Limits of optical transmission measurements with application to particle sizing techniques

Swanson, Nancy L.; Billard, Barton D.; Gennaro, Theresa L.

doi:10.1364/ao.38.005887

Cited by 33 publications

(22 citation statements)

References 17 publications

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“…To the best of our knowledge, there have been no reports on the use of photoacoustic spectroscopy to assess the enzymatic dye decolourization. This technique will be specially useful in cases where materials with high optical density (opaque samples) are to be analysed due to the fact that Beer-Lambert's law no longer applies when the sample presents high scattering and low/poor optical transmission (Swanson et al 1999). It should be added that photoacoustic spectroscopy is a non-destructive technique based on photothermal phenomena, which allows thermophysical parameter assessment and depth profile analysis of materials (Coelho et al 2010b).…”

Section: Pas Analysismentioning

confidence: 99%

Decolourization of Congo Red by Ganoderma lucidum Laccase: Evaluation of Degradation Products and Toxicity

Mota

Kato

Peralta

et al. 2015

Water Air Soil Pollut

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Several laccases from different sources have been used in dye decolourization processes. However, only in a reduced number of studies have efforts been done to identify the metabolites produced by the enzymatic treatment as well as to evaluate the toxicity of degradation products. Taking these gaps into account, the objective of this work was to use a laccase from Ganoderma lucidum in the decolourization of the synthetic dye Congo red (C.I. No. 22120, Direct Red 28), largely used in the textile industry. After 6 h of treatment at pH 4.0 and 40°C, the enzyme was able to decolourize 80 % of Congo red. Fourier transform infrared spectroscopy (FTIR), photoacoustic spectroscopy (PAS) and mass spectrometry allow concluding that laccase effectively changed the structure of Congo red, reducing the colour by modifying the chromophore groups and other parts of the molecule. Several degradation products with m/z + ranging from 298 to 745 were identified. It is proposed that the first degradation step could be an asymmetric cleavage of the azo bond present in the Congo red structure forming the intermediate with m/ z + 298. The results also suggest a reduction in the toxicity of Congo red after laccase treatment, as indicated by the lettuce seed germination model. In conclusion, G. lucidum laccase could be used in a novel azo dye bioremediation strategy.

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Section: Pas Analysismentioning

confidence: 99%

Decolourization of Congo Red by Ganoderma lucidum Laccase: Evaluation of Degradation Products and Toxicity

Mota

Kato

Peralta

et al. 2015

Water Air Soil Pollut

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“…The effect of coherent scattering has been studied in relation to the applicability of the Beer law, for which a beam radiation extinction follows an exponential law given by I (z) = I 0 exp(−N C ext z), [9] where N is the number density of the particles. This law is in fact a steady-state solution to the radiative transfer equation (RTE) when scattering is negligible, though it can be successfully applied to nonzero scattering if the detector's acceptance angle is small enough (20). It has been found in both experimental data and calculations that addressing the problem of coherent scattering by means of approximations such as the QCA (quasi-crystalline approximation) gives better agreement to experimental data than trying to calculate multiple incoherent scatterings.…”

Section: Figmentioning

confidence: 99%

Multiple Light Scattering by Spherical Particle Systems and Its Dependence on Concentration: A T-Matrix Study

Quirantes

Arroyo

Quirantes-Ros

2001

Journal of Colloid and Interface Science

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“…When light passes through a mixture, attenuation of the light intensity occurs by two mechanisms: in a homogeneous, single-phase solution, only absorbance contributes significantly to attenuation; in suspensions containing mixtures of two or more phases, light scattering due to difference in refractive index and the shape of this index mismatch also contribute to light attenuation [2]. The Beer-Lambert law only applies rigorously to single-phase solutions; however, certain assumptions and approximations allow the Beer-Lambert law to be extended to systems that exhibit significant scattering.…”

Section: Introductionmentioning

confidence: 99%

Improving accuracy of cell and chromophore concentration measurements using optical density

2013

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BackgroundUV–vis spectrophotometric optical density (OD) is the most commonly-used technique for estimating chromophore formation and cell concentration in liquid culture. OD wavelength is often chosen with little thought given to its effect on the quality of the measurement. Analysis of the contributions of absorption and scattering to the measured optical density provides a basis for understanding variability among spectrophotometers and enables a quantitative evaluation of the applicability of the Beer-Lambert law. This provides a rational approach for improving the accuracy of OD measurements used as a proxy for direct dry weight (DW), cell count, and pigment levels.ResultsFor pigmented organisms, the choice of OD wavelength presents a tradeoff between the robustness and the sensitivity of the measurement. The OD at a robust wavelength is primarily the result of light scattering and does not vary with culture conditions; whereas, the OD at a sensitive wavelength is additionally dependent on light absorption by the organism’s pigments. Suitably robust and sensitive wavelengths are identified for a wide range of organisms by comparing their spectra to the true absorption spectra of dyes. The relative scattering contribution can be reduced either by measurement at higher OD, or by the addition of bovine serum albumin. Reduction of scattering or correlation with off-peak light attenuation provides for more accurate assessment of chromophore levels within cells. Conversion factors between DW, OD, and colony-forming unit density are tabulated for 17 diverse organisms to illustrate the scope of variability of these correlations. Finally, an inexpensive short pathlength LED-based flow cell is demonstrated for the online monitoring of growth in a bioreactor at culture concentrations greater than 5 grams dry weight per liter which would otherwise require off-line dilutions to obtain non-saturated OD measurements.ConclusionsOD is most accurate as a time-saving proxy measurement for biomass concentration when light attenuation is dominated by scattering. However, the applicability of OD-based correlations is highly dependent on the measurement specifications (spectrophotometer model and wavelength) and culture conditions (media type; growth stage; culture stress; cell/colony geometry; presence and concentration of secreted compounds). These variations highlight the importance of treating literature conversion factors as rough approximations as opposed to concrete constants. There is an opportunity to optimize measurements of cell pigment levels by considering scattering and absorption-dependent wavelengths of the OD spectrum.

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Limits of optical transmission measurements with application to particle sizing techniques

Cited by 33 publications

References 17 publications

Decolourization of Congo Red by Ganoderma lucidum Laccase: Evaluation of Degradation Products and Toxicity

Decolourization of Congo Red by Ganoderma lucidum Laccase: Evaluation of Degradation Products and Toxicity

Multiple Light Scattering by Spherical Particle Systems and Its Dependence on Concentration: A T-Matrix Study

Improving accuracy of cell and chromophore concentration measurements using optical density

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