Polyaniline/poly (2-acrylamido-2-methyl-1-propanesulfonic acid) modified cellulose as promising material for sensors design.

A material based on cellulose coated with polyaniline/poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (Cell/PANI-PAMPSA) was synthesized in a simple way starting from cellulose fibres, aniline and using PAMPSA as dopant. The morphology, mechanical properties, thermal stability, and electrical conductivity were investigated by means of several complementary techniques. The obtained results highlight the excellent features of the Cell/PANI-PAMPSA composite with respect to the Cell/PANI one. Based on the promising performance of this material, novel device functions and wearable applications have been tested. We focused on its possible single use as: i) humidity sensors and ii) disposable biomedical sensors to provide immediate diagnostic services as close to the patient as possible for heart rate or respiration activity monitoring. To our knowledge, this is the first time that Cell/PANI-PAMPSA system has been used for such applications.

A simple and industrially scalable method for making a PANI-modified cellulose touch sensor.

In this work we present a simple, inexpensive, and easily scalable industrial paper process to prepare sheets of conductive cellulose fibers coated with polyanilines. First, bare fibers were coated by in situ oxidative polymerization of polyaniline then, the resulting composite fibers were used to fabricate electroactive sheets. The resistivity of the sheets is 14 ± 1 Ω sq-1, a value around 1000 times lower than those reported in literature. The superior electronic proprieties of the sheets were demonstrated by assembling a capacitive touch sensor device with optimized geometry. The touch sensor shows an increase of 3-4 % of the starting electric capacity after compression and a fast response time of 52 ms. To our knowledge this is the first time that a device is prepared in this way and therefore, the herein presented results can bring an significant improvement in the development of low-cost, green and high-tech electronic devices.

A planar impedance sensor for 3D spheroids.

Three dimensional cell culture systems have witnessed rapid expansion in the fields of tissue engineering and drug testing owing to their inherent ability to mimic native tissue microenvironments. High throughput technologies have also facilitated rapid and reproducible generation of spheroids and subsequently their use as in vitro tissue models in drug screening platforms. However, drug screening technologies are in need of monitoring platforms to study these 3D culture models. In this work we present a novel platform to measure the electrical impedance of 3D spheroids, through the use of a planar organic electrochemical transistor (OECT) and a novel circular-shaped microtrap. A new strategy was generated to overcome incompatibility of the integration of polydimethylsiloxane (PDMS) microdevices with OECT fabrication. The impedance platform for 3D spheroids was tested by using spheroids formed from mono-cultures of fibroblast and epithelial cells, as well as co-culture of the two cell types. We validated the platform by showing its ability to measure the spheroid resistance (Rsph) of the 3D spheroids and differences in Rsph were found to be related to the ion permeability of the spheroid. Additionally, we showed the potential use of the platform for the on-line Rsph monitoring when a co-culture spheroid was exposed to a porogenic agent affecting the integrity of the cell membrane.

A simple all-PEDOT:PSS electrochemical transistor for ascorbic acid sensing.

An ascorbic acid (AA) sensor was developed by employing an organic electrochemical transistor (OECT) based only on PEDOT:PSS as a conductive material. The device was prepared by spin coating using the CLEVIOS™ PH 1000 suspension (PEDOT:PSS) masking the gate and the channel areas with tape. The device was electrically characterized while the doping level of the PEDOT:PSS in the channel was controlled using both the gate electrode and the potentiostat. It was demonstrated that the current that flows in channel (Id) is controlled by the concentration of oxidized sites in the examined potential range. AA reacts with the conductive polymer leading to the extraction of charge carriers from the channel, and thus resulting in a decrease of the absolute value of Id. It was observed that Id linearly depends on the logarithm of the AA concentration between 10-6 and 10-3 M. The OECT response to AA was studied by varying the gate voltage or the PEDOT:PSS thickness. The performance of the device for optimized conditions shows a limit of detection equal to 10-8 M and a sensitivity of 4.5 ± 0.1 × 10-6 A decade-1.

Dopamine amperometric detection at a ferrocene clicked PEDOT:PSS coated electrode.

