Random packings of stiff rods are self-supporting mechanical structures stabilized by long-range interactions induced by contacts. To understand the geometrical and topological complexity of the packings, we first deploy X-ray computerized tomography to unveil the structure of the packing. This allows us to directly visualize the spatial variations in density, orientational order, and the entanglement, a mesoscopic field that we define in terms of a local average crossing number, a measure of the topological complexity of the packing. We find that increasing the aspect ratio of the constituent rods in a packing leads to a proliferation of regions of strong entanglement that eventually percolate through the system and correlated with a sharp transition in the mechanical stability of the packing. To corroborate our experimental findings, we use numerical simulations of contacting elastic rods and characterize their stability to static and dynamic loadings. Our experiments and computations lead us to an entanglement phase diagram which we also populate using published experimental data from pneumatically tangled filaments, worm blobs, and bird nests along with additional numerical simulations using these datasets. Together, these show the regimes associated with mechanically stable entanglement as a function of the statistics of the packings and loading, with lessons for a range of systems from reconfigurable architectures and textiles to active morphable filamentous assemblies.

Journal Article From Archeology to the Malaria Parasite, the Exciting Quests of Microscopy Get access David C Bell, David C Bell Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA Corresponding author: dcb@seas.harvard.edu Search for other works by this author on: Oxford Academic Google Scholar Hao-Yu Greg Lin, Hao-Yu Greg Lin Center for Nanoscale Systems, Harvard University, Cambridge, MA, USA Search for other works by this author on: Oxford Academic Google Scholar Austin Akey, Austin Akey Center for Nanoscale Systems, Harvard University, Cambridge, MA, USA Search for other works by this author on: Oxford Academic Google Scholar Stephan Kraemer, Stephan Kraemer Center for Nanoscale Systems, Harvard University, Cambridge, MA, USA Search for other works by this author on: Oxford Academic Google Scholar Jeffrey T Borenstein, Jeffrey T Borenstein Draper Laboratory, Cambridge, MA, USAResearch groups thereof Search for other works by this author on: Oxford Academic Google Scholar Jeffrey D Dvorin, Jeffrey D Dvorin Boston Children’s Hospital, Boston, MA, USAResearch groups thereof Search for other works by this author on: Oxford Academic Google Scholar Angela Chang Angela Chang Harvard Art Museums, Harvard University, Cambridge, MA, USAResearch groups thereof Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 86–87, https://doi.org/10.1093/micmic/ozad067.035 Published: 22 July 2023

Background Engineered nanomaterials (ENMs) have already made their way into myriad applications and products across multiple industries. However, the potential health risks of exposure to ENMs remain poorly understood. This is particularly true for the emerging class of ENMs know as 2-dimensional nanomaterials (2DNMs), with a thickness of one or a few layers of atoms arranged in a planar structure. Methods The present study assesses the biotransformations and in vitro cytotoxicity in the gastrointestinal tract of 11 2DNMs, namely graphene, graphene oxide (GO), partially reduced graphene oxide (prGO), reduced graphene oxide (rGO), hexagonal boron nitride (h-BN), molybdenum disulphide (MoS2), and tungsten disulphide (WS2). The evaluated pristine materials were either readily dispersed in water or dispersed with the use of a surfactant (Na-cholate or PF108). Materials dispersed in a fasting food model (FFM, water) were subjected to simulated 3-phase (oral, gastric, and small intestinal) digestion to replicate the biotransformations that would occur in the GIT after ingestion. A triculture model of small intestinal epithelium was used to assess the effects of the digested products (digestas) on epithelial layer integrity, cytotoxicity, viability, oxidative stress, and initiation of apoptosis. Results Physicochemical characterization of the 2DNMs in FFM dispersions and in small intestinal digestas revealed significant agglomeration by all materials during digestion, most prominently by graphene, which was likely caused by interactions with digestive proteins. Also, MoS2 had dissolved by ~75% by the end of simulated digestion. Other than a low but statistically significant increase in cytotoxicity observed with all inorganic materials and graphene dispersed in PF108, no adverse effects were observed in the exposed tricultures. Conclusions Our results suggest that occasional ingestion of small quantities of 2DNMs may not be highly cytotoxic in a physiologically relevant in vitro model of the intestinal epithelium. Still, their inflammatory or genotoxic potential after short- or long-term ingestion remains unclear and needs to be studied in future in vitro and in vivo studies. These would include studies of effects on co-ingested nutrient digestion and absorption, which have been documented for numerous ingested ENMs, as well as effects on the gut microbiome, which can have important health implications.

