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Measurement of Scattering and Absorption Cross Sections of Dyed Microspheres.

Gaigalas AK, Choquette S, Zhang YZ - J Res Natl Inst Stand Technol (2013)

Bottom Line: Therefore A was first analyzed using values of the other parameters obtained from a fit to the absorbance due to scattering, A1-A, with the imaginary part neglected.The imaginary part obtained from the analysis of A was then used to reanalyze A1-A, and obtain better estimates of the other parameters.After a few iterations, consistent estimates were obtained of the scattering and absorption cross sections in the wavelength region 300 nm to 800 nm.

View Article: PubMed Central - PubMed

Affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.

ABSTRACT
Measurements of absorbance and fluorescence emission were carried out on aqueous suspensions of polystyrene (PS) microspheres with a diameter of 2.5 µm using a spectrophotometer with an integrating sphere detector. The apparatus and the principles of measurements were described in our earlier publications. Microspheres with and without green BODIPY(@) dye were measured. Placing the suspension inside an integrating sphere (IS) detector of the spectrophotometer yielded (after a correction for fluorescence emission) the absorbance (called A in the text) due to absorption by BODIPY(@) dye inside the microsphere. An estimate of the absorbance due to scattering alone was obtained by subtracting the corrected BODIPY(@) dye absorbance (A) from the measured absorbance of a suspension placed outside the IS detector (called A1 in the text). The absorption of the BODIPY(@) dye inside the microsphere was analyzed using an imaginary index of refraction parameterized with three Gaussian-Lorentz functions. The Kramer-Kronig relation was used to estimate the contribution of the BODIPY(@) dye to the real part of the microsphere index of refraction. The complex index of refraction, obtained from the analysis of A, was used to analyze the absorbance due to scattering ((A1 - A) in the text). In practice, the analysis of the scattering absorbance, A1-A, and the absorbance, A, was carried out in an iterative manner. It was assumed that A depended primarily on the imaginary part of the microsphere index of refraction with the other parameters playing a secondary role. Therefore A was first analyzed using values of the other parameters obtained from a fit to the absorbance due to scattering, A1-A, with the imaginary part neglected. The imaginary part obtained from the analysis of A was then used to reanalyze A1-A, and obtain better estimates of the other parameters. After a few iterations, consistent estimates were obtained of the scattering and absorption cross sections in the wavelength region 300 nm to 800 nm.

No MeSH data available.


The absorbance of the microsphere suspension after subtraction of the absorbance of suspension of undyed microspheres. The absorbance above 600 nm is approximately zero. The ripples below 500 nm were due to small difference in the diameters of the dyed and the undyed microspheres. A suspension of undyed microspheres resulted in a better background subtraction than a sample of water. The uncertainty in the peak absorbance value is about 5 %.
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f3-jres.118.002: The absorbance of the microsphere suspension after subtraction of the absorbance of suspension of undyed microspheres. The absorbance above 600 nm is approximately zero. The ripples below 500 nm were due to small difference in the diameters of the dyed and the undyed microspheres. A suspension of undyed microspheres resulted in a better background subtraction than a sample of water. The uncertainty in the peak absorbance value is about 5 %.

Mentions: The comparison of absorbance measurements in holder 1 and holder 3 showed that the measurements in holder 3 were not very sensitive to scattering losses. There was a small background absorbance (of the order of 0.003 absorbance units) which was most likely due to the escape of backward scattered photons through the entrance aperture of the IS detector. The scattering background observed in holder 3 was relatively constant over the wavelength region between 600 nm and 800 nm and this region was used to estimate the scattering background. However there was a gentle rise in the scattering background in the region of BODIPY absorption which made it difficult to subtract the background using water as the reference for this spectral region. The trace in Fig. 3 shows the result of measurements of absorbance in holder 3 using a suspension of 2.5 µm blank(not dyed) microspheres as a reference and subtracting from measurements of dyed microspheres. The scattering background is minimal for wavelengths greater than 550 nm and shows a ripple structure for wavelengths less than 550 nm. The ripples are originated from small difference in the diameters of the dyed and blank 2.5 µm microspheres. The small differences in diameters lead to a small shift in the scattering pattern resulting in an incomplete subtraction of scattering signals from the two microsphere suspensions. The trace in Fig. 3 may still not represent the true absorbance because the microspheres fluoresce and the emitted fluorescence reduced the observed absorbance in Fig. 3.


