Abstract
Resonant waveguide gratings (RWG) − also called photonic crystal slabs (PCS) − have been established as reliable optical transducers for label-free biochemical assays as well as for cell-based assays. Current readout systems are based on mechanical scanning and spectrometric measurements with system sizes suitable for laboratory equipment. Here, we review recent progress in compact intensity-based readout systems for point-of-care (POC) applications. We briefly introduce PCSs as sensitive optical transducers and introduce different approaches for intensity-based readout systems. Photometric measurements have been realized with a simple combination of a light source and a photodetector. Recently a 96-channel, intensity-based readout system for both biochemical interaction analyses as well as cellular assays was presented employing the intensity change of a near cut-off mode. As an alternative for multiparametric detection, a camera system for imaging detection has been implemented. A portable, camera-based system of size 13cm×4.9cm×3.5cm with six detection areas on an RWG surface area of 11mm×7mm has been demonstrated for the parallel detection of six protein binding kinetics. The signal-to-noise ratio of this system corresponds to a limit of detection of 168M (24ng/ml). To further improve the signal-to-noise ratio advanced nanostructure designs are investigated for RWGs. Here, results on multiperiodic and deterministic aperiodic nanostructures are presented. These advanced nanostructures allow for the design of the number and wavelengths of the RWG resonances. In the context of intensity-based readout systems they are particularly interesting for the realization of multi-LED systems. These recent trends suggest that compact point-of-care systems employing disposable test chips with RWG functional areas may reach market in the near future.
Highlights
In the last years, the detection of proteins as one type of biomarker has become more and more important in diagnostics of slowly progressing diseases as well as for acute cases [1, 2]
We reviewed progress in intensity-based reader systems for resonant waveguide grating (RWG) biosensors
Changes of the refractive index caused by biomolecular binding or by a change of the cell number or cellular mass distribution in a cellular assay cause a shift of the guided-mode resonance (GMR) in the spectrum
Summary
The detection of proteins as one type of biomarker has become more and more important in diagnostics of slowly progressing diseases as well as for acute cases [1, 2]. Following Bragg theory, the resonance wavelength λres is a function of the grating period Λ, the effective refractive index neff of the guided mode and the angle of incidence Θ [18]: λres = Λ ⋅ (neff ± sin(Θ)). The resonance position becomes a mere function of the grating period and the effective refractive index of the quasi-guided mode. Due to the confinement of the mode to the waveguide, photonic-crystal slabs are only sensitive to refractive index changes close to the surface. This is highly advantageous for suppression of background effects in the sample volume. For intensity-based measurement setups, an intermediate quality factor of around Q ~ 160 has proven advantageous for combining a significant intensity change and a good signal-to-noise ratio
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
