We here provide visual summaries of some of our research projects and publications.
Electrokinetic scanning probe [ link ]
The non-contact electrokinetic scanning probe (ESP) has the ability to locally deliver and extract ionic species and fluids to- and from- substrates using a wide range of liquid processing solutions in conjunction with localized heating and analyte focusing, which opens the door to a range of new applications in deposition and extraction of biomolecules.
Spatially multiplexed RNA in situ hybridization to reveal tumor heterogeneity [ link ]
Multiplexed RNA in situ hybridization for the analysis of gene expression patterns plays an important role in investigating development and disease. Here, we present a microfluidic method for multiplexed RNA-ISH to detect spatial tumor heterogeneity in tissue sections.
Spatially resolved genetic analysis of tissue sections enabled by microscale flow confinement retrieval and isotachophoretic purification [ link ]
We have developed a method for spatially resolved genetic analysis of formalin‐fixed paraffin‐embedded (FFPE) cell block and tissue sections. This method involves local sampling using hydrodynamic flow confinement of a lysis buffer, followed by electrokinetic purification of nucleic acids from the sampled lysate. We characterized the method by locally sampling an array of points with a circa 200 μm diameter footprint, enabling the detection of single KRAS and BRAF point mutations in small populations of RKO and MCF‐7 FFPE cell blocks. To illustrate the utility of this approach for genetic analysis, we demonstrate spatially resolved genotyping of FFPE sections of human breast invasive ductal carcinoma.
Nip the bubble in the bud: a guide to avoid gas nucleation in microfluidics [ link ]
Gas bubbles are almost a routine occurrence encountered by researchers working in the field of microfluidics. The spontaneous and unexpected nature of gas bubbles represents a major challenge for experimentalists and a stumbling block for the translation of microfluidic concepts to commercial products. This is a startling example of successful scientific results in the field overshadowing the practical hurdles of day-to-day usage. We however believe such hurdles can be overcome with a sound understanding of the underlying conditions that lead to bubble formation. In this tutorial, we focus on the two main conditions that result in bubble nucleation: surface nuclei and gas supersaturation in liquids. We hope this tutorial will provide a reference guide in helping to deal with a familiar foe, the “bubble”.
Electroosmotic flow dipole: Experimental observation and flow field patterning [ Link ]
We experimentally demonstrate the phenomenon of electroosmotic dipole flow that occurs around a localized surface charge region under the application of an external electric field in a Hele-Shaw cell. We use localized deposition of polyelectrolytes to create well-controlled surface charge variations, and show that, for a disk-shaped spot, the internal pressure distribution that arises results in uniform flow within the spot and dipole flow around it. We further demonstrate the superposition of surface charge spots to create complex flow patterns, without the use of physical walls.
Quantitative microimmunohistochemistry for the grading of immunostains on tumour tissues [ Link ]
Immunohistochemistry is the gold-standard method for cancer-biomarker identification and patient stratification. Yet, owing to signal saturation, its use as a quantitative assay is limited as it cannot distinguish tumours with similar biomarker-expression levels. Here, we introduce a quantitative microimmunochemistry assay that enables the acquisition of dynamic information, via a metric of the evolution of the immunohistochemistry signal during tissue staining, for the quantification of relative antigen density on tissue surfaces. We also show that the assay enables the quantification of multiple biomarkers (human epidermal growth factor receptor, oestrogen receptor and progesterone receptor) in a standard breast-cancer panel.
Dynamic microscale flow patterning using electrical modulation of zeta potential [ Link ]
The ability to move fluids at the microscale is at the core of many scientific and technological advancements. Despite its importance, microscale flow control remains highly limited by the use of discrete channels and mechanical valves, and relies on fixed geometries. Here we present an alternative mechanism that leverages localized field-effect electroosmosis to create dynamic flow patterns, allowing fluid manipulation without the use of physical walls. We demonstrate a range of unique flow patterns that can be achieved, including regions of recirculating flow surrounded by quiescent fluid and volumes of complete stagnation within a moving fluid. We believe that the ability to create tailored microscale flow using solid-state actuation will open the door to entirely new on-chip functionalities.
High-Quality Immunohistochemical Stains Through Computational Assay Parameter Optimization [ Link ]
Accurate profiling of tumors using immunohistochemistry (IHC) is essential in cancer diagnosis. The inferences drawn from IHC-stained images depend to a great extent on the quality of immunostaining, which is in turn affected strongly by assay parameters. To optimize assay parameters, the available tissue sample is often limited. Moreover, with current practices in pathology, exploring the entire assay parameter space is not feasible. Thus, the evaluation of IHC stained slides is conventionally a subjective task, in which diagnoses are commonly drawn on images that are suboptimal. In this work, we introduce a framework to analyze IHC staining quality and its sensitivity to process parameters. Our methodology provides a promising step in automatically evaluating and quantifying staining quality of IHC stained tissue sections, and it can potentially standardize immunostaining across diagnostic laboratories.
Fluidic Bypass Structures for Improving the Robustness of Liquid Scanning Probes [ Link ]
We aim to improve operational robustness of liquid scanning probes. Two main failure modes to be addressed are an obstruction of the flow path of the processing liquid and a deviation from the desired gap distance between probe and sample. Methods: We introduce a multi-functional design element, a microfluidic bypass channel, which can be operated in dc and in ac mode, each preventing one of the two main failure modes. Significance: Liquid scanning probes enabling targeted interfacing with biological surfaces are compatible with a wide range of workflows and bioanalytical applications. An improved operational robustness would facilitate rapid and widespread adoption of liquid scanning probes in research as well as in diagnostics.
Underpinning transport phenomena for the patterning of biomolecules [ Link ]
Surface-based assays are increasingly being used in biology and medicine, which in turn demand increasing quantitation and reproducibility. This translates into more stringent requirements on the patterning of biological entities on surfaces (also referred to as biopatterning). This tutorial focuses on mass transport in the context of existing and emerging biopatterning technologies. We here develop a step-by-step analysis of how analyte transport affects surface kinetics, and of the advantages and limitations this entails in major categories of patterning methods, including evaporating sessile droplets, laminar flows in microfluidics or electrochemistry. Understanding these concepts is key to obtaining the desired pattern uniformity, coverage, analyte usage or processing time, and equally applicable to surface assays. We believe this tutorial will serve researchers to better understand available patterning methods/principles, optimize conditions and to help design protocols/assays. By highlighting fundamental challenges and available approaches, we wish to trigger the development of new surface patterning methods and assays.
Real-Time Monitoring of Fluorescence in Situ Hybridization Kinetics [ Link ]
We present a novel method for real-time monitoring and kinetic analysis of fluorescence in situ hybridization (FISH). We implement the method using a vertical microfluidic probe containing a microstructure designed for rapid switching between probe solution and nonfluorescent imaging buffer. The FISH signal is monitored in real time during the imaging buffer wash, during which signal associated with unbound probes is removed. We provide a theoretical description of the method as well as a demonstration of its applicability using a model system of centromeric probes (Cen17). We demonstrate the applicability of the method for characterization of FISH kinetics under conditions of varying probe concentration, destabilizing agent (formamide) content, volume exclusion agent (dextran sulfate) content, and ionic strength. We show that our method can be used to investigate the effect of each of these variables and provide insight into processes affecting in situ hybridization, facilitating the design of new assays.