Rongjin Yan

Label-free silicon photonic biosensor system with integrated detector array

An integrated, inexpensive, label-free photonic waveguide biosensor system with multi-analyte capability has been implemented on a silicon photonics integrated circuit from a commercial CMOS line and tested with nanofilms. The local evanescent array coupled (LEAC) biosensor is based on a new physical phenomenon that is fundamentally different from the mechanisms of other evanescent field sensors. Increased local refractive index at the waveguides upper surface due to the formation of a biological nanofilm causes local modulation of the evanescent field coupled into an array of photodetectors buried under the waveguide. The planar optical waveguide biosensor system exhibits sensitivity of 20%/nm photocurrent modulation in response to adsorbed bovine serum albumin (BSA) layers less than 3 nm thick. In addition to response to BSA, an experiment with patterned photoresist as well as beam propagation method simulations support the evanescent field shift principle. The sensing mechanism enables the integration of all optical and electronic components for a multi-analyte biosensor system on a chip.

Evanescent field response to immunoassay layer thickness on planar waveguides.

The response of a compact photonic immunoassay biosensor based on a planar waveguide to variation in antigen (C-reactive protein) concentration as well as waveguide ridge height has been investigated. Near-field scanning optical microscope measurements indicate 1.7%nm and 3.3%nm top surface optical intensity modulation due to changes in effective adlayer thickness on waveguides with 16.5 and 10 nm ridge heights, respectively. Beam propagation method simulations are in good agreement with the experimental sensitivities as well as the observation of leaky mode interference both within and after the adlayer region.

Waveguide biosensor with integrated detector array for tuberculosis testing

A label-free immunoassay using a local evanescent array coupled (LEAC) biosensor is reported. Complementary metal oxide semiconductor chips with integrated photoconductor arrays are used to detect an antibody to a M. tuberculosis protein antigen, HspX. The metrology limits of the LEAC sensor using dc and ac measurement systems correspond to average film thicknesses of 28 and 14 pm, respectively. Limits of detection are 87 and 108 pm, respectively, for mouse immunoglobulin G antibody patterning and antigen detection.

Response of Local Evanescent Array-Coupled Biosensors to Organic Nanofilms

A label-free planar optical waveguide immunosensor that operates on the novel principle of local evanescent field shift is demonstrated in this paper. Increased local refractive index at the waveguides upper surface due to the formation of an organic adlayer shifts the evanescent field distribution up, and hence, changes the light intensity both above and below the waveguide structure. Beam propagation simulations show increased modulation ratio sensitivity to adlayer thickness with increasing detection distance below the waveguide. The local nature of detection allows sensors to be implemented in array formats on a single waveguide for multiple-analyte sensing. Both near-field scanning optical microscopy and integrated buried detector arrays are employed to study the response to patterned organic nanofilms including immunocomplexes, photoresist, and adsorbed bovine serum albumin (BSA) layers. Buried polysilicon detector arrays integrated with silicon nitride waveguides in a commercial CMOS process exhibit a 15% photocurrent modulation ratio response to an approximately 1-nm-thick adsorbed film of BSA. CMOS compatibility enables a low-cost sensor system on a chip. Temperature dependence measurements show that sensor has a 0.3%/degC change in modulation ratio, which is thousands of times less than traditional resonant biosensors.

Detection of virus-like nanoparticles via scattering using a chip-scale optical biosensor

A local evanescent array coupled biosensor is used to detect spherical polystyrene nanoparticles with diameters of 40 nm and 200 nm, whose sizes and refractive index are similar to virus particles. The sensitivity is ∼1%/particle for 200 nm particles and 0.04%/particle for 40 nm particles. Mie scattering in an evanescent field theory is used to model the scattered light intensity for both sizes of nanoparticles.

Immunoassay demonstration using a local evanescent array coupled biosensor

A Label-free optical waveguide immunosensor is investigated both theoretically and experimentally. The local evanescent array coupled (LEAC) biosensor is based on a local evanescent field shift mechanism, which differs from those of other evanescent waveguide sensors. Antigens specifically bound by immobilized antibodies on the waveguide surface increase the refractive index of the upper cladding of the waveguide, and hence shift the evanescent field distribution up. This local detection mechanism grants the LEAC sensor multi-analyte ability in a single optical path. Compared to traditional biosensors, including surface plasmon resonance and ring resonance biosensors, the nonresonant and temperature/wavelength insensitive properties of the LEAC biosensor relax its requirement on the optical source. It requires no accessory off-chip instruments such as spectrometers, making it a chip-scale biosensing platform. The on-chip detection is accomplished by integrating buried polysilicon detector arrays into silicon nitride waveguide in a commercial complementary metal oxide semiconductor (CMOS) process. Protein antigens and IgG producing biologically relevant antibody-antigen interactions were used to test the clinical utility of the LEAC biosensor platform. Advanced analysis beam propagation method (BPM) simulations and chips with different geometric parameters were used to study the relationship between the sensitivity and structure of LEAC biosensor.

Demonstration of local evanescent array coupled biosensors with organic nanofilms

Patterned nanoscale organic films including photoresist and bovine serum albumin locally modulate the evanescent field distribution of a SiNx core waveguide and are sensed with an integrated photodetector array on a CMOS chip.

Optimization of waveguide structure for local evanescent field shift detection

The waveguide structure for the local evanescent array coupled (LEAC) biosensor is optimized theoretically with Beam Propagation Method (BPM) simulations. The LEAC biosensor has successfully demonstrated experimental results of a sensitivity of 16% /nm and a metrology limit of 14 pm. Considering the waveguide thickness detector position used in previous experiments are far from optimized values, the detection performance of the LEAC sensor can be significantly improved with the simulated optimal structure. With the optimized parameters, when the upper cladding is air the estimated metrology limit is 0.8 pm; with water as the upper cladding for real-time measurements in an intigrated microfluidic channel, the estimated metrology limit is 1.6 pm.

A novel low-loss y-type splitter with adjustable branching ratio

Low loss splitters based on two mode waveguides are evaluated using near-field scanning optical microscopy and computer simulations. The branching ratio is a temperature sensitive function of the relative mode phases at the splitter.

A Waveguide Biosensors Local Evanescent Field Response to an Immunoassay Complex

A compact photonic immunoassay biosensor that can simultaneously sense multiple analytes has been implemented. NSOM results indicate 8% modulation of the local evanescent field due to an 18 nm biological adlayer on the waveguides surface.