We report an experimental demonstration of an integrated biochemical sensor based on a slot-waveguide microring resonator. The microresonator is fabricated on a Si3N4-SiO2 platform and operates at a wavelength of 1.3 microm. The transmission spectrum of the sensor is measured with different ambient refractive indices ranging from n=1.33 to 1.42. A linear shift of the resonant wavelength with increasing ambient refractive index of 212 nm/refractive index units (RIU) is observed. The sensor detects a minimal refractive index variation of 2x10(-4) RIU.
We demonstrate label-free molecule detection by using an integrated biosensor based on a Si 3 N4/Si0 2 slotwaveguide microring resonator. Bovine serum albumin (BSA) and anti-BSA molecular binding events on the sensor surface are monitored through the measurement of resonant wavelength shifts with varying biomolecule concentrations. The biosensor exhibited sensitivities of 1.8 and 3.2 nm/(ng/mm 2 ) for the detection of anti-BSA and BSA, respectively. The estimated detection limits are 28 and 16 pg/mm 2 for anti-BSA and BSA, respectively, limited by wavelength resolution.Label-free biomolecule optical sensing technologies are of great interest because of their flexibility to analyze biomolecular interactions without using fluorescence, absorptive, or radio-labels. This simplifies the assay and allows time-resolved study of the kinetics of biomolecular interactions. Integrated photonic devices used as biosensors present important advantages, such as high sensitivity, small size, and high scale integration. Thus, label-free integrated optical biosensors based on Mach-Zehnder interferometers , directional couplers , microring , and disk resonators have been demonstrated to be very sensitive label-free biosensors.Recently, we have reported an integrated photonic sensor based on a slot-waveguide resonator . This photonic structure takes advantage of the remarkable property of slot-waveguides to provide high optical intensity in a subwavelength-size low refractive index region (slot-region) sandwiched between two high refractive index strips (rails) . This permits a very high interaction between the slot-waveguide mode probe and a liquid analyte. As a result, the reported slot-waveguide sensor exhibited a bulk ambient sensitivity as high as 212.1 nm/refractive index unit (RIU), which is more than twice as large as that exhibited by ring resonator optical sensors based on conventional strip waveguides. In this Letter we demonstrate the detection of label-free molecular binding reactions on the surface of a slot-waveguide ring resonator. Bovine serum albumin (BSA) protein and anti-BSA are used to study the biosensor performance.The device consists of a 70 /mm radius slotwaveguide ring resonator made of Si 3 N 4 on Si0 2 The Si 3 N4 rails of the slot-waveguide ring are separated by 200 nm (w sht ), and their widths are 400 and 550 nm for the outer and inner rails, respectively, as illustrated in Fig. 1(a). A beam propagation method calculation of the quasi-TE optical mode of the ring slot-waveguide at 1.3 /mm operation wavelength is
A significant amount of noteworthy articles reviewing different label-free biosensors are being published in the last years. Most of the times, the comparison among the different biosensors is limited by the procedure used of calculating the limit of detection and the measurement uncertainty. This article clarifies and establishes a simple procedure to determine the calibration function and the uncertainty of the concentration measured at any point of the measuring interval of a generic label-free biosensor. The value of the limit of detection arises naturally from this model as the limit at which uncertainty tends when the concentration tends to zero. The need to provide additional information, such as the measurement interval and its linearity, among others, on the analytical systems and biosensor in addition to the detection limit is pointed out. Finally, the model is applied to curves that are typically obtained in immunoassays and a discussion is made on the application validity of the model and its limitations.
We report on the first demonstration of guiding light in vertical slot-waveguides on silicon nitride/silicon oxide material system. Integrated ring resonators and Fabry-Perot cavities have been fabricated and characterized in order to determine optical features of the slot-waveguides. Group index behavior evidences guiding and confinement in the low-index slot region at O-band (1260-1370nm) telecommunication wavelengths. Propagation losses of <20 dB/cm have been measured for the transverse-electric mode of the slot-waveguides.
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