Huabing Yin

Microfluidics for single cell analysis

Substantial evidence shows that the heterogeneity of individual cells within a genetically identical population can be critical to their chance of survival. Methods that use average responses from a population often mask the difference from individual cells. To fully understand cell-to-cell variability, a complete analysis of an individual cell, from its live state to cell lysates, is essential. Highly sensitive detection of multiple components and high throughput analysis of a large number of individual cells remain the key challenges to realise this aim. In this context, microfluidics and lab-on-a-chip technology have emerged as the most promising avenue to address these challenges. In this review, we will focus on the recent development in microfluidics that are aimed at total single cell analysis on chip, that is, from an individual live cell to its gene and proteins. We also discuss the opportunities that microfluidic based single cell analysis can bring into the drug discovery process.

Spontaneous assembly and real-time growth of micrometre-scale tubular structures from polyoxometalate-based inorganic solids

We report the spontaneous and rapid growth of micrometre-scale tubes from crystals of a metal oxide-based inorganic solid when they are immersed in an aqueous solution containing a low concentration of an organic cation. A membrane immediately forms around the crystal, and this membrane then forms micrometre-scale tubes that grow with vast aspect ratios at controllable rates along the surface on which the crystal is placed. The tubes are composed of an amorphous mixture of polyoxometalate-based anions and organic cations. It is possible for liquid to flow through the tubes, and for the direction of growth and the overall tube diameter to be controlled. We demonstrate that tube growth is driven by osmotic pressure within the membrane sack around the crystal, which ruptures to release the pressure. These robust, self-growing, micrometre-scale tubes offer opportunities in many areas, including the growth of microfluidic devices and the self-assembly of metal oxide-based semipermeable membranes for diverse applications.

Separation of humic acid from a model surface water with PSU/SPEEK blend UF/NF membranes

Abstract Membranes made from blends of polysulphone and sulphonated poly(ether ether ketone) (PSU/SPEEK) have high porosity, high charge and a pore size at the boundary between nanofiltration (NF) and ultrafiltration (UF). Their application to the treatment of surface water for drinking purposes has been investigated through study of their ability to remove humic acid (HA) from a model water, in comparison with two commercial membranes. The PSU/SPEEK membranes, in planar or tubular form, showed excellent retention of HA and very high flux. Their high charges gave rise to critical fluxes for deposition. As an additional benefit, HA deposits forming on the charged membranes above the critical fluxes had a loose structure, as visualised by atomic force microscopy (AFM), and were consequently efficiently removed by rinsing. Three multivalent ions, Fe 3+ , Al 3+ and Mn 2+ , at their concentrations in a natural water did not affect the membrane process significantly.

Raman-Activated Cell Sorting Based on Dielectrophoretic Single-Cell Trap and Release

Raman-activated cell sorting (RACS) is a promising single-cell technology that holds several significant advantages, as RACS is label-free, information-rich, and potentially in situ. To date, the ability of the technique to identify single cells in a high-speed flow has been limited by inherent weakness of the spontaneous Raman signal. Here we present an alternative pause-and-sort RACS microfluidic system that combines positive dielectrophoresis (pDEP) for single-cell trap and release with a solenoid-valve-suction-based switch for cell separation. This has allowed the integration of trapping, Raman identification, and automatic separation of individual cells in a high-speed flow. By exerting a periodical pDEP field, single cells were trapped, ordered, and positioned individually to the detection point for Raman measurement. As a proof-of-concept demonstration, a mixture of two cell strains containing carotenoid-producing yeast (9%) and non-carotenoid-producing Saccharomyces cerevisiae (91%) was sorted, which enriched the former to 73% on average and showed a fast Raman-activated cell sorting at the subsecond level.

The effect of sulfonated poly(ether ether ketone) additives on membrane formation and performance

Sulfonated poly(ether ether ketone) (SPEEK), a strong polyelectrolyte, was investigated as an additive in polysulfone (PSU)/SPEEK/N-methyl-2-pyrrolidinone (NMP) systems. Membrane characterisation was carried out using filtration studies and by atomic force microscopy (AFM). The effect of SPEEK in the charged membrane formation was investigated through thermodynamic and viscosity studies and correlated with the structure and properties of the resulting membranes. A “Polyelectrolyte behaviour” of SPEEK was observed for the first time in the membrane forming systems. Charged ultrafiltration/nanofiltration membranes prepared from 20 wt.% PSU solutions with the ratio of SPEEK/PSU in the range of 0.005–0.05, have substantially increased permeability, salt rejection, porosity, and a greatly reduced fouling tendency compared to the base PSU membrane. The charged membranes offer the possibility of effective removal of humic substances from surface waters in a highly efficient manner.

