William R. de Araujo

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.

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.

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.

Development of a Molecularly Imprinted Modified Electrode to Evaluate Phenacetin Based on the Preconcentration of Acetaminophen

A glassy carbon electrode modified with a molecularly imprinted polymer (MIP) containing phenacetin recognition sites is introduced. The phenacetin-selective MIP was synthesised based on the electropolymerisation of pyrrole in a 1:1 (v/v) water/ethanol with HClO4 solution. The MIP-modified electrode showed higher recognition ability in comparison with a bare electrode for procaine and aminopyrine, reported to electrochemically interfere in the quantification of phenacetin in cocaine samples. In addition, the MIP was able to preconcentrate one of the intermediates of the phenacetin electrochemical oxidation, acetaminophen, indicating the possibility of monitoring phenacetin based on the acetaminophen oxidation. The acetaminophen oxidation peak is 15 times more detectable compared to the signal obtained by the non-molecularly imprinted polymer (NIP), and it occurs 450 mV below the phenacetin electrochemical oxidation signal. These achieved characteristics decrease the possibility of interference from other electrochemical reactions that may occur in the same potential range as phenacetin electrochemical process.

Portable and low-cost colorimetric office paper-based device for phenacetin detection in seized cocaine samples

An office paper-based colorimetric device is proposed as a portable, rapid, and low-cost sensor for forensic applications aiming to detect phenacetin used as adulterant in illicit seized materials such as cocaine. The proposed method uses white office paper as the substrate and wax printing technology to fabricate the detection zones. Based on the optimum conditions, a linear analytical curve was obtained for phenacetin concentrations ranging from 0 to 64.52µgmL‒1, and the straight line was in accordance with the following equation: (Magenta percentage color) = 1.19 + 0.458 (CPhe/µgmL‒1), R2 = 0.990. The limit of detection was calculated as 3.5µgmL‒1 (3σ/slope). The accuracy of the proposed method was evaluated using real seized cocaine samples and the spike-recovery procedure.

Forensics in hand: new trends in forensic devices (2013-2017)

Forensic chemistry is the application of analytical chemistry to forensic analysis and is today one of the hot topics in the scientific literature as it can provide valuable information regarding crimes that have been committed and assist in their resolution. The literature in the field of forensic chemistry has been exponentially growing and covers several different subjects. This review discusses works published between 2013 and 2017 regarding portable or potentially portable devices (such as electrochemical sensors), field tests and intelligent devices that can be used in different areas of forensic chemistry and covers the following subjects: explosives, gunshot residues (GSR), liquid fuels, illicit drugs, beverages, alternative biological fluids and agrochemicals.

Portable analytical platforms for forensic chemistry: A review

This current review article focuses on recent contributions to on-site forensic investigations. Portable and potentially portable methods are presented and critically discussed about (bio)chemical trace analysis and studies performed outside the controlled laboratory environment to rapidly help in crime scene inquiries or forensic intelligence purposes. A wide range of approaches including electrochemical sensors, microchip electrophoresis, ambient ionization on portable mass spectrometers, handheld Raman and NIR instruments as well as and point-of-need devices, like paper-based platforms, for in-field analysis of latent evidences, controlled substances, drug screening, hazards, and others to assist in law enforcements and solving crime more efficiently are highlighted. The covered examples have successfully demonstrated the huge potential of portable devices for on-site applications. Future investigations should consider analytical validation to compete equality and even replace current gold standard methods.

Introduction of Materials Used in Chemical Sensors

Since the advent of smartphone technologies, the word “sensor” has become more and more commonplace outside of the academic environment. Nowadays, it is easy to find smartphones with a variety of sensors, for example, proximity, motion, ambient light, gyroscopic, and magnetic. These sensors are devices that detect inputs from the physical environment, in order to generate an output signal that can be read and understood by a human and/or can be transmitted electrically by someone or a machine. A simple example of a sensor is the mercury-based glass thermometer that has a heat as input and as consequence of the change in temperature the liquid mercury expands, or contracts, indicating a value of the temperature measured in a calibrated marked gauge that can be detected by a natural sensor, the human eye. Basically, the physical devices highlighted above translate physical properties into a human-readable output just as some human analogues can do through, for example, touch, vision, or hearing. However, nature has given us sensorial systems responsible not only to translate physical quantities as an interpretation of the outside world, but also the ability to sense chemicals through taste and olfaction systems. This chapter will introduce key parameters in the definition of biological sensors leading to chemical sensors and will also serve as an introduction to the other chapters.

Electrochemical sensor for discrimination of carbamates and organophosphorus pesticides

Pesticides are chemicals used to eliminate and/or protect crops from pest infestations. Carbamates and organophosphorus are two of the most common classes of pesticides used worldwide. Although these compounds increase the quantity and quality of the foods, their excessive use could cause health problems for animals and humans. In this work were extracted electrochemical information from seven pesticides, four carbamates (propoxur, carbaryl, carbofuran and isoprocarb) and three organophosphorus (fenitrothion, parathion and methyl-parathion). The electrochemical information was recorded by cyclic voltammetry technique using a glassy carbon as working electrode. The current signals obtained from the pesticides were used as input data to perform the Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA). A satisfactory discrimination was verified by the score plot obtained by PCA and no misclassification between the two classes of pesticides was observed.