Crystal engineering is a practical approach for tailoring material properties. This approach has been widely studied for modulating optical and electrical properties of semiconductors. However, the properties of organic molecular crystals are difficult to control following a similar engineering route. In this Letter, we demonstrate that engineered crystals of Alq3 and Ir(ppy)3 complexes, which are commonly used in organic light-emitting technologies, possess intriguing functional properties. Specifically, these structures not only process efficient low-energy induced triplet excitation directly from the ground state of Alq3 but also can show strong emission at the Alq3 triplet energy level at room temperatures. We associate these phenomena with local deformations of the host matrix around the guest molecules, which in turn lead to a stronger host-guest triplet-triplet coupling and spin-orbital mixing.

The unique structure and mechanical properties of syringe-injectable mesh electronics have enabled seamless tissue integration and stable chronic recording of the activities of the same neurons on a year scale. Here, we report studies of a series of structural and mechanical mesh electronics design variations that allow injection using needles at least 4-fold smaller than those previously reported to minimize the footprint during injection of the electronics in soft matter and tissue. Characterization of new ultraflexible two-dimensional (2D) and one-dimensional (1D) probes has demonstrated reproducible injection of the newly developed mesh electronics designs via needles as small as 100 μm in inner diameter (ID) with reduced injection volumes. In vitro hydrogel and in vivo mouse brain studies have shown that ultraflexible 2D and 1D probes maintain their structural integrity and conformation post-injection after being transferred through the reduced diameter needles. In addition, analysis of the variation of the post-injection mesh cross sections suggests a smaller degree of tissue deformation and relaxation with decreasing needle diameters. The capability to implement rational design for mesh electronic probes that can be delivered via much smaller diameter needles should open up new opportunities for integration of electronics with tissue and soft matter in fundamental and translational studies.

Chip-scale chemical detections were demonstrated by mid-Infrared (mid-IR) integrated optics made by aluminum nitride (AlN) waveguides on flexible borosilicate templates. The AlN film was deposited using sputtering at room temperature, and it exhibited a broad infrared transmittance up to λ = 9 µm. The AlN waveguide profile was created by microelectronic fabrication processes. The sensor is bendable because it has a thickness less than 30 µm that significantly decreases the strain. A bright fundamental mode was obtained at λ = 2.50–2.65 µm without mode distortion or scattering observed. By spectrum scanning at the -OH absorption band, the waveguide sensor was able to identify different hydroxyl compounds, such as water, methanol, and ethanol, and the concentrations of their mixtures. Real-time methanol monitoring was achieved by reading the intensity change of the waveguide mode at λ = 2.65 μm, which overlap with the stretch absorption of the hydroxyl bond. Due to the advantages of mechanical flexibility and broad mid-IR transparency, the AlN chemical sensor will enable microphotonic devices for wearables and remote biomedical and environmental detection.

A mid-infrared (mid-IR) sensor chip was demonstrated for volatile organic compound (VOC) detection. The sensor consisted of As2Se3 optical waveguides built by microelectronic fabrication processes. The VOC sensing performance was characterized by measuring acetone and ethanol vapors at their characteristic C-H absorption from λ = 3.40 to 3.50 μm. Continuous VOC detection with <5 s response time was achieved by measuring the intensity attenuation of the waveguide mode. The miniaturized noninvasive VOC sensor can be applied to breath analysis and environmental toxin monitoring.

Mid-Infrared photonic circuits using epitaxial barium titanate thin films are demonstrated through complementary metal–oxide–semiconductor process. The c-axis oriented BTO films are transparent between λ=2.5-7 um and a sharp fundamental mode is observed.

Chip-scale chemical detection is demonstrated by using mid-Infrared (mid-IR) photonic circuits consisting of amorphous silicon (a-Si) waveguides on an epitaxial barium titanate (BaTiO 3 , BTO) thin film. The highly c-axis oriented BTO film was grown by the pulsed laser deposition (PLD) method and it exhibits a broad transparent window from λ = 2.5 μm up to 7 μm. The waveguide structure was fabricated by the complementary metal–oxide–semiconductor (CMOS) process and a sharp fundamental waveguide mode has been observed. By scanning the spectrum within the characteristic absorption regime, our mid-IR waveguide successfully perform label-free monitoring of various organic solvents. The real-time heptane detection is accomplished by measuring the intensity attenuation at λ = 3.0–3.2 μm, which is associated with -CH absorption. While for methanol detection, we track the -OH absorption at λ = 2.8–2.9 μm. Our monolithic Si-on-BTO waveguides establish a new sensor platform that enables integrated photonic device for label-free chemical detection.