Gradient Microfluidics Enables Rapid Bacterial Growth Inhibition Testing

Bacterial growth inhibition tests have become a standard measure of the adverse effects of inhibitors for a wide range of applications, such as toxicity testing in the medical and environmental sciences. However, conventional well-plate formats for these tests are laborious and provide limited information (often being restricted to an end-point assay). In this study, we have developed a microfluidic system that enables fast quantification of the effect of an inhibitor on bacteria growth and survival, within a single experiment. This format offers a unique combination of advantages, including long-term continuous flow culture, generation of concentration gradients, and single cell morphology tracking. Using Escherichia coli and the inhibitor amoxicillin as one model system, we show excellent agreement between an on-chip single cell-based assay and conventional methods to obtain quantitative measures of antibiotic inhibition (for example, minimum inhibition concentration). Furthermore, we show that our methods can provide additional information, over and above that of the standard well-plate assay, including kinetic information on growth inhibition and measurements of bacterial morphological dynamics over a wide range of inhibitor concentrations. Finally, using a second model system, we show that this chip-based systems does not require the bacteria to be labeled and is well suited for the study of naturally occurring species. We illustrate this using Nitrosomonas europaea, an environmentally important bacteria, and show that the chip system can lead to a significant reduction in the period required for growth and inhibition measurements (<4 days, compared to weeks in a culture flask).

Atomic force microscopy studies of membrane—solute interactions (fouling)☆

Abstract AFM has been proved to be a rapid method of assessing membrane—solute interactions (fouling) of membranes under process conditions. The interactions of developmental membranes (SPEEK/PSU and PSU) with different solutes have been directly measured and linked to process performance. Correlation of the performance of two commercial PCI membranes (ES404 and EM006) with AFM measurements has been carried out for two types of separation of industrial importance: ultrafiltration in the pulp and paper industry and protein concentration/ fractionation. AFM expertise has been further exploited in a study of the efficiency of membrane cleaning after a process of whey concentration.

Screening of biomineralization using microfluidics

Biomineralization is the process where biological systems produce well-defined composite structures such as shell, teeth, and bones. Currently, there is substantial momentum to investigate the processes implicated in biomineralization and to unravel the complex roles of proteins in the control of polymorph switching. An understanding of these processes may have wide-ranging significance in health care applications and in the development of advanced materials. We have demonstrated a microfluidic approach toward these challenges. A reversibly sealed T-junction microfluidic device was fabricated to investigate the influence of extrapallial (EP) fluid proteins in polymorph control of crystal formation in mollusk shells. A range of conditions were investigated on chip, allowing fast screening of various combinations of ion, pH, and protein concentrations. The dynamic formation of crystals was monitored on chip and combined with in situ Raman to reveal the polymorph in real time. To this end, we have demonstrated the unique advantages of this integrated approach in understanding the processes involved in biomineralization and revealing information that is impossible to obtain using traditional methods.

Miniaturized optoelectronic tweezers controlled by GaN micro-pixel light emitting diode arrays.

A novel, miniaturized optoelectronic tweezers (OET) system has been developed using a CMOS-controlled GaN micro-pixelated light emitting diode (LED) array as an integrated micro-light source. The micro-LED array offers spatio-temporal and intensity control of the emission pattern, enabling the creation of reconfigurable virtual electrodes to achieve OET. In order to analyse the mechanism responsible for particle manipulation in this OET system, the average particle velocity, electrical field and forces applied to the particles were characterized and simulated. The capability of this miniaturized OET system for manipulating and trapping multiple particles including polystyrene beads and live cells has been successfully demonstrated.

Poly(3,4-ethylenedioxythiophene)/MoS2 nanocomposites with enhanced electrochemical capacitance performance

Composites based on conducting polymers and two-dimensional (2D) layer structure transition metal oxides are expected to realize the combination of good mechanical properties and excellent capacitance. Here poly(3,4-ethylenedioxythiophene)/molybdenum disulfide (PEDOT/MoS2) intercalated composites were successfully synthesized via in situ polymerization in the presence of ammonium persulfate (APS). The thermal stability, conductivity and capacitance performance are improved significantly with increasing fraction of MoS2. When the content of MoS2 was 45% in weight, the maximum weight loss velocity temperature is 365 °C which is 52 °C higher than that of PEDOT; the specific capacitance was 405 F g−1, about 4 times that of a PEDOT electrode; also the capacity retention was around 90% after 1000 cycles. This study provides a facile preparation method of organic/inorganic nanocomposites with enhanced electrochemical capacitance performance.