Geometric optimisation of electrohydrodynamic fluid flows for enhanced biosensing

3D Concentric Electrodes-Based Alternating Current Electrohydrodynamics: Design, Simulation, Fabrication, and Potential Applications for Bioassays

Two-dimensional concentric asymmetric microelectrodes play a crucial role in developing sensitive and specific biological assays using fluid micromixing generated by alternating current electrohydrodynamics (ac-EHD). This paper reports the design, simulation, fabrication, and characterization of fluid motion generated by 3D concentric microelectrodes for the first time. Electric field simulations are used to compare electric field distribution at the electrodes and to analyze its effects on microfluidic micromixing in 2D and 3D electrodes. Three-dimensional devices show higher electric field peak values, resulting in better fluid micromixing than 2D devices. As a proof of concept, we design a simple biological assay comprising specific attachment of streptavidin beads onto the biotin-modified electrodes (2D and 3D), which shows ~40% higher efficiency of capturing specific beads in the case of 3D ac-EHD device compared to the 2D device. Our results show a significant contribution toward developing 3D ac-EHD devices that can be used to create more efficient biological assays in the future.

Next-Generation Molecular Discovery: From Bottom-Up In Vivo and In Vitro Approaches to In Silico Top-Down Approaches for Therapeutics Neogenesis

Protein and drug engineering comprises a major part of the medical and research industries, and yet approaches to discovering and understanding therapeutic molecular interactions in biological systems rely on trial and error. The general approach to molecular discovery involves screening large libraries of compounds, proteins, or antibodies, or in vivo antibody generation, which could be considered “bottom-up” approaches to therapeutic discovery. In these bottom-up approaches, a minimal amount is known about the therapeutics at the start of the process, but through meticulous and exhaustive laboratory work, the molecule is characterised in detail. In contrast, the advent of “big data” and access to extensive online databases and machine learning technologies offers promising new avenues to understanding molecular interactions. Artificial intelligence (AI) now has the potential to predict protein structure at an unprecedented accuracy using only the genetic sequence. This predictive approach to characterising molecular structure—when accompanied by high-quality experimental data for model training—has the capacity to invert the process of molecular discovery and characterisation. The process has potential to be transformed into a top-down approach, where new molecules can be designed directly based on the structure of a target and the desired function, rather than performing screening of large libraries of molecular variants. This paper will provide a brief evaluation of bottom-up approaches to discovering and characterising biological molecules and will discuss recent advances towards developing top-down approaches and the prospects of this.

The future of microfluidics in immune checkpoint blockade

Recent advances in microfluidic techniques have enabled researchers to study sensitivities to immune checkpoint therapy, to determine patients' response to particular antibody treatment. Utilization of this technology is helpful in antibody discovery and in the design of personalized medicine. A variety of microfluidic approaches can provide several functions in processes such as immunologic, genomic, and/or transcriptomic analysis with the aim of improving the efficacy and coverage of immunotherapy, particularly immune checkpoint blockade (ICB). To achieve this requires researchers to overcome the challenges in the current state of the technology. This review looks into the advancements in microfluidic technologies applied to researches on immune checkpoint blockade treatment and its potential shift from proof-of-principle stage to clinical application.

Simultaneous BRAFV600E Protein and DNA Aberration Detection in Circulating Melanoma Cells Using an Integrated Multimolecular Sensor

Liquid biopsy has emerged as the next generation target for diagnostics and therapeutic monitoring of many diseases including cancer. Liquid biopsy offers noninvasive analysis of aberrant biomolecular changes (e.g., aberrant protein expression, DNA mutation) which can provide crucial information on disease stages and therapy responses. As a diagnostically important biomarker for melanoma, the detection of the BRAF^V600E aberration at the DNA and protein level in liquid biopsies confers an attractive option. This method describes the preparation and operation of an integrated multimolecular sensor (IMMS) for simultaneous detection of the BRAF^V600E aberration in both molecular forms from circulating melanoma cells in liquid biopsy. IMMS integrates specific melanoma cell capture, cell release, cell lysis, and electrochemical BRAF^V600E detection on a single device. IMMS is demonstrated for a sample-to-answer workflow of plasma spiked with melanoma cells.

Single droplet detection of immune checkpoints on a multiplexed electrohydrodynamic biosensor

Monitoring soluble immune checkpoints in circulating fluids has the potential for minimally-invasive diagnostics and personalised therapy in precision medicine. Yet, the sensitive detection of multiple immune checkpoints from small volumes of liquid biopsy samples is challenging. In this study, we develop a multiplexed immune checkpoint biosensor (MICB) for parallel detection of soluble immune checkpoints PD-1, PD-L1, and LAG-3. MICB integrates a microfluidic sandwich immunoassay using engineered single chain variable fragments and alternating current electrohydrodynamic in situ nanofluidic mixing for promoting biosensor-target interaction and reducing non-specific non-target binding. MICB provides advantages of simultaneous analysis of up to 28 samples in <2 h, requires as little as a single sample drop (i.e., 20 μL) per target immune checkpoint, and applies high-affinity yeast cell-derived single chain variable fragments as a cost-effective alternative to monoclonal antibodies. We investigate the assay performance of MICB and demonstrate its capability for accurate immune checkpoint detection in simulated patient serum samples at clinically-relevant levels. MICB provides a dynamic range of 5 to 200 pg mL-1 for PD-1 and PD-L1, and 50 to 1000 pg mL-1 for LAG-3 with a coefficient of variation <13.8%. Sensitive immune checkpoint detection was achieved with limits of detection values of 5 pg mL-1 for PD-1, 5 pg mL-1 for PD-L1, and 50 pg mL-1 for LAG-3. The multiplexing capability, sensitivity, and relative assay simplicity of MICB make it capable of serving as a bioanalytical tool for immune checkpoint therapy monitoring.

