A light emitting diode (LED) sensor including a first LED device disposed on a support and configured to emit a radiation, and a second LED device disposed on the support and configured to receive the emitted radiation. A structure is formed on the support, the first LED device, and the second LED device. The structure defines a contoured surface. A material is located adjacently to the contoured surface, wherein the material includes a property adapted to reflect the emitted radiation from the first LED to the second LED. The structure includes an ellipsoid and the contoured surface defines an ellipsoidal surface. First and second foci are defined by the ellipsoid, wherein emitted radiation from the first LED device converges at the first foci and the second foci and is reflected to the second LED device. The device is configured to determine a temperature or a chemical property of an analyte.