Open clusters are groups of stars with the same age, chemistry, and velocity. These characteristics make open clusters powerful tools for tracing the dynamic and chemical evolution of our home galaxy, the Milky Way. The goal of the Open Cluster Chemical Abundance and Mapping (OCCAM) survey is to identify and analyze a large sample of open clusters with a wide range of chemical abundances. To do this, it utilizes the infrared spectra provided by the Sloan Digital Sky Survey’s (SDSS) APOGEE spectrograph and the kinematic data from the Gaia Space Telescope to form a large survey of open clusters with uniformly derived chemical abundances (e.g., C, Mg, Si, Al, Fe, Ni). Here, we present the results from the OCCAM analysis of the latest SDSS/APOGEE data release. This dataset of 153 different open clusters, including 2061 individual stars, is used to investigate the variation of the Milky Way’s chemistry for multiple different abundance groups. In addition to this dataset, we also present the current status of new optical observations that will allow us to expand the wavelength coverage for each star and trace more elements. These new observations enable us to accurately decipher the chemical fingerprints from ancient supernovae (e.g., Y, Ba, Ce, Nd, Eu) and expand our analysis.

Characterizing Galactic sub-structures is crucial to understanding the assembly history and evolution of the Milky Way. To accomplish this, we need to identify and analyze the accreted sub-structures. With ESA Gaia and SDSS-IV/APOGEE, studies have been done to analyze the kinematics and chemical abundances, respectively. However, one challenge that still remains is deriving reliable ages for these sub-structures. We utilize the new relationship between the carbon to nitrogen ratio and stellar age derived by the OCCAM team, which has recently been extended to the metal-poor regime, to probe stars within the sub-structures in the metallicity range -1.2 ≤ [Fe/H] ≤ +0.3 dex. This allows us to determine the ages of a greater number of stars within these sub-structures, which paints a more coherent picture of the original galaxies that have been disrupted to form the Milky Way’s halo. Using the sample of halo sub-structures in Horta et al. (2023), we apply the newly extended calibration to determine ages of stars within these sub-structures and compare them to previous age estimates.

Graphene quantum dots (GQDs) is an emerging nanocarbon platform that is now actively utilized for therapeutic applications. Their increasing popularity arises due to relatively high biocompatibility, water solubility, optical properties enabling multi-color fluorescence imaging and the ease of functionalization with a variety of therapeutic agents. Such properties pave the way for a variety of imaging and sensing applications. Herein, we are utilizing rGQDs (reduced graphene quantum dots) synthesized top down from reduced graphene oxide for dopamine sensing. Detecting dopamine can provide insights about the neural health and the activity of neurotransmitters in the brain. However, due to the presence of dopamine receptors throughout our body, this will also help assess other vital functions including secretion of pituitary hormones [1], gut motility [2], immunomodulatory effects in inflammation-related diseases [3][4] and cardiovascular effects (dopamine can act as both autocrine or paracrine compound in the mammalian heart) [5]. In our work rGQD near-infrared (NIR) fluorescence appears to react proportionally to dopamine concentration within the range of 1000ng/ml – 1ng/ml as assessed with NIR fluorescence imaging of dopamine/rGQD interactions on cotton discs and biocompatible gels as well as with NIR fluorescence spectroscopy. This rapid NIR response and the capability of dopamine sensing in gel matrix suggests the potential for detection of blood-relevant dopamine concentrations in vivo, which will be explored with GQD-based implantable sensors. In addition to the development of a novel non-invasive dopamine sensing mechanism, the present study will aid in gaining valuable insight into GQD properties in vivo and their potential for in vivo analyte detection.
References:
1. Nira Ben-Jonathan, Robert Hnasko, Dopamine as a Prolactin (PRL) Inhibitor, Endocrine Reviews, Volume 22, Issue 6, 1 December 2001, Pages 724–763, https://doi.org/10.1210/edrv.22.6.0451
2. Graeme Eisenhofer, Anders Åneman, Peter Friberg, Douglas Hooper, Lars Fåndriks, Hans Lonroth, Béla Hunyady, Eva Mezey, Substantial Production of Dopamine in the Human Gastrointestinal Tract, The Journal of Clinical Endocrinology & Metabolism, Volume 82, Issue 11, 1 November 1997, Pages 3864–3871, https://doi.org/10.1210/jcem.82.11.4339
3. Channer B, Matt SM, Nickoloff-Bybel EA, Pappa V, Agarwal Y, Wickman J, Gaskill PJ. Dopamine, Immunity, and Disease. Pharmacol Rev. 2023 Jan;75(1):62-158. doi: 10.1124/pharmrev.122.000618. Epub 2022 Dec 8. PMID: 36757901; PMCID: PMC9832385.
4. Feng YF and Lu Y (2021) Immunomodulatory Effects of Dopamine in Inflammatory Diseases. Front. Immunol. 12:663102. doi: 10.3389/fimmu.2021.663102
5. Neumann J, Hofmann B, Dhein S, Gergs U. Role of Dopamine in the Heart in Health and Disease. Int J Mol Sci. 2023 Mar 6;24(5):5042. doi: 10.3390/ijms24055042. PMID: 36902474; PMCID: PMC10003060.

