Additional human colon tissue biopsies were immersed for 20 min in Eppendorf tubes containing (1) pure MES buffer, (2) an equimolar mixture of 50-pM S493, S440, S482, S420, S481, and S421, (3) a stepwise mixture of 10-pM S493, 20-pM S440, 30-pM S482, 40-pM S420, 50-pM S481, and 60-pM S421, and (4) a stepwise mixture of 5-pM S493, 10-pM S440, 15-pM S482, 20-pM S420, 25-pM S481, and 30-pM S421 [Fig. 7(a)]. Each mixture was chosen to simulate ratiometric imaging of targeted SERS nanoparticles against a nontargeted control (S493). The tissues were placed on a parafilm-covered quartz slide and imaged by using our LabView program. Sets of background images (the empty slide without tissue, the slide with tissue but before incubation in SERS nanoparticles, and a droplet of MES buffer on the slide: 135 spectra total) were first collected, reduced with PCA, and then used to unmix the image of the treated tissues using the algorithm described in Sec. 2.6. Measurements of the equimolar mixture after tissue immersion were used to calibrate the weighting factors and quantify SERS flavor ratios. Due to the current state of the LabView program, which currently displays two flavors, the images containing six flavors of SERS nanoparticles were postprocessed in MATLAB. When quantifying ratiometric values of each flavor against S493, pixels for which the S493 signal was below 3% of its maximum value were set to zero ratiometric value.