We report an experimental demonstration of an integrated biochemical sensor based on a slot-waveguide microring resonator. The microresonator is fabricated on a ${\mathrm{Si}}_3{\mathrm{N}}_4–\mathrm{Si}{\mathrm{O}}_2$ platform and operates at a wavelength of $1.3\mu \mathrm{m}$. 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 $212\mathrm{nm}$/refractive index units (RIU) is observed. The sensor detects a minimal refractive index variation of $2\times {10}^{-4}\mathrm{RIU}$.

We demonstrate label-free molecule detection by using an integrated biosensor based on a ${\mathrm{Si}}_3{\mathrm{N}}_4∕{\mathrm{SiO}}_2$ slot-waveguide 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 $3.2\mathrm{nm}∕(\mathrm{ng}∕{\mathrm{mm}}^2)$ for the detection of anti-BSA and BSA, respectively. The estimated detection limits are 28 and $16\mathrm{pg}∕{\mathrm{mm}}^2$ for anti-BSA and BSA, respectively, limited by wavelength resolution.

In this paper, we report experiments on the scattering of surface-elastic waves by a periodic array of cylindrical holes. The experiments were performed in a marble quarry by drilling cylindrical holes in two different configurations: honeycomb and triangular lattices. The attenuation spectra of the surface waves show the existence of absolute band gaps for elastic waves in these semi-infinite two-dimensional crystals. Results are compared with theoretical calculations based on a scalar-wave approach. The scaling property of the underlying theory has led us to explore the possible application of the results obtained to the attenuation of surface waves in seismic movements.

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.