9626 IEEE SENSORS JOURNAL, VOL. 21, NO. 8, APRIL 15, 2021 Graphene Oxide/Urease Nanobiosensor Applied for Cadmium Detection in River Water Sandra Cristina Ballen, Greice M. Ostrowski, Juliana Steffens, and Clarice Steffens Abstract —The work reported an ultrasensitive cantilever nanobiosensor based on graphene oxide and urease for cadmium detection in river water. Since an efficient adsorp- tion between sensitive layer and the analyte was achieved, the biosensor showed high sensitivity (0.0147 nm/ppt) and low detection limit (18 ppt). Nanobiosensors were applied to analyze real water samples (river) collected in periods with and without rainfall. River water samples collected are a complex matrix, presented different physical and chemical characteristics for turbidity, conductivity and sodium concen- tration, which is related to the amount of rain in the period. While the values of pH, color, potassium, and magnesium concentration found in the samples collected did not show any significant difference. The response of the nanobiosensor was satisfactory and the effect of the matrix can be minimized with the cadmium fortification in the samples. Different interfering species as sodium, potassium, and magnesium were tested finding a negligible effect. The nanobiosensor based on graphene nanomaterial and urease enzyme has been satisfactorily applied to the determination of cadmium in river water samples. Index Terms— Rainfall, river water, cantilever, water quality, cadmium. I. I NTRODUCTION C ONTAMINATION of water by heavy metals has become a problem of global importance with increasing concern due to implications for human health [1]–[3]. Among these heavy metals, cadmium is the one with the highest toxicity [4]. It is found naturally, and the compounds are used as stabilizers in polyvinyl chloride (PVC) products, color pigments, various metal alloys, and in nickel-cadmium rechargeable batteries. Metallic cadmium is used mainly as an anti-corrosion agent (cadmiation). Products containing cadmium are rarely recycled [5], In this sense, the negligence occurs in treating industrial waste before dumping it in the rivers and is released in industrial effluents, contributing to the aquatic environment pollution. This metal, if released to the soil, is leached into the rivers by the runoff of surface water from the rains, and can persist in the aquatic environment. The World Health Manuscript received November 19, 2020; revised January 26, 2021; accepted January 28, 2021. Date of publication February 1, 2021; date of current version March 17, 2021. This work was supported in part by the National Council for Scientific and Technological Development–Brazil (CNPq), in part by the Coordination for the Improvement of Higher Education Personnel-Brazil (CAPES) under Grant Finance Code 001, in part by the Research Support Foundation of the State of Rio Grande of Sul–Brazil (FAPERGS), and in part by the Financiadora de Estudos e Projetos (Finep). The associate editor coordinating the review of this article and approving it for publication was Prof. Chih-Ting Lin. (Corresponding author: Clarice Steffens.) The authors are with the Department of Food Engineering, URI-Erechim, Erechim 99709-910, Brazil (e-mail: claristeffens@ yahoo.com.br). Digital Object Identifier 10.1109/JSEN.2021.3056042 Organization (WHO) and the United States Environmental Protection Agency (EPA) establishes maximum limits of cad- mium in drinking water of 3 and 5 ppb, respectively [6], [7]. So, the qualitative and quantitative detection of this heavy metal becomes important. In order to improve detection limits, cantilever nanobiosen- sors have emerged as a tool, which can be used as a fast quantitative analysis with high sensitivity [8]–[10]. This device has advantages as nanomechanical sensing technology for direct detection (label-free), in real time and in situ, not require solvent, has low cost and versatility in comparison to conventional sensing techniques [11]. The disadvantages are calibration of focused laser beam and thermal control during the experiments. Cantilever nanobiosensors are devices that detect biochem- ical reactions from biological events incorporated into the recognition elements such as nucleic acids, cells, enzymes and antibodies, producing electrical, thermal and/or optical signals, which are associated with a transduction system that converts the signal between the elements of recognition and the analyte in a detectable and measurable effect [11]–[15]. Various materials have been developed and applied as sensors layers [16], especially enzymatic elements that present high sensitivity, selectivity, specificity, and flexibility in appli- cation. Carbon-based nanomaterials, such as graphene deriva- tives, have also been considered as promising materials due to their cost-effectiveness, electronic properties, high mechanical strength, large specific surface area, one-atom thickness, and good biocompatibility [17]–[20]. The graphene oxide has good 1558-1748 © 2021 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See https://www.ieee.org/publications/rights/index.html for more information.