Microdroplet enabled cultivation of single yeast cells correlates with bulk growth and reveals subpopulation phenomena.

Yeast has been engineered for cost-effective organic acid production through metabolic engineering and synthetic biology techniques. However, cell growth assays in these processes were performed in bulk at the population level, thus obscuring the dynamics of rare single cells exhibiting beneficial traits. Here, we introduce the use of monodisperse picolitre droplets as bioreactors to cultivate yeast at the single-cell level. We investigated the effect of acid stress on growth and the effect of potassium ions on propionic acid tolerance for single yeast cells of different species, genotypes, and phenotypes. The results showed that the average growth of single yeast cells in microdroplets experiences the same trend to those of yeast populations grown in bulk, and microdroplet compartments do not significantly affect cell viability. This approach offers the prospect of detecting cell-to-cell variations in growth and physiology and is expected to be applied for the engineering of yeast to produce value-added bioproducts.

High-Throughput, Off-Chip Microdroplet Generator Enabled by a Spinning Conical Frustum.

Although droplet-based microfluidics has been broadly used as a versatile tool in biology, chemistry, and nanotechnology, its rather complicated microfabrication process and the requirement of specialized hardware and operating skills hinder researchers fully unleashing the potential of this powerful platform. Here, we develop an integrated microdroplet generator enabled by a spinning conical frustum for the versatile production of near-monodisperse microdroplets in a high-throughput and off-chip manner. The construction and operation of this generator are simple and straightforward without the need of microfabrication, and we demonstrate that the generator is able to passively and actively control the size of the produced microdroplets. In addition to water microdroplets, this generator can produce microdroplets of liquid metal that would be difficult to produce in conventional microfluidic platforms as liquid metal has high surface tension. Moreover, we demonstrate that this generator can produce solid hydrogel microparticles and fibers using integrated ultraviolet (UV) light. In the end, we further explore the ability of this generator for forming double emulsions by coflowing two immiscible liquids. Given the remarkable abilities demonstrated by this platform and the tremendous potential of microdroplets, this user-friendly method may revolutionize the future of droplet-based chemical synthesis and biological analysis.

Assessment of chimeric antigen receptor T cytotoxicity by droplet microfluidics in vitro.

Chimeric antigen receptor T (CAR-T) cells are cytotoxic T cells engineered to specifically kill cancer cells expressing specific target receptor(s). Prior CAR-T efficacy tests include CAR expression analysis by qPCR or ELISA, in vitro measurement of interferon-γ (IFNγ) or interleukin-2 (IL-2), and xenograft models. However, the in vitro measurements did not reflect CAR-T cytotoxicity, whereas xenograft models are low throughput and costly. Here, we presented a robust in vitro droplet microfluidic assay for CAR-T cytotoxicity assessment. This method not only enabled assessment of CAR-T cytotoxic activity under different fluid viscosity conditions, but also facilitated measurement of CAR-T expansion and dissection of mechanism of action via phenotype analysis in vitro. Furthermore, our data suggested that label-free cytotoxicity analysis is feasible by acquiring data before and after treatment. Hence, this study presented a novel in vitro method for assessment of cellular cytotoxicity that could potentially be applied to any cytotoxicity experiment with varying solvent composition.

Detection of rare prostate cancer cells in human urine offers prospect of non-invasive diagnosis.

Two molecular cytology approaches, (i) time-gated immunoluminescence assay (TGiA) and (ii) Raman-active immunolabeling assay (RiA), have been developed to detect prostate cancer (PCa) cells in urine from five prostate cancer patients. For TGiA, PCa cells stained by a biocompatible europium chelate antibody-conjugated probe were quantitated by automated time-gated microscopy (OSAM). For RiA, PCa cells labeled by antibody-conjugated Raman probe were detected by Raman spectrometer. TGiA and RiA were first optimized by the detection of PCa cultured cells (DU145) spiked into control urine, with TGiA-OSAM showing single-cell PCa detection sensitivity, while RiA had a limit of detection of 4-10 cells/mL. Blinded analysis of each patient urine sample, using MIL-38 antibody specific for PCa cells, was performed using both assays in parallel with control urine. Both assays detected very low abundance PCa cells in patient urine (3-20 PCa cells per mL by TGiA, 4-13 cells/mL by RiA). The normalized mean of the detected PCa cells per 1 ml of urine was plotted against the clinical data including prostate specific antigen (PSA) level and Clinical Risk Assessment for each patient. Both cell detection assays showed correlation with PSA in the high risk patients but aligned with the Clinical Assessment rather than with PSA levels of the low/intermediate risk patients. Despite the limited available urine samples of PCa patients, the data presented in this proof-of-principle work is promising for the development of highly sensitive diagnostic urine tests for PCa.

