Thiago R.L.C. Paixão

Wearable salivary uric acid mouthguard biosensor with integrated wireless electronics

This article demonstrates an instrumented mouthguard capable of non-invasively monitoring salivary uric acid (SUA) levels. The enzyme (uricase)-modified screen printed electrode system has been integrated onto a mouthguard platform along with anatomically-miniaturized instrumentation electronics featuring a potentiostat, microcontroller, and a Bluetooth Low Energy (BLE) transceiver. Unlike RFID-based biosensing systems, which require large proximal power sources, the developed platform enables real-time wireless transmission of the sensed information to standard smartphones, laptops, and other consumer electronics for on-demand processing, diagnostics, or storage. The mouthguard biosensor system offers high sensitivity, selectivity, and stability towards uric acid detection in human saliva, covering the concentration ranges for both healthy people and hyperuricemia patients. The new wireless mouthguard biosensor system is able to monitor SUA level in real-time and continuous fashion, and can be readily expanded to an array of sensors for different analytes to enable an attractive wearable monitoring system for diverse health and fitness applications.

Determination of nitrate in mineral water and sausage samples by using a renewable in situ copper modified electrode

A new approach for in situ electrodeposition of a renewable copper layer onto a copper electrode is reported. The active surface was obtained by anodic dissolution of a copper electrode at an appropriate potential and further redeposition of copper ions still remaining at the diffusion layer. Under optimal experimental conditions the peak current response increases linearly with nitrate concentration over a range of 0.1-2.5mmol L(-1). The repeatability of measurements for nitrate was evaluated as 1.8% (N=15) and the limit of detection of the method was found to be 11micromol L(-1) (S/N=3). Nitrate contents in two different samples (mineral water and sausages) compared well with those obtained from using the standard Griess protocol at a 95% of confidence level measured by the t-student test. The interference from chloride on the nitrate analysis and the possibility of simultaneous determination of nitrite were also examined.

Explosive colorimetric discrimination using a smartphone, paper device and chemometrical approach

In this report we introduce a novel approach for an inexpensive and disposable colorimetric paper sensor array for the detection and discrimination of five explosives – triacetone triperoxide (TATP), hexamethylene triperoxide diamine (HMTD), 4-amino-2-nitrophenol (4A2NP), nitrobenzene (NB), and picric acid (PA). The colorimetric sensor comprised a disposable paper array fabricated using a wax printer and three reagents (KI, creatinine, and aniline) that produced a unique color pattern for each explosive based on chemical interactions between the explosive species and the chemical reagents. The analytes were discriminated from one another as per the color change profiles, which were readily distinguishable after 15 min, using hierarchical clustering analysis (HCA) and principal component analysis (PCA); there were no misclassifications in any of the trials conducted. The colorimetric pattern values were extracted using a smartphone, custom-made software and a closed chamber to circumvent the illumination problems commonly found in other paper approach devices. A semi-quantitative analysis was performed and it was possible to use as low as 0.2 μg of explosives.

A renewable copper electrode as an amperometric flow detector for nitrate determination in mineral water and soft drink samples

A novel approach was developed for nitrate analysis in a FIA configuration with amperometric detection (E=-0.48 V). Sensitive and reproducible current measurements were achieved by using a copper electrode activated with a controlled potential protocol. The response of the FIA amperometric method was linear over the range from 0.1 to 2.5 mmol L(-1) nitrate with a detection limit of 4.2 micromol L(-1) (S/N=3). The repeatability of measurements was determined as 4.7% (n=9) at the best conditions (flow rate: 3.0 mL min(-1), sample volume: 150 microL and nitrate concentration: 0.5 mmol L(-1)) with a sampling rate of 60 samples h(-1). The method was employed for the determination of nitrate in mineral water and soft drink samples and the results were in agreement with those obtained by using a recommended procedure. Studies towards a selective monitoring of nitrite were also performed in samples containing nitrate by carrying out measurements at a less negative potential (-0.20 V).

Design and characterisation of a thin-layered dual-band electrochemical cell

Abstract The development of a thin-layered dual-band electrochemical cell operating at flow conditions is described. Influence of experimental parameters related to the geometric design of the channel electrode as well as the flow rate on the collection efficiency were studied by using ferricyanide as a probe, results being in agreement with predictions from literature. Fiagram responses obtained by injecting thiosulphate+iodide solutions to the carrier electrolyte (1 M Ac−/1 M HAc) were evaluated by measuring peak current and charge values at both electrodes. Data showed the influence of the flow rate and the ratio between iodide and thiosulphate concentrations on the profile of fiagrams recorded at the first electrode and the results are discussed on the basis of both sample dispersion and thickness of the reaction layer. Analytical applications of the proposed generator–collector cell involved titrations with electrogenerated iodine, thiosulphate concentrations as low as 1 μM being measured with high precision.

