title: Miniaturized metal oxide pH sensors for bacteria detection.
abstract: It is well known that the metabolic activity of some microorganisms results in changes of pH of the culture medium, a phenomenon that can be used for detection and quantification of bacteria. However, conventional glass electrodes that are commonly used for pH measurements are bulky, fragile and expensive, which hinders their application in miniaturized systems and encouraged to the search for alternatives. In this work, two types of metal oxide pH sensors have been tested to detect the metabolic activity of the bacterium Escherichia coli (E. coli). These pH sensors were produced on silicon chips with platinum metal contacts, onto which thin layers of IrOx or Ta2O5 were incorporated by two different methods (electrodeposition and e-beam sputtering, respectively). In order to facilitate measurement in small sample volumes, an Ag/AgCl pseudo-reference was also screen-printed in the chip and was assayed in parallel to an external Ag/AgCl reference electrode. As it is shown, the developed sensors generated results indistinguishable from those provided by a conventional glass pH-electrode but could be operated in significantly smaller sample volumes. After optimization of the detection conditions, the metal oxide sensors are successfully applied for detection of increasing concentrations of viable E. coli, with detection of less than 10(3)cfu mL(-1) in undiluted culture medium in just 5h.
authors.affiliation: Departament de Micro-Nano Sistemes, Institut de Microelectrònica de Barcelona (IMB-CNM), CSIC, 08290 Bellaterra, Spain. Electronic address: naroauriamolto@hotmail.com.
authors.forename: Naroa
authors.initials: N
authors.lastname: Uria
authors.affiliation: Departament de Micro-Nano Sistemes, Institut de Microelectrònica de Barcelona (IMB-CNM), CSIC, 08290 Bellaterra, Spain; Lab. Artificial Sensors Syst., ITMO University, Kronverskiy pr. 49, 197101 St. Petersburg, Russia.
authors.forename: Natalia
authors.initials: N
authors.lastname: Abramova
authors.affiliation: Departament de Micro-Nano Sistemes, Institut de Microelectrònica de Barcelona (IMB-CNM), CSIC, 08290 Bellaterra, Spain.
authors.forename: Andrey
authors.initials: A
authors.lastname: Bratov
authors.affiliation: Departament de Micro-Nano Sistemes, Institut de Microelectrònica de Barcelona (IMB-CNM), CSIC, 08290 Bellaterra, Spain.
authors.forename: Francesc-Xavier
authors.initials: FX
authors.lastname: Muñoz-Pascual
authors.affiliation: Diagnostic Nanotools, Cibbim-Nanomedicine, Vall d'Hebron Institut de Recerca (VHIR), Universitat Autònoma de Barcelona, Passeig de la Vall d'Hebron 119-129, 08035 Barcelona, Spain; Centro de Investigación Biomédica en Red - Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Spain. Electronic address: eva.baldrich@vhir.org.
authors.forename: Eva
authors.initials: E
authors.lastname: Baldrich
mesh_terms: D002138:Calibration; D002470:Cell Survival; D004926:Escherichia coli / Q000166:cytology / Q000302:isolation & purification*; D008670:Metals / Q000737:chemistry*; D008839:Microelectrodes; D055616:Microtechnology / Q000295:instrumentation*; D010087:Oxides / Q000737:chemistry*
chemical_list: D008670:Metals; D010087:Oxides
keywords: Bacterial viability; E. coli detection; Iridium oxide pH sensor; Microelectrodes; Tantalum pH sensor