Label-Free Multiplexed Microfluidic Analysis of Protein Interactions Based on Photonic Crystal Surface Mode Imaging.

High-throughput protein assays are crucial for modern diagnostics, drug discovery, proteomics, and other fields of biology and medicine. It allows simultaneous detection of hundreds of analytes and miniaturization of both fabrication and analytical procedures. Photonic crystal surface mode (PC SM) imaging is an effective alternative to surface plasmon resonance (SPR) imaging used in conventional gold-coated, label-free biosensors. PC SM imaging is advantageous as a quick, label-free, and reproducible technique for multiplexed analysis of biomolecular interactions. PC SM sensors are characterized by a longer signal propagation at the cost of a lower spatial resolution, which makes them more sensitive than classical SPR imaging sensors. We describe an approach for designing label-free protein biosensing assays employing PC SM imaging in the microfluidic mode. Label-free, real-time detection of PC SM imaging biosensors using two-dimensional imaging of binding events has been designed to study arrays of model proteins (antibodies, immunoglobulin G-binding proteins, serum proteins, and DNA repair proteins) at 96 points prepared by automated spotting. The data prove feasibility of simultaneous PC SM imaging of multiple protein interactions. The results pave the way to further develop PC SM imaging as an advanced label-free microfluidic assay for the multiplexed detection of protein interactions.

Photonic crystal biosensor based on optical surface waves.

A label-free biosensor device based on registration of photonic crystal surface waves is described. Angular interrogation of the optical surface wave resonance is used to detect changes in the thickness of an adsorbed layer, while an additional simultaneous detection of the critical angle of total internal reflection provides independent data of the liquid refractive index. The abilities of the device are demonstrated by measuring of biotin molecule binding to a streptavidin monolayer, and by measuring association and dissociation kinetics of immunoglobulin G proteins. Additionally, deposition of PSS / PAH polyelectrolytes is recorded in situ resulting calculation of PSS and PAH monolayer thicknesses separately.

A biosensor based on photonic crystal surface waves with an independent registration of the liquid refractive index.

A high-precision optical biosensor technique capable of independently determining the refractive index (RI) of liquids is presented. Photonic crystal surface waves were used to detect surface binding events, while an independent registration of the critical angle was used for accurate determination of the liquid RI. This technique was tested using binding of biotin molecules to a streptavidin monolayer at low and high biotin concentrations. The attained baseline noise is 5x10(-13) m/Hz(1/2) for adlayer thickness changes and 9x10(-8) RIU/Hz(1/2) for RI changes.

Long-range plasmons in lossy metal films on photonic crystal surfaces.

A one-dimensional (1D) photonic crystal structure with a terminal palladium layer supporting long-range surface plasmon polariton (LRSPP) waves in any gaseous environment is described. We show that LRSPP propagation may be achieved not only along "good plasmonic" metals such as Ag and Au but also along lossy metals such as Pd, which does not usually support plasmon propagation in the visible spectral range with ordinary Kretschmann excitation. The possibility of the LRSPP propagation along catalytically active metals such as Pd or Pt opens up new perspectives for studying of (photo)chemical surface reactions and offers the potential for more applications in the general area of catalysis, photocatalysis, and plasmon-mediated chemistry. We present experimental results that demonstrate the hydrogen sensitivity of this photonic structure incorporating a catalytically active 8-nm-thick Pd final layer. A 3% hydrogen concentration in nitrogen is detected with a signal-to-noise ratio of approximately 300, with a response time of about 10 s at room temperature.

Optical biosensors based on photonic crystal surface waves.

Optical biosensors have played a key role in the selective recognition of target biomolecules and in biomolecular interaction analysis, providing kinetic data about biological binding events in real time without labeling. The advantages of the label-free concept are the elimination of detrimental effects from labels that may interfere with fundamental interaction and the absence of a time-consuming pretreatment. The disadvantages of all label-free techniques--including the most mature one, surface plasmon resonance (SPR) technique, are a deficient sensitivity to a specific signal and undesirable susceptibilities to non-specific signals, e.g., to the volume effect of refraction index variations. These variations arise from temperature fluctuations and drifts and they are the limiting factor for many state-of-the-art optical biosensors. Here we describe a new optical biosensor technique based on the registration of dual optical s-polarized waves on a photonic crystal surface. The simultaneous registration of two different optical modes from the same surface spot permits the segregation of the volume and the surface signals, while the absence of metal damping permits an increase in the propagation length of the optical surface waves and the sensitivity of the biosensor. The technique was tested with the binding of biotin molecules to a streptavidin monolayer that has been detected with a signal/noise ratio of about 15 at 1 s signal accumulation time. The detection limit is about 20 fg of the analyte on the probed spot of the surface.

Photonic crystal surface waves for optical biosensors.

We present a new optical biosensor technique based on registration of dual optical s-polarized modes on a photonic crystal surface. The simultaneous registration of two optical surface waves with different evanescent depths from the same surface spot permits the segregation of the volume and the surface contributions from an analyte, while the absence of metal damping permits an increase in the propagation length of the optical surface waves and the sensitivity of the biosensor. Our technique was tested with the binding of biotin molecules to a streptavidin monolayer that has been detected with signal/noise ratio of approximately 15 at 1-s signal accumulation time. The detection limit is approximately 20 fg of the analyte on the probed spot of the surface.

Long-range propagation of plasmon polaritons in a thin metal film on a one-dimensional photonic crystal surface.

We present experimental results on ultralong-range surface plasmon polaritons, propagating in a thin metal film on a one-dimensional (1D) photonic crystal surface over a distance of several millimeters. This propagation length is about 2 orders of magnitude higher than the one in the ordinary Kretschmann configuration at the same optical frequency. We show that a long-range surface plasmon polaritons propagation may take place not only in a (quasi)symmetrical scheme, where a thin metal film is located between two media with (approximately) the same refraction index, but also in a scheme where the thin metal film is located between an appropriate 1D photonic crystal and an arbitrary (air, water, etc.) medium. The ultralong-range surface plasmon polaritons are potentially important for biosensors, plasmonics, and other applications.