Tunable Electroosmosis-Based Femto-Liter Pipette: A Promising Tool toward Living-Cell Surgery

Microfluidic Sampling of Undissolved Components from Subcellular Regions of Living Single Cells for Mass Spectrometry Analysis

Precise sampling of undissolved chemical components from subcellular regions of living single cells is a prerequisite for their in-depth analysis, which could promote understanding of subtle early stage physiological or pathological processes. Here we report a microfluidic method to extract undissolved components from subcellular regions for MS analysis. The target single cell was isolated by the microchamber beneath the microfluidic probe and washed by the injected biocompatible isotonic glucose aqueous solution (IGAS). Then, the sampling solvent was injected to extract undissolved components from the expected subcellular region of the living single cell, where the position and size of the sampling region could be controlled. The components immobilized by undissolved cellular structures were proven to be successfully extracted. Since unextracted subcellular regions were protected by IGAS, the single cell could survive after a tiny part was extracted, providing the possibility of repetitive sampling of the same living cell. Phospholipids extracted from the subcellular regions were successfully identified. The results demonstrated the feasibility of our method for subcellular sampling and analysis.

Microfluidic Surgery in Single Cells and Multicellular Systems

Microscale surgery on single cells and small organisms has enabled major advances in fundamental biology and in engineering biological systems. Examples of applications range from wound healing and regeneration studies to the generation of hybridoma to produce monoclonal antibodies. Even today, these surgical operations are often performed manually, but they are labor intensive and lack reproducibility. Microfluidics has emerged as a powerful technology to control and manipulate cells and multicellular systems at the micro- and nanoscale with high precision. Here, we review the physical and chemical mechanisms of microscale surgery and the corresponding design principles, applications, and implementations in microfluidic systems. We consider four types of surgical operations: (1) sectioning, which splits a biological entity into multiple parts, (2) ablation, which destroys part of an entity, (3) biopsy, which extracts materials from within a living cell, and (4) fusion, which joins multiple entities into one. For each type of surgery, we summarize the motivating applications and the microfluidic devices developed. Throughout this review, we highlight existing challenges and opportunities. We hope that this review will inspire scientists and engineers to continue to explore and improve microfluidic surgical methods.

Emerging open microfluidics for cell manipulation

Cell manipulation is the foundation of biochemical studies, which demands user-friendly, multifunctional and precise tools. Based on flow confinement principles, open microfluidics can control the movement of microscale liquid in open space. Every position of the circuit is accessible to external instruments, making it possible to perform precise treatment and analysis of cells at arbitrary target positions especially at the single-cell/sub-cell level. Benefiting from its unique superiority, various manipulations including patterned cell culture, 3D tissue modelling, localized chemical stimulation, online cellular factor analysis, single cell sampling, partial cell treatment, and subcellular free radical attack can be easily realized. In this tutorial review, we summarize two basic ideas to design open microfluidics: open microfluidic networks and probes. The principles of mainstream open microfluidic methods are explained, and their recent important applications are introduced. Challenges and developing trends of open microfluidics are also discussed.

Simple chemical detection based on a surface-modified electroosmotic pump via interval immobilization

Environmental water quality monitoring plays an important role in human health risk assessments for pharmaceuticals in water and pollutant source control. A new chemical detection method was developed to enhance molecular selectivity and portability by combining the molecularly imprinted technique and an electroosmotic pump (EOP), which requires only a small pump, batteries and stopwatch in principle. Selective chemical adsorption on the surface-modified EOP decreases the pumping performance of EOP due to a decrease in the surface electric charge. For proof of concept, the microfabricated EOPs with chemical surface treatment were used to investigate the effects of surface chemical change on pumping performance. The microfluidic EOP of a size of 20 mm × 20 mm × 1 mm was modified by an interval immobilization method using the template of 4-(tributylammonium-methyl)-benzyltributylammonium chloride (TBTA) and evaluated by measuring EOF. The pumping performance of the surface-modified EOP was decreased by the selective adsorption of TBTA to a two-point recognition site on the EOP surfaces. The relationships between the flow rate and the TBTA concentration were fitted to the Langmuir equation. The EOP can selectively detect the model substance even in a mixture solution with a different chemical compound. This molecular imprinted EOP does not require large and expensive instruments for driving the device and chemical detection, which can be applied to a portable analytical device for onsite analysis.

