Ultrahigh Enhancement of Electromagnetic Fields by Exciting Localized with Extended Surface Plasmons

Excitation of localized surface plasmons (LSPs) of metal nanoparticles (NPs) residing on a flat metal film has attracted great attentions recently due to the enhanced electromagnetic (EM) fields found to be higher than the case of NPs on a dielectric substrate. In the present work, it is shown that even much higher enhancement of EM fields is obtained by exciting the LSPs through extended surface plasmons (ESPs) generated at the metallic film surface using the Kretschmann-Raether configuration. We show that the largest EM field enhancement and the highest surface-enhanced fluorescence intensity are obtained when the incidence angle is the ESP resonance angle of the underlying metal film. The finite-difference time-domain simulations indicate that excitation of LSPs using ESPs can generate 1-3 orders higher EM field intensity than direct excitation of the LSPs using incidence from free space. The ultrahigh enhancement is attributed to the strong confinement of the ESP waves in the vertical direction. The drastically intensified EM fields are significant for highly-sensitive refractive index sensing, surface-enhanced spectroscopies, and enhancing the efficiency of optoelectronic devices.Comment: 25 pages, 5 figures and supplimentary informatio

Synthesis of Molecularly Imprinted Polymer Nanoparticles for SARS-CoV-2 Virus Detection Using Surface Plasmon Resonance

COVID-19 caused by a SARS-CoV-2 infection was first reported from Wuhan, China, and later recognized as a pandemic on March 11, 2020, by the World Health Organization (WHO). Gold standard nucleic acid and molecular-based testing have largely satisfied the requirements of early diagnosis and management of this infectious disease; however, these techniques are expensive and not readily available for point-of-care (POC) applications. The COVID-19 pandemic of the 21st century has emphasized that medicine is in dire need of advanced, rapid, and cheap diagnostic tools. Herein, we report on molecularly imprinted polymer nanoparticles (MIP-NPs/nanoMIPs) as plastic antibodies for the specific detection of SARS-CoV-2 by employing a surface plasmon resonance (SPR) sensor. High-affinity MIP-NPs directed against SARS-CoV-2 were manufactured using a solid-phase imprinting method. The MIP-NPs were then characterized using dynamic light scattering (DLS) and atomic force microscopy (AFM) prior to their incorporation into a label-free portable SPR device. Detection of SARS-CoV-2 was studied within a range of 104–106 PFU mL−1. The MIP-NPs demonstrated good binding affinity (KD = 0.12 pM) and selectivity toward SARS-CoV-2. The AFM, cyclic voltammetry, and square-wave voltammetry studies revealed the successful stepwise preparation of the sensor. A cross-reactivity test confirmed the specificity of the sensor. For the first time, this study demonstrates the potential of molecular imprinting technology in conjunction with miniaturized SPR devices for the detection of SARS-CoV-2 particles with high-affinity and specificity. Such sensors could help monitor and manage the risks related to virus contamination and infections also beyond the current pandemic

Nutritional Status among Children under Five Years in Amman, Jordan

Objectives: There is scarcity of data on malnutrition among children in Jordan. Therefore, this study was conducted to assess the nutritional status and estimate the prevalence rates of stunting, underweight, and wasting and their associated factors among children under five. Subjects and Methods: A cross-sectional study was conducted between January and April 2017 among children under five years in Amman, Jordan. All Jordanian children under five years who visited the selected health centers for vaccination or accompanied their mothers during the study period were included in this study. Mothers or caregivers of children were interviewed face-to face using the study questionnaire. Weight in kilograms and height in centimeters were measured for all children. Anthropometric indices were calculated using reference medians recommended by the World Health Organization. Results: This study included a total of 923 (463 boys and 460 girls) children. The prevalence rates of stunting, underweight, and wasting were 6.2%, 3.8%, and 2.8%, respectively. Multivariate analysis showed that low birth weight was significantly associated with stunting (OR = 2.9, 95% CI: 1.4,6.0; p-value=0.003) and underweight (OR =5.6, 95% CI: 2.5,12.3, p-value <0.001). Compared to exclusive breastfeeding, mixed feeding was associated with increased odds of stunting (OR =2, 95% CI: 1.1-3.9, p-value =0.029) and underweight (OR = 2.2, 95% CI: 1.002, 5.0; p = 0.049). None of the variables were significantly associated with wasting. Conclusions: The prevalence rates of stunting, wasting and undernutrition among children under five years in Jordan are low. Low birth weight and mixed feeding were associated with higher rates of malnutrition

Highly sensitive and specific detection of E. coli by a SERS nanobiosensor chip utilizing metallic nanosculptured thin films

