[Show abstract][Hide abstract] ABSTRACT: We describe here soft nanofabrication methods using spin-on glass (SOG) materials for the fabrication of both bulk materials and replica masters. The precision of soft nanofabrication using SOG is tested using features on size scales ranging from 0.6 nm to 1.0 μm. The performance of the embossed optics is tested quantitatively via replica patterning of new classes of plasmonic crystals formed by soft nanoimprinting of SOG. These crystals are found to offer significant improvements over previously reported plasmonic crystals fabricated using embossed polymeric substrate materials in several ways. The SOG structures are shown to be particularly robust, being stable in organic solvent environments and at high temperatures (∼450 °C), thus extending the capacities and scope of plasmonic crystal applications to sensing in these environments. They also provide a stable, and particularly high-performance, platform for surface-enhanced Raman scattering. We further illustrate that SOG embossed nanostructures can serve as regenerable masters for the fabrication of plasmonic crystals. Perhaps most significantly, we show how the design rules of plasmonic crystals replicated from a single master can be tuned during the embossing steps of the fabrication process to provide useful modifications of their optical responses. We illustrate how the strongest feature in the transmission spectrum of a plasmonic crystal formed using a single SOG master can be shifted precisely in a SOG replica between 700 and 900 nm for an exemplary design of a full 3D plasmonic crystal by careful manipulation of the process parameters used to fabricate the optical device.
[Show abstract][Hide abstract] ABSTRACT: We describe a class of plasmonic crystal that consists of square arrays of nanoposts formed by soft nanoimprint lithography. As sensors, these structure show somewhat higher bulk refractive index sensitivity for aqueous solutions in the visible wavelength range as compared to plasmonic crystals consisting of square arrays of nanowells with similar dimensions, with opposite trends for the case of surface bound layers in air. Three-dimensional finite-difference time-domain simulations quantitatively capture the key features and assist in the interpretation of these and related results.
[Show abstract][Hide abstract] ABSTRACT: This work provides plasmonic crystal platforms for quantitative imaging mode biosensing and multispectral immunoassays, establishing and validating both the optical and equilibrium bases for their operation. We investigated the distance-dependent refractive index sensitivity of full 3D plasmonic crystals to thin polymeric films formed using layer by layer (LbL) assembly of polyelectrolytes as a model system. LbL was also used to determine the preferred gold thickness and plasmonic crystal design rules (nanowell diameter and periodicity) for improved thin-film sensitivity, and full 3D finite-difference time-domain (FDTD) calculations were used to quantitatively model and confirm the experimentally observed thin film sensitivities. The integrated multispectral response of the crystals increases approximately linearly with film thickness for values <70 nm, which enables the use of molecular rulers with known thicknesses (such as self-assembled monolayers of alkanethiols on gold) to calibrate these optics for quantitative detection and speciation of surface binding events in a multiplexed imaging format. The utility of these sensors and multispectral analysis for applications in quantitative biosensing was further demonstrated by measuring the equilibrium response curve of an antibody/antigen pair (rabbit antigoat IgG/goat IgG) at increasing antigen concentrations. Fitting the integrated response to a Langmuir isotherm yielded a calculated binding constant on the order of approximately 10(7) M(-1), which is in agreement with the affinity constants reported in the literature for anti-IgG/IgG binding pairs and provides intrinsic detection limits of approximately 400 pM for such unamplified assays.
[Show abstract][Hide abstract] ABSTRACT: We study the refractive index sensitive transmission of a 3D plasmonic crystal that consists of a square array of subwavelength cylindrical nanowells in a polymer conformally coated with a gold film. Using extensive 3D finite-difference time-domain simulations, we investigate the effect of system parameters such as periodicity, well diameter and depth, and metal thickness on its refractive index sensitivity. These theoretical results are also confirmed experimentally in some cases. Our calculations predict an enhancement in sensitivity by an order of magnitude when the plasmonic crystal characteristics are optimized.
Full-text · Article · May 2009 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: The coherent oscillations of conduction electron on a metal surface excited by electromagnetic radiation at a metal-dielectric interface is the surface plasmons (Sps). Plasmonic is the growing field of research on such light-metal interactions, of which has attracted much attention caused by its potential applications in miniaturized optical devices, sensors, and photonic circuits, as well as in medical diagnostic and therapeutics. It is also a highly active area caused by the recent advances in nanofabrication methodologies. There are two types of surface plasmon resonances (SPRs) used in surfaced-based sensing such as propagating surface plasmon polaritons (SPPs) and nonpropagating localized SPRs (LSPRs). This review focuses mainly on LSPRs and its use in chemical and biological sensing and surface-improved spectroscopies.