Graphene quantum dots (GQDs) have emerged as a forerunner of carbon nano-biotechnology due to their multifunctional delivery and imaging capabilities as they exhibit fluorescence in the visible and near-infrared, high biocompatibility, and water solubility. These properties put GQDs forward as a compelling drug delivery platform that has already been utilized in a variety of applications including the delivery of chemotherapeutics, antibiotics as well as siRNA and CRISPR-based gene therapy. However, cellular entry pathways of this nanomaterial still remain largely undefined. In a number of studies describing GQD cellular internalization different and, often, conflicting results have been presented due to surveying only few endocytosis inhibitors and disregarding their potential off-target pathways. Understanding the cell internalization routes of GQDs is crucial while delivering drugs in different types of cell lines. Herein, we performed a holistic approach to cell uptake studies on GQDs of different charges by the comparative study of their preferred endocytosis paths in non-cancerous (HEK-293) and cancerous (HeLa) cell lines. The concentration and cell viability of GQDs were determined by MTT assays, while their endocytosis paths were investigated through confocal fluorescence microscopy on cells treated for up to 24 hours. The potential for GQD interactions with the cell membrane was also examined via zeta (ζ) potential measurements. Our findings provide insights into the internalization mechanisms of the GQDs into cell membranes of healthy and cancer cells. The optimization of these mechanisms can serve for the enhancement of a variety of novel GQD applications in biomedicine including therapeutic delivery, disease detection through sensing as well as diagnostic imaging.

Due to high tissue penetration depth and low autofluorescence backgrounds, near-infrared (NIR) fluorescence imaging has recently become an advantageous diagnostic technique used in a variety of fields. However, most of the NIR fluorophores do not have therapeutic delivery capabilities, exhibit low photostabilities, and raise toxicity concerns. To address these issues, we developed and tested five types of biocompatible graphene quantum dots (GQDs) exhibiting spectrally-separated fluorescence in the NIR range of 928–1053 nm with NIR excitation. Their optical properties in the NIR are attributed to either rare-earth metal dopants (Ho-NGQDs, Yb-NGQDs, Nd-NGQDs) or defect-states (nitrogen doped GQDS (NGQDs), reduced graphene oxides) as verified by Hartree-Fock calculations. Moderate up to 1.34% quantum yields of these GQDs are well-compensated by their remarkable >4 h photostability. At the biocompatible concentrations of up to 0.5–2 mg ml−1 GQDs successfully internalize into HEK-293 cells and enable in vitro imaging in the visible and NIR. Tested all together in HEK-293 cells five GQD types enable simultaneous multiplex imaging in the NIR-I and NIR-II shown for the first time in this work for GQD platforms. Substantial photostability, spectrally-separated NIR emission, and high biocompatibility of five GQD types developed here suggest their promising potential in multianalyte testing and multiwavelength bioimaging of combination therapies.