Rapid and Direct Perfluorooctanoic Acid Sensing with Selective Ionomer Coatings on Screen-Printed Electrodes under Environmentally Relevant Concentrations.

Per- and polyfluoroalkyl substances (PFASs) pose a significant health threat to humans at trace levels. Because of its ubiquity across the globe, there have been intense efforts to rapidly quantify PFASs in the environment while also mitigating their release. This work reports an electrochemical sensor with a selective perfluorinated anion exchange ionomer (PFAEI) coating for direct sensing of perfluorooctanoic acid (PFOA)-a type of PFAS. Notably, the sensor operates without the need of redox probes and has a limit of detection around 6.51 ± 0.2 ppb (15 nM) in buffered deionized water and drinking water. By testing the sensor with different ionomer electrode coatings, it was inferred that the PFAEI favors PFOA anions over other competing anions in solution through a combination of electrostatic and van der Waal interactions.

Multimodal Label-Free Monitoring of Adipogenic Stem Cell Differentiation Using Endogenous Optical Biomarkers.

Stem cell-based therapies carry significant promise for treating human diseases. However, clinical translation of stem cell transplants for effective treatment requires precise non-destructive evaluation of the purity of stem cells with high sensitivity (<0.001% of the number of cells). Here, a novel methodology using hyperspectral imaging (HSI) combined with spectral angle mapping-based machine learning analysis is reported to distinguish differentiating human adipose-derived stem cells (hASCs) from control stem cells. The spectral signature of adipogenesis generated by the HSI method enables identifying differentiated cells at single-cell resolution. The label-free HSI method is compared with the standard techniques such as Oil Red O staining, fluorescence microscopy, and qPCR that are routinely used to evaluate adipogenic differentiation of hASCs. HSI is successfully used to assess the abundance of adipocytes derived from transplanted cells in a transgenic mice model. Further, Raman microscopy and multiphoton-based metabolic imaging is performed to provide complementary information for the functional imaging of the hASCs. Finally, the HSI method is validated using matrix-assisted laser desorption/ionization-mass spectrometry imaging of the stem cells. The study presented here demonstrates that multimodal imaging methods enable label-free identification of stem cell differentiation with high spatial and chemical resolution.

Printed Electrode for Measuring Phosphate in Environmental Water.

Phosphate is a major nonpoint source pollutant in both the Louisiana local streams as well as in the Gulf of Mexico coastal waters. Phosphates from agricultural run-off have contributed to the eutrophication of global surface waters. Phosphate environmental dissemination and eutrophication problems are not yet well understood. Thus, this study aimed to monitor phosphate in the local watershed to help identify potential hot spots in the local community (Mississippi River, Louisiana) that may contribute to nutrient loading downstream (in the Gulf of Mexico). An electrochemical method using a physical vapor deposited cobalt microelectrode was utilized for phosphate detection using cyclic voltammetry and amperometry. The testing results were utilized to evaluate the phosphate distribution in river water and characterize the performance of the microsensor. Various characterizations, including the limit of detection, sensitivity, and reliability, were conducted by measuring the effect of interferences, including dissolved oxygen, pH, and common ions. The electrochemical sensor performance was validated by comparing the results with the standard colorimetry phosphate detection method. X-ray photoelectron spectroscopy (XPS) measurements were performed to understand the phosphate sensing mechanism on the cobalt electrode. This proof-of-concept sensor chip could be utilized for on-field monitoring using a portable, hand-held potentiostat.

Concurrent atom transfer radical polymerization and nitroxide radical coupling relay polymerization.

Simultaneous atom transfer radical polymerization (ATRP) and nitroxide radical coupling (NRC) seems impossible because the presence of nitroxide radicals would quench the radical polymerization immediately. However, by combining a nitroxide radical and an ATRP active halogen, a halogen group that can initiate one polymer chain by ATRP, into one functional reagent and adding this functional reagent to an ATRP system, concurrent ATRP-NRC relay polymerization was carried out successfully under proper reaction conditions. The key to success was the conjugate radical trapping and re-initiation took place repeatedly, resulting in polymers with inserted alkoxyamine linkages. This novel relay polymerization method provides numerous possibilities for macromolecular architecture/functionality tailoring by using of different functional reagents.