Regulating the aggregation of colloidal particles in an electro-osmotic micropump

Unrestricted particle transport through microfluidic channels is of paramount importance to a wide range of applications, including lab-on-a-chip devices. In this article, we study via video microscopy the electro-osmotic aggregation of colloidal particles at the opening of a micrometer-sized silica channel in the presence of a salt gradient. Particle aggregation eventually leads to clogging of the channel, which may be undone by a time-adjusted reversal of the applied electric potential. We numerically model our system via the Stokes-Poisson-Nernst-Planck equations in a geometry that approximates the real sample. This allows us to identify the transport processes induced by the electric field and salt gradient and to provide evidence that a balance thereof leads to aggregation. We further demonstrate experimentally that a net flow of colloids through the channel may be achieved by applying a square-waveform electric potential with an appropriately tuned duty cycle. Our results serve to guide the design of microfluidic and nanofluidic pumps that allow for controlled particle transport and provide new insights for anti-fouling in ultra-filtration.

A Performance-enhanced Electroosmotic Pump with Track-etched Polycarbonate Membrane by Allylhydridopolycarbosilane Coating

Nanochannel plastic membranes are excellent materials for electroosmotic pump (EOP) elements owing to their surface charge properties, flexibility and cost-effectiveness. However, the surface charge properties of plastics are inferior to those of silicate-based materials. This paper reports a performance-enhanced EOP equipped with a glassified track-etch polycarbonate membrane (PC), which has a nanochannel surface covered by allylhydridopolycarbosilane (AHPCS). The effects of applied voltage, pH and membrane pore size on the electroosmotic flow velocity, along with a comparative study of the EOP with coated and pure membranes were investigated. It was found that when low DC voltage (10 - 40 V) was applied to both ends of the pump, the magnitude of the electroosmotic flow was linearly proportional to the voltage when the pore size of the membrane was less than 600 nm. A higher flow rate was obtained with larger pore size membranes. Compared with the uncoated film, the coated one showed faster electroosmosis velocity, with higher stability under the same conditions. For pH 10.0 buffer solution, a flow rate of 89.13 μL/min was obtained in the modified membrane-based EOP with excellent repeatability and durability, while the flow rate was only 37.89 μL/min in the bare PC membrane under 20 V. In order to demonstrate the performance of the developed EOP, the EOP was used for microcomplexometric titration to determine actual tap water hardness. The measured results were highly consistent with the results of a conventional complexometric titration methed. The EOP with an AHPCS-coated plastic membrane expanded the application range to harsh condition solutions, such as high-concentration acids or bases.

Spray-Capillary: An Electrospray-Assisted Device for Quantitative Ultralow-Volume Sample Handling

The analysis of low-volume samples provides valuable insight into complex biological systems. However, the proteomic and metabolomic analysis of low-volume samples remains challenging due to the lack of simple, efficient, and reproducible microsampling techniques. We have developed an electrospray-assisted device for quantitative low-volume sample extraction, referred to here as "Spray-Capillary". Stable electrospray was achieved through a chemically etched tip from a long (e.g., 50 cm) capillary with a conductive sheath flow. This electrospray provided the driving force to quantitatively draw low-volume samples into the capillary. We evaluated the precision and accuracy of sample injection volumes using our spray-capillary as the electrospray voltage, capillary ID, and column length were varied. Our results demonstrate that spray-capillary allows for reproducible and quantitative microsampling with low injection flow rates (as low as 15 pL/s). Furthermore, spray-capillary can be directly coupled with capillary zone electrophoresis (CZE) for separation. Overall, spray-capillary is a simple microsampling device that holds great potential for high-throughput quantitative omics analysis of ultralow-volume samples.

Advancement of electroosmotic pump in microflow analysis: A review

This review (with 152 references) covers the progress made in the development and application of electroosmotic pumps in a period from 2009 through 2018 in microflow analysis. Following a short introduction, the review first categorizes various electroosmotic pumps into five subclasses based on the materials used for pumping: i) open channel EOP, 2) packed-column EOP, iii) porous monolith EOP, iv) porous membrane EOP, and v) other types of EOP. Pumps in each subclass are discussed. A next section covers EOP applications, primarily the applications of EOPs in micro flow analysis and micro/nano liquid chromatography. Other scattered applications are also examined. Perspectives, trends and challenges are discussed in the final section.

Molecular profiling of single axons and dendrites in living neurons using electrosyringe-assisted electrospray mass spectrometry

Electrosyringe-assisted electrospray mass spectrometry (MS) is established for the first time to achieve intracellular sampling from one axon or dendrite in living neurons for mass spectrometric analysis.