Out-of-plane integration of a multimode optical fiber for single particle/cell detection at multiple points on a microfluidic device with applications to particle/cell counting, velocimetry, size discrimination and the analysis of single cell lysate injections

A state-of-the-art review of the recent advances in exosome isolation and detection methods in viral infection

Proteins, RNA, DNA, lipids, and carbohydrates are only some of the molecular components found in exosomes released by tumor cells. They play an essential role in healthy and diseased cells as messengers of short- and long-distance intercellular communication. However, since exosomes are released by every kind of cell and may be found in blood and other bodily fluids, they may one day serve as biomarkers for a wide range of disorders. In many pathological conditions, including cancer, inflammation, and infection, they play a role. It has been shown that the biogenesis of exosomes is analogous to that of viruses and that the exosomal cargo plays an essential role in the propagation, dissemination, and infection of several viruses. Bidirectional modulation of the immune response is achieved by the ability of exosomes associated with viruses to facilitate immunological escape and stimulate the body's antiviral immune response. Recently, exosomes have received a lot of interest due to their potential therapeutic use as biomarkers for viral infections such as human immunodeficiency virus (HIV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Epstein-Barr virus (EBV), and SARS-CoV-2. This article discusses the purification procedures and detection techniques for exosomes and examines the research on exosomes as a biomarker of viral infection.

In Situ Single-Cell Stimulation and Real-Time Electrochemical Detection of Lactate Response Using a Microfluidic Probe

Metabolism of a single cell, even within the same organization, differs from other cells by orders of magnitude. Single-cell analysis provides key information for early diagnosis of cancer as well as drug screening. Any slight change in the microenvironment may affect the state of a single cell. Timely and effective cell monitoring is conducive to better understand the behavior of single cells. The immediate response of a single cell described in this study is a liquid transfer-based approach for real-time electrochemical detection. The cell was in situ stimulated by continuous flow with glucose, and lactate secreted from the cell would diffuse into the microflow. The microflow was aspirated into the detection channel where lactate was then decomposed by coupled enzyme reactions and detected by an electrode. This work provides a novel approach for detecting lactate response from a single cell by noninvasive measurements, and the position resolution of the microfluidic probe reaches the level of a single cell and permits individual heterogeneity in cells to be explored in the diagnosis and treatment of cancer as well as in many other situations.

Cyclic on-chip bacteria separation and preconcentration

Nanoparticles and biological molecules high throughput robust separation is of significant interest in many healthcare and nanoscience industrial applications. In this work, we report an on-chip automatic efficient separation and preconcentration method of dissimilar sized particles within a microfluidic platform using integrated membrane valves controlled microfiltration. Micro-sized E. coli bacteria are sorted from nanoparticles and preconcentrated on a microfluidic chip with six integrated pneumatic valves (sub-100 nL dead volume) using hydrophilic PVDF filter with 0.45 μm pore diameter. The proposed on-chip automatic sorting sequence includes a sample filtration, dead volume washout and retentate backflush in reverse flow. We showed that pulse backflush mode and volume control can dramatically increase microparticles sorting and preconcentration efficiency. We demonstrate that at the optimal pulse backflush regime a separation efficiency of E. coli cells up to 81.33% at a separation throughput of 120.45 μL/min can be achieved. A trimmed mode when the backflush volume is twice smaller than the initial sample results in a preconcentration efficiency of E. coli cells up to 121.96% at a throughput of 80.93 μL/min. Finally, we propose a cyclic on-chip preconcentration method which demonstrates E. coli cells preconcentration efficiency of 536% at a throughput of 1.98 μL/min and 294% preconcentration efficiency at a 10.9 μL/min throughput.

Measuring stimulation and inhibition of intracellular nitric oxide production in SIM-A9 microglia using microfluidic single-cell analysis

Chronic neuroinflammation has long been considered to be a central factor in accelerating the progression of neurodegenerative diseases such as Alzheimer's diseases, Parkinson's disease and chronic traumatic encephalopathy. Under pathological conditions microglia produce inflammatory signaling molecules, such as nitric oxide (NO), that can damage DNA and proteins and ultimately induce neuronal apoptosis. One strategy for treating neurodegenerative diseases is to specifically target NO production through inhibition of inducible nitric oxide synthase (iNOS). However, accurately measuring changes in microglial NO production in response to potential therapeutics is challenging due to NO's short half-life and microglial heterogeneity. In this paper we report the application of a microfluidic device for the high-throughput measurement of intracellular NO in SIM-A9 microglial cells. NO production was measured in response to treatment with lipopolysaccharides (LPS) and interferon gamma (IFN-γ) with and without a potent iNOS inhibitor (1400 W dihydrochloride). Cells were labeled with a fluorogenic NO probe, 4-amino-5-methylamino-2',7'-difluorofluoescein diacetate (DAF-FM DA), and 6-carboxyfluorescein diacetate (6-CFDA) as an internal standard. Separation and quantitation of intracellular NO was achieved using microchip electrophoresis and laser induced fluorescence detection (LIF). Statistical analysis suggests that the populations fit a lognormal distribution and are better represented by their geometric mean values. Comparison of the geometric means indicated a 1.6-fold increase in NO production between untreated and stimulated cells and a decrease by a factor of approximately 0.5 comparing stimulated and inhibited cells. Additionally, we report experimental data demonstrating the improvement in the sensitivity of our integrated optical fiber-based detection system through the use of refractive index matching gel.

