Wei Ru Wong

Serological Diagnosis of Dengue Infection in Blood Plasma Using Long-Range Surface Plasmon Waveguides

We present a compact, cost-effective, label-free, real-time biosensor based on long-range surface plasmon polariton (LRSPP) gold (Au) waveguides for the detection of dengue-specific immunoglobulin M (IgM) antibody, and we demonstrate detection in actual patient blood plasma samples. Two surface functionalization approaches are proposed and demonstrated: a dengue virus serotype 2 (DENV-2) functionalized surface to capture dengue-specific IgM antibody in blood plasma and the reverse, a blood plasma functionalized surface to capture DENV-2. The results obtained via these two surface functionalization approaches are comparable to, or of greater quality, than those collected by conventional IgM antibody capture enzyme linked immunosorbent assay (MAC-ELISA). Our second functionalization approach was found to minimize nonspecific binding, thus improving the sensitivity and accuracy of the test. We also demonstrate reuse of the biosensors by regenerating the sensing surface down to the virus (or antibody) level or down to the bare Au.

Optimization of Long-Range Surface Plasmon Waveguides for Attenuation-Based Biosensing

The design and optimization of straight long-range surface plasmon waveguides to maximize attenuation surface sensitivity in biochemical sensing applications are discussed. The sensor consists of a Au stripe embedded in CYTOP, with a microfluidic channel etched into the top cladding to expose the surface of the Au stripe and define the sensing channel. The attenuation α_s of the structure changes as a biological adlayer grows on the Au surface. The dimensions of the stripe (thickness, width), the sensing length and the refractive index of the sensing buffer were varied in order to understand their impact on sensor performance. The attenuation sensitivity ∂α_s/∂a dominates over a wide range of waveguide designs, so we define a parameter K = (∂α_s/∂a)/αs where maximizing |K| and selecting the optimal sensing length as L_opt = 1/(2α_s) maximizes the overall sensitivity of the structure. Experimental results based on observing the physisorption of bovine serum albumin (BSA) on bare Au waveguides agree qualitatively and quantitatively with theory. Detection limits of ΔΓ_min <; 0.1 pg·mm^-2 are predicted for optimal designs, and a detection limit of ΔΓ_min = 4.1pg/mm² (SNR = 1) is demonstrated experimentally for a sub-optimal structure.

Long-range surface plasmon Y-junctions for referenced biosensing.

Long-range surface plasmon Y-junctions are demonstrated as sensors for the detection of bulk refractive index changes in solution and for protein binding. Using a fully-cladded Au stripe waveguide as a reference channel, common drift and noise in the system can be eliminated, relaxing the need for precise optical alignments. The performance of the structure is discussed theoretically, then bulk sensing is carried out experimentally with five solutions of different refractive indices, and protein sensing is demonstrated through physisorption of bovine serum albumin on a carboxyl-terminated Au stripe. The Y-junction biosensor demonstrated a very good ability to perform drift and noise suppression for fast and accurate biosensing.

Long-Range Surface Plasmon-Polariton Waveguide Biosensors for Disease Detection

We review recent progress on the application of long-range surface plasmon-polariton waveguide biosensors for disease detection. The biosensors are constructed from metal stripe waveguides cladded in Cytop with etched microfluidic channels to expose the stripe surface to the sensing fluid. The waveguides support long-range surface plasmons in integrated optics geometries when excited in an end-fire manner. Application to the detection of leukemia, dengue fever, and urinary tract infection is discussed.

Detection of Small Molecules Using Long-Range Surface Plasmon Polariton Waveguides

An optical biosensor utilizing long-range surface plasmon-polariton waveguides is discussed. This paper first reviews the technology and its various applications such as protein sensing, cell detection, and disease diagnostics, and then presents results on the detection of small molecules using the biosensor. The surface was functionalized with 16-mercaptohexadecanoic acid and activated using carbodiimide chemistry. Covalent attachment of N-hydroxysulfosuccinimide ester (Sulfo-NHS) of molecular weight ~200 Da produced a significant response with a signal-to-noise ratio of ~81 as a result of molecular monolayer formation. Since carbodiimide chemistry is a protein coupling approach commonly used to functionalize biosensors, a calibration scheme for extracting the actual amount of attached protein based on biosensor responses to NHS is proposed.

Enhancement of evanescent field exposure in a photonic crystal fibre with interstitial holes

Abstract In this work, a modified photonic crystal fibre (PCF) that we refer to as Sunny PCF with enhanced evanescent field exposure structure is proposed. The Sunny PCF with triangular interstitial air holes surrounding the core region increases the interaction of the guided mode with the air. Full-vectorial finite element method with perfectly matched layer boundary condition is used to design and simulate the sensitivity and confinement loss characteristics of the proposed Sunny PCF. By adding sunny structure to a conventional PCF with air-filling ratio of 0.9, the highest achievable sensitivity with negligible confinement loss can be boosted up to 21.23% from 15.83% at the operating wavelength of 1550 nm. Sunny PCF can achieve the same sensitivity as suspended-core holey fibre with lower confinement loss. A preliminary Sunny PCF has been fabricated to prove the feasibility of the proposed structure.

Biosensing using long-range surface plasmon waveguides

Long-range surface plasmon waveguides, and their application to various transducer architectures for amplitude- or phase-sensitive biosensing, are discussed. Straight and Y-junction waveguides are used for direct intensity-based detection, whereas Bragg gratings and single-, dual- and triple-output Mach Zehnder interferometers are used for phasebased detection. In either case, multiple-output biosensors which provide means for referencing are very useful to eliminate common perturbations and drift. Application of the biosensors to disease detection in complex fluids is discussed. Application to biomolecular interaction analysis and kinetics extraction is also discussed.

Surface plasmon in slab waveguide: A verification test-bed

Since its first use in a real-time analysis of a biological system in 1990s, surface plasmon resonance (SPR) has become an important optical biosensing technology for its real-time, label-free, and noninvasive nature. In this paper we review electromagnetic theory of surface plasmons in dielectric-metal-dielectric planar waveguides and verify capabilities of an emerging computational package, COMSOL, that uses finite element methods (FEM) for analysis of plasmonic phenomena. Results of analytical and numerical methods are compared and accuracy of FEM solver is discussed.

Dispersion modeling of solid core photonic crystal fiber

In this paper we calculate the dispersion values of our home-made solid core photonic crystal fiber (PCF) based on step index fiber model. Material dispersion and waveguide dispersion is taken into account while carrying out the calculation. The dispersion values predicted by this model agree well with that obtained by a commercial finite element method (FEM) solver.