Copper oxide nanoflakes as highly sensitive and fast response self-sterilizing biosensors

Abstract

Vertical copper oxide nanoflakes were synthesized on a Cu foil through oxidation in alkaline conditions. X-ray photoelectron spectroscopy showed that after exposing the nanoflakes to an Escherichia coli bacterial suspension, the outermost surface of the nanoflakes was chemically reduced through the glycolysis process of the bacteria. Current–voltage (I–V) characteristics of the nanoflakes (measured perpendicular to surface of the Cu foil by using conductive atomic force microscopy) indicated that electrical resistivity of the nanoflakes increased about one order of magnitude after exposure to the bacterial suspension. The nanoflakes reduced by the bacterial suspension could also be reoxidized by ex-situNaOH treatment at 60 °C. The response time and recovery time of the bacterial sensor were measured as ∼2 min. Furthermore, the lower detection limit of the sensor was found to be ∼10²CFU mL⁻¹. The bacteria could also not survive on the nanoflakes. For example, after 30 min, 88 ± 11 and 97 ± 2% of the bacteria were inactivated on the surface of the as-prepares nanoflakes, in the dark and under light irradiation, respectively. Therefore, the copper oxide nanoflakes can be used as highly sensitive and fast response self-sterilizing biosensors for microorganisms contributing a glycolysis process.