Microfluidic devices with disposable enzyme electrode for electrochemical monitoring of glucose concentrations.

This article describes the fabrication of tube-like microchannels made of UV curable polymer on a glass substrate and the device assembling with a disposable enzyme-working electrode for high-sensitivity electrochemical detection. While both reference and counter electrodes are patterned on the surface of the glass substrate, the working electrode is flipped on the top of the channel with an open access, providing a face-to-face probing configuration. When the enzyme electrode is contaminated or degraded, it can be easily replaced by a new one, keeping the main body of the device and the detection schema unchanged. Using glucose oxidase-coated gold electrodes, we were able to determine a linear amperometry response to the glucose concentrations in the range of 2-16 mM. By replacing the as-prepared working electrode by the one after thermal treatments, we showed a much more degraded enzyme electrode activity, enabling efficient determination of the electrode quality as well as the whole process optimization.

Improving Single-Cell Encapsulation Efficiency and Reliability through Neutral Buoyancy of Suspension.

Single-cell analysis is of critical importance in revealing cell-to-cell heterogeneity by characterizing individual cells and identifying minority sub-populations of interest. Droplet-based microfluidics has been widely used in the past decade to achieve high-throughput single-cell analysis. However, to maximize the proportion of single-cell emulsification is challenging due to cell sedimentation and aggregation. The purpose of this study was to investigate the influence of single-cell encapsulation and incubation through the use of neutral buoyancy. As a proof of concept, OptiPrep™ was used to create neutrally buoyant cell suspensions of THP-1, a human monocytic leukemia cell line, for single-cell encapsulation and incubation. We found that using a neutrally buoyant suspension greatly increased the efficiency of single-cell encapsulation in microdroplets and eliminated unnecessary cell loss. Moreover, the presence of OptiPrep™ was shown to not affect cellular viability. This method significantly improved the effectiveness of single-cell study in a non-toxic environment and is expected to broadly facilitate single-cell analysis.

Enabling Sensitive Phenotypic Profiling of Cancer-Derived Small Extracellular Vesicles Using Surface-Enhanced Raman Spectroscopy Nanotags.

Circulating cancer-derived small extracellular vesicles (EVs) are nanoscale membranous vesicles shed from cancer cells that are released into surrounding body fluids. Small EVs contain biomolecules associated with cancer such as DNA and proteins for cell-to-cell communication. Therefore, small EVs have been regarded as important cancer biomarkers for liquid biopsy-based cancer diagnosis and drug treatment monitoring. However, because of the high heterogeneity and low level of small EVs in body fluids, there is a high demand for sensitive detection and characterization of such vesicles at a molecular level. In this study, we have developed a sensitive and effective approach to simultaneously profile multiple protein biomarkers expressed on cancer-derived small EVs using surface-enhanced Raman spectroscopy (SERS) nanotags in a single test, without complex isolation steps. Rapid and multiplexed phenotypic profiling of small EVs is achieved by mixing specific detection antibody-coated SERS nanotags, filtered conditioned EV-suspended medium (conditioned EVs), and capture antibody (CD63)-conjugated magnetic beads to form a sandwich immunoassay. As a proof-of-concept demonstration, we applied this approach to characterize pancreatic cancer-derived EVs by simultaneously detecting three specific EV surface receptors including Glypican-1, epithelial cell adhesion molecules (EpCAMs), and CD44 variant isoform 6 (CD44V6). The sensitivity of this method was measured down to 2.3 × 106 particles/mL, which is more sensitive and shows higher multiplexing capability than most other reported EV profiling techniques, such as western blot, enzyme-linked immunosorbent assay, and flow cytometry. Furthermore, phenotypic profiling of small EVs from colorectal cancer and bladder cancer cell lines (SW480 and C3) was conducted and compared to those derived from pancreatic cancer (Panc-1), highlighting the significant difference in EV phenotypes for various cancer cell types suspended in both phosphate-buffered saline and plasma. Thus, we believe that this technology enables a comprehensive evaluation of small secreted EV heterogeneity with high sensitivity, offering strong potential for accurate noninvasive cancer diagnosis and monitoring of drug treatment. In addition, this assay provides point-of-care use because of the easy sample preparation and portable nature of the Raman spectrometer.

