Pencil‐drawn paper supported electrodes as simple electrochemical detectors for paper‐based fluidic devices

Abstract

A simple procedure for preparing inexpensive paper-based three-electrode electrochemical cells is described here. They consist of small circular pads of hydrophilic paper defined by hydrophobic barriers printed on paper with wax-based ink. The back face of these pads is insulated by thermally laminating a polyethylene layer and working, reference and counter electrodes are drawn on paper by using commercial pencil leads. At last, a controlled volume of sample containing a supporting electrolyte was laid to soak in paper channels. Their performance was evaluated by assaying these devices as both simple cells suitable for recording voltammograms on static samples and low-cost detectors for flowing systems. Voltammetric tests, conducted by using potassium hexacyanoferrate(II) as model prototype, were also exploited for identifying the brand and softness of graphite sticks enabling paper to be marked with lines displaying the best conductivity. By taking advantage of the satisfactory information thus gained, pencil drawn electrodes were tested as amperometric detectors for the separation of ascorbic acid and sunset yellow, which were chosen as prototype electroactive analytes because they are frequently present concomitantly in several food matrices, such as soft drinks and fruit juices. This separation was performed by planar thin layer chromatography conducted on microfluidic paper-based devices prepared by patterning on filter paper two longitudinal hydrophobic barriers, once again printed with wax-based ink. Factors affecting both separation and electrochemical detection were examined and optimised, with best performance achieved by using a 20 mM acetate running buffer (pH 4.5) and by applying a detection potential of 0.9 V. Under these optimum conditions, the target analytes could be separated and detected within 6 min. The recorded peaks were well separated and characterized by good repeatability and fairly good sensitivity, thus proving that this approach is indeed suitable for rapidly assembling inexpensive and reliable electrochemical detectors for flow analysis systems.

The voltammetric behaviour of lead at a hand drawn pencil electrode and its trace determination in water by stripping voltammetry

“…However, there have only been a small number of reports on the application of these devices using voltammetry and until now its application has been generally only in the characterisation of the electrode [15]. Recently, Santhiago and Kubota [16] have developed a glucose biosensor employing paper and a pencil drawn working electrode modified with the mediator 4-aminophenylboronic acid and glucose oxidase (GOD).…”

Fully-drawn carbon-based chemical sensors on organic and inorganic surfaces

“…The fabrication of sensing devices by printing 33–38 , dip coating 36,38,39 , drop casting 40 , photolithography 41 , or drawing 34–39,42–44 has advantages of being simple and low-cost without the need for highly specialized facilities. Drawing is particularly attractive because it directly deposits carbon-based solid composite materials that require no solution-phase processing.…”

Desenvolvimento de sensores eletroquímicos e colorimétricos para aplicações em amostras de interesse forense

“…Algumas das vantagens do dispositivo proposto é o baixo custo do papel sulfite utilizado como substrato, como previamente mencionado, sem necessidade de um processo de isolamento com um polímero sobre a face de trás do dispositivo para evitar perda de solução durante as medições [47,48,134], além de que não foi observado deformações do papel quando molhado pelo líquido durante as análises como observado com os dispositivos feitos com papel cromatografico. A Tabela 5 apresenta uma comparação entre os substratos, eletrodos, materiais e instrumentação necessária para a fabricação de alguns dispositivos baseados em papel relatados na literatura.…”

“…Podem ainda ser confeccionados os eletrodos usando métodos mais sofisticados como a deposição metálica por sputtering [42,43]. Para uso de eletrodos carbonáceos, além do uso de tinta condutiva, há trabalhos que fazem o uso do grafite [44,45] e da pintura direta no papel com minas de grafite [46][47][48]. Uma abordagem alternativa é o uso de fios metálicos fixados sobre a superfície do substrato de papel [49,50].…”

“…No campo que concerne o desenvolvimento de sensores eletroquímicos descartáveis e portáteis, há diversas pesquisas realizadas na literatura para a fabricação de eletrodos do tipo impressos através de diferentes tecnologias, mas basicamente utilizando tintas condutivas de carbono e outros metais [125][126][127], utilizando fios metálicos [49,128], construção de dispositivos em circuitos eletrônicos [78,129], confecção a partir de CDs (CDtrodos) [130][131][132], utilização direta de grafites [45,101] ou ainda "pintando/desenhando" com grafite sobre um substrato, comumente papel [47,48], entre outras formas.…”