title: Gold-modified indium tin oxide as a transparent window in optoelectronic diagnostics of electrochemically active biofilms.
abstract: Microbial electrochemical technologies (METs) are one of the emerging green bioenergy domains that are utilizing microorganisms for wastewater treatment or electrosynthesis. Real-time monitoring of bioprocess during operation is a prerequisite for understanding and further improving bioenergy harvesting. Optical methods are powerful tools for this, but require transparent, highly conductive and biocompatible electrodes. Whereas indium tin oxide (ITO) is a well-known transparent conductive oxide, it is a non-ideal platform for biofilm growth. Here, a straightforward approach of surface modification of ITO anodes with gold (Au) is demonstrated, to enhance direct microbial biofilm cultivation on their surface and to improve the produced current densities. The trade-off between the electrode transmittance (critical for the underlying integrated sensors) and the enhanced growth of biofilms (crucial for direct monitoring) is studied. Au-modified ITO electrodes show a faster and reproducible biofilm growth with three times higher maximum current densities and about 6.9 times thicker biofilms compared to their unmodified ITO counterparts. The electrochemical analysis confirms the enhanced performance and the reversibility of the ITO/Au electrodes. The catalytic effect of Au on the ITO surface seems to be the key factor of the observed performance improvement since the changes in the electrode conductivity and their surface wettability are relatively small and in the range of ITO. An integrated platform for the ITO/Au transparent electrode with light-emitting diodes was fabricated and its feasibility for optical biofilm thickness monitoring is demonstrated. Such transparent electrodes with embedded catalytic metals can serve as multifunctional windows for biofilm diagnostic microchips.
authors.affiliation: Institut für Ökologische und Nachhaltige Chemie (IÖNC), Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
authors.forename: Igor
authors.initials: I
authors.lastname: Schmidt
authors.affiliation: Institut für Halbleitertechnik (IHT), Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany; Laboratory for Emerging Nanometrology (LENA), Langer Kamp 6a, 38106 Braunschweig, Germany; Inorganic Chemistry Department, National Research Centre (NRC), El Buhouth St., Dokki, 12622 Cairo, Egypt.
authors.forename: Alaaeldin
authors.initials: A
authors.lastname: Gad
authors.affiliation: Institut für Halbleitertechnik (IHT), Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany; Laboratory for Emerging Nanometrology (LENA), Langer Kamp 6a, 38106 Braunschweig, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Scholz
authors.affiliation: Institut für Halbleitertechnik (IHT), Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany; Laboratory for Emerging Nanometrology (LENA), Langer Kamp 6a, 38106 Braunschweig, Germany.
authors.forename: Heidi
authors.initials: H
authors.lastname: Boht
authors.affiliation: Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik (EMG), Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany; Laboratory for Emerging Nanometrology (LENA), Langer Kamp 6a, 38106 Braunschweig, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Martens
authors.affiliation: Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik (EMG), Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany; Laboratory for Emerging Nanometrology (LENA), Langer Kamp 6a, 38106 Braunschweig, Germany.
authors.forename: Meinhard
authors.initials: M
authors.lastname: Schilling
authors.affiliation: Institut für Halbleitertechnik (IHT), Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany; Laboratory for Emerging Nanometrology (LENA), Langer Kamp 6a, 38106 Braunschweig, Germany.
authors.forename: Hutomo
authors.initials: H
authors.lastname: Suryo Wasisto
authors.affiliation: Institut für Halbleitertechnik (IHT), Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany; Laboratory for Emerging Nanometrology (LENA), Langer Kamp 6a, 38106 Braunschweig, Germany. Electronic address: a.waag@tu-braunschweig.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Waag
authors.affiliation: Institut für Ökologische und Nachhaltige Chemie (IÖNC), Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany. Electronic address: uwe.schroeder@tu-braunschweig.de.
authors.forename: Uwe
authors.initials: U
authors.lastname: Schröder
mesh_terms: D001419:Bacteria / Q000254:growth & development / Q000302:isolation & purification*; D018441:Biofilms / Q000254:growth & development*; D015374:Biosensing Techniques / Q000379:methods*; D002384:Catalysis; D004563:Electrochemistry / Q000379:methods*; D006046:Gold / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry; D017971:Tin Compounds / Q000737:chemistry; D062065:Wastewater / Q000382:microbiology
chemical_list: D006046:Gold; D017971:Tin Compounds; D062065:Wastewater; C109984:indium tin oxide
keywords: Au-sputtered ITO; Electrochemically active biofilms; Microbial fuel cells; Optoelectronic integrated microchip; Transparent conductive oxide