Microelectrophoretic single-cell measurements with microfluidic devices

Here we describe in detail the design, fabrication and operation of our automated high-throughput single cell microchip electrophoresis device with laser induced fluorescence detection. Our device features on-board integrated peristaltic pumps that generate flow directly within the microfluidic channels. Additionally, we have incorporated an optical fiber bridge that enables simultaneous fluorescence detection at two points of interest within the device without the need for additional optical components or detectors. The second detection spot is used to detect the intact cell immediately prior to lysis giving a signal at t=0s for each single-cell electropherogram. We can also use this signal to measure the absolute migration time of the separated analytes to confidently determine the identity of each peak. Finally, we demonstrate the application of our device for the measurement of intracellular nitric oxide (NO) levels in T-lymphocytes. Changes in NO levels within cells is associated with a number of chronic diseases including neurodegenerative, cardiovascular and cancers. We show that our system is capable of measuring NO levels under the following conditions: native, lipopolysaccharide stimulation, and inhibition of inducible nitric oxide synthase. It is our hope that the information and procedures described in this chapter may enable others to use or adapt our system for other analyses at the single cell level.

Design and Application of Sensors for Chemical Cytometry

The bulk cell population response to a stimulus, be it a growth factor or a cytotoxic agent, neglects the cell-to-cell variability that can serve as a friend or as a foe in human biology. Biochemical variations among closely related cells furnish the basis for the adaptability of the immune system but also act as the root cause of resistance to chemotherapy by tumors. Consequently, the ability to probe for the presence of key biochemical variables at the single-cell level is now recognized to be of significant biological and biomedical impact. Chemical cytometry has emerged as an ultrasensitive single-cell platform with the flexibility to measure an array of cellular components, ranging from metabolite concentrations to enzyme activities. We briefly review the various chemical cytometry strategies, including recent advances in reporter design, probe and metabolite separation, and detection instrumentation. We also describe strategies for improving intracellular delivery, biochemical specificity, metabolic stability, and detection sensitivity of probes. Recent applications of these strategies to small molecules, lipids, proteins, and other analytes are discussed. Finally, we assess the current scope and limitations of chemical cytometry and discuss areas for future development to meet the needs of single-cell research.

Escherichia coli Fiber Sensors Using Concentrated Dielectrophoretic Force with Optical Defocusing Method

A sensitive tapered optical fiber tip combined with dielectrophoretic (DEP) trapping was used for rapid and label-free detection of bacteria in water. The angular spectrum of the optical field at the fiber tip was changed with the surrounding refractive index (RI). By measuring far-field intensity change at the defocus plane, the intensity sensitivity was up to 95 200%/RIU (RI unit), and the detection limit was 5.2 × 10^-6 RIU at 0.5% intensity stability. By applying an AC voltage to a Ti/Al coated fiber tip and an indium-tin-oxide glass, the DEP force effectively trapped the Escherichia coli ( E. coli) near the fiber tip. Those bacteria can be directly measured from optical intensity change due to the increase of surrounding RI. By immobilizing the antibody on the Ti/Al fiber tip, the tests for specific K12 bacteria and nonspecific BL21 bacteria verified the specificity. The antibody-immobilized Ti/Al coated fiber tip with DEP trapping can detect bacteria at a concentration about 100 CFU/mL.

Photochemical device for selective detection of phenol in aqueous solutions

We demonstrate that a lab-on-a-chip device (hereafter termed a photochemical phenol sensor) that integrates a photocatalytic long-period fiber grating (PLPFG), fiber Bragg grating (FBG), polymer membrane, ultraviolet (UV) visible light, and microchannels can be exploited to selectively detect phenol in aqueous solutions. The novel PLPFG consisted of a thinned long-period fiber grating (LPFG) and a UV-visible-light-driven Er3+:YAlO3/SiO2/TiO2 (EYST) coating. The polymer membrane with high phenol permselectivity was synthesized using PEBA2533 doped with β-cyclodextrin and was wrapped around the EYST surface, thus forming a microchannel between the membrane and PLPFG to enable the injection and outflow of standard analytes. Subsequently, a Z-shaped microchannel in a PMMA plate was fabricated and employed as a storage chamber for phenol analytes. To realize the EYST photocatalyst, UV-visible-light was irradiated using a tapered UV optical array. Thereafter, to eliminate the effect of temperature on the device, a FBG sensor as a temperature-compensating element was presented. To demonstrate the sensitivity and selectivity of the proposed device, we investigated the effects of the EYST coating's thickness, phenol-based analytes and temperature on the sensitivity and accuracy of the device for measuring phenol concentrations. The results of our present study suggest that the photochemical sensor is effective over a wide range of concentrations (7.5 μg L-1 to 100 mg L-1), pH values (2.0 to 14.0), and temperatures (10 to 48 °C) for selective detection of phenol in aqueous solutions. Thus, the proposed lab-on-a-chip device may be useful for accurate determination of phenol concentrations in real samples.