Microfluidic Magnetic Mixing at Low Reynolds Numbers and in Stagnant Fluids

Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically designed geometrical features can enhance the effect of diffusion and provide efficient mixing by inducing chaotic fluid flow. This scheme is known as “passive” mixing. In addition, when rapid and global mixing is essential, “active” mixing can be applied by exploiting an external source. In particular, magnetic mixing (where a magnetic field acts to stimulate mixing) shows great potential for high mixing efficiency. This method generally involves magnetic beads and external (or integrated) magnets for the creation of chaotic motion in the device. However, there is still plenty of room for exploiting the potential of magnetic beads for mixing applications. Therefore, this review article focuses on the advantages of magnetic bead mixing along with recommendations on improving mixing in low Reynolds number flows (Re ≤ 1) and in stagnant fluids.

An integrated multi-molecular sensor for simultaneous BRAFV600E protein and DNA single point mutation detection in circulating tumour cells

The analysis of circulating cancer biomarkers in the form of liquid biopsies confers several potential benefits as compared to traditional surgical tissue sampling. As a common key anomaly strongly implicated across several cancer types, the BRAFV600E mutation is one of the most valuable oncogenic biomarkers available in liquid biopsies. Crucially, BRAFV600E is also an actionable mutation which could be arrested by clinically beneficial drug inhibitors. Yet, as is true for most single base disease mutations, current BRAFV600E detection in either its DNA or protein molecular state is still liable to false positive/negative outcomes, thus impacting patient treatment benefit. Here we present an integrated multi-molecular sensor (IMMS) for an entire sample-to-answer workflow from melanoma cell capture to simultaneous quantification of both intracellular BRAFV600E DNA and protein levels on a single platform. The IMMS combines (i) specific capture and release of circulating melanoma cells; (ii) electric field-induced cell lysis; (iii) simultaneous quantification of BRAFV600E DNA and protein levels. We investigated the IMMS system's analytical performance in cell capture, release and lysis, and intracellular BRAFV600E detection by ligase-mediated DNA amplification and antibody-based protein hybridization. As a proof-of-concept, we successfully demonstrated circulating BRAFV600E detection at both DNA and protein molecular levels in simulated melanoma plasma samples. With its capabilities in integrated and miniaturized analysis, the IMMS could lead the emergence of a new generation of multi-molecular lab-on-chip biosensors for enabling more accurate and extensive analysis of powerful circulating biomarkers in patient liquid biopsies.

Label-free detection of exosomes using a surface plasmon resonance biosensor

The development of a sensitive and specific detection platform for exosomes is highly desirable as they are believed to transmit vital tumour-specific information (mRNAs, microRNAs, and proteins) to remote cells for secondary metastasis. Herein, we report a simple method for the real-time and label-free detection of clinically relevant exosomes using a surface plasmon resonance (SPR) biosensor. Our method shows high specificity in detecting BT474 breast cancer cell-derived exosomes particularly from complex biological samples (e.g. exosome spiked in serum). This approach exhibits high sensitivity by detecting as low as 8280 exosomes/μL which may potentially be suitable for clinical analysis. We believe that this label-free and real-time method along with the high specificity and sensitivity may potentially be useful for clinical settings.

Interfacial nano-mixing in a miniaturised platform enables signal enhancement and in situ detection of cancer biomarkers

Interfacial biosensing performs the detection of biomolecules at the bare-metal interface for disease diagnosis by comparing how biological species derived from patients and healthy individuals interact with bare metal surfaces. This technique retrieves clinicopathological information without complex surface functionalisation which is a major limitation of conventional techniques. However, it is still challenging to detect subtle molecular changes by interfacial biosensing, and the detection often requires prolonged sensing times due to the slow diffusion process of the biomolecules towards the sensor surface. Herein, we report on a novel strategy for interfacial biosensing which involves in situ electrochemical detection under the action of an electric field-induced nanoscopic flow at nanometre distance to the sensing surface. This nanomixing significantly increases target adsorption, reduces sensing time, and enables the detection of small molecular changes with enhanced sensitivity. Using a multiplex electrochemical microdevice that enables nanomixing and in situ label-free electrochemical detection, we demonstrate the detection of multiple cancer biomarkers on the same device. We present data for the detection of aberrant phosphorylation in the EGFR protein and hypermethylation in the EN1 gene region. Our method significantly shortens the assay period (from 40 min and 20 min to 3 minutes for protein and DNA, respectively), increases the sensitivity by up to two orders of magnitude, and improves detection specificity.