Incorporating a Hybrid Urease-Carbon Nanotubes Sensitive Nanofilm on Capacitive Field-Effect Sensors for Urea Detection

• Published in: Analytical chemistry (Washington) 2014-06, Vol.86 (11), p.5370-5375
• Main Authors: Siqueira, José R, Molinnus, Denise, Beging, Stefan, Schöning, Michael J
• Format: Article
• Language: English
• Subjects: Architecture; Atomic force microscopy; Biomolecules; Biosensing Techniques - methods; Biosensors; Dendrimers - chemistry; Electrolytes; Enzymes; Enzymes, Immobilized - chemistry; Microscopy, Atomic Force; Molecules; Morphology; Nanomaterials; Nanostructure; Nanotubes; Nanotubes, Carbon - chemistry; Semiconductors; Sensors; Urea - analysis; Ureas; Urease - chemistry
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac500458s

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.