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• One-dimensional plasmonic grating consisting of polymer and quantum dots is fabricated. • CdS quantum dot (CdQDs) are immobilized on poly(glycidyl methacrylate) (PGMA) grating. • Fluorescence intensity of CdQDs is enhanced by surface lattice resonances of grating. • Streptavidin induces assembling of biotin modified-CdQD resulting collapse of PGMA. One dimensional plasmonic grating is a kind of resonant electromagnetic wave absorber with a characteristic wavelength. This study focusses on one-dimensional plasmonic grating consisting of poly (glycidyl methacrylate) (PGMA) brushes and CdS quantum dots (CdQDs) fabrication and PGMA chains grafted on a primary substrate in a line array continued by the immobilization of biotin-modified CdQDs. PGMA brush line array (PBLA) of plasmonic grating exhibited an absorptance at 441 nm while at the same time, CdQDs immobilized with PBLA showed characteristic absorbance at 396 nm. The blue-shift from 441 nm matches the absorbance peak of biotin-modified CdQDs resulting in the enhancement of photoluminescence emission of CdQDs. With streptavidin incubation to assemble CdQDs at 50 nM, the significant decrease in grating height resulted in the red-shift of the absorbance peak to 536 nm. Due to the deviation in absorbance, the intensity of the PL emission decreased gradually with the increase in concentration of streptavidin. In addition, our results showed that streptavidin incubation altered the color reflected from the surface due to effective changes in the refractive index of the layer as well. The limit of detection of the grating for streptavidin detection was determined to be 50 nM. Thus, PBLA-CdQD has the potential to act as a highly-sensitive, label-free optical biosensor. [ABSTRACT FROM AUTHOR]

Some directional characteristics of observed clutter and reverberation are presented using line arrays with cardioid elements. It is shown that the cardioid arrays break the left/right ambiguity for reverberation sources above ~600-700 Hz. Data analysis uses a cardioid beamforming algorithm developed by researchers at the NATO Undersea Research Centre (NURC, La Spezia, Italy) but the normalization for this algorithm is derived by the author. It is shown that this normalized algorithm has an upper frequency limitation not previously noted. Reverberation data are taken from two recent experiments. One was the 2004 Boundary Characterization Experiment near the Malta Plateau. The area is rich in clutter objects like wrecks and mud-volcanoes and has some subbottom features that may be important. Sources were monostatic coherent pulses and impulsive sources. The receiver was the NURC cardioid array. The other experiment was the U.S. Office of Naval Research's 2003 Geoclutter effort to study shallow-water bottom reverberation and clutter in the STRATAFORM area off New Jersey. Sources were bistatic coherent pulses. The receiver was the five-octave research array (FORA). The STRATAFORM has benign surface morphology but strong clutter is observed. Some highlights of the reverberant returns from that area are discussed that include returns from probable fish schools. From these two data sets, it is shown that up to 15-20-dB left/right discrimination is attainable on broadside cardioid beams in the 1200-1750-Hz region for both linear frequency modulation (LFM) pulses and sound-underwater-source (SUS) broadband data. Also, a (previously developed) constrained simulated annealing (SA) inversion technique is applied to the directional reverberation data from the NURC array. A two-layer fluid model of the bottom is assumed. The algorithm is best at estimating compressional speeds, layer thickness, and attenuations in that order. Extracted bottom parameters at the site are compared with independent inversion results previously reported by Holland. Inverting reverberation from directional arrays is shown to give somewhat better quality results since, unlike standard line arrays, the reverberation data apply to only one bearing along the seafloor. [ABSTRACT FROM AUTHOR]

This paper presents some new results from measurements of seafloor reverberation and pulse spreading using horizontal and vertical line arrays. The principal objective of this paper is to extract useful geoacoustic and bottom-scattering parameters that apply over a large ocean area. Analysis is presented on reverberation data from the 2000 Boundary Characterization Experiment performed jointly with North Atlantic Treaty Organization (NATO) Undersea Research Center (NURC), Applied Research Laboratory (ARL) of Pennsylvania State University, Defence Research and Development Canada (DRDC), and Naval Research Laboratory (NRL). Sources were SUS charges and coherent pulses. The receivers were horizontal arrays used mono-statically. Data were analyzed in hands from 80 to 4000 Hz. Highlights of the reverberant returns are discussed. The experiment site is the Malta Plateau area south of Sicily, a relatively flat heavily sedimented area, but with a rocky ridge to the east. An original aspect of this paper is the design and implementation of a new automated inverse method using towed-array data to accomplish that goal. For each data set, a multiple-step simulated annealing (SA) algorithm is used together with the Generic Sonar Model (GSM). After automatically adjusting bottom loss and scattering strength, good agreement is achieved between the diffuse reverberation data and model predictions in relatively flat areas. Model/data differences are generally correlated with bottom-scattering features. Since reverberation from SUS charges typically lasts 10-40 s or more, extracted parameters apply over wide areas. Independent acoustic measurements provided a basis for a comparison with extracted values. Local bottom-loss and backscattering measurements were made by Holland in these areas. Additionally, chirp-sonar measurements were analyzed by Turgut. A comparison of geoacoustic models obtained with their methods and with this one was quite good. Comparing transmission loss (TL) predicted with Turgut's local inverse method and TL predicted with the method presented here gave answers that were usually within 3 dB of each other. Typical two-way time spreads of 0.25 s were seen at a range of 7.5 km, with normalized peak correlations of 0.5, and which were fairly consistent with predictions made using the inverse results. [ABSTRACT FROM AUTHOR]