Measurement of Scattering and Absorption Cross Sections of Dyed Microspheres.

Gaigalas AK, Choquette S, Zhang YZ - J Res Natl Inst Stand Technol (2013)

The absorbance of the microsphere suspension after subtraction of the absorbance of suspension of undyed microspheres. The absorbance above 600 nm is approximately zero. The ripples below 500 nm were due to small difference in the diameters of the dyed and the undyed microspheres. A suspension of undyed microspheres resulted in a better background subtraction than a sample of water. The uncertainty in the peak absorbance value is about 5 %.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4487309&req=5

f3-jres.118.002: The absorbance of the microsphere suspension after subtraction of the absorbance of suspension of undyed microspheres. The absorbance above 600 nm is approximately zero. The ripples below 500 nm were due to small difference in the diameters of the dyed and the undyed microspheres. A suspension of undyed microspheres resulted in a better background subtraction than a sample of water. The uncertainty in the peak absorbance value is about 5 %.
Mentions: The comparison of absorbance measurements in holder 1 and holder 3 showed that the measurements in holder 3 were not very sensitive to scattering losses. There was a small background absorbance (of the order of 0.003 absorbance units) which was most likely due to the escape of backward scattered photons through the entrance aperture of the IS detector. The scattering background observed in holder 3 was relatively constant over the wavelength region between 600 nm and 800 nm and this region was used to estimate the scattering background. However there was a gentle rise in the scattering background in the region of BODIPY absorption which made it difficult to subtract the background using water as the reference for this spectral region. The trace in Fig. 3 shows the result of measurements of absorbance in holder 3 using a suspension of 2.5 µm blank(not dyed) microspheres as a reference and subtracting from measurements of dyed microspheres. The scattering background is minimal for wavelengths greater than 550 nm and shows a ripple structure for wavelengths less than 550 nm. The ripples are originated from small difference in the diameters of the dyed and blank 2.5 µm microspheres. The small differences in diameters lead to a small shift in the scattering pattern resulting in an incomplete subtraction of scattering signals from the two microsphere suspensions. The trace in Fig. 3 may still not represent the true absorbance because the microspheres fluoresce and the emitted fluorescence reduced the observed absorbance in Fig. 3.

Bottom Line: Therefore A was first analyzed using values of the other parameters obtained from a fit to the absorbance due to scattering, A1-A, with the imaginary part neglected.The imaginary part obtained from the analysis of A was then used to reanalyze A1-A, and obtain better estimates of the other parameters.After a few iterations, consistent estimates were obtained of the scattering and absorption cross sections in the wavelength region 300 nm to 800 nm.

View Article: PubMed Central - PubMed

Affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.

ABSTRACT
Measurements of absorbance and fluorescence emission were carried out on aqueous suspensions of polystyrene (PS) microspheres with a diameter of 2.5 µm using a spectrophotometer with an integrating sphere detector. The apparatus and the principles of measurements were described in our earlier publications. Microspheres with and without green BODIPY(@) dye were measured. Placing the suspension inside an integrating sphere (IS) detector of the spectrophotometer yielded (after a correction for fluorescence emission) the absorbance (called A in the text) due to absorption by BODIPY(@) dye inside the microsphere. An estimate of the absorbance due to scattering alone was obtained by subtracting the corrected BODIPY(@) dye absorbance (A) from the measured absorbance of a suspension placed outside the IS detector (called A1 in the text). The absorption of the BODIPY(@) dye inside the microsphere was analyzed using an imaginary index of refraction parameterized with three Gaussian-Lorentz functions. The Kramer-Kronig relation was used to estimate the contribution of the BODIPY(@) dye to the real part of the microsphere index of refraction. The complex index of refraction, obtained from the analysis of A, was used to analyze the absorbance due to scattering ((A1 - A) in the text). In practice, the analysis of the scattering absorbance, A1-A, and the absorbance, A, was carried out in an iterative manner. It was assumed that A depended primarily on the imaginary part of the microsphere index of refraction with the other parameters playing a secondary role. Therefore A was first analyzed using values of the other parameters obtained from a fit to the absorbance due to scattering, A1-A, with the imaginary part neglected. The imaginary part obtained from the analysis of A was then used to reanalyze A1-A, and obtain better estimates of the other parameters. After a few iterations, consistent estimates were obtained of the scattering and absorption cross sections in the wavelength region 300 nm to 800 nm.

No MeSH data available.