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Monitoring of degradation of porous silicon photonic crystals using digital photography.

Ariza-Avidad M, Nieto A, Salinas-Castillo A, Capitan-Vallvey LF, Miskelly GM, Sailor MJ - Nanoscale Res Lett (2014)

Bottom Line: As the nanostructured porous silicon matrix dissolved, a hypsochromic shift in the wavelength of the rugate reflectance peak resulted in visible color changes from red to green.A monotonic relationship was observed between the wavelength of the rugate reflectance peak and an H parameter value calculated from the average red-green-blue (RGB) values of each image by first independently normalizing each channel (R, G, and B) using their maximum and minimum value over the time course of the degradation process.Spectrophotometric measurements and digital image analysis using this H parameter gave consistent relative stabilities of the samples as fpSi > pSi-ch.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358, USA ; Department of Analytical Chemistry, University of Granada, Faculty of Sciences, Avda. Fuentenueva s/n, Granada E-18071, Spain.

ABSTRACT
We report the monitoring of porous silicon (pSi) degradation in aqueous solutions using a consumer-grade digital camera. To facilitate optical monitoring, the pSi samples were prepared as one-dimensional photonic crystals (rugate filters) by electrochemical etching of highly doped p-type Si wafers using a periodic etch waveform. Two pSi formulations, representing chemistries relevant for self-reporting drug delivery applications, were tested: freshly etched pSi (fpSi) and fpSi coated with the biodegradable polymer chitosan (pSi-ch). Accelerated degradation of the samples in an ethanol-containing pH 10 aqueous basic buffer was monitored in situ by digital imaging with a consumer-grade digital camera with simultaneous optical reflectance spectrophotometric point measurements. As the nanostructured porous silicon matrix dissolved, a hypsochromic shift in the wavelength of the rugate reflectance peak resulted in visible color changes from red to green. While the H coordinate in the hue, saturation, and value (HSV) color space calculated using the as-acquired photographs was a good monitor of degradation at short times (t < 100 min), it was not a useful monitor of sample degradation at longer times since it was influenced by reflections of the broad spectral output of the lamp as well as from the narrow rugate reflectance band. A monotonic relationship was observed between the wavelength of the rugate reflectance peak and an H parameter value calculated from the average red-green-blue (RGB) values of each image by first independently normalizing each channel (R, G, and B) using their maximum and minimum value over the time course of the degradation process. Spectrophotometric measurements and digital image analysis using this H parameter gave consistent relative stabilities of the samples as fpSi > pSi-ch.

No MeSH data available.


Plot showing hue derived from as-acquired images and scaled H-parameter derived from pre-processed RGB values. The H parameter has been scaled for this plot so that hue and the H parameter have the same numerical value at 100 min.
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Figure 8: Plot showing hue derived from as-acquired images and scaled H-parameter derived from pre-processed RGB values. The H parameter has been scaled for this plot so that hue and the H parameter have the same numerical value at 100 min.

Mentions: The degradation of porous Si, typically monitored by reflection or transmission measurements using a spectrophotometer, can also be monitored using digital photography if the degradation results in a perceived color change. Since previous studies have reported that the H coordinate of the HSV color space can provide a robust single parameter that corresponds to changes in the position of the main band in a reflectance spectrum of an optical sensor [9,10], we investigated whether this H coordinate could be used to monitor the shifts in wavelength and intensity of the narrow rugate reflectance band as porous silicon degrades. We initially investigated calculating the H coordinate for the as-acquired images, Figures 7 and 8. As the porous silicon degradation process occurred this H coordinate (hue) increased from ca. 0.033 to a maximum value of 0.18. These changes in the H coordinate values were manifested in a visible color change from red to green and a decrease and increase in the red and green channels of the images, respectively (Figure 7). Once all the pSi had dissolved, the mirror-like silicon wafer substrate was exposed. Reflection of the tungsten light source from this bare silicon surface was yellow as captured by the camera. This reflection from the substrate resulted in a reduction in the magnitude of the hue from ca. 0.18 to 0.11 at long times (at time >100 min), Figure 8.