Characterization of fibrillar collagen isoforms in infarcted mouse hearts using second harmonic generation imaging.

We utilized collagen specific second harmonic generation (SHG) signatures coupled with correlative immunofluorescence imaging techniques to characterize collagen structural isoforms (type I and type III) in a murine model of myocardial infarction (MI). Tissue samples were imaged over a four week period using SHG, transmitted light microscopy and immunofluorescence imaging using fluorescently-labeled collagen antibodies. The post-mortem cardiac tissue imaging using SHG demonstrated a progressive increase in collagen deposition in the left ventricle (LV) post-MI. We were able to monitor structural morphology and LV remodeling parameters in terms of extent of LV dilation, stiffness and fiber dimensions in the infarcted myocardium.

Dark-field hyperspectral imaging for label free detection of nano-bio-materials.

Nanomaterials are playing an increasingly important role in cancer diagnosis and treatment. Nanoparticle (NP)-based technologies have been utilized for targeted drug delivery during chemotherapies, photodynamic therapy, and immunotherapy. Another active area of research is the toxicity studies of these nanomaterials to understand the cellular uptake and transport of these materials in cells, tissues, and environment. Traditional techniques such as transmission electron microscopy, and mass spectrometry to analyze NP-based cellular transport or toxicity effect are expensive, require extensive sample preparation, and are low-throughput. Dark-field hyperspectral imaging (DF-HSI), an integration of spectroscopy and microscopy/imaging, provides the ability to investigate cellular transport of these NPs and to quantify the distribution of them within bio-materials. DF-HSI also offers versatility in non-invasively monitoring microorganisms, single cell, and proteins. DF-HSI is a low-cost, label-free technique that is minimally invasive and is a viable choice for obtaining high-throughput quantitative molecular analyses. Multimodal imaging modalities such as Fourier transform infrared and Raman spectroscopy are also being integrated with HSI systems to enable chemical imaging of the samples. HSI technology is being applied in surgeries to obtain molecular information about the tissues in real-time. This article provides brief overview of fundamental principles of DF-HSI and its application for nanomaterials, protein-detection, single-cell analysis, microbiology, surgical procedures along with technical challenges and future integrative approach with other imaging and measurement modalities. This article is categorized under: Diagnostic Tools > in vitro Nanoparticle-Based Sensing Diagnostic Tools > in vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

Ultrasensitive Three-Dimensional Orientation Imaging of Single Molecules on Plasmonic Nanohole Arrays Using Second Harmonic Generation.

Recently, fluorescence-based super-resolution techniques such as stimulated emission depletion (STED) and stochastic optical reconstruction microscopy (STORM) have been developed to achieve near molecular-scale resolution. However, such a super-resolution technique for nonlinear label-free microscopy based on second harmonic generation (SHG) is lacking. Since SHG is label-free and does not involve real-energy level transitions, fluorescence-based super-resolution techniques such as STED cannot be applied to improve the resolution. In addition, due to the coherent and non-isotropic emission nature of SHG, single-molecule localization techniques based on isotropic emission of fluorescent molecule such as STORM will not be appropriate. Single molecule SHG microscopy is largely hindered due to the very weak nonlinear optical scattering cross sections of SHG scattering processes. Thus, enhancing SHG using plasmonic nanostructures and nanoantennas has recently gained much attention owing to the potential of various nanoscale geometries to tightly confine electromagnetic fields into small volumes. This confinement provides substantial enhancement of electromagnetic field in nanoscale regions of interest, which can significantly boost the nonlinear signal produced by molecules located in the plasmonic hotspots. However, to date, plasmon-enhanced SHG has been primarily applied for the measurement of bulk properties of the materials/molecules, and single molecule SHG imaging along with its orientation information has not been realized yet. Herein, we achieved simultaneous visualization and three-dimensional (3D) orientation imaging of individual rhodamine 6G (R6G) molecules in the presence of plasmonic silver nanohole arrays. SHG and two-photon fluorescence microscopy experiments together with finite-difference time-domain (FDTD) simulations revealed a ∼106-fold nonlinear enhancement factor at the hot spots on the plasmonic silver nanohole substrate, enabling detection of single molecules using SHG. The position and 3D orientation of R6G molecules were determined using the template matching algorithm by comparing the experimental data with the calculated dipole emission images. These findings could enable SHG-based single molecule detection and orientation imaging of molecules which could lead to a wide range of applications from nanophotonics to super-resolution SHG imaging of biological cells and tissues.

