Chemical sensors such as carbon dioxide sensors and methods for making such sensors are disclosed. An example carbon dioxide sensor may include a substrate, with a sensing beam supported by the substrate. The sensing beam may be configured to resonant. A sensing layer may be disposed on the sensing beam, wherein the sensing layer may include an amino group and is configured to sense carbon dioxide. In some instances, a reference beam may also be supported by the substrate, and may be configured to resonant. A reference layer may be disposed on the reference beam, wherein the reference layer may includes an amino group that has been poisoned so that it will be substantially non-sensitive to carbon dioxide.