Optofluidic detection for cellular phenotyping

Quantitative analysis of the output of processes and molecular interactions within a single cell is highly critical to the advancement of accurate disease screening and personalized medicine. Optical detection is one of the most broadly adapted measurement methods in biological and clinical assays and serves cellular phenotyping. Recently, microfluidics has obtained increasing attention due to several advantages, such as small sample and reagent volumes, very high throughput, and accurate flow control in the spatial and temporal domains. Optofluidics, which is the attempt to integrate optics with microfluidics, shows great promise to enable on-chip phenotypic measurements with high precision, sensitivity, specificity, and simplicity. This paper reviews the most recent developments of optofluidic technologies for cellular phenotyping optical detection.     

Optofluidic micro-sensors for the determination of liquid concentrations

We present a novel optofluidic device for non-invasive and label-free determination of liquid concentrations. A microfluidic channel filled with the sample solution is hit by laser light in an angle close to the critical angle for total internal reflection. Due to the intentionally defined divergence of the incident beam, parts of the rays will experience total internal reflection while another part will be transmitted. Both reflected and transmitted light signals are recorded and the ratio of these signals is used for sample characterization. The stability compared to single signal analyses is significantly improved, resulting in a resolution of approximately 40 mmol L(-1). The typical working range of the device under investigation is between a few tens of mmol L(-1) and 5 mol L(-1) making it useful for applications in the food industry, for example to determine the amount of phosphates in liquid products.     

Optofluidic device for label-free cell classification from whole blood

We demonstrated a unique optofluidic lab-on-a-chip device that can measure optically encoded forward scattering signals. From the design of the spatial pattern, we can measure the position and velocity of each cell in the flow and generate a 2-D cell distribution plot over the cross section of the channel. Moreover, we have demonstrated that the cell distribution is highly sensitive to its size and stiffness. The latter is an important biomarker for cell classification and our method offers a simple and unequivocal method to classify cells by their size and stiffness. We have proved the concept using live and fixed HeLa cells. Due to the stiffness and size difference of neutrophils compared to other types of white blood cells, we have demonstrated detection of neutrophils from other blood cells. Finally, we have performed the test using 5 μL of human blood. In a greatly simplified blood preparation process, skipping the usual steps of anticoagulation, centrifuge, antibody labelling or staining, filtering, etc., we have demonstrated that our device and detection principle can count neutrophils in whole human blood. Our system is compact, inexpensive and simple to fabricate and operate, having a commodity laser diode and a Si PIN photoreceiver as the main pieces of hardware. Although the results are still preliminary, the studies indicate that this optofluidic device holds promise to be a point-of-care and home care device to measure neutrophil concentration, which is the key indicator of the immune functions for cancer patients undergoing chemotherapy.     

Optofluidic differential spectroscopy for absorbance detection of sub-nanolitre liquid samples

We present a novel optofluidic differential method for carrying out absorbance spectroscopy of sub-nanolitre volumes of liquid samples on a microfluidic chip. Due to the reduction of liquid volume, the absorbance detection in microfluidics is often hindered by either low sensitivity or complex fabrication. To address this issue, we introduced an optofluidic modulator which can be easily integrated into a PDMS (polydimethylsiloxane) based microfluidic chip. The modulator was controlled by the fluid pressure and the absorbance spectrum of the analyte was obtained by taking differential measurements between the analyte and reference medium. An advantage is that this method doesn't need a complicated fabrication step. It is compatible with conventional microfluidic chips and measurements can be carried out on a normal transmission microscope. The performance of the device was tested by measuring solutions containing methylene blue, with concentrations as low as 13 μM.     

Optofluidic integrated cell sorter fabricated by femtosecond lasers

The main trend in optofluidics is currently towards full integration of the devices, thus improving automation, compactness and portability. In this respect femtosecond laser microfabrication is a very powerful technology given its capability of producing both optical waveguides and microfluidic channels. The current challenge in biology is the possibility to perform bioassays at the single cell level to unravel the hidden complexity in nominally homogeneous populations. Here we report on a new device implementing a fully integrated fluorescence-activated cell sorter. This non-invasive device is specifically designed to operate with a limited amount of cells but with a very high selectivity in the sorting process. Characterization of the device with beads and validation with human cells are presented.     

