization in dye aggregate systems is a phenomenon that is revealed by spectral features, such as Davydov splitting, J- and H-aggregate behavior, and fluorescence suppression. Using DNA as an architectural template to assemble dye aggregates enables specific control of the aggregate size and dye type, proximal and precise positioning of the dyes within the aggregates, and a method for constructing large, modular two- and three-dimensional arrays. Here, we report on dye aggregates, organized via an immobile Holliday junction DNA template, that exhibit large Davydov splitting of the absorbance spectrum (125 nm, 397.5 meV), J- and H-aggregate behavior, and near-complete suppression of the fluorescence emission (∼97.6% suppression). Because of the unique optical properties of the aggregates, we have demonstrated that our dye aggregate system is a viable candidate as a sensitive absorbance and fluorescence optical reporter. DNA-templated aggregates exhibiting exciton delocalization may find application in optical detection and imaging, light-harvesting, photovoltaics, optical information processing, and quantum computing

Coherent Exciton Delocalization in a Two-State DNA-Templated Dye Aggregate System

Coherent exciton delocalization in dye aggregate systems gives rise to a variety of intriguing optical phenomena, including J- and H-aggregate behavior and Davydov splitting. Systems that exhibit coherent exciton delocalization at room temperature are of interest for the development of artificial light-harvesting devices, colorimetric detection schemes, and quantum computers. Here, we report on a simple dye system templated by DNA that exhibits tunable optical properties. At low salt and DNA concentrations, a DNA duplex with two internally functionalized Cy5 dyes (i.e., dimer) persists and displays predominantly J-aggregate behavior. Increasing the salt and/or DNA concentrations was found to promote coupling between two of the DNA duplexes via branch migration, thus forming a four-armed junction (i.e., tetramer) with H-aggregate behavior. This H-tetramer aggregate exhibits a surprisingly large Davydov splitting in its absorbance spectrum that produces a visible color change of the solution from cyan to violet and gives clear evidence of coherent exciton delocalization

Sex Differences in Pediatric Poisonings by Age Group: a Toxicology Investigators\u27 Consortium (ToxIC) Analysis (2010-2016)

OBJECTIVE: To review pediatric poisonings evaluated at the bedside by medical toxicologists and reported in the ToxIC registry, by sex and age group. METHODS: Pediatric poisoning cases age \u3c /=18 years, reported between January 2010 and December 2016, were reviewed. Descriptive statistics were used to describe study variables by age group and sex. RESULTS: A total of 12,699 cases were analyzed. There were 7517 females and 5182 males. Those \u3c 2 years old represented 12.5% of the study group (n = 1584), 17.2% were 2-6 years old (n = 2178), 8.6% were 7-12 years old (n = 1097), and 61.7% were 13-18 years old (n = 7840). The most common primary reasons for encounter were intentional pharmaceutical with 4900 females and 1836 males; intentional non-pharmaceutical with 952 females and 1213 males; unintentional pharmaceutical with 539 females and 644 males; and unintentional non-pharmaceutical with 435 females and 593 males. Overall, pharmaceuticals were the most commonly involved agents, including analgesics (20.9% of cases) and antidepressants (11% of cases): 27.8% of females and 10.7% of males were reportedly exposed to an analgesic.13.7% of females and 7.0% of males were reportedly exposed to an antidepressant. Among 1584 cases under 2 years, there were 747 females and 837 males; among 2178 cases aged 2-6 years, there were 954 females and 1224 males; among 1097 cases aged 7-12 years, there were 555 females and 542 males; and among 7840 cases aged 13-18 years, there were 5261 females and 2579 males. Death was reported in 0.7% of the cases: 20 females and 18 males. 6.1% of cases were managed with intubation: 421 females and 351 males. CONCLUSIONS: Sex-based characteristics of poisonings varied by age group among pediatric poisoning presentations reported to the ToxIC registry and further research is needed to determine implications for education and prevention efforts