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November 05, 2019

[16] Aluminum Metasurface with Hybrid Multipolar Plasmons for 1000-Fold Broadband Visible Fluorescence Enhancement and Multiplexed Biosensing

Radwanul Hasan Siddique, Shailabh Kumar, Vinayak Narasimhan, Hyounghan Kwon, Hyuck Choo 

ACS Nano 13(12), 13775 - 13783

Aluminum (Al)-based nanoantennae traditionally suffer from weak plasmonic performance in the visible range, necessitating the application of more expensive noble metal substrates for rapidly expanding biosensing opportunities. We introduce a metasurface comprising Al nanoantennae of nanodisks-in-cavities that generate hybrid multipolar lossless plasmonic modes to strongly enhance local electromagnetic fields and increase the coupled emitter’s local density of states throughout the visible regime. This results in highly efficient electromagnetic field confinement in visible wavelengths by these nanoantennae, favoring real-world plasmonic applications of Al over other noble metals. Additionally, we demonstrate spontaneous localization and concentration of target molecules at metasurface hotspots, leading to further improved on-chip detection sensitivity and a broadband fluorescence-enhancement factor above 1000 for visible wavelengths with respect to glass chips commonly used in bioassays. Using the metasurface and a multiplexing technique involving three visible wavelengths, we successfully detected three biomarkers, insulin, vascular endothelial growth factor, and thrombin relevant to diabetes, ocular and cardiovascular diseases, respectively, in a single 10 μL droplet containing only 1 fmol of each biomarker.

July 25, 2019

[15] Enhanced broadband fluorescence detection of nucleic acids using multipolar gap-plasmons on biomimetic Au metasurfaces

Vinayak Narasimhan, Radwanul Hasan Siddique, Magnus Hoffmann, Shailabh Kumar, Hyuck Choo 

Nanoscale 11, 13750 - 13757

Recent studies on metal-insulator–metal-based plasmonic antennas have shown that emitters could couple with higher-order gap-plasmon modes in sub-10-nm gaps to overcome quenching. However, these gaps are often physically inaccessible for functionalization and are not scalably manufacturable. Here, using a simple biomimetic batch-fabrication, a plasmonic metasurface is created consisting of closely-coupled nanodisks and nanoholes in a metal-insulator-metal arrangement. The quadrupolar mode of this system exhibits strong broadband resonance in the visible-near-infrared regime with minimal absorptive losses and effectively suppresses quenching, making it highly suitable for broadband plasmon-enhanced fluorescence. Functionalizing the accessible insulator nanogap, analytes are selectively immobilized onto the plasmonic hotspot enabling highly-localized detection. Sensing the streptavidin-biotin complex, a 91-, 288-, 403- and 501-fold fluorescence enhancement is observed for Alexa Fluor 555, 647, 750 and 790, respectively. Finally, the detection of single-stranded DNA (gag, CD4 and CCR5) analogs of genes studied in the pathogenesis of HIV-1 between 10 pM–10 μM concentrations and then CD4 mRNA in the lysate of transiently-transfected cells with a 5.4-fold increase in fluorescence intensity relative to an untransfected control is demonstrated. This outcome promises the use of biomimetic Au metasurfaces as platforms for robust detection of low-abundance nucleic acids.

October 29, 2018

[14] Glucose Sensing Using Surface-Enhanced Raman-Mode Constraining

Daejong Yang, Sajjad Afroosheh, Jeong Oen Lee, Hyunjun Cho, Shailabh Kumar, Radwanul Hasan Siddique, Vinayak Narasimhan, Young-Zoon Yoon, Alexey T. Zayak, Hyuck Choo 

Analytical Chemistry 90 (24), 14269-14278

Diabetes mellitus is a chronic disease, and its management focuses on monitoring and lowering a patient’s glucose level to prevent further complications. By tracking the glucose-induced shift in the surface-enhanced Raman-scattering (SERS) emission of mercaptophenylboronic acid (MPBA), we have demonstrated fast and continuous glucose sensing in the physiologically relevant range from 0.1 to 30 mM and verified the underlying mechanism using numerical simulations. Bonding of glucose to MPBA suppresses the “breathing” mode of MPBA at 1071 cm–1 and energizes the constrained-bending mode at 1084 cm–1, causing the dominant peak to shift from 1071 to 1084 cm–1. MPBA–glucose bonding is also reversible, allowing continuous tracking of ambient glucose concentrations, and the MPBA-coated substrates showed very stable performance over a 30 day period, making the approach promising for long-term continuous glucose monitoring. Using Raman-mode-constrained, miniaturized SERS implants, we also successfully demonstrated intraocular glucose measurements in six ex vivo rabbit eyes within ±0.5 mM of readings obtained using a commercial glucose sensor.

