María Teresa Fernández-Abedul

Universal mobile electrochemical detector designed for use in resource-limited applications

Significance The ability to perform electrochemical testing in the field, and in resource-limited environments, and to transmit data automatically to “the cloud” can enable a broad spectrum of analyses useful for personal and public health, clinical analysis, food safety, and environmental monitoring. Although the developed world has many options for analysis and web connection, the developing world does not have broad access to either the expensive equipment necessary to perform these tests or the advanced technologies required for network connectivity. To overcome these limitations, we have developed a simple, affordable, handheld device that can perform all the most common electrochemical analyses, and transmit the results of testing to the cloud from any phone, over any network, anywhere in the world. This paper describes an inexpensive, handheld device that couples the most common forms of electrochemical analysis directly to “the cloud” using any mobile phone, for use in resource-limited settings. The device is designed to operate with a wide range of electrode formats, performs on-board mixing of samples by vibration, and transmits data over voice using audio—an approach that guarantees broad compatibility with any available mobile phone (from low-end phones to smartphones) or cellular network (second, third, and fourth generation). The electrochemical methods that we demonstrate enable quantitative, broadly applicable, and inexpensive sensing with flexibility based on a wide variety of important electroanalytical techniques (chronoamperometry, cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, and potentiometry), each with different uses. Four applications demonstrate the analytical performance of the device: these involve the detection of (i) glucose in the blood for personal health, (ii) trace heavy metals (lead, cadmium, and zinc) in water for in-field environmental monitoring, (iii) sodium in urine for clinical analysis, and (iv) a malarial antigen (Plasmodium falciparum histidine-rich protein 2) for clinical research. The combination of these electrochemical capabilities in an affordable, handheld format that is compatible with any mobile phone or network worldwide guarantees that sophisticated diagnostic testing can be performed by users with a broad spectrum of needs, resources, and levels of technical expertise.

MCE-electrochemical detection for following interactions of ssDNA and dsDNA with methylene blue

The interaction between the organic dye, methylene blue and DNA has been studied by MCE with electrochemical detection. Interaction produces two different signals, one corresponding to free methylene blue and other, for the complex methylene blue–DNA. The hybridization between a ssDNA and a complementary sequence, specific to the severe acute respiratory syndrome virus, has been performed and studied in a thermoplastic olefin polymer of amorphous structure CE‐microchip with an end‐channel gold wire detector. Moreover, studies with a longer dsDNA, an expression vector involved in the transitory or stable expression in mammals cells, pFLAG‐CMV4, has also been performed.

Multiple-point electrochemical detection for a dual-channel hybrid PDMS-glass microchip electrophoresis device

A new PDMS‐based dual‐channel MCE with multiple‐point amperometric detection has been evaluated. Electrophoresis has been optimised in a single‐channel device. Pretreatment with 0.1 M NaOH is very important for increasing and stabilising the EOF. The precision is adequate for a days work in terms of both peak current and migration time. The RSD of the peak current for five successive signals was 1.9, 2.4 and 3.1% for dopamine, p‐aminophenol and hydroquinone. RSD for the migration time was always less than 1.3%, which demonstrates the stability of the EOF and the possibility of running multiple experiments in the same microchip. The adequate inter‐microchip precision as well as the rapid and simple manufacturing procedure indicates the disposable nature of the PDMS microchips. A dual‐channel device with very simple multiple‐point amperometric detection is proposed here. Elasticity of the PDMS allows removing the polymer slightly and aligning gold wires working electrodes. Injection can be performed from each of the sample reservoirs or from both simultaneously. The distance between the separation channels is critical for obtaining adequate signals as well as the introduction of a high‐voltage electrode in the buffer reservoir. Simultaneous measurement of the same analytes in both channels is possible by applying the same potential. Moreover, since no cross‐separation is produced, different analytes or samples can be simultaneously measured.

Procedure 36 Genosensor on gold thin-films with enzymatic electrochemical detection of a SARS virus sequence

Publisher Summary This chapter presents a procedure for the construction of a hybridization-based genosensor for a SARS (severe acute respiratory syndrome) virus sequence on a 100nm sputtered gold film, which works as immobilization and transduction surface. The chapter tests the sensitivity and the selectivity of the SARS genosensor using complementary strands of SARS virus and three-base mismatch strands. Genosensor construction include following steps: a drop of 5 mL of 1.02 mM thiolated probe deposited on the gold film and maintain at 37°C for 20 min or at 41°C for 12 h; it is cleaned with 0.1M Tris-HCl buffer; further a15 mL drop of a 2% 1-hexanethiol solution is deposited on the gold film and maintained for 10 min and again cleaned with a 2×SSC buffer solution pH 7. From the results of hybridization assay and recording of the analytical signal no significant difference found between the analytical signal obtained for a 3.03nM solution of the complementary target strand and three-base mismatch strand. The limit of detection, calculated as the concentration corresponding to a signal which is three times the standard deviation of the intercept, results to be 5 pM. This means an improvement of various orders of magnitude when compared with limits of detection reported in the bibliography for DNA assays.

Chapter 26 Thick- and thin-film DNA sensors

Publisher Summary The use of thick- and thin film electrodes as supports for genosensor devices offers enormous opportunities for their application in molecular diagnosis. The technologies used in the fabrication of both thick- and thin-film electrodes allow the mass production of reproducible, inexpensive and mechanically robust strip solid electrodes. Other important advantages of these electrodes are the possibility of miniaturization as well as their ease of manipulation in a disposable manner and therefore the use of small volumes. To detect transcriptional profiling and single nucleotide polymorphism thin-film arrays of 14, 20, 25, 48, and 64 electrodes have been fabricated, using lithographic techniques. Readout systems for these arrays based on electrical detection have also been developed. Moreover, a thick-film sensor array suitable for automation combined to readout based on intermittent pulse amperometry (IPA) has been commercialized. These genosensors and the readout instruments provide a simple, accurate and inexpensive platform for patient diagnosis. It is more than probable that arrays for 50–100 DNA sequences will be needed for some clinical applications. Although it is not difficult to design electrode pads with reproducible dimensions of a micron or less, the electrochemical readout requires mechanical connections to each individual electrode.