Contact Conductivity Detection in Poly(methyl methacylate)-Based Microfluidic Devices for Analysis of Mono- and Polyanionic Molecules

Abstract

An on-column contact conductivity detector was developed for the analysis of various mono- and polyanionic compounds separated by electrophoresis chips fabricated in poly(methyl methacrylate) (PMMA) using hot embossing techniques from Ni electroforms. The detector consisted of a pair of Pt wires (127 microm diameter) with an end-to-end spacing of approximately 20 microm and situated within the fluidic channel. The waveform applied to the electrode pair was a bipolar pulse with a frequency of 5.0 kHz and was used to reduce the charging current from measurement so that the current recorded at the end of one pulse is more representative of the solution conductivity. Using the detector, separations of amino acids, peptides, proteins, and oligonucleotides were demonstrated. For the amino acids and peptides, free-solution zone electrophoresis was performed. A calibration plot for the amino acid alanine was found to be linear from approximately 10 to 100 nM in a carrier electrolyte consisting of 10 mM triethylamonium acetate. The concentration detection limit was found to be 8.0 nM, with the corresponding mass detection limit equal to 3.4 amol (injection volume = 425 pL). The protein separations with conductivity detection were performed using MEKC, in which the carrier electrolyte contained the anionic surfactant sodium dodecyl sulfate (SDS) above its cmc. Near baseline resolution was achieved in the PMMA microchip for a solution containing 8 different proteins. In the case of the DNA fragments, capillary electrochromatography was used with a C18-modified PMMA chip and a carrier electrolyte containing an ion-pairing agent.

Highly Efficient Circulating Tumor Cell Isolation from Whole Blood and Label-Free Enumeration Using Polymer-Based Microfluidics with an Integrated Conductivity Sensor

“…44 The chemical composition of CTCs make them ideal candidates for detection using conductivity due to their unique electrical properties compared to erythrocytes or leukocytes. For example, CTCs in general possess very low membrane potential and low impedance resulting from the intracellular migration of sodium ions (Na + ) in compensation for the depleted potassium ion concentration (K + ) of the intracellular fluid.…”

A three-layer PMMA electrophoresis microchip with Pt microelectrodes insulated by a thin film for contactless conductivity detection

“…[1][2][3][4][5][6][7] Conductivity detection can be classified into two modes: contact mode and contactless mode. In contact mode, the microelectrode directly contacts the solution.…”

“…In contact mode, the microelectrode directly contacts the solution. 1,2 In contactless mode, the microelectrode is insulated from the solution by an insulating layer. [3][4][5][6][7] Compared with contact mode, contactless mode has several advantages because of the insulation of the electrode from the solution, such as the elimination of electrode fouling, bubble generation, and the isolation from the separation voltage.…”

Characterization of low viscosity polymer solutions for microchip electrophoresis of non-denatured proteins on plastic chips

“…13 For this report, we chose microchips made of poly(methyl methacrylate) (PMMA) which is one of the most common polymeric substrates for fabrication of microchips and it has been applied for protein separation. 6,[14][15][16] Previously our group reported a covalent coating on PMMA microchannels by polyethyleneglycol (PEG) which successfully controlled protein adsorption on surfaces, 6 and dynamic coating by using linear polysaccharides such as cellulose derivatives which have a self-coating ability has been applied to prevent sample adsorption on the surface of PMMA microchips. [17][18][19] As well, we systematically characterized spontaneous adsorption of surfactants and cellulose on PMMA surface using atomic force microscopy (AFM) and infrared external-reflection (IR-ER) spectroscopy.…”