We report a label-free, highly sensitive biosensor using a vertical cavity surface emitting laser (VCSEL) based measurement system for the detection and monitoring of biomolecular interactions. The sensor system consists of a VCSEL, a plastic guided mode resonant (GMR) filter, and two pin detectors. The system has several advantages such as extreme compactness, high sensitivity, high throughput, fast measurements, low power consumption, low cost, and the potential to become portable. Experimentally, the biosensor system has shown to be highly sensitive to the surface modifications due to molecular bindings, with the ability to detect the thickness variations <10Å and refractive index variations <0.005. The biosensor also has demonstrated its high sensitivity for the detection of antibody-antigen proteins bindings, with the mouse IgG concentration as low as 1pg/ml (6.7 femto-Molar), and its ability for measuring both static and dynamic interactions among proteins.