Rational control of hydrothermal nanowire synthesis and its applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.Includes bibliographical references (p. 172-182).Hydrothermal nanowire synthesis is a rapidly emerging nanowire discipline that enables low temperature growth and batch process. It has a major impact on the development of novel energy conversion devices, high density electronics, and optical devices. However, detailed growth mechanism is still in early stage of its development. This thesis presents the fundamental understanding of controlled zinc oxide nanowire synthesis in a hydrothermal system based on thermodynamic / kinetic analysis of heterogeneous chemical reactions. Governing parameters of hydrothermal growth were evaluated with experimental growth rates and calculated solubility plots. Supersaturation was shown to be a key parameter for the hydrothermal nanowire synthesis. Morphology control of the nanowire synthesis was tested with various additional cations during synthesis. Changes in morphology and aspect ratio with different cations were explained by electrostatic competing ion model. Based on experimental results and complex ion charge distribution, the growth direction was biased via electrostatic competition from cation-complexes that adsorb to the crystal in a face-specific manner, thereby reducing zinc ion-complex adsorption and suppressing growth along that face. Dynamic control of nanowire synthesis was investigated under microfluidic environment with continuous flow. Microfluidic growth conditions were analyzed with the parametric experiments and finite element modeling. Nanowire growth under complex geometry was also evaluated. This rational control of hydrothermal nanowire synthesis was applied to fabricate high efficiency alternative current electroluminescent devices, in-situ fabricated light emitting diodes, photovoltaic devices, and field emission devices.by Jaebum Joo.Ph.D

Face-selective electrostatic control of hydrothermal zinc oxide nanowire synthesis

Rational control over the morphology and the functional properties of inorganic nanostructures has been a long-standing goal in the development of bottom-up device fabrication processes. We report that the geometry of hydrothermally grown zinc oxide nanowires can be tuned from platelets to needles, covering more than three orders of magnitude in aspect ratio (~0.1–100). We introduce a classical thermodynamics-based model to explain the underlying growth inhibition mechanism by means of the competitive and face-selective electrostatic adsorption of non-zinc complex ions at alkaline conditions. The performance of these nanowires rivals that of vapour-phase-grown nanostructures and their low-temperature synthesis (<60 °C) is favourable to the integration and in situ fabrication of complex and polymer-supported devices. We illustrate this capability by fabricating an all-inorganic light-emitting diode in a polymeric microfluidic manifold. Our findings indicate that electrostatic interactions in aqueous crystal growth may be systematically manipulated to synthesize nanostructures and devices with enhanced structural control.National Science Foundation (U.S.) (MIT Center for Bits and Atoms (NSF CCR0122419))Massachusetts Institute of Technology. Media LaboratoryKorea Foundation for Advanced StudiesSamsung Electronics Co. (research internship)Harvard University. Society of FellowsWallace H. Coulter Foundation (Early Career Award)Brain & Behavior Research Foundation (Young Investigator Award)National Science Foundation (U.S.)National Institutes of Health (U.S.) (Director’s New Innovator Award

Sustainable bioremediation technologies for algal toxins and their ecological significance

The emergence of algal toxins in water ecosystems poses a significant ecological and human health concern. These toxins, produced by various algal species, can lead to harmful algal blooms, and have far-reaching consequences on biodiversity, food chains, and water quality. This review explores the types and sources of algal toxins, their ecological impacts, and the associated human health risks. Additionally, the review delves into the potential of bioremediation strategies to mitigate the effects of algal toxins. It discusses the role of microorganisms, enzymes, and algal-bacterial interactions in toxin removal, along with engineering approaches such as advanced oxidation processes and adsorbent utilization. Microbes and enzymes have been studied for their environmentally friendly and biocompatible properties, which make them useful for controlling or removing harmful algae and their toxins. The challenges and limitations of bioremediation are examined, along with case studies highlighting successful toxin control efforts. Finally, the review outlines future prospects, emerging technologies, and the need for continued research to effectively address the complex issue of algal toxins and their ecological significance.This study was supported by the National Research Foundation of Korea (Grant Numbers 2020R1A5A1018052).Peer reviewe

Recent advances in point-of-care testing of COVID-19

Advances in microfluidic device miniaturization and system integration contribute to the development of portable, handheld, and smartphone-compatible devices. These advancements in diagnostics have the potential to revolutionize the approach to detect and respond to future pandemics. Accordingly, herein, recent advances in point-of-care testing (POCT) of coronavirus disease 2019 (COVID-19) using various microdevices, including lateral flow assay strips, vertical flow assay strips, microfluidic channels, and paper-based microfluidic devices, are reviewed. However, visual determination of the diagnostic results using only microdevices leads to many false-negative results due to the limited detection sensitivities of these devices. Several POCT systems comprising microdevices integrated with portable optical readers have been developed to address this issue. Since the outbreak of COVID-19, effective POCT strategies for COVID-19 based on optical detection methods have been established. They can be categorized into fluorescence, surface-enhanced Raman scattering, surface plasmon resonance spectroscopy, and wearable sensing. We introduced next-generation pandemic sensing methods incorporating artificial intelligence that can be used to meet global health needs in the future. Additionally, we have discussed appropriate responses of various testing devices to emerging infectious diseases and prospective preventive measures for the post-pandemic era. We believe that this review will be helpful for preparing for future infectious disease outbreaks. This review explores various point-of-care optical diagnostic systems combined with microdevices developed during the recent COVID-19 pandemic for clinical diagnostics

Highly Uniform Self-Assembly of Gold Nanoparticles by Butanol-Induced Dehydration and Its SERS Applications in SARS-CoV-2 Detection

