Flexible and Efficient Eletrokinetic Stacking of DNA and Proteins at an HF Etched Porous Junction on a Fused Silica Capillary

Local nano-electrode fabrication utilizing nanofluidic and nano-electrochemical control

Miniaturized systems have attracted much attention with the recent advances in microfluidics and nanofluidics. From the capillary electrophoresis, the development of glass-based microfluidic and nanofluidic technologies has supported advances in microfluidics and nanofluidics. Most microfluidic systems, especially nanofluidic systems, are still simple, such as systems constructed with simple straight nanochannels and bulk-scale electrodes. One of the bottlenecks to the development of more complicated and sophisticated systems is to develop the locally integrated nano-electrodes. However, there are still issues with integrating nano-electrodes into nanofluidic devices because it is difficult to fit the nano-electrode size into a nanofluidic channel at the nanometer level. In this study, we propose a new method for the fabrication of local nano-electrodes in nanofluidic devices with nanofluidic and nano-electrochemistry-based experiments. An electroplating solution was introduced to a nanochannel with control of the flow and the electroplating reaction, by which nano-electrodes were successfully fabricated. In addition, a nanofluidic device was available for nanofluidic experiments with the application of 200 kPa. This method can be applied to any electroplating material such as gold and copper. The local nano-electrode will make a significant contribution to the development of more complicated and sophisticated nanofluidic electrophoresis systems and to local electric detection methods for various nanofluidic devices.

Salty Biofluidic Sample Clean-Up and Preconcentration with a Paper-Based Ion Concentration Polarization Interface

Charged species from complex media could be separated and enriched taking advantage of ion concentration polarization (ICP) effect; thus, ICP can be used for sample purification and improvement of detection sensitivity. In this paper, a novel and reliable ICP interface was established on a paper-based analytical device (PAD) by using ion exchange membrane, and electrokinetic stacking of target analytes from salty media was successfully demonstrated. Steady ICP effect was well observed in aqueous solution with up to 400 mM NaCl as shown by a fluorescent probe, which makes it possible to directly process salty physiological samples such as blood and urine with this type of PAD. Application of this method was demonstrated by direct online stacking of total protein from urine samples and image-based colorimetric detection by a smartphone camera. The linear response was in the range of 50-350 mg/L (R² = 0.99), with recovery rate in the range of 94.8-107.6% and relative standard deviation below 7.1%. The obtained results were consistent with that of the clinical method. As an off-line sample pretreatment method, the feasibility for rapid tandem mass spectrometry detection of amino acids from serum samples was also investigated, and promising results were obtained. This PAD method is of low cost, easy to operate, and reliable. As a disposable PAD, it is useful not only for sensitive point-of-care testing but also for direct purification and concentration of complex and highly conductive physiological samples for fast and accurate detection with advanced analytical instruments.

High-performance bioanalysis based on ion concentration polarization of micro-/nanofluidic devices

Micro-/nanofluidics has received considerable attention over the past two decades, which allows efficient biomolecule trapping and preconcentration due to ion concentration polarization (ICP) within nanostructures. The rich scientific content related to ICP has been widely exploited in different applications including protein concentration, biomolecules sensing and detection, cell analysis, and water purification. Compared to pure microfluidic devices, micro-/nanofluidic devices show a highly efficient sample enrichment capacity and nonlinear electrokinetic flow feature. These two unique characterizations make the micro-/nanofluidic systems promising in high-performance bioanalysis. This review provides a comprehensive description of the ICP phenomenon and its applications in bioanalysis. Perspectives are also provided for future developments and directions of this research field.

Making of a single solid-state nanopore on the wall of fused silica capillary

A channel of nanometre size is an important platform for nanofluidic investigations. In this work, we show that a single solid nanopore can be generated by hydrogen fluoride etching of the outside wall of commercially available fused silica capillary. The geometry, size and the singleness were characterized by various means, including scanning electron microscope, electrolyte conductance measurement and a fluorescent microscope. The generation principle is also discussed. The nanopore thus generated features in low aspect ratio and exhibits typical nanofluidic effects such as ion concentration polarization, rectification and molecular translocation.

Applications and theory of electrokinetic enrichment in micro-nanofluidic chips

This review reports the progress on the recent development of electrokinetic enrichment in micro-nanofluidic chips. The governing equations of electrokinetic enrichment in micro-nanofluidic chips are given. Various enrichment applications including protein analysis, DNA analysis, bacteria analysis, viruses analysis and cell analysis are illustrated and discussed. The advantages and difficulties of each enrichment method are expatiated. This paper will provide a particularly convenient and valuable reference to those who intend to research the electrokinetic enrichment based on micro-nanofluidic chips.

Electrokinetics for sample preparation of biological molecules in biological samples using microfluidic systems

Sample preparation is the first part of every analytical method, but is often considered only after the optimization of the method. It is traditionally performed using a range of techniques requiring extensive manual handling, with solid-phase extraction, liquid–liquid extraction, protein precipitation and ultracentrfiguation, among others, being used depending on the targets and the application. In this article, we will focus on alternatives based on electrokinetics for applications including sample clean-up, concentration and derivatization of large biological molecules (DNA, peptides and proteins) of diagnostic importance, as well as small molecules as a tool for therapeutic drug monitoring. This article describes these approaches in terms of mechanisms, applicability and potential to be integrated into a lab-on-a-chip device for directly processing biological samples. Examples dealing with treated or clean samples have been excluded except where they show exceptionally high value.

Capillary electrophoresis based on the nucleic acid detection in the application of cancer diagnosis and therapy

This review focuses on capillary electrophoresis-based nucleic acid detection as it is applied to cancer diagnosis and therapy, and provides an introduction to the drawbacks and future developments of analysis with CE.