This study investigates the scaling of photobioreactor productivity based on the growth of Nannochloropsis salina incorporating the effects of direct and diffuse light. The scaling and optimization of photobioreactor geometry was analyzed by determining the growth response of a small‐scale system designed to represent a core sample of a large‐scale photobioreactor. The small‐scale test apparatus was operated at a variety of light intensities on a batch time scale to generate a photosynthetic irradiance (PI) growth dataset, ultimately used to inform a PI growth model. The validation of the scalability of the PI growth model to predict productivity in large‐scale systems was done by comparison with experimental growth data collected from two geometrically different large‐scale photobioreactors operated at a variety of light intensities. For direct comparison, the small‐scale and large‐scale experimental systems presented were operated similarly and in such a way to incorporate cultivation relevant time scales, light intensities, mixing, and nutrient loads. Validation of the scalability of the PI growth model enables the critical evaluation of different photobioreactor geometries and design optimization incorporating growth effects from diffuse and direct light. Discussion focuses on the application of the PI growth model to assess the effect of diffuse light growth compared to direct light growth for the evaluation of photobioreactors followed by the use of the model for photobioreactor geometry optimization on the metric of areal productivity. Biotechnol. Bioeng. 2012; 109:363–370. © 2011 Wiley Periodicals, Inc.

A low-cost, fast, and noninvasive method for early diagnosis of malignant lesions of oral mucosa based on diffuse reflectance spectral signatures is presented. In this technique, output of a tungsten halogen lamp is guided to the tissue through the central fiber of a reflection probe whose surrounding six fibers collects tissue reflectance. Ex vivo diffuse reflectance spectra in the 400 to 600-nm region is measured from surgically removed oral cavity lesions using a miniature fiber optic spectrometer connected to a computer. Reflectance spectral intensity is higher in malignant tissues and shows dips at 542 and 577 nm owing to absorption from oxygenated hemoglobin (HbO2). Measurements carried out, within an hour of surgical excision, on malignant lesion and adjoining uninvolved mucosa show that these absorption features are more prominent in neoplastic tissues owing to increased microvasculature and blood content. It is observed that reflectance intensity ratio of hemoglobin bands, R540/R575, from malignant sites are always lower than that from normal sites and vary according to the histological grade of malignancy. The diffuse reflectance intensity ratio R540/R575 of the hemoglobin bands appears to be a useful tool to discriminate between malignant lesions and normal mucosa of the oral cavity in a clinical setting.

Diffuse reflectance (DR) spectroscopy is a simple, low-cost, and noninvasive modality with potential for distinguishing oral precancer. Recently, in an ex vivo study, the DR spectral ratio (R545/R575) of oxygenated hemoglobin bands at 545 and 575 nm was used for grading malignancy. This work presents the results of clinical trials conducted in 29 patients to detect oral precancer using this ratio. We use site-specific normal spectra from a group of 36 healthy volunteers for comparison with those of patients. Toward this, in vivo DR spectra from 14 anatomical sites of the oral cavity of healthy volunteers are recorded on a miniature fiber optic spectrometer with white light excitation. The R545/R575 ratio is lowest for healthy tissues and appears to increase with the grade of malignancy. As compared to scatter plots that use the mean DR ratio from all anatomical sites, those using site-specific data show improved sensitivity and specificity for early diagnosis and grading of oral cancer. In the case of buccal mucosa, using scatter plots of R545/R575 ratio, we obtain a sensitivity of 100% and specificity of 86% for discriminating precancer (dysplasia) from hyperplasia, and a sensitivity of 97% and specificity of 86% for discriminating hyperplasia from normal.

The LIAF/DR technique, in conjunction with curve-fitting, differentiates different grades of dysplasia and SCC in this clinical trial and proves its potential for early detection of oral cavity cancer and tissue grading.

We present the clinical applicability of fluorescence ratio reference standard (FRRS) to discriminate different stages of dental caries. Toward this, laser-induced autofluorescence emission spectra are recorded in vivo in the 400- to 800-nm spectral range on a miniature fiber optic spectrometer from 65 patients, with a 404-nm diode laser as the excitation source. Autofluorescence spectra of sound teeth consist of a broad emission at 500 nm that is typical of natural enamel, whereas in caries teeth additional peaks are seen at 635 and 680 nm due to emission from porphyrin compounds in oral bacteria. Scatter plots are developed to differentiate sound teeth from enamel caries, sound teeth from dentinal caries, and enamel caries from dentinal caries using the mean fluorescence intensity (FI) and ratios F500F635 and F500F680 measured from 25 sites of sound teeth and 65 sites of carious teeth. The sensitivity and specificity of both the FI and FRRS are determined. It is observed that a diagnostic algorithm based on FRRS scatter plots is able to discriminate enamel caries from sound teeth, dentinal caries from sound teeth, and enamel from dentinal caries with overall sensitivities of 85, 100, and 88% and specificities of 90, 100, and 77%, respectively.

Nitrogen laser-excited fluorescence spectral studies were found to be more suited for detection of caries lesions. The LIF measurement with spectral analysis, done by curve fitting, outscores the diffuse reflectance methodology and shows the potential to screen different levels of tooth decay in a clinical setting.

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Nitrogen laser-induced fluorescence (LIF) and tungsten halogen lamp excited diffuse reflectance spectra were recorded in 350- to 700-nm range on a miniature fiber-optic spectrometer from in vitro premolar tooth during various stages of artificial erosion with 36% phosphoric acid. Both the LIF spectral intensity and the diffuse reflectance intensity gradually increased during tooth erosion. The LIF spectra were analyzed by curve fitting using Gaussian spectral functions to determine the true contribution of different bands in the spectra during erosion. Thus, the broad bands at 440 and 490 nm in the LIF spectra of sound enamel were resolved into four peaks centered at 409.1, 438.1, 492.4 and 523.1 nm and of sound dentin into peaks at 412.0, 440.1, 487.8 and 523.4 nm. The F410/F525 ratios derived from curve-fitted Gaussian peak amplitudes and curve areas were found to be more sensitive to erosion as compared to the diffuse reflectance ratio R500/R700 or the raw LIF spectral ratio F440/F490.