Optofluidic microscopy--a method for implementing a high resolution optical microscope on a chip

We report a novel microfluidics-based lensless imaging technique, termed optofluidic microscopy (OFM), and demonstrate Caenorhabditis elegans imaging with an OFM prototype that gives comparable resolution to a conventional microscope and a measured resolution limit of 490 +/- 40 nm.     

Optofluidic encapsulation of crystalline colloidal arrays into spherical membrane

Double emulsion droplets encapsulating crystalline colloidal arrays (CCAs) with a narrow size distribution were produced using an optofluidic device. The shell phase of the double emulsion was a photocurable resin that was photopolymerized downstream of the fluidic channel within 1 s after drop generation. The present optofluidic synthesis scheme was very effective for fabricating highly monodisperse spherical CCAs that were made structurally stable by in situ photopolymerization of the encapsulating shells. The shell thickness and the number of core emulsion drops could be controlled by varying the flow rates of the three coflowing streams in the dripping regime. The spherical CCAs confined in the shell exhibited distinct diffraction patterns in the visible range, in contrast to conventional film-type CCAs. As a result of their structure, the spherical CCAs exhibited photonic band gaps for normal incident light independent of the position on the spherical surface. This property was induced by heterogeneous nucleation at the smooth wall of the spherical emulsion drop during crystallization into a face-centered cubic (fcc) structure. On the other hand, the solidified shells did not permit the penetration of ionic species, enabling the CCAs to maintain their structure in a continuous aqueous phase of high ionic strength for at least 1 month. In addition, the evaporation of water molecules inside the shell was slowed considerably when the core-shell microparticles were exposed to air: It took approximately 6 h for a suspension encapsulated in a thick shell to evaporate completely, which is approximately 1000 times longer than the evaporation time for water droplets with the same volume. Finally, the spherical CCAs additionally exhibited enhanced stability against external electric fields. The spherical geometry and high dielectric constant of the suspension contributed to reducing the electric field inside the shell, thereby inhibiting the electrophoretic movement of the charged particles.     

Optofluidic devices and applications in photonics, sensing and imaging

Optofluidics integrates the fields of photonics and microfluidics, providing new freedom to both fields and permitting the realization of optical and fluidic property manipulations at the chip scale. Optofluidics was formed only after many breakthroughs in microfluidics, as understanding of fluid behaviour at the micron level enabled researchers to combine the advantages of optics and fluids. This review describes the progress of optofluidics from a photonics perspective, highlighting various optofluidic aspects ranging from the device's property manipulation to an interactive integration between optics and fluids. First, we describe photonic elements based on the functionalities that enable fluid manipulation. We then discuss the applications of optofluidic biodetection with an emphasis on nanosensing. Next, we discuss the progress of optofluidic lenses with an emphasis on its various architectures, and finally we conceptualize on where the field may lead.     

Acoustofluidic platforms for particle manipulation

There is an increasing interest in acoustics for microfluidic applications. This field, commonly known as acoustofluidics involves the interaction of ultrasonic standing waves with fluids and dispersed microparticles. The combination of microfluidics and the so-called acoustic standing waves (ASWs) led to the development of integrated systems for contact-less on-chip cell and particle manipulation where it is possible to move and spatially localize these particles based on the different acoustophysical properties. While it was initially suggested that the acoustic forces could be harmful to the cells and could impact cell viability, proliferation, or function via phenotypic or even genotypic changes, further studies disproved such claims. This review is summarizing some interesting applications of acoustofluidics in the manipulations of biomaterials, such as cells or subcellular vesicles, in works published mainly within the last 5 years.     

Dielectrophoresis for the manipulation of nanobioparticles

Dielectrophoresis (DEP) is a nondestructive electrokinetic mechanism with great potential for the manipulation of bioparticles. DEP is the movement of particles induced by polarization effects in nonuniform electric fields. Since the 1960s, this technique has been successfully used for the manipulation of microbioparticles, such as microorganisms. Moreover, due to the advances in microfabrication techniques, that allowed progressively smaller microstructures to be constructed, DEP can now be used for the manipulation of nanobioparticles. The first research studies on the DEP of nanobioparticles started in the 1990s. Since then, many research groups have carried out outstanding work with DEP of nanobioparticles such as macromolecules, virus, and spores. However, the need of a critical report that integrates these findings is evident. The aim of the present review is to depict the state-of-the-art on the use of DEP for the separation of nanobioparticles and the potential trends of novel applications of this technique. This review compiles and analyzes the significant findings obtained by many researchers. This publication is intended to provide the reader with state-of-the-art information on many research studies focused on DEP to handle nanobioparticles.     