Wereport the development of a reproducible and highly sensitivesurface-enhanced Raman scattering (SERS) substrate using a butanol-inducedself-assembly of gold nanoparticles (AuNPs) and its application asa rapid diagnostic platform for severe acute respiratory syndromecoronavirus 2 (SARS-CoV-2). The butanol-induced self-assembly processwas used to generate a uniform assembly of AuNPs, with multiple hotspots,to achieve high reproducibility. When an aqueous droplet containingAuNPs and target DNAs was dropped onto a butanol droplet, butanol-induceddehydration occurred, enriching the target DNAs around the AuNPs andincreasing the loading density of the DNAs on the AuNP surface. TheSERS substrate was evaluated by using Raman spectroscopy, which showedstrong electromagnetic enhancement of the Raman signals. The substratewas then tested for the detection of SARS-CoV-2 using SERS, and avery low limit of detection (LoD) of 3.1 x 10(-15) M was obtained. This provides sufficient sensitivity for the SARS-CoV-2screening assay, and the diagnostic time is significantly reducedas no thermocycling steps are required. This study demonstrates amethod for the butanol-induced self-assembly of AuNPs and its applicationas a highly sensitive and reproducible SERS substrate for the rapiddetection of SARS-CoV-2. The results suggest the potential of thisapproach for developing rapid diagnostic platforms for other biomoleculesand infectious diseases

Reproducible and Sensitive Plasmonic Sensing Platforms Based on Au-Nanoparticle-Internalized Nanodimpled Substrates

Electromagnetic enhancement effects through localized surface plasmon resonance considerably amplify the intensity of incident light when molecules are positioned in the vicinity of miniscule nanogaps. The aggregation of plasmonic nanoparticles synthesized using bottom-up methods has been extensively used to generate hot spots in solutions. These methods assist in obtaining non-periodic plasmonic signals, because the realization of uniform nanogaps through particle aggregation is difficult. Nanostructured substrates with gaps of 20-100 nm have also been fabricated using the top-down approach. However, the fabrication of smaller nanogap templates using these methods is difficult owing to high costs and low throughput. Therefore, a nanodimple array internalized with AuNPs is developed in this study to mitigate the challenges encountered in the bottom-up and top-down approaches. Precise nanogaps are generated by regularly internalizing AuNPs in the cavities of nanodimples through DNA hybridization. Simulations of the electric field distribution indicate that the incorporation of 80 nm-sized AuNPs into a curved nanodimpled Au substrate generate high-density volumetric hot spots within a detection volume, and result in a high plasmonic enhancement factor of 8.25 x 10(7). The tremendous potential of the proposed plasmonic platform as an SERS-based biomedical diagnostic device is also verified

Raman Thermometry Nanopipettes in Cancer Photothermal Therapy

Raman thermometry based on surface-enhanced Raman scattering has been developed using nanopipettes in cancer cell photothermal therapy (PTT). Gold nanorods (AuNRs) are robustly epoxied on glass pipettes with a high surface coverage of similar to 95% and less than 10 nm-wide nanogaps for intracellular thermometry and photothermal cancer therapy. The temperature changes could be estimated from the N equivalent to C band shifts of 4-fluorophenyl isocyanide (FPNC)-adsorbed AuNRs on the Raman thermometry nanopipette (RTN) surfaces. An intracellular temperature change of similar to 2.7 degrees C produced by altering the [Ca2+] in A431 cells was detected using the RTN in vitro, as checked from fura-2 acetoxymethyl ester (fura-2 AM) fluorescence images. For in vivo experiments, local temperature rises of similar to 19.2 degrees C were observed in the mouse skin, whereas infrared camera images could not tract due to spatial resolution. In addition, a tumor growth suppression was observed in the PTT processes after an administration of the three AuNR-coated nanopipettes combined with a 671 nm laser irradiation for 5 min in 30 days. These results demonstrate not only the localized temperature sensing ability of FPNC-tagged AuNR nanopipettes in cell biology but also anti-cancer effects in photothermal cancer therapy.N

Coumarin-lipoic acid conjugates on silver nanoparticle-supported nanopipettes for in situ dual-mode monitoring of intracellular Cu(II) and potential chemodynamic therapy applications

Intracellular Cu(II) in the human body is essential to many physiological functions, and its disruption is connected to several diseases. Synthetic coumarin-lipoic acid (Cou-LA) conjugate-functionalized silver-nanoparticles decorated on nanopipettes (CSNs) were fabricated herein for the determination of intracellular Cu(II) via in situ dual Raman/fluorescence spectroscopy. The CSNs selectively sensed Cu(II) over other metal ions to induce enhanced Raman intensities and fluorescence quenching. The determination of Cu(II) in single HeLa cells was achieved in accordance with changes in the ratio of Raman intensities at 500 and 597 cm(-1) and fluorescence at 469 nm, which was ascribed to the capturing of Cu(II) by the CSNs. The Raman signals exhibited a good linear relationship with Cu(II) concentration from 10 to 75 mu M with R-2 = 0.956. The calibration curve indicated a local Cu(II) concentration of similar to 42.6 +/- 8.6 mu M in a single HeLa cell after pretreatment with 100 mu M Cu(II) for 1 h. CouLA exhibited negligible cytotoxicity in both normoxic and hypoxic HeLa cells. However, a significant reduction in cell viability occurred with the Cu(II)-Cou-LA complex. This cytotoxicity was attributed to the generation of reactive oxygen species via a Cu-catalyzed Fenton-like process in tumor microenvironments and was found to be applicable to chemodynamic therapy (CDT). The system fabricated in this study represents a novel strategy for intracellular dual-mode Cu(II) detection and CDT applications in cancer research.N