The breakthrough we foresee within the duration of the project is the design of a single instrument delivering:
- Simultaneous visualization of embedded structures and formations/deformations in 3D.
- Information of biochemical processes.
- Information on generation and abundance of specific species.
- Information of structural changes caused by specific species.
A schematic of the optical principle of InFeRa is shown in Fig. 1.
In this project, the system will be tested on bioelectrochemical systems (BESs): BESs use microbes to catalyze different electrochemical reactions for diverse purposes. Experiments on BES of the bacterium Geobacter sulfurreducens have been performed to investigate direct electron transfer between the cathode and the bacteria. This research is in collaboration with Biochemical Process Engineering at the Department of Civil, Environmental and Natural Resources Engineering, see:
The Raman lines of cytochrome c, an electron donor protein, have been identified [1,2]. Control and characterization of 3D biofilm formation and the action of mitochondrial biomarkers will finally be performed by InFeRa.
Currently (spring 2021) we are working separately on the development of interferometric imaging and stimulated Raman scattering (SRS) combined with a spatial light modulator (SLM). Upcoming sections contains preliminary results of both parts.
Depth-resolved Speckle Correlation with Quasi-Incoherent interferometric imaging
The interferometric imaging part of InFeRa is depicted by the dashed red square in Fig. 1. Fig. 2 shows a prototype setup that applies a rotating diffusor to the emitted light of an He-Ne laser, to generate an incoherent light source. Fig. 3 shows the effects of depth-gating, by having correlated the speckle pattern in the reference arm with that of the object arm at varying optical path differences. Fig. 4 shows an example of image reconstruction using phase shifting.
Spatial Control of Stimulated Raman Scattering using a Spatial light Modulator
The SRS process will only take place if two beams overlap in a material that has a Raman shift equal to the difference in wavelength of the two beams. In Fig. 5 a sketch of the current experimental setup is seen. The CH2 asymmetric stretching ethanol Raman band at 2934cm -1 is investigated. This part is included in the dashed green square of Fig. 1 that shows a prototype of the InFeRa setup. Fig. 6 illustrates how the SLM can be used to probe the sample at different locations in the glass cuvette and Fig. 7 shows the results obtained by imaging the SRS signal due to such motion.
In the near future (fall 2021) the two imaging parts will be combined. First measurements will be carried out on polymer beads on a glass surface. After that, first experiments on BES will be performed.
This project is financially supported by the Swedish Foundation for Strategic Research (ITM17-0056) the Kempe Foundation and LTUs lab fund.
: Krige, A., et al., On-Line Raman Spectroscopic Study of Cytochromes’ Redox State of Biofilms in Microbial Fuel Cells. Molecules, 2019. 24(3): p. 646.
: Krige, A., et al., A New Approach for Evaluating Electron Transfer Dynamics by Using In Situ Resonance Raman Microscopy and Chronoamperometry in Conjunction with a Dynamic Model. Applied and Environmental Microbiology, 2020. 86(20).