[Show abstract][Hide abstract] ABSTRACT: Plasmonic crystal optics: Highly uniform, fully 3D plasmonic crystals exhibiting exceptional analytical sensitivity at visible wavelengths can image surface binding events with high spatial resolution and can distinguish adsorbates with masses that differ by only 25 amu. The picture shows a transmitted white-light plasmonic image of microcontact-printed lines (ca. 8 μm wide) of 1-octadecanethiol on the Au surface of a 3D plasmonic crystal. (Figure Presented).
Full-text · Article · Feb 2008 · Angewandte Chemie International Edition
[Show abstract][Hide abstract] ABSTRACT: This paper describes composite patterning elements that use a commercially available acryloxy perfluoropolyether (a-PFPE) in various soft lithographic techniques, including microcontact printing, nanotransfer printing, phase-shift optical lithography, proximity field nanopatterning, molecular scale soft nanoimprinting, and solvent assisted micromolding. The a-PFPE material, which is similar to a methacryloxy PFPE (PFPE-DMA) reported recently, offers a combination of high modulus (10.5 MPa), low surface energy (18.5 mNm(-1)), chemical inertness, and resistance to solvent induced swelling that make it useful for producing high fidelity patterns with these soft lithographic methods. The results are comparable to, and in some cases even better than, those obtained with the more widely explored material, high modulus poly(dimethylsiloxane) (h-PDMS).
[Show abstract][Hide abstract] ABSTRACT: Conventional photolithography uses rigid photomasks of fused quartz and high-purity silica glass plates covered with patterned microstructures of an opaque material. We introduce new, traneparent, elastomeric molds (or stamps) of poly(dimethylsiloxane) (PDMS) that can be employed as photomasks to produce the same resist patten of the recessed (or non-contact) regions of stamps, in contrast to other reports in the literature() of using PDMS is lower than that of the contact regions. Therfore, we employ a difference in the effective exposure dose between the contact and non-contact regions through the PDMS stamp to generate the same pattern as the PDMS photomask. The photomasking capability of the PDMS stamps, which is similar to rigid photomasks in conventional photolithography, widens the application boundaries of soft-contact optical lithography and makes the photolithography process and equipment very simple. This soft-contact optical lithogarphy process can be widely used to perform photolithography on flexible substrates, avoiding metal or resist cracks, as it uses soft, conformable, intimate contact with photoresist without any external pressure. To this end, we demonstrate soft-contact optical lithography on the gold-coated PDMS substrate and utilized the patterned Au/PDMS substrate with feature sizes into the nanometer regime as a top electrode in organic light emitting diodes that are formed by soft-contact lamination.
[Show abstract][Hide abstract] ABSTRACT: This article briefly describes two recently developed soft-lithographic techniques that can be used to fabricate complex, well-defined three-dimensional (3D) nanostructures. The first relies on the single or multilayer transfer of thin solid 'ink' coatings from high-resolution rubber stamps. The second uses these stamps as conformable phase masks for proximity field nanopatterning of thin layers of transparent photopolymers. Although both techniques use the same pattern-transfer elements, they rely on completely different physical principles and they provide complementary patterning capabilities. The operational simplicity of the techniques, their ability to pattern large areas quickly, and the flexibility in the geometry of structures that can be formed with them suggest general utility for 3D nanomanufacturing.
[Show abstract][Hide abstract] ABSTRACT: This paper describes an approach for using conventional photoresist materials to pattern structures with dimensions as small as 50 nm. This method, known as near field phase shift lithography (NFPSL), is an experimentally simple approach to nanofabrication that relies on ultraviolet exposure of a layer of resist while it is in conformal, atomic scale contact with such an elastomeric phase mask. This paper presents some representative structures produced with this method; it illustrates an example of its use in patterning the critical dimensions of organic transistors; and it outlines some new modeling results of the optics associated with this technique.
Preview · Article · Aug 2004 · Journal of Photochemistry and Photobiology A Chemistry