Disclosed herein are sensors that include a flexible mounting member comprising an adhesive surface configured to attach directly to a sample and to assume a shape corresponding to at least a portion of the sample when it attaches to the sample； and a plurality of radiation sources, a spectral detector, and an electronic processor attached to the mounting member, wherein the electronic processor is configured to cause at least two of the radiation sources to direct incident radiation to a sample, to cause the spectral detector to analyze radiation from the sample, and to determine one or more properties of the sample based on the radiation from the sample.
