A method comprising: providing a fluidic conduit for conveying a fluid from a first region to a second region, the second region being optically coupled with a first waveguide resonator mirror comprising one or two linear waveguides (504, 512) evanescently coupled to a disc resonator or a ring resonator, such that the first waveguide resonant mirror reflects a first spectral component back to a laser when the fluid in the second region is analyte-free and reflects a second spectral component back to the laser when the fluid in the second region comprises an analyte, and whose optical resonance is based on the refractive index of the fluid in the second region, and wherein the first waveguide resonator mirror and the laser collectively define an external cavity laser that provides a first light signal whose center wavelength (902, 906) is based on the optical resonance of the first waveguide resonator mirror; inducing a flow of a fluid from the first region to the second region; introducing a sample comprising an analyte to the fluid, wherein the sample is introduced to the fluid conduit at the first region and at a first time, t, and wherein the fluid has a first refractive index when it is analyte-free and a second refractive index when it comprises the analyte; detecting the presence of an analyte in the buffer solution at the second region with a detector providing an electrical signal whose magnitude is based on the intensity of the first light signal and computing a time differential between a first time t, at which the analyte is present at the first regio, and a second time, t, at which a change from a first magnitude of the electrical signal occurs. providing a fluidic conduit for conveying a fluid from a first region to a second region, the second region being optically coupled with a first waveguide resonator mirror comprising one or two linear waveguides (504, 512) evanescently coupled to a disc resonator or a ring resonator, such that the first waveguide resonant mirror reflects a first spectral component back to a laser when the fluid in the second region is analyte-free and reflects a second spectral component back to the laser when the fluid in the second region comprises an analyte, and whose optical resonance is based on the refractive index of the fluid in the second region, and wherein the first waveguide resonator mirror and the laser collectively define an external cavity laser that provides a first light signal whose center wavelength (902, 906) is based on the optical resonance of the first waveguide resonator mirror; inducing a flow of a fluid from the first region to the second region; introducing a sample comprising an analyte to the fluid, wherein the sample is introduced to the fluid conduit at the first region and at a first time, t, and wherein the fluid has a first refractive index when it is analyte-free and a second refractive index when it comprises the analyte; detecting the presence of an analyte in the buffer solution at the second region with a detector providing an electrical signal whose magnitude is based on the intensity of the first light signal and computing a time differential between a first time t, at which the analyte is present at the first regio, and a second time, t, at which a change from a first magnitude of the electrical signal occurs.