Force measurements for membrane protein manipulation

The force curve measurement mode of the atomic force microscope (AFM) enables us to measure hitherto unobservable mechanical properties of nanometer sized biological specimens. By applying this mode, we attempted to conduct such mechanical manipulations of membrane proteins as: (1) measurement of the separation force between a membrane bound receptor and a covalently cross-linked ligand molecule on the AFM tip; and (2) extraction of membrane proteins after harnessing them on a modified tip with covalent cross-linkers. Since the limiting tensile force of the covalent system used in our experiment was a crucial factor for successful manipulations, we first estimated the force to terminate the covalent cross-linking system at the single molecular level to be 1.6–1.7 nN, based on our previous data. The method was then applied to measure the force required to separate α₂-macroglobulin (α₂-M) from its receptor on the cell membrane using an AFM tip coated with the receptor binding form of the protein. From a bimodal distribution of rupture force, we obtained an average value of 120 pN as the force to separate a non-covalent association of α₂-M with its receptor. When modified tips with covalent cross-linkers aimed at amino groups on the cell surface were used, distribution of the rupture force shifted toward higher values, with a peak in the histogram ≈400–500 pN. Since the force to sever covalent cross-linking system was 1.6–1.7 nN, the observed force was ascribed to the force required to extract membrane proteins from the cell membrane after covalent bond formation.     

Optofluidic microsystem with quasi-3 dimensional gold plasmonic nanostructure arrays for online sensitive and reproducible SERS detection

Practical applications of chemical and biological detections through surface-enhanced Raman scattering (SERS) require high reproducibility, sensitivity, and efficiency, along with low-cost, straightforward fabrication. In this work, we integrated a poly-(dimethylsiloxane) (PDMS) chip with quasi-3D gold plasmonic nanostructure arrays (Q3D-PNAs), which serve as SERS-active substrates, into an optofluidic microsystem for online sensitive and reproducible SERS detections. The Q3D-PNA PDMS chip was fabricated through soft lithography to ensure both precision and low-cost fabrication. The optimal dimension of the Q3D-PNA in PDMS was designed using finite-difference time-domain (FDTD) electromagnetic simulations with a simulated enhancement factor (EF) of 1.6 × 10⁶. The real-time monitoring capability of the SERS-based optofluidic microsystem was investigated by kinetic on/off experiments through alternatively flowing Rhodamine 6G (R6G) and ethanol in the microfluidic channel. A switch-off time of ∼2 min at a flow rate of 0.3 mL min⁻¹ was demonstrated. When applied to the detection of low concentration malathion, the SERS-based optofluidic microsystem with Q3D-PNAs showed high reproducibility, significantly improved efficiency and higher detection sensitivity via increasing the flow rate. The optofluidic microsystem presented in this paper offers a simple and low-cost approach for online, label-free chemical and biological analysis and sensing with high sensitivity, reproducibility, efficiency, and molecular specificity.     

Solvent response of polymers for micromachine manipulation

A novel solvent responsive polymer micromachine has been successfully fabricated by two-photon photopolymerization (TPP) of methacrylate-based photoresists. The moving part of the micromachine could be easily driven by interfacial solvent polarity induced swelling and shrinking of the photopolymer networks. Furthermore, the driving performance of the micromachine could be precisely modulated by varying the laser scanning step length during fabrication.     

On-chip syringe pumps for picoliter-scale liquid manipulation

On-chip microsyringes are developed by integrating parallel micro actuators and a microfluidic chip. Sliders of an Electrostatically Controlled Linear Inchworm Actuator (ECLIA) are applied to manipulate microsyringes in the nanometer range, which allows liquid control on the picoliter scale. ECLIA drives sliders in parallel with high accuracy and a large stroke. The requirements for syringe performance, such as parallel and precise liquid control, can be satisfied by the above features of ECLIA. A total volume of a few microL is manipulated at a flow rate of 19-27 pL s(-1) by the stepwise motion of ECLIA sliders in a fluidic channel. Microsyringes integrated into the driving mechanism are a key component of Micro Total Analysis Systems (microTAS) due to the possibility of on-chip integration. In addition, the proposed approach has a significant implication in MEMS in that the electrostatic micro actuator performs a physical task that affects the outside structure.     

