To evaluate this method for the detection of OP residues in food products, we have tested apples that were sprayed with 0, 30, 60,and 100 g/mL solutions of malathion. The quantity of malathion pesticide residing on the apple peels was quantified by both colorimetric and spectroscopic methods for a direct comparison. As shown in Fig. 5, the quantitation of malathion pesticide residues with the colorimetric microchip/scanner correlates well with the results determined with a standard spectrophotometer.