Flow injection analysis of picric acid explosive using a copper electrode as electrochemical detector.

A simple and fast electrochemical method for quantitative analysis of picric acid explosive (nitro-explosive) based on its electrochemical reduction at copper surfaces is reported. To achieve a higher sample throughput, the electrochemical sensor was adapted in a flow injection system. Under optimal experimental conditions, the peak current response increases linearly with picric acid concentration over the range of 20-300 μmol L(-1). The repeatability of the electrode response in the flow injection analysis (FIA) configuration was evaluated as 3% (n=10), and the detection limit of the method was estimated to be 6.0 μmol L(-1) (S/N=3). The sample throughput under optimised conditions was estimated to be 550 samples h(-1). Peroxide explosives like triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) were tested as potential interfering substances for the proposed method, and no significant interference by these explosives was noticed. The proposed method has interesting analytical parameters, environmental applications, and low cost compared with other electroanalytical methods that have been reported for the quantification of picric acid. Additionally, the possibility to develop an in situ device for the detection of picric acid using a disposable sensor was evaluated.

A copper interdigitated electrode and chemometrical tools used for the discrimination of the adulteration of ethanol fuel with water.

A new approach for the discrimination of the adulteration process of ethanol fuel with water is reported using a copper interdigitated electrode and chemometrical tools. The sensor was constructed using copper sheets with non-chemical modification of the electrode surface. The discrimination process was performed using capacitance values recorded at different frequencies (1,000 Hz to 0.1 MHz) as the input data for non-supervised pattern recognition methods (PCA: principal component analysis and HCA: hierarchical cluster analysis). The relative standard deviation for the capacitance signals obtained from ten independent interdigitated sensors was below 5.0%. The ability of the device to differentiate non-adulterated ethanol samples from those adulterated with water was demonstrated. In all analysed cases, there was good separation between the different samples in the score plots and the dendrograms obtained from PCA and hierarchical cluster analyses, respectively. Furthermore, the water content was quantified using a PCA approach. The results were consistent with those obtained using the Karl-Fischer method at a 95% confidence level, as measured using Students t-test.

Simple and Sensitive Paper-Based Device Coupling Electrochemical Sample Pretreatment and Colorimetric Detection

We report the development of a simple, portable, low-cost, high-throughput visual colorimetric paper-based analytical device for the detection of procaine in seized cocaine samples. The interference of most common cutting agents found in cocaine samples was verified, and a novel electrochemical approach was used for sample pretreatment in order to increase the selectivity. Under the optimized experimental conditions, a linear analytical curve was obtained for procaine concentrations ranging from 5 to 60 μmol L(-1), with a detection limit of 0.9 μmol L(-1). The accuracy of the proposed method was evaluated using seized cocaine samples and an addition and recovery protocol.

Diffusion layer titration of dipyrone in pharmaceuticals at a dual-band electrochemical cell

This paper describes the use of a thin-layered dual-band electrochemical cell operating at flow conditions to determine dipyrone (sodium salt of 1-phenil-2,3-dimethyl-4-methylaminomethanesulfonate-5-pyrazolone) by reaction with electrogenerated iodine. The electrolytic cell consisted of two closely spaced gold electrodes, the upper stream electrode serving as the generator electrode and the downstream electrode working as the collector electrode. A linear dynamic range from 2 to 15 mumol l(-1) dipyrone was obtained by using a sample volume of 100 mul, with a detection limit of 1.1 mumol l(-1). Standard deviation (S.D.) of 3.4% for 20 repetitive injections of a 40 mumol l(-1) dipyrone solution and sampling frequency of 90 h(-1) were achieved. The results obtained with the thin-layered dual-band electrochemical cell for dipyrone determination in three different pharmaceutical samples compared well with those found by iodimetry with coulometrically generated iodine.

Identification of Four Wood Species by an Electronic Nose and by LIBS

This paper presents two complementary methods capable of identifying four wood species (Cedrela fissilis, Ocotea porosa, Hymenolobium petraeum, and Aspidosperma subincanum) both by their volatile organic compounds and by the presence of 10 chemical elements: Al, B, Ca, Mg, Zn, Cu, Mn, Fe, Na, and Si. The volatile compounds were detected by an electronic nose formed by an array of three different conductive polymer gas sensors. The elemental determination was made by laser-induced breakdown spectrometry (LIBS). The emissions measured were treated by principal component analysis (PCA). Leave-one-out analysis showed a rate of hits of 100%.