Plasmon-Assisted Audio Recording

We present the first demonstration of the recording of optically encoded audio onto a plasmonic nanostructure. Analogous to the ‘‘optical sound’’ approach used in the early twentieth century to store sound on photographic film, we show that arrays of gold, pillar-supported bowtie nanoantennas could be used in a similar fashion to store sound information that is transferred via an amplitude modulated optical signal to the near field of an optical microscope. Retrieval of the audio information is achieved using standard imaging optics. We demonstrate that the sound information can be stored either as time-varying waveforms or in the frequency domain as the corresponding amplitude and phase spectra. A ‘‘plasmonic musical keyboard’’ comprising of 8 basic musical notes is constructed and used to play a short song. For comparison, we employ the correlation coefficient, which reveals that original and retrieved sound files are similar with maximum and minimum values of 0.995 and 0.342, respectively. We also show that the pBNAs could be used for basic signal processing by ablating unwanted frequency components on the nanostructure thereby enabling physical notch filtering of these components. Our work introduces a new application domain for plasmonic nanoantennas and experimentally verifies their potential for information processing.University of Illinois at Urbana-Champaig

Amorphous, self-healed, geopolymers (ASH-G and ceramics (ASH-C) made by the geopolymer processing route

This work describes the cross fertilization of conventional whiteware production by a low energy, geopolymer processing method. Bone china is conventionally made using natural cow bone ash (calcined) of hydroxyapatite (HA). In this study HA and dicalcium phosphate (DCP) particulate reinforcements were investigated in potassium-based geopolymer composites (KGP). Particulate reinforcements of 5, 10 and 15 wt % each of hydroxyapatite and dicalcium phosphate particulate were added to potassium geopolymer to compare with composites made from BASF® Metamax metakaolin (KGP MT), Mymensingh clay metakaolin, KGP(MW) and synthetic Mymensingh clay metakaolin, KGP(MW-SYN). Microstructural properties using SEM, XRD and mechanical properties using Instron were investigated for the geopolymer samples at both room and high temperature. The XRD of pure and reinforced geopolymer samples at RT confirmed the formation of geopolymer analogues with the characteristic X-ray amorphous hump at 280 in 2θ, along with the crystalline peaks observed in KGP (MW), as well as in potassium geopolymer reinforced with hydroxyapatite and dicalcium phosphate. Thermally treated geopolymer composites at 11500C/1h exhibited crystalline peaks of leucite, kalsilite, monetite and quartz confirming the signature of geopolymer ceramics at elevated temperature. SEM revealed fully reacted and homogenous aluminosilicate matrix in all the geopolymer samples cured at room temperature for 7 days. Geopolymer composites KGP (MT)-15 DCP, KGP(MW)-15DCP and KGP(MW-SYN)-15DCP after thermal exposure at 11500C revealed microstructural integrity with the formation of phosphate glass, while a self-glazed surface was developed in KGP (MW) after being heated at 1125 0C/1h. Their high temperature properties are superior to RT properties due to amorphous self-healed glass formation (ASH) from the DCP phosphate glass. Their high temperature properties were superior to RT properties due to amorphous self-healed glass formation (ASH) from the DCP phosphate glass. The optimum DCP content was 10 wt % which gave flexure strengths of ~32 MPa after heat treatment at 1150 °C/1h

Highly sensitive and label-free digital detection of whole cell E. coli with interferometric reflectance imaging

Bacterial infectious diseases are a major threat to human health. Timely and sensitive pathogenic bacteria detection is crucial in identifying the bacterial contaminations and preventing the spread of infectious diseases. Due to limitations of conventional bacteria detection techniques there have been concerted research efforts towards development of new biosensors. Biosensors offering label free, whole bacteria detection are highly desirable over those relying on label based or pathogenic molecular components detection. The major advantage is eliminating the additional time and cost required for labeling or extracting the desired bacterial components. Here, we demonstrate rapid, sensitive and label free E. coli detection utilizing interferometric reflectance imaging enhancement allowing for visualizing individual pathogens captured on the surface. Enabled by our ability to count individual bacteria on a large sensor surface, we demonstrate a limit of detection of 2.2 CFU/ml from a buffer solution with no sample preparation. To the best of our knowledge, this high level of sensitivity for whole E. coli detection is unprecedented in label free biosensing. The specificity of our biosensor is validated by comparing the response to target bacteria E. coli and non target bacteria S. aureus, K. pneumonia and P. aeruginosa. The biosensor performance in tap water also proves that its detection capability is unaffected by the sample complexity. Furthermore, our sensor platform provides high optical magnification imaging and thus validation of recorded detection events as the target bacteria based on morphological characterization. Therefore, our sensitive and label free detection method offers new perspectives for direct bacterial detection in real matrices and clinical samples.First author draf

