Femtogram detection of horseradish peroxidase by a common desktop scanner

We report an image-based detection of horseradish peroxidase (HRP) by different color spaces. The results show excellent correlation between color saturation and absorbance (Pearson correlation coefficient; 0.9868) with respect to HRP. The present method can detect 185 and 46.45 fg/ml of HRP using o-phenylenediamine dihydrochloride and 3,3′,5,5′-tetramethylbenzidine as chromogenic substrates respectively.