Shu Yuen Wu

White-light spectral interferometry for surface plasmon resonance sensing applications.

A novel differential phase detecting surface plasmon resonance (SPR) sensor based on white-light spectral interferometry is presented. Our proposed scheme employs a white-light source for SPR excitation and measures the corresponding SPR phase change at the optimized coupling wavelength with fixed angle of incidence across the visible spectrum. Compared to existing laser based phase detecting schemes, this system offers optimal sensitivity and extended dynamic range of measurement without any compromise in phase detection resolution. Results obtained from sodium chloride solutions indicate that the detection limit is u20282.6×10⁻⁷ RIU over a refractive index range of 10⁻² RIU, which is considerably wider than that achievable by existing laser based approach, thus making our scheme very attractive for practical SPR sensing applications.

Common-path spectral interferometry with temporal carrier for highly sensitive surface plasmon resonance sensing

Incorporating the temporal carrier technique with common-path spectral interferometry, we have successfully demonstrated an advanced surface plasmon resonance (SPR) biosensing system which achieves refractive index resolution (RIR) up to 2 × 10(-8) refractive index unit (RIU) over a wide dynamic range of 3 × 10(-2) RIU. While this is accomplished by optimizing the SPR differential phase sensing conditions with just a layer of gold, we managed to address the spectral phase discontinuity with a novel spectral-temporal phase measurement scheme. As the new optical setup supersedes its Michelson counterpart in term of simplicity, we believe that it is a significant contribution for practical SPR sensing applications.

Detection of Panton-Valentine Leukocidin DNA from methicillin-resistant Staphylococcus aureus by resistive pulse sensing and loop-mediated isothermal amplification with gold nanoparticles

This report describes a novel diagnostic assay for rapid detection of the Panton-Valentine Leukocidin (PVL) toxin of methicillin-resistant Staphylococcus aureus (MRSA) utilizing resistive pulse sensing (RPS), loop-mediated isothermal DNA amplification (LAMP) in combination with gold nanoparticles (AuNPs). The PVL DNA from MRSA was specifically amplified by LAMP using four primers at one temperature (65 °C). The DNA products with biotin were then conjugated to a first AuNP1 (55±2 nm) through biotin-avidin binding. A second AuNP2 (30±1.5 nm) coated with a specific DNA probe hybridized with the LAMP DNA products at the loop region to enhance assay sensitivity and specificity, to generate supra-AuNP1-DNA-AuNP2 assemblies. Scanning electron microscopy confirmed the presence of these supra-assemblies. Using RPS, detection and quantitation of the agglomerated AuNPs were performed by a tunable fluidic nanopore sensor. The results demonstrate that the LAMP-based RPS sensor is sensitive and rapid for detecting the PVL DNA. This technique could achieve a limit of detection (LOD) up to about 500 copies of genomic DNA from the bacteria MRSA MW2 and the detection can be completed within two hours with a straightforward signal-to-readout setup. It is anticipated that this LAMP-based AuNP RPS may become an effective tool for MRSA detection and a potential platform in clinical laboratory to report the presence or absence of other types of infectious agents.

Application of surface plasmon resonance sensing to studying elastohydrodynamic lubricant films.

We present a new technique based on the spectral characteristics associated with the surface plasmon resonance (SPR) effect for studying lubricants in elastohydrodynamic (EHD) dimples. The pressure inside the EHD dimple causes a localized change of the refractive index (RI) of the entrapped lubricant. This also results in a shift in the spectral SPR absorption dip. By monitoring the color changes within the SPR image, one can obtain a direct measurement of the RI of the entrapped lubricant, from which the pressure distribution within the elastohydrodynamic lubrication (EHL) dimple can be deduced by means of a predetermined relation of pressure and RI of the tested lubricant. Dimples formed with the lubricants PB 2400 and H 1900 were studied in our experiments. Because SPR is sensitive only to the RI variation within a thin region (approximately one wavelength) close to the sensors surface, the new technique does not require any measurement of the absolute film thickness of the lubricant. This is much simpler than the existing two-beam interferometric technique for measuring the RI of lubricants in EHD dimples, which requires simultaneous measurements of optical film thickness by use of two beams of different angles of incidence. In light of this advantage we anticipate that the new technique can be applied to pressure field mapping in highly loaded rolling and sliding EHL contacts.

A scanning thermocouple probe for temperature mapping

A simple thermocouple probe with tip diameter less than 10 /spl mu/m has been developed for mapping temperature distribution on surfaces. The fabrication procedures of the thermocouple tip involve fixing a fine tungsten wire inside a glass capillary tube and coating the exposed tip with gold. We have successfully used the thermocouple tip to obtain a two-dimensional temperature map on the heatsink of a high-power light-emitting diode (LED), thus demonstrating this device as a low-cost alternative to expensive infrared cameras for near-field thermal imaging.