The surface electronic structures of catalysts need to be carefully engineered in CO2 reduction reaction (CO2RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lowers the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO2RR reaction intermediates, which may significantly improve the catalytic activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO2RR performances. A comparative investigation on air-annealed Ag (Air-Ag) catalyst with or without the post-treatment of H-2 thermal annealing (H-2-Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O-Ag delta+) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H-2 in CO2RR electrolysis. As a result, though the maximal CO Faradaic efficiency of H-2-Ag is at similar to 30%, the Air-Ag catalyst presented a high CO selectivity of more than 90% under a current density of similar to 21 mA/cm(2).

Chip-scale chemical sensors were demonstrated using optical waveguides consisting of amorphous silicon (a-Si) and aluminum nitride (AlN). A mid-infrared (mid-IR) transparent AlN thin film was prepared by room-temperature sputtering, which exhibited high Al/N elemental homogeneity. The Si-on-AlN waveguides were fabricated by a complementary metal-oxide-semiconductor process. A sharp fundamental mode and low optical loss of 2.21 dB/cm were obtained. Label-free chemical identification and real-time monitoring were performed by scanning the mode spectrum while the waveguide was exposed to various chemicals. Continuous tracing of heptane and methanol was accomplished by measuring the waveguide intensity attenuation at λ = 2.5-3.0 μm, which included the characteristic -CH and -OH absorptions. The monolithically integrated Si-on-AlN waveguides established a new sensor platform that can operate over a broad mid-IR regime, thus enabling photonic chips for label-free chemical detection.

We report here the synthesis of graphene quantum dots with tunable size, surface chemistry, and fluorescence properties. In the size regime 15-35 nm, these quantum dots maintain strong visible light fluorescence (mean quantum yield of 0.64) and a high two-photon absorption (TPA) cross section (6500 Göppert-Mayer units). Furthermore, through noncovalent tailoring of the chemistry of these quantum dots, we obtain water-stable quantum dots. For example, quantum dots with lysine groups bind strongly to DNA in solution and inhibit polymerase-based DNA strand synthesis. Finally, by virtue of their mesoscopic size, the quantum dots exhibit good cell permeability into living epithelial cells, but they do not enter the cell nucleus.

A chip-scale and label-free glucose sensor is developed by utilizing mid-IR silicon nitride waveguides. For a dry glucose covered waveguide, strong intensity attenuation is found at λ > 2.73 μm due to the OH stretches absorption. Using this characteristic spectrum, a glucose detection limit less than 0.5 ng is experimentally demonstrated.

We experimentally demonstrate a sophisticated mid-IR microphotonics platform adopting engineered Si-rich and low-stress silicon nitride (SiNx) thin films where an extensive infrared transparency up to λ = 8.5 μm is achieved. Furthermore, because of the designed low-stress property, the SiNx deposition is able to reach a thickness > 2 μm that significantly reduces mid-IR waveguide loss to less than 0.2 dB/cm. We show directional couplers functioning over a broad infrared spectrum, thus enabling monolithic mid-IR multiplexing schemes for integrated linear and nonlinear photonics leading to sophisticated label-free sensing technologies.

A mid-infrared sensor for label-free on-chip chemical detection was developed using an engineered nanofluidic channel consisting of a Si-liquid-Si slot-structure. A sensitivity with 75 times improvement was achieved compared to conventional evanescent-wave sensing. Mid-infrared spectroscopy is a detection technique commonly used for identifying biochemicals and tracing of toxic molecules, and is free of target labels and sensor surface functionalization. The use of mid-IR spectrum circumvents the need for labeling the sample, because the characteristic wavelength of absorption by many functional groups present in chemical or biological molecules falls within this region of the spectrum. Herein, we present a new chip-scale optofluidic device that utilizes mid-IR techniques for label-free and surface functionalization-free chemical sensing. The optofluidic platform is built using CMOS processes, and is capable of accomplishing broad mid-IR spectral sensing. Fig. 1 schematically illustrates the structure of the mid-IR opto-nanofluidic device. The sensing element is a nanofluidic-channel slot-waveguide with its two ends connected to Si-SiO2-Si slot-waveguides. We embed the entire nanofluidic channel and part of the silicon-oxide slot-waveguides in the PDMS chamber. Upon filling the interior of the chamber with liquid analyte, the solution inside the nanofluidic channel converts the fluid-filled channel into a fluidic slot-waveguide. The mid-IR probe light, after passing through the nanofluidic channel, propagates into the second SiO2 slot-waveguide at the other end. The transmitted light is encoded with the absorption spectrum of the analyte in the fluid because the absorption of probe light by the analyte that fills the nanofluidic channel heavily modulates the intensity of the guided light at the characteristic absorption wavelengths. The enhancement of chemical sensitivity of our fluidic slot-waveguide is evaluated. Fig. 2 (a) compares the predicted optical-field profiles for propagating mid-IR (? = 3.3 μm) radiation within a rectangular-strip waveguide, to that of a nanofluidic slot waveguide. In the case of the rectangular strip-waveguide, the optical field is mainly retained inside the Si core and its penetration as an evanescent wave into the surrounding fluid is small. In the slot-waveguide the optical field is highly concentrated at the center of the fluidic channel and interacts strongly with the liquid inside the channel. Thus, even a slight change in the concentration of analyte will result in a significant modulation of intensity to the guided mid-IR that consequently boosts the sensitivity when sensing chemicals. From the plot in Fig. 2 (b), the enhancement-factor Sslot/Sstrip rises to 75 times as the slot-width narrows to d = 80 nm.

