A non-invasive method of determining the concentration of an analyte uses Raman or fluorescence spectral information. A high-intensity band of light is applied to one side of skin tissue. The high-intensity light enters the skin tissue and generates a Raman or fluorescence signal. A Raman-generating material or fluorescence-generating material is placed in a location nearest the other side of skin tissue. The Raman-generating or fluorescence-generating material is located generally opposite of the entry of the applied high-intensity light. The Raman or fluorescence signal is collected and the analyte concentration is determined using the collected Raman signal.