April 30, 2018

[13] Multifunctional biophotonic nanostructures inspired by the longtail glasswing butterfly for medical devices

Vinayak Narasimhan*, Radwanul Hasan Siddique*, Jeong Oen Lee, Shailabh Kumar, Blaise Ndjamen, Juan Du, Natalie Hong, David Sretavan, Hyuck Choo (* Equally contributed) 

Nature Nanotechnology 13, 512-519

Numerous living organisms possess biophotonic nanostructures that provide colouration and other diverse functions for survival. While such structures have been actively studied and replicated in the laboratory, it remains unclear whether they can be used for biomedical applications. Here, we show a transparent photonic nanostructure inspired by the longtail glasswing butterfly (Chorinea faunus) and demonstrate its use in intraocular pressure (IOP) sensors in vivo. We exploit the phase separation between two immiscible polymers (poly(methyl methacrylate) and polystyrene) to form nanostructured features on top of a Si3N4 substrate. The membrane thus formed shows good angle-independent white-light transmission, strong hydrophilicity and anti-biofouling properties, which prevent adhesion of proteins, bacteria and eukaryotic cells. We then developed a microscale implantable IOP sensor using our photonic membrane as an optomechanical sensing element. Finally, we performed in vivo testing on New Zealand white rabbits, which showed that our device reduces the mean IOP measurement variation compared with conventional rebound tonometry without signs of inflammation.

December 22, 2017

[12] Rainbow peacock spiders inspire miniature super-iridescent optics

Bor-Kai Hsiung, Radwanul Hasan Siddique, Doekele G Stavenga, Jürgen C Otto, Michael C Allen, Ying Liu, Yong-Feng Lu, Dimitri D Deheyn, Matthew D Shawkey, Todd A Blackledge

Nature communications 8.1, 2278

Colour produced by wavelength-dependent light scattering is a key component of visual communication in nature and acts particularly strongly in visual signalling by structurally-coloured animals during courtship. Two miniature peacock spiders (Maratus robinsoni and M. chrysomelas) court females using tiny structured scales (~ 40 × 10 μm2) that reflect the full visual spectrum. Using TEM and optical modelling, we show that the spiders’ scales have 2D nanogratings on microscale 3D convex surfaces with at least twice the resolving power of a conventional 2D diffraction grating of the same period. Whereas the long optical path lengths required for light-dispersive components to resolve individual wavelengths constrain current spectrometers to bulky sizes, our nano-3D printed prototypes demonstrate that the design principle of the peacock spiders’ scales could inspire novel, miniature light-dispersive components.

October 19, 2017

[11] Bioinspired phase-separated disordered nanostructures for thin photovoltaic absorbers

Radwanul Hasan Siddique*^, Yidenekachew J. Donie*, Guillaume Gomard, Sisir Yalamanchili, Tsvetelina Merdzhanova, Uli Lemmer and Hendrik Hölscher (* Equally contributed) (^ Corresponding Author)

Science Advances 3, e1700232

The wings of the black butterfly, Pachliopta aristolochiae, are covered by micro- and nanostructured scales that harvest sunlight over a wide spectral and angular range. Considering that these properties are particularly attractive for photovoltaic applications, we analyze the contribution of these micro- and nanostructures, focusing on the structural disorder observed in the wing scales. In addition to microspectroscopy experiments, we conduct three-dimensional optical simulations of the exact scale structure. On the basis of these results, we design nanostructured thin photovoltaic absorbers of disordered nanoholes, which combine efficient light in-coupling and light-trapping properties together with a high angular robustness. Finally, inspired by the phase separation mechanism of self-assembled biophotonic nanostructures, we fabricate these bioinspired absorbers using a scalable, self-assembly patterning technique based on the phase separation of binary polymer mixture. The nanopatterned absorbers achieve a relative integrated absorption increase of 90% at a normal incident angle of light to as high as 200% at large incident angles, demonstrating the potential of black butterfly structures for light-harvesting purposes in thin-film solar cells.

July 31, 2017

[10] Quantitative analysis of a III-V tapered horn-shaped metal-clad nano-cavity as an on-chip light source

Sukmo Koo, Radwanul Hasan Siddique, Hyuck Choo

AIP Advances​ 7 (7), 075017

A horn-shaped metal-clad InGaAsP nano-cavity with sloped sidewalls is proposed as a platform for nanoscale light sources. The nano-cavity’s physical dimensions are 350 × 350 × 350 nm^3, and its mode volume is 0.5 (λ_0/n)^3. In our numerical simulations and quantitative analysis, we have shown that the sloped sidewalls reduce metallic absorption and improve resonant mode confinement; and adjusting their slope from 0 to 16° increased the Q factor from 150 to 900 and laser modulation 3dB bandwidth from 4.3 to 36 GHz. The lasing threshold current was expected to be 35 μA at 16°. In a simulated feasibility study, we demonstrate 60 Gbps modulated laser signal (5 fJ/bit), producing 20 μW output power at the 1.5 μm wavelength with injection current 100 μA, as an implementation of horn-shaped nano-cavity platform to the low power and ultra-fast on-chip nano-laser.