A mid-infrared (mid-IR) label-free chemical sensor was developed using opto-nanofluidics consisting of a Si-liquid-Si slot-structure. A broadband mid-IR lightwave can be strongly confined within a nanofluidic capillary by utilizing the large refractive index contrast (Δn ~ 2) between the liquid core waveguide and the Si cladding. Through an optical-field enhancement together with a direct interaction between the probe light and the analyte, the sensitivity for chemical detection is increased by 50 times when compared to evanescent-wave sensing. This spectral characterization distinguished several common organic liquids (e.g., n-bromohexane, toluene, isopropanol) accurately, and could determine the ratio of chemical species (e.g., acetonitrile and ethanol) at low concentration (<; 5 μL/mL) in a mixture through spectral scanning over their characteristic mid-IR absorption peaks. The combination of CMOS-compatible planar mid-IR microphotonics, and a high-throughput nanofluidic sensor system, provides a unique platform for chemical detection.

A mid-infrared (mid-IR) spectrometer for label-free on-chip chemical sensing was developed using an engineered nanofluidic channel consisting of a Si-liquid-Si slot-structure. Utilizing the large refractive index contrast (Δn ∼ 2) between the liquid core of the waveguide and the Si cladding, a broadband mid-IR lightwave can be efficiently guided and confined within a nanofluidic capillary (≤100 nm wide). The optical-field enhancement, together with the direct interaction between the probe light and the analyte, increased the sensitivity for chemical detection by 50 times when compared to evanescent-wave sensing. This spectrometer distinguished several common organic liquids (e.g., n-bromohexane, toluene, isopropanol) accurately and could determine the ratio of chemical species (e.g., acetonitrile and ethanol) at low concentration (<5 μL/mL) in a mixture through spectral scanning over their characteristic absorption peaks in the mid-IR regime. The combination of CMOS-compatible planar mid-IR microphotonics, and a high-throughput nanofluidic sensor system, provides a unique platform for chemical detection.

Implementation of mid-infrared (mid-IR) chip-scale microphotonic circuits is critical to advancing the science for applications such as (i) ultra-fast telecommunications that require wider bandwidth and (ii) integrated biochemical sensors which can finger-print using infrared absorption signatures. Though substantial progress has been made in the development of light sources and detectors, a monolithic mid-IR Si-CMOS-compatible platform remains a challenge. Here we experimentally demonstrate a sophisticated mid-IR microphotonics platform adopting engineered Si-rich and low-stress silicon nitride (SiNx) thin films where an extensive infrared transparency up to lambda = 8.5 mu m is achieved. Furthermore, because of the designed low-stress property, the SiNx deposition is able to reach a thickness > 2 mu m that significantly reduces mid-IR waveguide loss to less than 0.2 dB/cm. We show directional couplers functioning over a broad infrared spectrum, thus enabling monolithic mid-IR multiplexing schemes for integrated linear and nonlinear photonics leading to sophisticated label-free sensing.

Mid-Infrared optofluidics based silicon sensor platforms are demonstrated. Silicon is a great candidate for mid-infrared optofluidics for the following reasons: (1) Silicon has a broad transmission window up to 7 um (2) Silicon offers CMOS compatible and monolithic fabrication (3) Silicon has high chemical resistance that can withstand high temperature, acid/base solution and organic solvents. (4) Silicon is a non-toxic environmentally friendly material. The fabricated mid-infrared optofluidic sensor can replace bulky instruments, such as FTIR, with a lab-on-a-chip system, while achieving much higher sensitivity.