Surface plasmon resonance measurement of pyridoxal kinase-pyridoxamine binding on self-assembled monolayer

Abstract Pyridoxamine-modified surface was prepared from self-assembly of pyridoxamine-linked 11-mercapto-undecan-1-one (PMU), which is synthesized via the chemistry of EDC/NHS activating 11-mercapto-undecanoic acid to link with pyridoxamine, on gold surface for the study of interaction between pyridoxamine and pyridoxal kinase (PK). This interaction was monitored by a low-cost red light-emitting-diode-based surface plasmon resonance technique. Addition of either 11-mercapto-undecan-1-ol (MU) or 1-dodecanethiol (DDT) to PMU for generating a mixed film can improve the performance of the monolayer of PMU for PK binding. Mixture of PMU and DDT in the mole ratio as low as 1:5 can achieve a significant enhancement (at least 89%) to the responses of PK binding.

Wavelength-Scanning SPR Imaging Sensors Based on an Acousto-Optic Tunable Filter and a White Light Laser

A fast surface plasmon resonance (SPR) imaging biosensor system based on wavelength interrogation using an acousto-optic tunable filter (AOTF) and a white light laser is presented. The system combines the merits of a wide-dynamic detection range and high sensitivity offered by the spectral approach with multiplexed high-throughput data collection and a two-dimensional (2D) biosensor array. The key feature is the use of AOTF to realize wavelength scan from a white laser source and thus to achieve fast tracking of the SPR dip movement caused by target molecules binding to the sensor surface. Experimental results show that the system is capable of completing a SPR dip measurement within 0.35 s. To the best of our knowledge, this is the fastest time ever reported in the literature for imaging spectral interrogation. Based on a spectral window with a width of approximately 100 nm, a dynamic detection range and resolution of 4.63 × 10−2 refractive index unit (RIU) and 1.27 × 10−6 RIU achieved in a 2D-array sensor is reported here. The spectral SPR imaging sensor scheme has the capability of performing fast high-throughput detection of biomolecular interactions from 2D sensor arrays. The design has no mechanical moving parts, thus making the scheme completely solid-state.

Application of surface plasmon resonance to measurement of hydrostatic pressure in tribological lubricant layers

A new method for studying elastohydrodynamic lubrication (EHL) dimple is demonstrated. This technique uses the spectral characteristics of surface plasmon resonance (SPR) to perform imaging of the dimple. Due to SPR absorption shift for different refractive index values, the refractive index variation across the dimple can be investigated by the color variation in the reflecting dimple image. Several dimples produced at different impact force levels have been studied in our experiments and the refractive index changes associated with such experimental conditions have been successfully identified by the spectral SPR imaging. The internal pressure distribution within the dimple is discussed.

Allergy Testing and Drug Screening on an ITO-Coated Lab-on-a-Disc

A lab-on-a-disc (LOAD) is a centrifugal microfluidic set-up based on centrifugal force without using micro-pumps to drive reagents and cells to various chambers through channels and valves for reactions. A LOAD coated with conductive transparent indium tin oxide (ITO) for thermal control was developed to screen allergy-blocking agents. When the acridine orange (AO)-loaded KU-812 human basophilic cells were activated in the LOAD by stimuli, AO trapped in the cytoplasmic granules was released externally as an allergic mediator mimetic to report degranulation. This response was monitored by fluorescence when the released AO in supernatant had been transferred, with a higher spinning speed, from the reaction chamber to detection chamber in the LOAD where AO reacted with exogenous DNA. We report here the principles of the system and an improved LOAD set-up with the ITO-coated glass resistive microheater to run assays at 37 °C. By using this platform, we demonstrate here for the first time that triptolide, an active ingredient from the Chinese medicine herb Tripterygium wilfordii Hook f., was able to suppress the fMLP-mediated degranulation in basophils. This serves as an example how LOADs can be used to screen agents to alleviate symptoms of allergy.

Two dimensional phase sensitive surface plasmon resonance biosensor array using microfluidic flow circuit platform

The integration between 2D SPR differential phase imaging sensor and microfluidic flow circuit is presented. It provides the advantages of high throughput, high sensitivity and label free detection to meet the present needs in biomechnical market. The differential phase scheme between p- and s- polarization enable elimination of all common-path phase noise while keeping the phase change caused by SPR effect. System sensitivity of the detection sensitivity of our setup is 0.44μg /ml is obtained for salt / water mixture sensing. BSA antigen and antibody binding reaction detection is further demonstrated. The system shows the capability of simultaneous detection for both specific and non-specific binding reactions in a micro-chamber array.