April 21, 2017

[9] Bio-inspired, large scale, highly-scattering films for nanoparticle-alternative white surfaces

Julia Syurik, Radwanul Hasan Siddique, Antje Dollmann, Guillaume Gomard, Marc Schneider, Matthias Worgull, Gabriele Wiegand & Hendrik Hölscher

Scientific Reports 7, 46637

Subwavelength metal-dielectric plasmonic metasurfaces enable light management beyond the diffraction limit. However, a cost-effective and reliable fabrication method for such structures remains a major challenge hindering their full exploitation. Here, we propose a simple yet powerful manufacturing route for plasmonic metasurfaces based on a bottom-up approach. The fabricated metasurfaces consist of a dense distribution of randomly oriented nanoscale scatterers consisting of aluminum (Al) nanohole-disk pairs, which exhibit angle-independent scattering that is tunable across the entire visible spectrum. The macroscopic response of the metasurfaces is controlled via the properties of an isolated Al nanohole-disk pair at the nanoscale. In addition, the optical field confinement at the scatterers and their random distribution of sizes result in a strongly enhanced Raman signal that enables broadly tunable excitation using a single substrate. This unique combination of a reliable and lithography-free methodology with the use of aluminum permits the exploitation of the full potential of random plasmonic metasurfaces for diagnostics and coloration.

February 17, 2017

[8] Scalable and controlled self-assembly of aluminum-based random plasmonic metasurfaces

Radwanul Hasan Siddique^, Jan Mertens, Hendrik Hölscher, Silvia Vignolini (^ Corresponding Author)

Light: Science & Applications 6, e17015

Subwavelength metal-dielectric plasmonic metasurfaces enable light management beyond the diffraction limit. However, a cost-effective and reliable fabrication method for such structures remains a major challenge hindering their full exploitation. Here, we propose a simple yet powerful manufacturing route for plasmonic metasurfaces based on a bottom-up approach. The fabricated metasurfaces consist of a dense distribution of randomly oriented nanoscale scatterers consisting of aluminum (Al) nanohole-disk pairs, which exhibit angle-independent scattering that is tunable across the entire visible spectrum. The macroscopic response of the metasurfaces is controlled via the properties of an isolated Al nanohole-disk pair at the nanoscale. In addition, the optical field confinement at the scatterers and their random distribution of sizes result in a strongly enhanced Raman signal that enables broadly tunable excitation using a single substrate. This unique combination of a reliable and lithography-free methodology with the use of aluminum permits the exploitation of the full potential of random plasmonic metasurfaces for diagnostics and coloration.

November 02, 2016

[7] Colour formation on the wings of the butterfly Hypolimnas salmacis by scale stacking

Radwanul Hasan Siddique^, Silvia Vignolini, Carolin Bartels, Irene Wacker, Hendrik Hölscher (^ Corresponding Author)

Scientific Reports 6, 36204

The butterfly genus Hypolimnas features iridescent blue colouration in some areas of its dorsal wings. Here, we analyse the mechanisms responsible for such colouration on the dorsal wings of Hypolimnas salmacisand experimentally demonstrate that the lower thin lamina in the white cover scales causes the blue iridescence. This outcome contradicts other studies reporting that the radiant blue in Hypolimnas butterflies is caused by complex ridge-lamellar architectures in the upper lamina of the cover scales. Our comprehensive optical study supported by numerical calculation however shows that scale stacking primarily induces the observed colour appearance of Hypolimnas salmacis.

October 11, 2016

[6] Tarantula‐Inspired Noniridescent Photonics with Long‐Range Order

Bor‐Kai Hsiung, Radwanul Hasan Siddique, Lijia Jiang, Ying Liu, Yongfeng Lu, Matthew D Shawkey, Todd A Blackledge

Advanced Optical Materials 5, 1600599

Photonic structures with long-range order are inherently iridescent, suggesting by current theory. Contrary to this paradigm and inspired by biological photonic structures from hairs of blue tarantulas, a noniridescent photonic structure with long-range order is shown here. This photonic structure is hierarchical and has high degrees of rotational symmetry in suitable spatial scales.

