Application of Laser-Induced Fluorescence in Functional Studies of Photosynthetic Biofilms

Abstract

Biofilms are a ubiquitous form of life for microorganisms. Photosynthetic biofilms such as microphytobenthos (MPB) and biological soil crusts (BSC) play a relevant ecological role in aquatic and terrestrial ecosystems, respectively. On the other hand, photosynthetic epilithic biofilms (PEB) are major players in the microbial-induced decay of stone structures of cultural heritage. The use of fluorescence techniques, namely, pulse-amplitude-modulated fluorometry, was crucial to understanding the photophysiology of these microbial communities, since they made it possible to measure biofilms' photosynthetic activity without disturbing their delicate spatial organization within sediments or soils. The use of laser-induced fluorescence (LIF) added further technical advantages, enabling measurements to be made at a considerable distance from the samples, and under daylight. In this Perspective, we present state-of-the-art LIF techniques, show examples of the application of LIF to MPB and present exploratory results of LIF application to BSC, as well as to PEB colonizing stone structures of cultural heritage. Thereafter, we discuss the perspectives of LIF utilization in environmental research and monitoring, in cultural heritage conservation and assessment, and in biotechnological applications of photosynthetic biofilms.Processes 2018, 6, 227 2 of 15 by a lamp or a laser. The use of laser-induced fluorescence (LIF) brought further advances in the study of photosynthetic biofilms, as it allows measurements under daylight and at a considerable distance from the samples. In this Perspective, we present the state-of-the-art in LIF techniques and show examples of their application to MPB. In addition, we present exploratory results of LIF application to BSC and PEB. To conclude, we discuss the perspectives of LIF utilization in environmental research and monitoring, in cultural heritage conservation and assessment, as well as in biotechnological applications of photosynthetic biofilms. Laser-Induced Fluorescence (LIF)A typical setup used for LIF measurements is shown in Figure 1. Fluorescence is excited by a pulsed laser with a pulse duration of several nanoseconds. The most commonly used source is an Nd:YAG Q-switched solid-state laser emitting at the wavelength of 355 or 532 nm (correspondingly, in the frequency-tripled or -doubled mode): it combines robustness and low fabrication and maintenance costs with high electrical-to-optical power efficiency and significant quantum yield. The freshly emitted laser pulse irradiates the sample and excites the fluorescence emission. A part of this emission is collected by light-gathering optics, which can easily be developed based on off-the-shelf low-cost collimators (e.g., several F810SMA collimation packages, optimized for specific but rather wide wavelength regions [10]). To prevent backscattered laser radiation from entering the collimator and saturating or damaging the spectrometer, a longpass filter, with a cut-off wavelength slightly larger than the operating wavelength of the...

Current State of Laser-Induced Fluorescence Spectroscopy for Designing Biochemical Sensors

“…Laser light offers many advantages not possible with the other above-mentioned sources. Firstly, unlike lamps and LEDs, lasers produce thin beams of light with photons moving in the same direction, and thus do not diminish in intensity as quickly as other light sources [43]. This allows for a longer distance covered between the light source and sample without losing excitation light intensity by the inversesquare law [44].…”

Potential Phenotyping Methodologies to Assess Inter- and Intravarietal Variability and to Select Grapevine Genotypes Tolerant to Abiotic Stress

“…Relevant information on stress conditions can also be obtained from the analysis of the spectral signature of chlorophyll fluorescence, which is collected after laser excitation in the laser induced fluorescence technique ( Gameiro et al, 2016 ). This technique does not require sample dark adaptation or close proximity to the sample and therefore might be suitable for field HTPP ( Marques da Silva, 2016 ; Marques da Silva and Utkin, 2018 ).…”

A Technological Understanding of Biofilm Detection Techniques: A Review

“…To obtain a scan of the complete inner surface of a bioreactor is a time-consuming process. The properties of LIF-spectroscopy make the technique non-destructive and in situ when applied on stone structures and cultural heritage [ 53 ] due to the setup of the technique and its application for biofilm detection in bioreactors is also deemed to also be non-destructive and in situ.…”

“…In the research of Bengtsson et al (2005) and Wallstrom et al (2005), respectively, the aim was to identify critical spots of fungal and biological growth on high-voltage outdoor insulators to eventually overcome the failure of these cables [49,50]. Another example of the application of LIF-spectroscopy is the determination of biofilm contamination of stone structures and cultural heritage [52,53]. In both applications, a laser and a spectrometer are used to obtain information regarding the microorganisms present in the different samples.…”