SmartFluo: A Method and Affordable Adapter to Measure Chlorophyll a Fluorescence with Smartphones.

Anna Friedrichs,Julia Busch,Oliver Zielinski,Hendrik Van Der Woerd

doi:10.3390/s17040678

Anna Friedrichs, Julia Busch + Show 2 more

Open Access

https://doi.org/10.3390/s17040678

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Abstract

In order to increase the monitoring capabilities of inland and coastal waters, there is a need for new, affordable, sensitive and mobile instruments that could be operated semi-automatically in the field. This paper presents a prototype device to measure chlorophyll a fluorescence: the SmartFluo. The device is a combination of a smartphone offering an intuitive operation interface and an adapter implying a cuvette holder, as well as a suitable illumination source. SmartFluo is based on stimulated fluorescence of water constituents such as chlorophyll a. The red band of the digital smartphone camera is sensitive enough to detect quantitatively the characteristic red fluorescence emission. The adapter contains a light source, a strong light emitting diode and additional filters to enhance the signal-to-noise ratio and to suppress the impact of scattering. A novel algorithm utilizing the red band of the camera is provided. Laboratory experiments of the SmartFluo show a linear correlation (R = 0.98) to the chlorophyll a concentrations measured by reference instruments, such as a high-performance benchtop laboratory fluorometer (LS 55, PerkinElmer).

Highlights

Chlorophyll a fluorescence is well investigated and commonly used as a proxy for phytoplankton biomass [1] indicating the state of a marine water body, e.g., oligotrophic, mesotrophic or eutrophic [2].Different processes are related to the state of algal biomass, such as net primary production [3] and harmful algal blooms [4]
Excitation: Two alternative light sources were examined as excitation sources for chlorophyll a fluorescence: (a) the internal S3 mini smartphone light emitting diode (LED) and (b) an external blue LED
Due to the availability of light to be absorbed by algae changes, chlorophyll a fluorescence signal depends on the absence or presence of other absorbing or scattering particles

Summary

Introduction

Chlorophyll a fluorescence is well investigated and commonly used as a proxy for phytoplankton biomass [1] indicating the state of a marine water body, e.g., oligotrophic, mesotrophic or eutrophic [2].Different processes are related to the state of algal biomass, such as net primary production [3] and harmful algal blooms [4]. An understanding of the marine algal biomass is a key element of the European Union marine monitoring framework and addressed by legislation such as the Marine. The fluorescence emission process occurs randomly [10] and is defined as the ratio of moles photons emitted as fluorescence divided by the moles photons absorbed by all pigments [11]: Φ=. Strength of the fluorescence signal is, on first approximation, dependent on the concentration of photo-active pigments in the sample and intensity of the excitation source (see Equation (1)). Because algal pigments can absorb radiation near 685 nm [17] (self-shading effect), small deviations from linearity can occur at higher chlorophyll a concentrations due to absorption of the fluorescence signal

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