Multifunctional plasmonic film for recording near-field optical intensity

We demonstrate the plasmonic equivalent of photographic film for recording optical intensity in the near field. The plasmonic structure is based on gold bowtie nanoantenna arrays fabricated on SiO2 pillars. We show that it can be employed for direct laser writing of image data or recording the polarization structure of optical vector beams. Scanning electron micrographs reveal a careful sculpting of the radius of curvature and height of the triangles composing the illuminated nanoantennas, as a result of plasmonic heating, that permits spatial tunability of the resonance response of the nanoantennas without sacrificing their geometric integrity. In contrast to other memory-dedicated approaches using Au nanorods embedded in a matrix medium, plasmonic film can be used in multiple application domains. To demonstrate this functionality, we utilize the structures as plasmonic optical tweezers and show sequestering of SiO2 microparticles into optically written channels formed between exposed sections of the film. The plasmonic film offers interesting possibilities for photonic applications including optofluidic channels “without walls,” in situ tailorable biochemical sensing assays

Design, Fabrication, and Characterization of Near-IR Gold Bowtie Nanoantenna Arrays

We demonstrate tunable, near-IR plasmonic nanoantennas using a 2D array of relatively large Au bowtie nanoantennas (BNAs) as the design template. We explore the geometric conditions for enhanced plasmonic response for BNAs bound to an SiO₂ substrate as well as for BNAs supported on SiO₂ pillars. Contrary to previous reports, we perform both systematic experimental and simulation studies exploring the influence of BNA gap spacing, array periodicity, and pillar height on plasmon-resonance-wavelength tunability and maximum field enhancement. We demonstrate that the peak of the plasmon resonance response can be tuned from ∼1.3 to 2.2 μm with respect to array periodicity, and a maximum field enhancement of ∼16 000 is theoretically achievable for pillar-supported BNAs (p-BNAs) of height 2.5 μm and array periodicity of 1.8 μma factor of 4× larger field enhancement than that from substrate-bound BNAs. We also find that the p-BNAs possess a maximum refractive index sensitivity of 1763 nm RIU^–1, which is among the highest values reported to date, making the structure attractive for high-sensitivity probing of chemical and biological systems

Multifunctional Plasmonic Film for Recording Near-Field Optical Intensity

We demonstrate the plasmonic equivalent of photographic film for recording optical intensity in the near field. The plasmonic structure is based on gold bowtie nanoantenna arrays fabricated on SiO₂ pillars. We show that it can be employed for direct laser writing of image data or recording the polarization structure of optical vector beams. Scanning electron micrographs reveal a careful sculpting of the radius of curvature and height of the triangles composing the illuminated nanoantennas, as a result of plasmonic heating, that permits spatial tunability of the resonance response of the nanoantennas without sacrificing their geometric integrity. In contrast to other memory-dedicated approaches using Au nanorods embedded in a matrix medium, plasmonic film can be used in multiple application domains. To demonstrate this functionality, we utilize the structures as plasmonic optical tweezers and show sequestering of SiO₂ microparticles into optically written channels formed between exposed sections of the film. The plasmonic film offers interesting possibilities for photonic applications including optofluidic channels “without walls,” in situ tailorable biochemical sensing assays, and near-field particle manipulation and sorting

Isolation, Identification and Genetic Characterization of Antibiotic Resistant <i>Escherichia coli</i> from Frozen Chicken Meat Obtained from Supermarkets at Dhaka City in Bangladesh

Antimicrobials have been used to improve animal welfare, food security, and food safety that promote the emergence, selection, and dissemination of antimicrobial-resistant (AMR) bacteria. In this study, 50 E. coli were isolated from frozen chicken meat samples in Dhaka city. Antibiotic sensitivity patterns were assessed through the disk diffusion method and finally screened for the presence of antimicrobial resistance genes (ARG) using the polymerase chain reaction (PCR). Among the 160 samples, the prevalence of E. coli was observed in fifty samples (31.25%). All of these isolates were found resistant to at least one antimicrobial agent, and 52.0% of the isolates were resistant against 4–7 different antimicrobials. High resistance was shown to tetracycline (66.0%), followed by resistance to erythromycin (42.0%), ampicillin and streptomycin (38.0%), and sulfonamide (28.0%). In addition, the most prevalent ARGs were tet(A) (66.0%), ereA (64.0%), tet(B) (60.0%), aadA1 and sulI (56.0%), blaCITM (48.0%) and blaSHV (40.0%). About 90.0% of isolates were multidrug resistant. This study reveals for the first time the current situation of E. coli AMR in broilers, which is helpful for the clinical control of disease as well as for the development of policies and guidelines to reduce AMR in broilers production in Bangladesh

Amplification-free detection of SARS-CoV-2 with CRISPR-Cas13a and mobile phone microscopy.

The December 2019 outbreak of a novel respiratory virus, SARS-CoV-2, has become an ongoing global pandemic due in part to the challenge of identifying symptomatic, asymptomatic, and pre-symptomatic carriers of the virus. CRISPR diagnostics can augment gold-standard PCR-based testing if they can be made rapid, portable, and accurate. Here, we report the development of an amplification-free CRISPR-Cas13a assay for direct detection of SARS-CoV-2 from nasal swab RNA that can be read with a mobile phone microscope. The assay achieved ∼100 copies/μL sensitivity in under 30&nbsp;min of measurement time and accurately detected pre-extracted RNA from a set of positive clinical samples in under 5&nbsp;min. We combined crRNAs targeting SARS-CoV-2 RNA to improve sensitivity and specificity and directly quantified viral load using enzyme kinetics. Integrated with a reader device based on a mobile phone, this assay has the potential to enable rapid, low-cost, point-of-care screening for SARS-CoV-2