In general, ideas are patentable under the US patent law, if it is not too abstract. The question is whether other people can make the invention according to your idea without doing extensive experimentation. To get a patent, you also need to satisfy other elements. You can consult a patent attorney or a patent agent and ask him to do some research for you. You also can do some preliminary search by yourself. Check www.uspto.gov website for US patents, see if there is anything similar to your idea. Also check the scientific journals in the field where your idea belongs.