A nanobiosensor chip, utilizing surface enhanced Raman spectroscopy (SERS) on nanosculptured thin films (nSTFs) of silver, was shown to detect Escherichia coli (E. coli) bacteria down to the concentration level of a single bacterium. The sensor utilizes highly enhanced plasmonic nSTFs of silver on a silicon platform for the enhancement of Raman bands as checked with adsorbed 4-aminothiophenol molecules. T-4 bacteriophages were immobilized on the aforementioned surface of the chip for the specific capture of target E. coli bacteria. To demonstrate that no significant non-specific immobilization of other bacteria occurs, three different, additional bacterial strains, Chromobacterium violaceum, Paracoccus denitrificans and Pseudomonas aeruginosa were used. Furthermore, experiments performed on an additional strain of E. coli to address the specificity and reusability of the sensor showed that the sensor operates for different strains of E. coli and is reusable. Time resolved phase contrast microscopy of the E. coli-T4 bacteriophage chip was performed to study its interaction with bacteria over time. Results showed that the present sensor performs a fast, accurate and stable detection of E. coli with ultra-small concentrations of bacteria down to the level of a single bacterium in 10 μl volume of the sample

Liraglutide effects on glycemic control and weight in patients with Type 2 Diabetes mellitus: a real-world, observational study and brief narrative review

Background Glycemic control and weight gain are two essential considerations in the pharmacological management of type 2 diabetes mellitus. Pharmacological agents are effective in lowering blood glucose levels but may result in significant weight gain. Liraglutide effectively maintains glycemic control while reducing weight. Methods This is a real-world study and brief narrative review of the effects of liraglutide on glycemic control and weight in adult patients with type 2 diabetes mellitus. The study uses data extracted from the electronic health record of the Ministry of National Guard-Health Affairs. Results In this study of 348 subjects, there was a statistically significant reduction in hemoglobin A1c of 0.9% (P < .0001) and weight of 2.3 kg (P < .0001). The majority (77.3%) were on concomitant insulin. Subjects with a baseline hemoglobin A1c greater than 9% had a significantly greater reduction than those below 9% (−0.7%; P < .0001). Those with a weight more than 100 kg had a significantly greater reduction than those below 100 kg (-0.9 kg; P = .0096). Conclusion In this real-world, observational study, liraglutide was shown to be effective in improving glycemic control and reducing weight in adult patients with type 2 diabetes mellitus

Coupling configurations between extended surface electromagnetic waves and localized surface plasmons for ultrahigh field enhancement

Local enhancement of electromagnetic (EM) fields near dielectric and metallic surfaces is usually associated with the existence of a confined EM wave at least in one direction. This phenomenon finds applications in enhancing optical spectroscopic signals, optical emission, nonlinear optical processes, biosensing, imaging contrast and superresolution, photovoltaics response, local heating, photocatalysis, and enhanced efficiency of optoelectronic devices. A well-known example is when the surface electromagnetic wave (SEW) is excited at the interface of two media, the field gets enhanced normally to that interface. This article reviews the different configurations revealing enhanced EM fields, particularly those giving ultrahigh enhancement, such as when a localized SEW is excited not from free space but via an extended SEW. Of particular interest are surface plasmon waves (SPWs) excited at the surface of metal-dielectric and particularly when exciting localized SPWs using extended ones. The latter case so far gave the highest local field enhancement; however, configurations involving Bloch SEWs, guided mode resonances, and cavity resonances have also been shown to give significant enhancement when used to excite localized surface plasmons. With this strategy, field enhancement by more than an order of magnitude can be attained. Using this ultrahigh enhancement, the strong coupling experiments between molecules and the intense optical field will be possible and new devices may emerge from those new methodologies for ultrahigh sensitive sensing for environmental and medical applications, as well as for improved optoelectronic devices

Plasmonic sensing using metallic nano-sculptured thin films

Nano-sculptured thin films (nSTFs) is a group of meterials prepared by the oblique or the glancing angle deposition technique. They take the form of rods having different shapes such as nanocolumns, nanoscrews, nanozigzags and many other nanoshapes. Their potential for biosensing is highlighted in this review particularly the metallic ones due to their remarkable plasmonic properties. The techniques that have been shown so far to be of high potential are: extended surface plasmon resonance (SPR), localised SPR, surface enhanced flourescence (SEF) and Raman scattering (SERS). The use of metal nSTFs in SPR biosensors with Kretschmann-Raether configuration enhances both the angular and the spectral sensitivities due to the porosity and adds more degrees of freedom in designing evanescent waves based techniques. The metallic nSTFs, exhibit remarkable localised plasmonic properties that make them a promising substrate for enhanced spectroscopies. Their long term stability in water environment makes them suitable candidates for biosensing in water as it is already demonstrated for several water pollutants. The influences of the nanostructures' size, topology, the substrate features, and the preparation conditions on the enhancement of SEF and SERS are highlighted with emphases on the unresolved issues and future trends

Figure-of-merit enhancement of surface plasmon resonance sensors in the spectral interrogation

We show that adding a thin dielectric layer with high refractive index on top of the metallic layer in surface plasmon resonance sensors in the Kretschmann–Raether configuration in the spectral mode causes a redshift of the resonance wavelength, narrowing of the resonance dip, and an enhancement to the spectral sensitivity. Surprisingly, together with the sensitivity enhancement, the dip becomes much narrower and the figure of merit is considerably improved, particularly in the IR range.Published versio