Effect of Mono- and Divalent Metal Ions on Current-Voltage Features of a λ-DNA Solution Electrically Driven in a Microfluidic Capillary

The interactions of DNA molecules and metal ions lead to changes in their configuration and conformation, which in turn influence the current characteristics of the solution as DNA molecules are translocated through a micro/nanofluidic channel and ultimately cause serious impacts on the practical applications of DNA/gene chips for precisely manipulating and studying the molecular properties of single DNA molecules. In this study, the current characteristics of λ-DNA solutions without or with metal ions (i.e., K⁺, Na⁺, Mg²⁺, and Ca²⁺) were experimentally investigated when they were transported through a 5 μm microcapillary under an external electric field with asymmetric electrodes. Experimental data indicated some meaningful results. First, the current-voltage relations of the metal ion solutions were all linear, while those of λ-DNA solutions without or with metal ions were all nonlinear and followed power functions, of which the indices were related to the type, valence, and mobility of ions. Furthermore, as the concentrations of metal ions increased, the power indices of the λ-DNA solutions with monovalent metal ions increased, while those of the λ-DNA solutions with divalent ions decreased. Finally, the main reasons for the current characteristics were theoretically attributed to two possible mechanisms: the polarizations on the asymmetric electrodes and the interactions between λ-DNA and metal ions. These findings are helpful for the design of new biomedical micro/nanofluidic sensors and labs on a chip for accurately manipulating single DNA molecules.

Single-step electrohydrodynamic separation of 1-150 kbp in less than 5 min using homogeneous glass/adhesive/glass microchips

Electrohydrodynamic migration, which is based on hydrodynamic actuation with an opposing electrophoretic force, enables the separation of DNA molecules of 3-100 kbp in glass capillary within 1 h. Here, we wish to enhance these performances using microchip technologies. This study starts with the fabrication of microchips with uniform surfaces, as motivated by our observation that band splitting occurs in microchannels made out of heterogeneous materials such as glass and silicon. The resulting glass-adhesive-glass microchips feature the highest reported bonding strength of 11 MPa for such materials (115 kgf/cm²), a high lateral resolution of critical dimension 5 μm, and minimal auto-fluorescence. These devices enable us to report the separation of 13 DNA bands in the size range of 1-150 kbp in one experiment of 5 min, i.e. 13 times faster than with capillary. In turn, we observe that bands split during electrohydrodynamic migration in heterogeneous glass-silicon but not in homogeneous glass-adhesive-glass microchips. We suggest that this effect arises from differential Electro-Osmotic Flow (EOF) in between the upper and lower walls of heterogeneous channels, and provide evidence that this phenomenon of differential EOF causes band broadening in electrophoresis during microchip electrophoresis. We finally prove that our electrohydrodynamic separation compares very favorably to microchip technologies in terms of resolution length and features the broadest analytical range reported so far.

Voltage control for microchip capillary electrophoresis analyses

This paper presents an inexpensive and easy-to-implement voltage sequencer instrument for use in microchip capillary electrophoresis (MCE) actuation. The voltage sequencer instrument takes a 0-5 V input signal from a microcontroller and produces a reciprocally proportional voltage signal with the capability to achieve the voltages required for MCE actuation. The unit developed in this work features four independent voltage channels, measures 105 × 143 × 45 mm (width × length × height), and the cost to assemble is under 60 USD. The system is controlled by a peripheral interface controller and commands are given via universal serial bus connection to a personal computer running a command line graphical user interface. The performance of the voltage sequencer is demonstrated by its integration with a fluorescence spectroscopy MCE sensor using pinched sample injection and electrophoretic separation to detect ciprofloxacin in samples of milk. This application is chosen as it is particularly important for the dairy industry, where fines and health concerns are associated with the shipping of antibiotic-contaminated milk. The voltage sequencer instrument presented represents an effective low-cost instrumentation method for conducting MCE, thereby making these experiments accessible and affordable for use in industries such as the dairy industry.