Sensitive and Multiplexed SERS Nanotags for the Detection of Cytokines Secreted by Lymphoma.

The sensitive and simultaneous detection of cytokines will provide new insights into the physiological process and disease pathways due to the complex nature of cytokine networks. However, the key challenge is the lack of probes that can simultaneously detect multiple cytokines in a single sample. In this contribution, we proposed an alternative approach for sensitive cytokine detection in a multiplex manner by the use of a new set of surface-enhanced Raman spectroscopy (SERS) nanotags. Typically, the newly designed SERS nanotags are composed of gold nanoparticles as the core, tuneable Raman molecules as the reporters, and a thin silver layer as the shell. As demonstrated through rigorous numerical simulations, enhanced Raman signal is achieved due to a strong localization of light in the 0.2 nm thin, optically deep-subwavelength region between the Au core and the Ag shell. Sensitive detection of cytokines is realized by forming a sandwich immunoassay. The detection limit is down to 4.5 pg mL-1 (S/N = 3). The specificity of the assay is proved as negligible signals were detected for the false targets. Furthermore, multiple cytokines are simultaneously detected in a single assay from the secretion of B-lymphocyte cell line (Raji) after concanavalin A (Con A) stimulation. The results indicate that our method holds a significant potential for sensitive and multiplexed detection of cytokines and offers the opportunity for future applications in clinical settings.

Application of capillary electrophoresis to study phenolic profiles of honeybee-collected pollen.

Honeybee-collected pollen is promoted as a health food with a wide range of nutritional and therapeutic properties. A high-performance capillary electrophoresis with amperometric detection method has been developed for the simultaneous determination of bioactive ingredients in 10 samples of honeybee-collected pollen in this work. Under the optimum conditions, 13 phenolic components can be well-separated or nearly baseline-separated (apigenin and vanillic acid peaks) within 29 min at the separation voltage of 14 kV in a 50 mM borax running buffer (pH 9.0), and adequate extraction was obtained with ethanol for the determination of the above 13 compounds. Recovery (94.1-104.0%), repeatability of the peak current (<5.4%), and detection limits (6.9 x 10(-7)-6.4 x 10(-9) g mL(-1)) for the method were evaluated. This procedure was successfully used for the analysis and comparison of the phenolic content of honeybee-collected pollen samples originating from different floral origins based on their electropherograms or "phenolic profiles".

Determination of phenolic disinfectants in consumer products by capillary electrophoresis with amperometric detection.

Numerous disinfection products are widely used in daily life to kill pathogenic microorganisms. However, most disinfectants are organic compounds that might be hazardous to the environment and humans when used excessively. Phenolic disinfectants in disinfection products are investigated using a high-performance capillary electrophoresis-amperometric detection method. Under the optimum conditions, five commonly used disinfectants can be well-separated within 19 min at the separation voltage of 18 kV in a 80 mmol/L borax running buffer (pH 9.2), and adequate extraction was obtained with ethanol for the determination of the five compounds. Satisfactory recovery (93.5-106.0%), intra-day repeatability of the peak current (< 2.9%), and detection limits (1.6 x 10(-7) - 3.8 x 10(-8) g/mL) for the method are achieved. This proposed procedure is successfully used to analyze different samples of disinfection products.

Rapid determination of acetaminophen and p-aminophenol in pharmaceutical formulations using miniaturized capillary electrophoresis with amperometric detection.

Capability of fast analysis of a novel miniaturized capillary electrophoresis with carbon disk electrode amperometric detection (mini-CE-AD) system was demonstrated by determining acetaminophen and p-aminophenol in dosage forms. Factors influencing the separation and detection processes were examined and optimized. Under the optimum conditions, the end-capillary 300 microm carbon disc electrode amperometric detector offered favorable signal-to-noise characteristics at a relatively low potential (+600 mV versus Ag/AgCl) for detecting acetaminophen and p-aminophenol. Two analytes can been separated within 150 s in a 8.5 cm length capillary at a separation voltage of 2000V using a Na2B4O7-KH2PO4 running buffer (pH 7.2). Acetaminophen and p-aminophenol could be detected down to the 1.4 x 10(-6)-5.9 x 10(-7) molL(-1) level with linearity up to the 1.0 x 10(-3) molL(-1) level examined. The inter-day repeatability for analytes in peak current (R.S.D.< or =2.3%) and migration times (R.S.D.< or =1.3%) were excellent. The proposed mini-CE-AD system should find a wide range of analytical applications in pharmaceutical formulations as an alternative to conventional CE and mu-CE.