Richard Loo

A quantitative diffraction-based sandwich immunoassay.

It is shown that diffraction-based sensing can be enhanced for diagnostic purposes through the use of a secondary label. The limit of detection for anti-rabbit IgG was reduced more than 40-fold by using a gold-conjugated secondary antibody. The response to secondary antibody binding was linear for concentrations from 25 to 500 ng/ml of anti-rabbit IgG, suggesting that quantitative determinations can be readily done. Moreover, the binding of the secondary antibody was observed as soon as 1 min after its introduction to the surface-bound primary complex.

Demonstration of diffraction enhancement via Bloch surface waves in a-SiN:H multilayers

Using the excitation of a Bloch Surface Wave (BSW), we demonstrate a 45-fold diffraction enhancement for a protein grating printed on a-SiN:H multilayers. This may lead to a new generation of high sensitivity diffraction-based biosensors.

In vitro Synthesis of Native, Fibrous Long Spacing and Segmental Long Spacing Collagen

Collagen fibrils are present in the extracellular matrix of animal tissue to provide structural scaffolding and mechanical strength. These native collagen fibrils have a characteristic banding periodicity of ~67 nm and are formed in vivo through the hierarchical assembly of Type I collagen monomers, which are 300 nm in length and 1.4 nm in diameter. In vitro, by varying the conditions to which the monomer building blocks are exposed, unique structures ranging in length scales up to 50 microns can be constructed, including not only native type fibrils, but also fibrous long spacing and segmental long spacing collagen. Herein, we present procedures for forming the three different collagen structures from a common commercially available collagen monomer. Using the protocols that we and others have published in the past to make these three types typically lead to mixtures of structures. In particular, unbanded fibrils were commonly found when making native collagen, and native fibrils were often present when making fibrous long spacing collagen. These new procedures have the advantage of producing the desired collagen fibril type almost exclusively. The formation of the desired structures is verified by imaging using an atomic force microscope.

Enhancement of light-matter interaction using surface states in photonic crystal structures

Bloch Surface Waves (BSWs) are propagation modes that exist at the interface between a homogeneous medium and a photonic crystal (PhC). The confinement at the interface of the media relies on total internal reflection in the homogeneous medium and on the photonic band gap in the PhC. The dispersion relation of BSWs can be easily tailored through the design of the PhC. This makes BSWs extremely flexible and suitable for applications in the field of optical sensors, light emitters, and photovoltaic devices, where the capability to confine and amplify the electromagnetic field in micro- and nano-structures allows for the enhancement of the light-matter interaction. In particular, we present two different configurations for the detection of Bloch surface waves in silicon nitride multilayers: attenuated total reflectance and photoluminescence measurements. In the first, we measured a 50-fold enhancement of the diffraction signal by a protein grating printed on the multilayer when the incident light beam is coupled to the surface waves. In the second, we observe a significant modification of the spontaneous emission by a monolayer of rhodamine molecules bonded to the photonic crystal surface. These results may found application in the field of optical sensors, particularly for biosensing.