Abstract: A method of diagnosing, staging or monitoring cancer, the method comprising the steps of: (a) providing a sensor array comprising at least two sensors, wherein each sensor comprises a protein barrel that comprises five or more alpha helices arranged as an alpha-helical barrel, and a reporter dye, wherein the protein barrel defines a lumen, the reporter dye is bound to the lumen reversibly; and wherein the protein barrel is different in structure in the at least two sensors; (b) contacting the sensor array with a sample obtained from a patient; and then (c) comparing the sensor array to a predetermined standard.