An apparatus for inspecting a biological tissue uses a pH-sensitive coating material to determine whether the tissue is normal or cancerous. The coating material is placed in contact with the tissue to be excited by an excitation light. The coating material is arranged to provide a response signal indicative of the pH value of the tissue. Using a fiber bundle having a plurality of optical fibers forming a linear array or a two-dimensional array adjacent the coating material, the imaging of localized surface pH in the biological tissue can be achieved using the response signal through each of the optical fibers. The fiber bundle can be arranged as a probe to examine the tissue for providing direct mapping of the tumor margin via a display, so that a surgeon can inspect the tissue in real-time.
