Artificial Siderophore-Fe(III) Complexes-Modified Au Substrates for Microbe-Adsorption/Detection Tools
Authors: Inomata Tomohiko , Endo Suguru , Ido Hiroki , Murase Takanori , Ozawa Tomohiro , Masuda Hideki 
Published: February 2020

Siderophores are small biomolecules produced and secreted by microbes and plant cells for Fe(III) ion uptake.1 The secreted siderophores coordinate to Fe(III) ions and form very stable siderophore-Fe(III) complexes. The highly specific receptors or binding proteins on the outer membrane of microbes recognize the siderophore-Fe(III) complexes and transport the complexes into the periplasm.
Artificial siderophores act as functional model compounds of natural siderophores. We have previously reported the immobilization of microbes using an artificial siderophore-Fe(III) complexes-modified substrate.2 Microbes have been immobilized onto the substrate by the interaction between the artificial siderophore complexes on the substrate and the siderophore receptors at the cell membrane. Our purpose is the development of the efficient and selective microbe-sensing tools using the artificial siderophore-Fe(III) complex-modified substrates like Au electrodes and Au nanoparticles (AuNPs). Herein, we report the preparation of several types of artificial siderophre-Fe(III) complexes and Au substrates modified with them. The substrates have indicated the selective and efficient microbe-adsorption/detection ability.
Three types of artificial siderophores (catecholate-, hydroxamate- and these hybrid types) were newly synthesized and their Fe(III) complexes-modified Au electrodes and AuNPs were prepared. The obtained electrodes were dipped into the broth including various types of microbes and have indicated the selective microbe adsorption ability. The receptor proteins displayed at the cell membrane of microbes recognize the structure of the artificial siderophore-Fe(III) complexes on the surface and bind them, resulting microbes are immobilized on the surface selectively. We have applied this microbe adsorption mechanism to a microbe-detection device based on a quartz crystal microbalance (QCM) sensor.3,4 The QCM sensor modified with artificial siderophore-Fe(III) complex was prepared in the same manner as that of the Au electrode. The QCM sensor has indicated the selective microbe detection corresponding to the types of artificial siderophore-Fe(III) complexes modified on the surface. Furthermore, the artificial siderophore-Fe(III) complexes-modified AuNPs have showed selective aggregation of microbes.5 The AuNPs have improved the detection limit of the QCM sensor. The AuNPs induce the aggregation of microbes and the aggregated microbes adsorb on the QCM sensor. The frequency changes of the QCM sensor quite magnify and the sensitivity of the sensor increases about 100 fold.

References

1) Crosa, J. H.; Mey, A. R.; Payne, S. M. (Eds.), Iron Transport in Bacteria, ASM Press,Washington D. C., 2004.
2) Inomata, T.; Eguchi, H.; Matsumoto, K.; Funahashi, Y.; Ozawa, T.; Masuda, H. Biosens. Bioelectron.,
2007, 23, 751.
3) Inomata, T.; Eguchi, H.; Funahashi, Y.; Ozawa, T.; Masuda, H., Langmuir,
2012, 28, 1611.
4) Inomata, T.; Tanabashi, H.; Funahashi, Y.; Ozawa, T.; Masuda, H., Dalton Trans.,
2013, 43, 16043.
5) Inomata, T.; Murase, T.; Ido, H.; Ozawa, T.; Masuda, H., Chem. Lett., 2014, 43, 1146-1148.

Figure 1