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Additional file 1: Figure S1. Growth rate (GRPDW,in-line) of the algal cells based on ��s��. Growth rate is based on the slope within the time increments (��s��/time). Original data from ��s�� was smoothed before analysis with a simple moving average based on 31 data points. Plotting of growth rate is done with simple moving average based on 11 data points. ��s�� is plotted as unsmoothed data as given in figure 2 A. Figure S2. Correlation of both reference analyses.

Photon Density Wave (PDW) spectroscopy[1] is one of the very few optical methods for the characterization of the optical properties of highly concentrated liquid emulsions or suspensions. Such materials often exhibit multiple light scattering - the basis for successful PDW experiments. Since this analytical technique can quantitatively separate light absorption and light scattering properties[2], chemical and structural information of such materials can be obtained. PDW spectroscopy has been applied to investigate the Ostwald ripening of concentrated o/w-nano-scaled emulsions, produced by a phase inversion temperature (PIT) emulsification. Even for volume fractions of 20% of the oil phase (isohexadecane), ripening rates in dependency of the emulsifier concentration (tetraoxyethylene laurylether, 2-8 vol%) can be obtained with high precision and high temporal resolution. Furthermore, the inline monitoring of high solid content (up to 55 wt%) polymer particles has been investigated. Polyvinyl acetate nanoparticles (400-700 nm) were successfully synthesized by starved feed radical emulsion polymerization, characterized by PDW spectroscopy, and compared to reference methods like DLS. As a third topic, hard sphere and electrostatic nano-particle interactions have been studied by PDW spectroscopy. Through appropriate theoretical modelling, the experimentally obtained optical properties of polymer particles in highly concentrated suspensions (> 5 vol%) can be used to determine their ionic strength, particle surface charge and size. Conversely, PDW spectroscopy can be applied to adjust the optical properties of suspensions with nano-scaled particles, e.g. by changing the ionic strength of the system. [1] L. Bressel, R. Hass, O. Reich, J. Quant. Spec. Rad. Transfer 2013, 126, 122–129. [2] O. Reich, H.-G. Löhmannsröben, F. Schael, Phys. Chem. Chem. Phys. 2003, 5, 5182-5187. &nbsp

A simple, convenient, and inexpensive method to fabricate optical fiber based biosensors which utilize periodic hole arrays in gold films for signal transduction is reported. The process of hole array formation mainly relies on self-assembly of hydrogel microgels in combination with chemical gold film deposition and subsequent transfer of the perforated film onto an optical fiber tip. In the fabrication process solely chemical wet lab techniques are used, avoiding cost-intensive instrumentation or clean room facilities. The presented method for preparing fiber optic plasmonic sensors provides high throughput and is perfectly suited for commercialization using batch processing. The transfer of the perforated gold film onto an optical fiber tip does not affect the sensitivity of the biosensor ((420 +/- 83) nm/refractive index unit (RIU)), which is comparable to sensitivities of sensor platforms based on periodic hole arrays in gold films prepared by significantly more complex methods. Furthermore, real-time and in-line immunoassay studies with a specially designed 3D printed flow cell are presented exploiting the presented optical fiber based biosensors.

Quality attributes of fruit determine its acceptability by the retailer and consumer. The objective of this work was to investigate the potential of absorption (μa) and reduced scattering (μs’) coefficients of European pear to analyze its fruit flesh firmness and soluble solids content (SSC). The absolute reference values, μa* (cm−1) and μs’* (cm−1), of pear were invasively measured, employing multi-spectral photon density wave (PDW) spectroscopy at preselected wavelengths of 515, 690, and 940 nm considering two batches of unripe and overripe fruit. On eight measuring dates during fruit development, μa and μs’ were analyzed non-destructively by means of laser light backscattering imaging (LLBI) at similar wavelengths of 532, 660, and 830 nm by means of fitting according to Farrell’s diffusion theory, using fix reference values of either μa* or μs’*. Both, the μa* and the μa as well as μs’* and μs’ showed similar trends. Considering the non-destructively measured data during fruit development, μa at 660 nm decreased 91 till 141 days after full bloom (dafb) from 1.49 cm−1 to 0.74 cm−1 due to chlorophyll degradation. At 830 nm, μa only slightly decreased from 0.41 cm−1 to 0.35 cm−1. The μs’ at all wavelengths revealed a decreasing trend as the fruit developed. The difference measured at 532 nm was most pronounced decreasing from 24 cm−1 to 10 cm−1, while at 660 nm and 830 nm values decreased from 15 cm−1 to 13 cm−1 and from 10 cm−1 to 8 cm−1, respectively. When building calibration models with partial least-squares regression analysis on the optical properties for non-destructive analysis of the fruit SSC, μa at 532 nm and 830 nm resulted in a correlation coefficient of R = 0.66, however, showing high measuring uncertainty. The combination of all three wavelengths gave an enhanced, encouraging R = 0.89 for firmness analysis using μs’ in the freshly picked fruit.