title: Metalless electrodes for capacitively coupled contactless conductivity detection on electrophoresis microchips.
abstract: This paper describes the use of ionic solutions as sensing electrodes for capacitively coupled contactless conductivity detection on electrophoresis microchips. Initially, two channels were engraved in a PMMA holder by using a CO2 laser system and sealed with a thin adhesive membrane. PDMS electrophoresis chips were fabricated by soft lithography and reversibly sealed against the polymer membrane. Different ionic solutions were investigated as metalless electrodes. The electrode channels were filled with KCl solutions prepared in conductivity values from approximately 10 to 40 S/m. The best analytical response was achieved using the KCl solution with 21.9 S/m conductivity (2 mol/L). Besides KCl, we also tested NaCl and LiCl solutions for actuating as detection electrodes. Taking into account the same electrolyte concentration (2 mol/L), the best response was recorded with KCl solution due to its higher ionic conductivity. The optimum operating frequency (400 kHz) and the best sensing electrode (2 mol/L KCl) were used to monitor electrophoretic separations of a mixture containing K(+) , Na(+) , and Li(+) . The use of liquid solutions as sensing electrodes for capacitively coupled contactless conductivity detection measurements has revealed great performance to monitor separations on chip-based devices, avoiding complicated fabrication schemes to include metal deposition and encapsulation of electrodes. The LOD values were estimated to be 28, 40, and 58 μmol/L for K(+) , Na(+) , and Li(+) , respectively, what is comparable to that of conventional metal electrodes. When compared to the use metal electrodes, the proposed approach offers advantages regarding the easiness of fabrication, simplicity, and lower cost per device.
authors: Instituto de Química, Universidade Federal de Goiás, Goiânia, Goiás, Brasil.
authors: Gerson F
authors: GF
authors: Duarte Junior
authors: Instituto de Química, Universidade Estadual de Campinas, Campinas São Paulo, Brasil.|Instituto Nacional de Ciência e Tecnologia de Bioanalítica, Campinas, São Paulo, Brasil.
authors: José Alberto
authors: JA
authors: Fracassi da Silva
authors: Instituto de Química, Universidade de São Paulo, São Paulo, São Paulo, Brasil.
authors: Kelliton José
authors: KJ
authors: Mendonça Francisco
authors: Instituto de Química, Universidade de São Paulo, São Paulo, São Paulo, Brasil.
authors: Claudimir Lucio
authors: CL
authors: do Lago
authors: Instituto Nacional de Ciência e Tecnologia de Bioanalítica, Campinas, São Paulo, Brasil.|Instituto de Química de São Carlos, Universidade de São Paulo, São Carlos São Paulo, Brasil.
authors: Emanuel
authors: E
authors: Carrilho
authors: Instituto de Química, Universidade Federal de Goiás, Goiânia, Goiás, Brasil.|Instituto Nacional de Ciência e Tecnologia de Bioanalítica, Campinas, São Paulo, Brasil.
authors: Wendell K T
authors: WK
authors: Coltro
mesh_terms: D004553:Electric Conductivity; D004566:Electrodes; D046209:Electrophoresis, Microchip / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D052578:Ionic Liquids / Q000737:chemistry; D008672:Metals, Alkali / Q000737:chemistry / Q000302:isolation & purification; D011189:Potassium Chloride / Q000737:chemistry
chemical_list: D052578:Ionic Liquids; D008672:Metals, Alkali; D011189:Potassium Chloride
keywords: Analytical instrumentation; Electrochemical detection; Ionic liquids; Micro-fluidic devices; Sensing electrodes