Measurement of the color evolution using this H parameter confirmed the previously observed trend regarding the stability of the porous silicon samples towards degradation. We then used this H parameter to compare the degradation of the two porous silicon

samples. Thus, Figure 9 shows a comparison of the normalized value ((H - H initial)/(H max - H initial)) for the fpSi and pSi-ch samples. The stability of the different silicon surfaces can be ranked by their initial rate of degradation, with the stabilities being in the order: freshly etched porous Si > chitosan-coated pSi. Figure 9 Evolution of the normalized H parameter during the first 300 min for fpSi and pSi-ch. The experimental conditions are as given for Figure 6. By comparing the degradation kinetics of the porous silicon samples using normalized reflectance values (either rugate position PARP inhibitor or EOT) and normalized H parameter values, we conclude that it is possible to obtain semiquantitative information about porous silicon stability using color data. In contrast, MG-132 manufacturer using the hue of the as-acquired images to monitor complete degradation is limited due to the interfering effect of the reflection of the broad light source spectrum from the porous silicon, silicon substrate, and other surfaces within the light path. However,

the use of a different light source with increased intensity in the blue-green regions of the spectrum compared to the lamp used may reduce this problem. The behavior of the hue parameter for porous rugate samples with the reflectance band at λ < 560 nm is also very dependent on the white balance value used during the image pre-processing step. Conclusions We have demonstrated that the degradation of porous silicon in basic aqueous buffers can be monitored in situ by digital imaging with a consumer-grade science digital camera and have validated this approach with simultaneous spectrophotometric measurement of the optical

reflectance spectra. An approximately linear correlation between the wavelength of the maximum of the rugate reflectance band and an H parameter derived from the HSV color space was observed during the degradation process. A similar relationship was also noted between the H parameter and the effective optical thickness of the samples. These results indicate that the samples were degrading via dissolution of the pore walls, rather than just dissolution from the top of the porous silicon layer downwards. The relative stabilities of the two porous silicon types obtained by the three measurement methods were consistent, indicating that all methods could be used to monitor relative sample degradation.