抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

基礎講座 電気泳動(Electrophoresis)

Microfluidics consist of microfabricated structures for liquid handling, with cross-sections in the 1–500 μm range, and small volume capacity (fL-nL) Capillary tubes connected with fittings,1 although utilizing small volumes, are not considered microfluidics for the purposes of this paper since they are not microfabricated Likewise, millifluidic systems, made by conventional machining tools, are excluded due to their larger feature sizes (>500 μm)

Though micromachined systems for gas chromatography were introduced in the 1970’s,2 the field of microfluidics did not gain much traction until the 1990’s3 Silicon and glass were the original materials used, but then the focus shifted to include polymer substrates, and in particular, polydimethylsiloxane (PDMS) Since then the field has grown to encompass a wide variety of materials and applications The successful demonstration of electrophoresis and electroosmotic pumping in a microfluidic device provided a nonmechanical method for both fluid control and separation4 Laser induced fluorescence (LIF) enabled sensitive detection of fluorophores or fluorescently labeled molecules The expanded availability of low-cost printing allowed for cheaper and quicker mask fabrication for use in soft lithography5 Commercial microfluidic systems are now available from Abbott, Agilent, Caliper, Dolomite, Micralyne, Microfluidic Chip Shop, Micrux Technologies and Waters, as a few prominent examples For a more thorough description of the history of microfluidics, we refer the reader to a number of comprehensive, specialized reviews,3, 6–11 as well as a more general 2006 review12

The field of microfluidics offers many advantages compared to carrying out processes through bulk solution chemistry, the first of which relates to a lesson taught to every first-year chemistry student Simply stated, diffusion is slow! Thus, the smaller the distance required for interaction, the faster it will be Smaller channel dimensions also lead to smaller sample volumes (fL-nL), which can reduce the amount of sample or reagents required for testing and analysis Reduced dimensions can also lead to portable devices to enable on-site testing (provided the associated hardware is similarly portable) Finally, integration of multiple processes (like labeling, purification, separation and detection) in a microfluidic device can be highly enabling for many applications

Microelectromechanical systems (MEMS) contain integrated electrical and mechanical parts that create a sensor or system Applications of MEMS are ubiquitous, including automobiles, phones, video games and medical and biological sensors13 Micro-total analysis systems, also known as labs-on-a-chip, are the chemical analogue of MEMS, as integrated microfluidic devices that are capable of automating multiple processes relevant to laboratory sciences For example, a typical lab-on-a-chip system might selectively purify a complex mixture (through filtering, antibody capture, etc), then separate target components and detect them

Microfluidic devices consist of a core of common components Areas defined by empty space, such as reservoirs (wells), chambers and microchannels, are central to microfluidic systems Positive features, created by areas of solid material, add increased functionality to a chip and can consist of membranes, monoliths, pneumatic controls, beams and pillars Given the ubiquitous nature of negative components, and microchannels in particular, we focus here on a few of their properties Microfluidic channels have small overall volumes, laminar flow and a large surface-to-volume ratio Dimensions of a typical separation channel in microchip electrophoresis (μCE) are: 50 μm width, 15 μm height and 5 cm length for a volume of 375 nL Flow in these devices is normally nonturbulent due to low Reynolds numbers For example, water flowing at 20°C in the above channel at 1 μL/min (222 cm/s) results in a Reynolds number of ~05, where <2000 is laminar flow Since flow is nonturbulent, mixing is normally diffusion-limited Small channel sizes also have a high surface-to-volume ratio, leading to different characteristics from what are commonly found in bulk volumes The material surface can be used to manipulate fluid movement (such as by electroosmotic flow, EOF) and surface interactions For a solution in contact with a charged surface, a double layer of charge is created as oppositely charged ions are attracted to the surface charges This electrical double layer consists of an inner rigid or Stern Layer and an outer diffuse layer An electrostatic potential known as the zeta potential is formed, with the magnitude of the potential decreasing as distance from the surface increases The electrical double layer is the basis for EOF, wherein an applied voltage causes the loosely bound diffuse layer to move towards an electrode, dragging the bulk solution along Charges on the exposed surface also exert a greater influence on the fluid in a channel as its size decreases Larger surface-to-volume ratios are more prone to nonspecific adsorption and surface fouling In particular, non-charged and hydrophobic microdevice surfaces can cause proteins in solution to denature and stick

We focus our review on advances in microfluidic systems since 2008 In doing this, we occasionally must cover foundational work in microfluidics that is considerably less recent We do not focus on chemical synthesis applications of microfluidics although it is an expanding area, nor do we delve into lithography, device fabrication or production costs Our specific emphasis herein is on four areas within microfluidics: properties and applications of commonly used materials, basic functions, integration, and selected applications For each of these four topics we provide a concluding section on opportunities for future development, and at the end of this review, we offer general conclusions and prospective for future work in the field Due to the considerable scope of the field of microfluidics, we limit our discussion to selected examples from each area, but cite in-depth reviews for the reader to turn to for further information about specific topics We also refer the reader to recent comprehensive reviews on advances in lab-on-a-chip systems by Arora et al10 and Kovarik et al14

/pdf/advances-in-microfluidic-materials-functions-integration-and-27mmao3n1o.pdf

Advances in microfluidic materials, functions, integration, and applications.

