Visible LED-Based Instrumentation for Photometric Determination of Electroosmotic Flow in Microchannels

Abstract

A instrumentação para a determinação fotométrica do fluxo eletrosmótico (EOF) em dispositivos microfluídicos é descrita neste trabalho. A instrumentação é baseada em componentes acessíveis e consiste em um microscópio trinocular e no fotodiodo integrado OPT101. Um diodo emissor de luz (LED) de alta intensidade foi utilizado como fonte de radiação. Para as determinações foram utilizadas soluções aquosas dos corantes azul patente V e azul de metileno. O sistema foi utilizado no monitoramento do EOF em microdispositivos de poli(dimetilsiloxano) (PDMS) e híbridos de toner/vidro. As mobilidades do EOF determinadas em pH 7,0 foram (5,75 ± 0,01)10 -4 cm 2 V -1 s -1 e (3,2 ± 0,1)10 -4 cm 2 V -1 s -1 para os dispositivos de toner/vidro e PDMS, respectivamente. Medidas reprodutíveis foram obtidas em todos os experimentos, levando a uma alta precisão na determinação. O método proposto foi comparado com o método tradicional de determinação do EOF que envolve a medida da corrente nos microcanais.An instrumental setup for electroosmotic flow (EOF) determination in microfluidic devices is described. The system is based on a trinocular microscope and an integrated photodiode OPT101. The radiation was provided by a high-intensity white LED. For the determinations, patent blue V and methylene blue aqueous solutions were used. The setup was applied for EOF monitoring in hybrid toner/glass and PDMS microchips. For the toner/glass device, the EOF mobility was determined to be (5.75 ± 0.01) 10 -4 cm 2 V -1 s -1 at pH 7.0. For PDMS devices the measured EOF mobility was (3.2 ± 0.1) 10 -4 cm 2 V -1 s -1 . Reproducible measurements were obtained in all experiments, which produced results with small errors. The proposed method was compared to the conventional current monitoring method.Keywords: electroosmotic flow, mTAS, Lab-on-a-chip, photometric methods, microfluidic devices IntroductionElectroosmotic flow (EOF) is the movement of solvent molecules caused by an applied voltage in a capillary system. EOF plays an essential role in electromigration separation techniques, such as capillary zone electrophoresis (CZE or free solution capillary electrophoresis, FSCE) or microchip electrophoresis, 1 since the velocity of the ions is influenced by the magnitude of the EOF. As an example, both positively and negatively charged species can be simultaneously analyzed due to the EOF. Moreover, the EOF magnitude could bring some information about the condition of the surface of the capillary or microchannel wall. In particular, the knowledge about the surface charge density (including not only the EOF magnitude but also the zeta potential) can be of paramount importance for preventing adsorption of analyte to the wall.It is well accepted that EOF has its origin on the unbalanced charge distribution in the region closer to the capillary/microchannel wall, the so called electrical double layer (EDL). More precisely, the flow is caused by the movement of excess ions in the diffuse portion of the EDL. Mathematical treatment of the EOF combines the Newto...

Electroosmotic flow in fused deposition modeling (FDM) 3D‐printed microchannels

“…The µ EOF was determined at room temperature (25 • C) using the current monitoring method [12,13]. For these measures, the 3D-printed device was assembled over a platform (Figure S2) that was also 3D printed.…”