Recently, cheap silicon-on-insulator label-free biosensors have been demonstrated that allow fast and accurate quantitative detection of biologically relevant molecules for applications in medical diagnostics and drug development. However, whereas the sensor chip can be made cheaply, an expensive tunable laser is typically required to accurately monitor spectral shifts in the sensor’s transmission spectrum (wavelength interrogation). To address this issue, we integrated a very sensitive Vernier-cascade sensor with an arrayed waveguide grating spectral filter that divides the sensor’s transmission spectrum in multiple wavelength channels and transmits them to spatially separated output ports, allowing wavelength interrogation with a much cheaper broadband light source. Experiments show that this sensor can monitor refractive index changes of watery solutions in real time with a detection limit ( $1.6·{10}^{-5}\mathrm{RIU}$ ) competitive with more expensive interrogation schemes, indicating its applicability in low-cost label-free biosensing. The relaxation on the complexity of the source, moreover, offers the prospect to integrate the source and detectors to further reduce the device cost and to increase its portability.