MicroRNA Biosensing with Two-Dimensional Surface Plasmon Resonance Imaging.

Two-dimensional surface plasmon resonance (2D-SPR) imaging, which provides a real-time, sensitive, and high-throughput analysis of surface events in a two dimensional manner, is a valuable tool for studying biomolecular interactions and biochemical reactions without using any tag labels. The sensing principle of 2D-SPR includes angular, wavelength, and phase interrogation. In this chapter, the 2D-SPR imaging technique is applied for sensing a target microRNA by its corresponding oligonucleotide probes, with sequence complementarity, immobilized on the gold SPR sensing surface.

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.

High-throughput imaging surface plasmon resonance biosensing based on an adaptive spectral-dip tracking scheme.

Imaging-based spectral surface plasmon resonance (λSPR) biosensing is predominantly limited by data throughput because of the multiplied data capacity emerging from 2-dimensional sensor array sites and the many data points required to produce an accurate measurement of the absorption dip. Here we present an adaptive feedback approach to address the data throughput issue in λSPR biosensing. A feedback loop constantly tracks the dip location while target-molecule binding occurs at the sensor surface.

Fast spectral surface plasmon resonance imaging sensor for real-time high-throughput detection of biomolecular interactions.

A fast surface plasmon resonance (SPR) imaging biosensor system based on wavelength interrogation using a liquid crystal tunable filter (LCTF) is presented. The system combines the merits of wide-dynamic detection range offered by the spectral approach and multiplexed high-throughput data collection with a two-dimensional (2-D) biosensor array. The key feature of the reported scheme is a feedback loop that drives the LCTF to achieve fast tracking of the SPR dip movement caused by the binding of target molecules to the sensor surface.

Thermal gradient induced tweezers for the manipulation of particles and cells.

Optical tweezers are a well-established tool for manipulating small objects. However, their integration with microfluidic devices often requires an objective lens. More importantly, trapping of non-transparent or optically sensitive targets is particularly challenging for optical tweezers.

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.

Trapping and assembling of particles and live cells on large-scale random gold nano-island substrates.

We experimentally demonstrated the use of random plasmonic nano-islands for optical trapping and assembling of particles and live cells into highly organized pattern with low power density. The observed trapping effect is attributed to the net contribution due to near-field optical trapping force and long-range thermophoretic force, which overcomes the axial convective drag force, while the lateral convection pushes the target objects into the trapping zone. Our work provides a simple platform for on-chip optical manipulation of nano- and micro-sized objects, and may find applications in physical and life sciences.

Allergen screening bioassays: recent developments in lab-on-a-chip and lab-on-a-disc systems.

Allergies occur when a person's immune system mounts an abnormal response with or without IgE to a normally harmless substance called an allergen. The standard skin-prick test introduces suspected allergens into the skin with lancets in order to trigger allergic reactions. This test is annoying and sometimes life threatening.

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.

A lab-in-a-droplet bioassay strategy for centrifugal microfluidics with density difference pumping, power to disc and bidirectional flow control.

In this paper, we present a lab-in-a-droplet bioassay strategy for a centrifugal microfluidics or lab-on-a-disc (LOAD) platform with three important advancements including density difference pumping, power to disc and bidirectional flow control. First, with the water based bioassay droplets trapped in a micro-channel filled with mineral oil, centrifugal force due to the density difference between the water and oil phases actuates droplet movement while the oil based medium remains stationary. Second, electricity is coupled to the rotating disc through a split-core transformer, thus enabling on-chip real-time heating in selected areas as desired and wireless programmable functionality.

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.

Wavelength-multiplexing phase-sensitive surface plasmon imaging sensor.

A wavelength-multiplexing phase-sensitive surface plasmon resonance (SPR) imaging sensor offering wide dynamic detection range and microarray capability is reported. Phase detection is accomplished by performing self-interference between the s- and p- polarizations within the signal beam. A liquid crystal tunable filter is used to sequentially select the SPR excitation wavelength from a white light source.

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.

Differential spectral phase interferometry for wide dynamic range surface plasmon resonance biosensing.

We introduce a novel wide dynamic range phase-sensitive surface plasmon resonance (SPR) biosensor based on differential spectral interferometry. Superseding conventional spectroscopic approach where only the SPR dip is monitored, our system acquires the spectral phase information of the entire electromagnetic field that undergoes SPR transformation. Since the SPR-induced phase change is highly wavelength specific with fixed incident angle, ultra-high sensitivity achievable through phase-sensitive detection, as reported herein, is maintained continuously across the spectral domain in response to refractive index changes.

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.