The Myth of Visible Light Photocatalysis Using Lanthanide Upconversion Materials.

Upconversion luminescence is a nonlinear optical process achieved by certain engineered materials, which allows conversion of low energy photons into higher energy photons. Of particular relevance to environmental technology, lanthanide-based upconversion phosphors have appeared in dozens of publications as a tool for achieving visible light activation of wide-band gap semiconductor photocatalysts, such as TiO2, for degradation of water contaminants. Supposedly, the phosphor particles act to convert sub-band gap energy photons (e.g., solar visible light) into higher energy ultraviolet photons, thus driving catalytic aqueous contaminant degradation. Herein, however, we reexamined the photophysical properties of the popular visible-to-UV converters Y2SiO5:Pr3+ and Y3Al5O12:Er3+, and found that their efficiencies are not nearly high enough to induce catalytic degradations under the reported excitation conditions. Furthermore, our experiments indicate that the false narrative of visible-to-UV upconversion-sensitized photocatalysis likely arose due to coincidental enhancements of dye degradation via direct electron injection that occur in the presence of dielectric-semiconductor (phosphor-catalyst) interfaces. These effects were unrelated to upconversion and only occurred for dye solutions illuminated within the chromophore absorption bands. We conclude that upconversion using Pr3+ or Er3+-activated systems is not a technologically appealing mechanism for visible light photocatalysis, and provide experimental guidelines for avoiding future misinterpretation of these phenomena.

Bacteria Inactivation via X-ray-Induced UVC Radioluminescence: Toward in Situ Biofouling Prevention in Membrane Modules.

Germicidal UVC radiation is a highly effective, chemical-free tool for bacteria inactivation, but its application is limited to reactors and open areas that can accommodate lamps/LEDs and wiring. A relevant example of problematic bacterial colonization within UV-inaccessible confines where chemical techniques have found only limited success is biofouling of feed channels in high-pressure membrane elements for water treatment. Herein we demonstrate a unique method of generating UV internally using embedded radioluminescent (RL) particles excited by an external X-ray source. We further show that the magnitude of the emitted UV intensity and required X-ray dose rates are likely within effective and practical ranges for future application to antibiofouling technology. Assessment of three Pr3+-activated RL phosphor candidates revealed LaPO4:Pr3+ to have the most favorable luminescence properties, achieving over 2-log inactivation of E. coli in a thin water film with a 74 Gy dose of 150 kVp X-rays. The effect of UVC RL resulted in a doubling of inactivation rates over X-ray irradiation alone. Further efforts targeting membrane applications, which included X-ray penetration modeling, RO membrane UVC tolerance, and economic analysis, suggested that UVC RL shows promise for application to bacteria control in seawater RO.

Nanoscale 3D tracking with conjugated polymer nanoparticles.

Small ( approximately 15 nm diameter), highly fluorescent conjugated polymer nanoparticles were evaluated for nanoscale 2D and 3D tracking applications. Nanoparticles composed of conjugated polymers possess high absorption cross sections, high radiative rates, and low or moderate aggregation quenching, resulting in extraordinarily high fluorescent brightness. The bright fluorescence ( approximately 200 000 photons detected per particle per 20 ms exposure) yields a theoretical particle tracking uncertainty of less than 1 nm. A lateral tracking uncertainty of 1-2 nm was determined from analysis of trajectories of fixed and freely diffusing particles. Axial (Z) position information for 3D particle tracking was obtained by defocused imaging. Nanoscale tracking of single particles in fixed cells was demonstrated, and a range of complex behaviors, possibly due to binding/unbinding dynamics, were observed.