April 22, 2015

[5] The role of random nanostructures for the omnidirectional anti-reflection properties of the glasswing butterfly

Radwanul Hasan Siddique, Guillaume Gomard, Hendrik Hölscher

Nature Communications 6, 6909

The glasswing butterfly (Greta oto) has, as its name suggests, transparent wings with remarkable low haze and reflectance over the whole visible spectral range even for large view angles of 80°. This omnidirectional anti-reflection behaviour is caused by small nanopillars covering the transparent regions of its wings. In difference to other anti-reflection coatings found in nature, these pillars are irregularly arranged and feature a random height and width distribution. Here we simulate the optical properties with the effective medium theory and transfer matrix method and show that the random height distribution of pillars significantly reduces the reflection not only for normal incidence but also for high view angles.

May 01, 2015

[4] Fabrication of hierarchical photonic nanostructures inspired by Morpho butterflies utilizing laser interference lithography

Radwanul Hasan Siddique, Ruben Hünig, Abrar Faisal, Uli Lemmer, Hendrik Hölscher

Optical Materials Express 5 (5), 996-1005

We introduce laser interference lithography (LIL) as a tool to fabricate hierarchical photonic nanostructures inspired by blue Morpho butterflies. For that, we utilize the interference pattern in vertical direction in addition to the conventional horizontal one. The vertical interference creates the lamellae by exploiting the back reflection from the substrate. The horizontal interference patterns the ridges of the hierarchical Christmas tree like structure. The artificial Morpho replica produced with this technique feature a brilliant blue iridescence up to an incident angle of 40°.

September 08, 2014

[3] Utilizing laser interference lithography to fabricate hierarchical optical active nanostructures inspired by the blue Morpho butterfly

Radwanul Hasan Siddique, Abrar Faisal, Ruben Hünig, Carolin Bartels, Irene Wacker, Uli Lemmer, Hendrik Hölscher

SPIE Proceedings 9187, 9187

The famous non-iridescent blue of the Morpho butter by is caused by a `Christmas tree' like nanostructure which is a challenge for common fabrication techniques. Here, we introduce a method to fabricate this complex morphology utilizing dual beam interference lithography. We add a reflective coating below the photoresist to create a second interference pattern in vertical direction by exploiting the back reflection from the substrate. This vertical pattern exposes the lamella structure into the photosensitive polymer while the horizontal interference pattern determines the distance of the ridges. The photosensitive polymer is chosen accordingly to create the Christmas tree' like tapered shape. The resulting artificial Morpho replica shows brilliant non-iridescent blue up to an incident angle of 40. Its optical properties are close to the original Morpho structure because the refractive index of the polymer is close to chitin. Moreover, the biomimetic surface is water repellent with a contact angle of 110.

June 17, 2013

[2] Theoretical and experimental analysis of the structural pattern responsible for the iridescence of Morpho butterflies

Radwanul Hasan Siddique, Silvia Diewald, Juerg Leuthold, Hendrik Hölscher

Optics Express 21 (12), 14351-14361

Morpho butterflies are well-known for their iridescence originating from nanostructures in the scales of their wings. These optical active structures integrate three design principles leading to the wide angle reflection: alternating lamellae layers, “Christmas tree” like shape, and offsets between neighboring ridges. We study their individual effects rigorously by 2D FEM simulations of the nanostructures of the Morpho sulkowskyi butterfly and show how the reflection spectrum can be controlled by the design of the nanostructures. The width of the spectrum is broad (≈ 90 nm) for alternating lamellae layers (or “brunches”) of the structure while the “Christmas tree” pattern together with a height offset between neighboring ridges reduces the directionality of the reflectance. Furthermore, we fabricated the simulated structures by e-beam lithography. The resulting samples mimicked all important optical features of the original Morpho butterfly scales and feature the intense blue iridescence with a wide angular range of reflection.

December 17, 2009

[1] Performance of Solar Home Systems in Rural Bangladesh

Shahriar A Chowdhury, SM Raiyan Kabir, SM Moududul Islam, Radwanul Hasan Siddique, ATM Golam Sarwar

IEEE Proceedings

Solar Home System based rural electrification has seen dramatic progress since the start of the Rural Electrification and Renewable Energy Development Project (RREDP), which is financed by Infrastructure Development Company Limited (IDCOL) since 2003. Recently a technical audit was done for the Solar Home Systems. This paper illustrates the findings of the technical audit during the field visits to four different areas of Bangladesh. The study has revealed some technical shortcomings of the SHS packages sold in Bangladesh. These include incompatible component combinations, faulty installation, lack of quality control of component parts and lack of adequate quality standards and quality enforcement. The paper also proposes some simple solutions to address these issues so that the SHS industry will enjoy continued success in Bangladesh.

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