Monitoring of degradation of porous silicon photonic crystals using digital photography.

Ariza-Avidad M, Nieto A, Salinas-Castillo A, Capitan-Vallvey LF, Miskelly GM, Sailor MJ - Nanoscale Res Lett (2014)

Plot showing hue derived from as-acquired images and scaled H-parameter derived from pre-processed RGB values. The H parameter has been scaled for this plot so that hue and the H parameter have the same numerical value at 100 min.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4155483&req=5

Figure 8: Plot showing hue derived from as-acquired images and scaled H-parameter derived from pre-processed RGB values. The H parameter has been scaled for this plot so that hue and the H parameter have the same numerical value at 100 min.
Mentions: The degradation of porous Si, typically monitored by reflection or transmission measurements using a spectrophotometer, can also be monitored using digital photography if the degradation results in a perceived color change. Since previous studies have reported that the H coordinate of the HSV color space can provide a robust single parameter that corresponds to changes in the position of the main band in a reflectance spectrum of an optical sensor [9,10], we investigated whether this H coordinate could be used to monitor the shifts in wavelength and intensity of the narrow rugate reflectance band as porous silicon degrades. We initially investigated calculating the H coordinate for the as-acquired images, Figures 7 and 8. As the porous silicon degradation process occurred this H coordinate (hue) increased from ca. 0.033 to a maximum value of 0.18. These changes in the H coordinate values were manifested in a visible color change from red to green and a decrease and increase in the red and green channels of the images, respectively (Figure 7). Once all the pSi had dissolved, the mirror-like silicon wafer substrate was exposed. Reflection of the tungsten light source from this bare silicon surface was yellow as captured by the camera. This reflection from the substrate resulted in a reduction in the magnitude of the hue from ca. 0.18 to 0.11 at long times (at time >100 min), Figure 8.

Bottom Line: As the nanostructured porous silicon matrix dissolved, a hypsochromic shift in the wavelength of the rugate reflectance peak resulted in visible color changes from red to green.A monotonic relationship was observed between the wavelength of the rugate reflectance peak and an H parameter value calculated from the average red-green-blue (RGB) values of each image by first independently normalizing each channel (R, G, and B) using their maximum and minimum value over the time course of the degradation process.Spectrophotometric measurements and digital image analysis using this H parameter gave consistent relative stabilities of the samples as fpSi > pSi-ch.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358, USA ; Department of Analytical Chemistry, University of Granada, Faculty of Sciences, Avda. Fuentenueva s/n, Granada E-18071, Spain.

ABSTRACT
We report the monitoring of porous silicon (pSi) degradation in aqueous solutions using a consumer-grade digital camera. To facilitate optical monitoring, the pSi samples were prepared as one-dimensional photonic crystals (rugate filters) by electrochemical etching of highly doped p-type Si wafers using a periodic etch waveform. Two pSi formulations, representing chemistries relevant for self-reporting drug delivery applications, were tested: freshly etched pSi (fpSi) and fpSi coated with the biodegradable polymer chitosan (pSi-ch). Accelerated degradation of the samples in an ethanol-containing pH 10 aqueous basic buffer was monitored in situ by digital imaging with a consumer-grade digital camera with simultaneous optical reflectance spectrophotometric point measurements. As the nanostructured porous silicon matrix dissolved, a hypsochromic shift in the wavelength of the rugate reflectance peak resulted in visible color changes from red to green. While the H coordinate in the hue, saturation, and value (HSV) color space calculated using the as-acquired photographs was a good monitor of degradation at short times (t < 100 min), it was not a useful monitor of sample degradation at longer times since it was influenced by reflections of the broad spectral output of the lamp as well as from the narrow rugate reflectance band. A monotonic relationship was observed between the wavelength of the rugate reflectance peak and an H parameter value calculated from the average red-green-blue (RGB) values of each image by first independently normalizing each channel (R, G, and B) using their maximum and minimum value over the time course of the degradation process. Spectrophotometric measurements and digital image analysis using this H parameter gave consistent relative stabilities of the samples as fpSi > pSi-ch.

No MeSH data available.