Chemically modified electrodes are widely employed in electroanalytical chemistry and an important goal is to strongly anchor redox mediators on the electrode surface. In this work, indium tin oxide (ITO) electrodes have been coated with PEDOT:PSS that has been ferrocene-functionalized, by a two-step procedure consisting of the electrodeposition of PEDOT-N3 followed by copper-catalyzed azide-alkyne cycloaddition of ethynylferrocene. The coated electrodes have been characterized by XPS, showing successful ferrocene immobilization, by AFM, and by cyclic voltammetry (CV), which is dominated by the stable and highly reversible response of ferrocene. The electrocatalytical performance of the device is assessed by analyzing 3,4-dihydroxyphenyl ethylamine, also commonly known as dopamine (DA). The sensor presents a linear range between 0.01 and 0.9 mM, a mean sensitivity of 196 mA M-1 cm-2 and a limit of detection (LoD) of 1 µM.

Nanogenerators based on ZnO or TiO2 oxides.

Recently, an approach for converting nanoscale mechanical energy into electrical energy has been suggested by using piezoelectric zinc oxide (ZnO) nanowire arrays. Such devices have been shown to convert ultrasonic energy into electric energy by a deflection of the nanowires via a corrugated electrode operated up and down by the ultrasound. A typical approximately 1 pW output power for a device of a approximately 1 mm2 area and a density of approximately 10(7)/mm2 nanowires can be obtained. In order to reach the approximately 10 nW power needed to operate a nanodevice, nanogenerators of this kind need to be optimized. With the aim of fabricating low cost to efficiency ratio nanogenerators, we have considered ZnO films grown by an electrochemical technique, based on the direct precipitation of Zn hydroxide on a conducting ITO/glass substrate and subsequent heat treatment, and TiO2 films deposited from a colloidal suspension of anatase/rutile commercial powders. These methods allowed us to obtain disordered but quite uniform arrays distributed on the surface of the substrate. Preliminary results on the electrical properties are presented. Under input mechanical strain we find output powers of approximately 10(-9)/cm2 W, which are comparable to those obtained with the ZnO nanoarrays. Possible interpretations of results in terms of piezoelectricity (ZnO) and incipient ferroelectricity (TiO2) are presented and improvements of the devices are discussed.

Optimization of a glucose biosensor setup based on a Ni/Al HT matrix.

An amperometric glucose biosensor was developed using an anionic clay matrix of hydrotalcitic nature (Ni/Al-NO3 HT) as enzyme support, which was electrochemically synthesized at -0.90 V versus SCE, using a rotating disk Pt electrode to assure homogeneity of the electrodeposition suspension. The biorecognition element was glucose oxidase (GOx) immobilized on HT during the electrosynthesis, which was followed by cross-linking with glutaraldehyde vapours to avoid the enzyme release. The performances of the biosensor, in terms of sensitivity to glucose calculated from the slope of the calibration curve, are dependent on parameters related to the electrodeposition. An experimental design was applied to detect the optimal conditions of electrosynthesis in order to optimize the glucose biosensor performance. The factors taken into account were enzyme concentration and Ni/Al molar ratio. A full factorial design was performed to study linear interactions between factors and their quadratic effects and the optimal setup was evaluated by the isoresponse curves. The significant factors were enzyme concentration (linear and quadratic terms) and the interaction between enzyme concentration and Ni/Al molar ratio. Under the optimized electrodeposition conditions, the reproducibility of the biosensor fabrication was very good, being the RSD of the sensitivity about 5%.

Nickel hexacyanoferrate membrane as a coated wire cation-selective electrode.

Nickel hexacyanoferrates containing alkali metal cations as counter ions were used to prepare ion-selective electrodes for potentiometric sensing of intercalated species in the coated wire electrode (CWE) configuration. All the electrodes developed display a quasi-Nernstian response towards potassium ion, whereas the highest sensitivity is generally achieved when Cs+ is the counter cation in the sensing material. The selectivity constants of the electrodes were calculated by the matched potential method considering K+ as the primary ion. The selectivity order is Cs+ > K+ > Na+ > Li+ and reflects the effective dimension of the hydrated cations.