The recent outbreak of novel coronavirus (SARS-CoV-2) causing COVID-19 disease spreads rapidly in the world. Rapid and early detection of SARS-CoV-2 facilitates early intervention and prevents the disease spread. Here, we present an All-In-One Dual CRISPR-Cas12a (AIOD-CRISPR) assay for one-pot, ultrasensitive, and visual SARS-CoV-2 detection. By targeting SARS-CoV-2's nucleoprotein gene, two CRISPR RNAs without protospacer adjacent motif (PAM) site limitation are introduced to develop the AIOD-CRISPR assay and detect the nucleic acids with a sensitivity of few copies. We validate the assay by using COVID-19 clinical swab samples and obtain consistent results with RT-PCR assay. Furthermore, a low-cost hand warmer (~$0.3) is used as an incubator of the AIOD-CRISPR assay to detect clinical samples within 20 min, enabling an instrument-free, visual SARS-CoV-2 detection at the point of care. Thus, our method has the significant potential to provide a rapid, sensitive, one-pot point-of-care assay for SARS-CoV-2.

/pdf/ultrasensitive-and-visual-detection-of-sars-cov-2-using-all-40peni3fhp.pdf

Ultrasensitive and visual detection of SARS-CoV-2 using all-in-one dual CRISPR-Cas12a assay.

https://ddd.uab.cat/pub/artpub/2015/200195/biobio_a2015m11v73p47.pdf

Nanoparticle-based lateral flow biosensors.

A self-contained, integrated, disposable, sample-to-answer, polycarbonate microfluidic cassette for nucleic acid—based detection of pathogens at the point of care was designed, constructed, and tested. The cassette comprises on-chip sample lysis, nucleic acid isolation, enzymatic amplification (polymerase chain reaction and, when needed, reverse transcription), amplicon labeling, and detection. On-chip pouches and valves facilitate fluid flow control. All the liquids and dry reagents needed for the various reactions are pre-stored in the cassette. The liquid reagents are stored in flexible pouches formed on the chip surface. Dry (RT-)PCR reagents are pre-stored in the thermal cycling, reaction chamber. The process operations include sample introduction; lysis of cells and viruses; solid-phase extraction, concentration, and purification of nucleic acids from the lysate; elution of the nucleic acids into a thermal cycling chamber and mixing with pre-stored (RT-)PCR dry reagents; thermal cycling; and detection. The PCR amplicons are labeled with digoxigenin and biotin and transmitted onto a lateral flow strip, where the target analytes bind to a test line consisting of immobilized avidin-D. The immobilized nucleic acids are labeled with up-converting phosphor (UCP) reporter particles. The operation of the cassette is automatically controlled by an analyzer that provides pouch and valve actuation with electrical motors and heating for the thermal cycling. The functionality of the device is demonstrated by detecting the presence of bacterial B.Cereus, viral armored RNA HIV, and HIV I virus in saliva samples. The cassette and actuator described here can be used to detect other diseases as well as the presence of bacterial and viral pathogens in the water supply and other fluids.

/pdf/an-integrated-self-contained-microfluidic-cassette-for-137jr3x0uh.pdf

An integrated, self-contained microfluidic cassette for isolation, amplification, and detection of nucleic acids

An inexpensive, hand-held, point-of-care, disposable, self-contained immunoassay cassette comprised of air pouches for pumping, a metering chamber, reagents storage chambers, a mixer, and a lateral flow strip was designed, constructed, and tested. The assay was carried out in a consecutive flow format. The detection was facilitated with up-converting phosphor (UCP) reporter particles. The automated, timely pumping of the various reagents was driven by a spring-loaded timer. The utility of the cassette was demonstrated by detecting antibodies to HIV in saliva samples and further evaluated with a non-contagious, haptenized DNA assay. The cassette has several advantages over dip sticks such as sample preprocessing, integrated storage of reagents, and automated operation that reduces operator errors and training. The cassette and actuator described herein can readily be extended to detect biomarkers of other diseases in body fluids and other fluids at the point of care. The system is particularly suitable for resource-poor countries, where funds and trained personnel are in short supply.

/pdf/a-timer-actuated-immunoassay-cassette-for-detecting-1kkag0p2xd.pdf

A timer-actuated immunoassay cassette for detecting molecular markers in oral fluids

The building blocks for an inexpensive, disposable, luminescence-based microfluidic immunoassay cassette are described, and their integration in a point-of-care diagnostic system is demonstrated. Fluid motion in the cassette is driven by depressing finger-actuated pouches. All reagents needed for the immunoassay can be stored in the cassette in liquid form. Prior to use, the cassette consists of two separate parts. A top storage component contains pouches, sealed storage chambers, a metering chamber, and needle seats. The bottom processing component contains connection needles, a mixing chamber, and a detection chamber with immobilized proteins. Subsequent to sample introduction, the storage and processing components are mated. The needles form hydraulic connections between the two parts and, in some cases, close valves. The pouches are then actuated sequentially to induce flow of various reagents and facilitate process operations. The cassette is compatible with different detection modalities. Both a cassette with immunochromatographic-based detection and a cassette with microbead-based detection were constructed and evaluated. The immunochromatographic cassette was used to detect antibodies to HIV in saliva samples. The bead-based cassette was used to detect the proinflammatory chemokine IL-8. The experimental data demonstrates good repeatability and reasonable sensitivity.

/pdf/finger-actuated-self-contained-immunoassay-cassettes-1qnwjqp6gr.pdf

Finger-Actuated, Self-Contained Immunoassay Cassettes

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An integrated, self-contained microfluidic cassette for isolation, amplification, and detection of nucleic acids

A timer-actuated immunoassay cassette for detecting molecular markers in oral fluids

Finger-Actuated, Self-Contained Immunoassay Cassettes