Self-assembled films of dendrimers and metallophthalocyanines as FET-based glucose biosensors

Separative extended gate field effect transistor (SEGFET) type devices have been used as an ion sensor or biosensor as an alternative to traditional ion sensitive field effect transistors (ISFETs) due to their robustness, ease of fabrication, low cost and possibility of FET isolation from the chemical environment. The layer-by-layer technique allows the combination of different materials with suitable properties for enzyme immobilization on simple platforms such as the extended gate of SEGFET devices enabling the fabrication of biosensors. Here, glucose biosensors based on dendrimers and metallophthalocyanines (MPcs) in the form of layer-by-layer (LbL) films, assembled on indium tin oxide (ITO) as separative extended gate material, has been produced. NH3+ groups in the dendrimer allow electrostatic interactions or covalent bonds with the enzyme (glucose oxidase). Relevant parameters such as optimum pH, buffer concentration and presence of serum bovine albumin (BSA) in the immobilization process were analyzed. The relationship between the output voltage and glucose concentration shows that upon detection of a specific analyte, the sub-products of the enzymatic reaction change the pH locally, affecting the output signal of the FET transducer. In addition, dendritic layers offer a nanoporous environment, which may be permeable to H+ ions, improving the sensibility as modified electrodes for glucose biosensing.CAPESCNPqFAPESPFAPEMI

Nanostructured polyaniline thin films as pH sensing membranes in FET-based devices

Polyaniline (PANI) has become an important conducting polymer for sensing due to its morphological and electrical properties. However, the processing of polyaniline in the form of nanostructured thin films is often limited by the low solubility of the polymer in water. We synthesized nanostructured polyaniline (N-PANI) aimed at improving its solubility to form layer-by-layer (LbL) thin films in conjunction with poly(vinyl sulfonic acid) (PVS) as counter ion. N-PANI was characterized via spectroscopic measurements and SEM images. After assembled as LbL thin films onto gold (Au) substrates, the PVS/N-PANI were employed as separative extended gate pH sensing membrane in FET-based devices presenting pH sensitivity around 58 mV/pH with small voltage drift. The results suggest that N-PANI can be easily processed to form suitable thin films for pH sensing and can be combined with biomolecules to be applied in FET-based biosensors.CAPESCNPqFAPES

Ion-sensing properties of 1D vanadium pentoxide nanostructures

The application of one-dimensional (1D) V2O5 center dot nH(2)O nanostructures as pH sensing material was evaluated. 1D V2O5 center dot nH(2)O nanostructures were obtained by a hydrothermal method with systematic control of morphology forming different nanostructures: nanoribbons, nanowires and nanorods. Deposited onto Au-covered substrates, 1D V2O5 center dot nH(2)O nanostructures were employed as gate material in pH sensors based on separative extended gate FET as an alternative to provide FET isolation from the chemical environment. 1D V2O5 center dot nH(2)O nanostructures showed pH sensitivity around the expected theoretical value. Due to high pH sensing properties, flexibility and low cost, further applications of 1D V2O5 center dot nH(2)O nanostructures comprise enzyme FET-based biosensors using immobilized enzymes.CAPESCAPESCNPqCNPqFAPESPFAPES

Nanostructured polyaniline thin films as urea-sensing membranes in field-effect devices

We report the development of a urea biosensor based on a separative field-effect structure containing polyaniline in nanostructured form. Urea is normally produced by the nitrogen metabolism in the body, but its excess is indicative of kidney malfunction. Layer-by-layer (LbL) films of polyaniline in nanostructured form (N-PANI) and poly(vinylsulfonic acid) (PVS) were fabricated in a simple and low-cost way and used as pH-sensitive membranes. Urease was further immobilized on N-PANI by a reticulation process using glutaraldehyde (GA) as a crosslinking agent. The PVS/N-PANI-urease membrane was previously studied as a pH sensor using a junction field-effect transistor (JFET) input operational amplifier as a read-out circuit and showed a Nernstian behaviour (∼59 mV/pH) in the 6-8 pH range with a small voltage drift. The analytical curve of the biosensor showed a wide dynamic range of urea detection (0.05-10.0 mM), which covers the usual urea concentration in human blood, indicating that the proposed biosensor can be used in clinical analyses.CNPqCAPESFAPES

Immobilization of Poly(propylene imine) Dendrimer/Nickel Phtalocyanine as Nanostructured Multilayer Films To Be Used as Gate Membranes for SEGFET pH Sensors

We describe the assembly of layer-by-layer films based on the poly(propylene imine) dendrimer (PPID) generation 3 and nickel tetrasulfonated phthalocyanine (NiTsPc) for application as chemically sensitive membranes in sepal alive extended-gate field effect transistor (SEGFET) pH sensors PPID/NiTsPc films wet e adsorbed on quartz, glass. indium tin oxide. or gold (Au)-covered glass substrates Multilayer formation was monitored via UV-vis absorption upon following the increment in the Q-band intensity (615 nm) of NiTsPc The nanostructured membranes were very stable in a pH range of 4-10 and displayed a good sensitivity toward H(+), ca 30 mV/pH for PPID/N(1)TsPc films deposited on Au-covered substrates For films deposited on ITO, the sensitivity was ca 52 4 mV/pH. close to the expected theoretical value for ton-sensitive membranes. The use of chemically stable PPID/NiTsPc films as gate membranes in SEGFETs, as introduced here, may represent an alternative for the fabrication of nanostructured, porous platforms for enzyme immobilization to be used in enzymatic biosensors.Financiadora de Estudos e Projetos (FINEP)FinepCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPESCNPqConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESPFAPEMIGFundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG

Self-assembled films containing crude extract of avocado as a source of tyrosinase for monophenol detection

This paper reports on the use of the crude extract of avocado (CEA) fruit (Persea americana) as a source of tyrosinase enzyme. CEA was immobilized via layer by layer (LbL) technique onto indium tin oxide (ITO) substrates and applied in the detection of monophenol using a potentiometric biosensor. Poly(propylene imine) dendrimer of generation 3 (PPI-G3) was used as a counter ion in the layer by layer process due to its highly porous structure and functional groups suitable for enzyme linkage. After the immobilization of the crude CEA as multilayered films, standard samples of monophenol were detected in the 0.25-4.00 mM linear range with approximately 28 mV mM-1 of sensitivity. This sensitivity is 14 times higher than the values found in the literature for a similar system. The results show that it is possible to obtain efficient and low-cost biosensors for monophenol detection using potentiometric transducers and alternative sources of enzymes without purification.CNPqCAPESFINE

Layer-by-layer films containing SiO2 nanoparticles as field-effect pH sensors

Devices for pH monitoring based on separative structures and high input impedance readout circuit were fabricated using silicon dioxide nanoparticles (SiO2-Np). SiO2-Np were self-assembled onto gold substrates via layer-by-layer (LbL) technique using poly(allylamine) hydrochloride (PAH) as the counter-ion. The pH sensing properties of PAH/SiO2-Np LbL films were examined upon buffer solutions from pH 2 to 12, exhibiting pH sensitivity in agreement with other pH sensitivity membranes based on SiO2. The presence of nanoparticles improved the electrode contact area, ideal for enzyme immobilization, suggesting that PAH/SiO2-Np are suitable platforms to be applied in field-effect based biosensors