Livia Della Seta

Screen printed graphite biosensors based on bacterial cells

A microbial biosensor was developed for the determination of phenolic compounds and the measurement was based on oxygen consumption in relation to analyte oxidation. Induced cells of Pseudomonas putidaDSM 50026 were immobilised on the surface of SPG electrodes covered with cellulose acetate membrane by means of gelatine which was then cross linked with glutaraldehyde. The systems were calibrated for different phenolic substances. Detection ranges were 0.1–1.0 M for phenol and 0.05–1.0M for l-tyrosine and l-DOPA, respectively, with a response time of 3 min. Furthermore, phenol detection was performed in the presence of synthetic wastewater samples.

Tyrosinase biosensor based on modified screen printed electrodes: measurements of total phenol content

A disposable tyrosinase biosensor has been developed for the analysis of phenols and polyphenols, by modifying screen printed electrodes (SPEs) with addition of suitable mediators of redox processes directly into the conductive pastes. The percent ratio of mediator in the pastes was chosen depending on the electrochemical sensitivity either in batch or standard flow conditions. Ferrocene modified carbon electrodes have been used on whose surface the enzyme tyrosinase was immobilized in a glutaraldehyde cross-linked matrix of bovine serum albumin. Mixing the mediator to the electrode pastes should overcome transport limitations, due to its dissolution, which occur in commonly used immobilization procedures. Different immobilization techniques of tyrosinase on SPEs in the detection of phenolic compounds were tested and compared. Modified SPEs showed relatively good reproducibility and detection limits in the micromolar range for all phenolic compounds used. Major sensor parameters have been optimized in flow systems putting special attention on operating potential, pH and buffer composition, which strongly affect the detection of polyphenols and operational stability in wine. The resulting biosensors were stored and dried for a minimum of 8 h at 4°C, and showed a shelf stability of about 30 days. The procedure has been applied both on a synthetic wine matrix and on real samples, to determine the ‘pool’ of phenolic composition in terms of phenol concentration.

Biosensors based on gold nanoelectrode ensembles and screen printed electrodes

Gold nanowires were synthesized within polycarbonate membranes according to an electroless deposition method, obtaining nanoelectrode ensembles (NEEs) with special electrochemical features. NEEs were coupled with home-produced carbon graphite screen printed electrodes and the electrochemical properties of the original nanoelectrode ensemble on screen printed substrate (NEE/SPS) assembly has been tested for sensors application. Glucose oxidase has been used as model enzyme in order to verify the feasibility of disposable gold NEE/SPS biosensors. Finally, different immobilisation and electrochemical deposition techniques based on either self assembled monolayers of cysteamine (CYS) or amino-propyl-triethoxysilane (APTES) and conductive polyaniline (PANI) molecular wires were used. Spatial patterning of the enzyme on the polycarbonate surface and of PANI wires on gold nanoelectrodes was obtained. Possible direct electron transfer between the enzyme and the PANI modified gold nanoelectrodes has been evaluated.

A preliminary study on electrochemical biosensors for the determination of total cholinesterase inhibitors in strawberries

Organophosphorous (OP) insecticides reveal acute toxicity because of their capability to affect the nervous system through the inhibition of acetyl cholinesterase function in regulating the neurotransmitter acetylcholine. The present work shows an example of an easy to be handled inhibition electrochemical biosensor, based on thick film technology for low cost production of screen printed electrodes. Anti-cholinesterase activity in specific fruits was determined measuring the inhibition of acetyl cholinesterase enzyme owing to the presence of OP pesticides. Paraoxon was taken as reference pesticide for each measurement. The main fluidic critical parameters were investigated under flow injection analysis, through the comparison of different enzymatic immobilisation methods. Analytical features were evaluated as a function of experimental parameters. The analytical detection was developed in a three step procedure and the pesticides content was measured in strawberries samples taken from the local market. The separation between the acetyl cholinesterase inhibition and the electrochemical detection with the choline oxidase biosensor decreases the total analysis time, allowing improvements in reproducibility and stability of the system. A comparison with reference materials and standard analytical procedures for pesticides will be required in the future for evaluating the reliability of the method.

Long-Term Performance of Electrodes Based on Vinyl Acetate Homo-Polymer Binder

In this work we propose the use of a hydro-dispersible polymer such as the poly vinyl acetate as a binder for the production of electrodes for lithium-ion batteries. To increase the film forming properties of the polymer the poly vinyl was added with triacetin that acts as a plasticizer. The electrochemical stability of the polymer was tested by a polarizing electrode, formed by mixing the polymer with carbon. Subsequently, an electrode tape was prepared by using LiNi 0.5 Mn 1.5 O 4 as the active material and characterized by SEM, EDS and TGA. Lithium metal cells were assembled and tested to evaluate specific capacity, power and energy density at various discharge rates. The cycle life of the cell was evaluated by galvanostatic charge/discharge cycles. The tests showed that the electrodes prepared with PVA plasticized with triacetin have very good electrochemical performance in terms of capacity retention as a function of the discharge rate and the cycle number. Our work demonstrates that the use of triacetin to plasticize the PVA allows to increase the electrochemical stability of the electrode likely due to an improvement of the slurry filmability. The proposed method could represent a promising technology for the production of long-term performance lithium batteries.

Electrochemical and Morphological Investigation on Gold Bio-Nano-Electrodes. Preliminary Results

Gold nano-electrode ensembles were synthesized within nanoporous polycarbonate membranes and coupled with screen printed substrates. A disposable and versatile electrochemical system for biosensing and bio analytical applications has been obtained. Scanning Electron Microscopy and Scanning Probe Microscopy techniques were used to characterize the membrane surface, the nanostructured surfaces and the resulting biosensing devices. Efficiency and response of nano-probes were tested with several enzymatic immobilizations on the sensitive surface. Herein, the model case of a glucose oxidase biosensor based on nanoelectrodes is taken into account, for further evaluations on the accuracy of the biosensor system.

Engineering a continuous flow electrochemical micro-cell for biosensor applications: new achievements

The functional tests of a previously obtained continuous flow micro-cell revealed a rather low value of the sensitivity of the chronoamperometric measurements as well as a poor reliability of both fluidic and electric connections. The engineering of the micro-cell regards the improvement of the following characteristics: (1) integrating the reference electrode on the chip, (2) designing a specific pattern of the electrodes and (3) serially distributing them along the pipeline reservoir. Thus, a plug-flow device is obtained and the preliminary tests confirm its functionality together with an improved sensitivity. The use of photosensitive glass (Foturan®) for obtaining the reservoir and its vertical openings allowed an improvement of the transversal shape and thus of the fluid flow. Better connections are achieved by the development of more reliable and rigid glass fluidic connections as well as of flexible elastomer-based solderless electric connections combined with both a standard DIL40 socket and standard flat cable connectors.