title: Incorporating a hybrid urease-carbon nanotubes sensitive nanofilm on capacitive field-effect sensors for urea detection.
abstract: The ideal combination among biomolecules and nanomaterials is the key for reaching biosensing units with high sensitivity. The challenge, however, is to find out a stable and sensitive film architecture that can be incorporated on the sensor's surface. In this paper, we report on the benefits of incorporating a layer-by-layer (LbL) nanofilm of polyamidoamine (PAMAM) dendrimer and carbon nanotubes (CNTs) on capacitive electrolyte-insulator-semiconductor (EIS) field-effect sensors for detecting urea. Three sensor arrangements were studied in order to investigate the adequate film architecture, involving the LbL film with the enzyme urease: (i) urease immobilized directly onto a bare EIS [EIS-urease] sensor; (ii) urease atop the LbL film over the EIS [EIS-(PAMAM/CNT)-urease] sensor; and (iii) urease sandwiched between the LbL film and another CNT layer [EIS-(PAMAM/CNT)-urease-CNT]. The surface morphology of all three urea-based EIS biosensors was investigated by atomic force microscopy (AFM), while the biosensing abilities were studied by means of capacitance-voltage (C/V) and dynamic constant-capacitance (ConCap) measureaments at urea concentrations ranging from 0.1 mM to 100 mM. The EIS-urease and EIS-(PAMAM/CNT)-urease sensors showed similar sensitivity (~18 mV/decade) and a nonregular signal behavior as the urea concentration increased. On the other hand, the EIS-(PAMAM/CNT)-urease-CNT sensor exhibited a superior output signal performance and higher sensitivity of about 33 mV/decade. The presence of the additional CNT layer was decisive to achieve a urea based EIS sensor with enhanced properties. Such sensitive architecture demonstrates that the incorporation of an adequate hybrid enzyme-nanofilm as sensing unit opens new prospects for biosensing applications using the field-effect sensor platform.
authors.affiliation: Institute of Exact Sciences, Naturals and Education, Federal University of Triângulo Mineiro (UFTM) , 38064-200 Uberaba, Brazil.
authors.forename: José R
authors.initials: JR
authors.lastname: Siqueira
authors.forename: Denise
authors.initials: D
authors.lastname: Molinnus
authors.forename: Stefan
authors.initials: S
authors.lastname: Beging
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Schöning
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D050091:Dendrimers / Q000737:chemistry; D004800:Enzymes, Immobilized / Q000737:chemistry; D018625:Microscopy, Atomic Force; D037742:Nanotubes, Carbon / Q000737:chemistry*; D012666:Semiconductors; D014508:Urea / Q000032:analysis*; D014510:Urease / Q000737:chemistry*
chemical_list: D050091:Dendrimers; D004800:Enzymes, Immobilized; D037742:Nanotubes, Carbon; C104700:PAMAM Starburst; D014508:Urea; D014510:Urease