注入型人工晶状体材料的研究进展

注入型人工晶状体具有正常晶状体位置和生理调节功能的双重特性,因此,对其进行合成与制备已成为世界各国科学家研究的热点之一.本文介绍了国内外有关注入型人工晶状体材料的研究进展,重点阐述了硅酮聚合物、光聚合物、聚氨酯共聚物、巯基聚合物这四类注入型人工晶状体材料的结构、基本性能和医用特性,对每种材料的优缺点进行了评述.     

Size-dependent lens angles for small oil lenses on water

Line tension is the excess energy associated with unit length of a three-phase contact line and it has long been of interest, in part because if sufficiently large, it can affect various processes of industrial and biological importance. Most recently, interest has centred on the magnitude and sign of experimentally determined values. Reported line tensions in systems with liquid alkanes in contact with aqueous phases include values from about +10⁻¹⁰ to 10⁻⁹ N on the one hand, and −10⁻⁶ N on the other. If the actual values of line tension lie close to the lower end of the spectrum quoted above, the influence on many systems of interest will be negligible. The higher values, however, could lead to pronounced effects. A study to determine line tension in the three-phase contact line around lenses of dodecane resting on a water subphase is presented. The method involves measuring, by interferometry, the variation of lens angle with the contact line radius. In order to bring the angles into a convenient range for measurement (around 2°), small amounts of dodecanol (ca. 2 mmol dm⁻³) have been added to the dodecane. The line tension is found to be +1.6±0.3×10⁻¹¹ N. The magnitude and sign of the line tension is discussed in terms of surface forces.     

Probing nucleation pathways for morphological manipulation of platinum nanocrystals

Understanding the formation process in the controlled synthesis of nanocrystals will lead to the effective manipulation of the morphologies and properties of nanomaterials. Here, in-situ UV-vis and X-ray absorption spectroscopies are combined to monitor the tracks of the nucleation pathways in the solution synthesis of platinum nanocrystals. We find experimentally that the control over nucleation pathways through changing the strength of reductants can be efficiently used to manipulate the resultant nanocrystal shapes. The in-situ measurements show that two different nucleation events involving the formation of one-dimensional "Pt(n)Cl(x)" complexes from the polymerization of linear "Cl(3)Pt-PtCl(3)" dimers and spherical "Pt(n)(0)" clusters from the aggregation of Pt(0) atoms occur for the cases of weak and strong reductants; and the resultant morphologies are nanowires and nanospheres, respectively. This study provides a crucial insight into the correlation between the particle shapes and nucleation pathways of nanomaterials.     

Interfacial nanoarchitectonics for molecular manipulation and molecular machine operation

The nanoarchitectonics concept enables us to produce functional systems and materials from nanoscale units through nanotechnological approaches together with the processes including chemical syntheses, atom/molecule manipulations, self-assemblies, self-organizations, field-induced material regulations, and bio-related processes. Especially, manipulations of molecules (molecular machines) and sophisticated organization would be attractive targets in interfacial nanoarchitectonics. In this short review, we introduce several typical examples on manipulations of functional molecules and molecular machines at interfacial media. The examples are classified roughly according to driving forces of manipulations; (i) manipulations through chemical reactions and interactions; (ii) light-driven manipulations; (iii) electrically controlled manipulations; (iv) mechanical manipulations. Future possibilities of molecular manipulations at interfaces such as usages in biological systems are discussed in perspective section.     

A survey of electrokinetically-driven microfluidics for cancer cells manipulation

Cancer is one of the leading causes of annual deaths worldwide, accounting for nearly 10 million deaths each year. Metastasis, the process by which cancer spreads across the patient's body, is the main cause of death in cancer patients. Because the rising trend observed in statistics of new cancer cases and cancer-related deaths does not allow for an optimistic viewpoint on the future—in relation to this terrible disease—the scientific community has sought methods to enable early detection of cancer and prevent the apparition of metastatic tumors. One such method is known as liquid biopsy, wherein a sample is taken from a bodily fluid and analyzed for the presence of CTCs or other cancer biomarkers (e.g., growth factors). With this objective, interest is growing by year in electrokinetically-driven microfluidics applied for the concentration, capture, filtration, transportation, and characterization of CTCs. Electrokinetic techniques—electrophoresis, dielectrophoresis, electrorotation, and electrothermal and EOF—have great potential for miniaturization and integration with electronic instrumentation for the development of point-of-care devices, which can become a tool for early cancer diagnostics and for the design of personalized therapeutics. In this contribution, we review the state of the art of electrokinetically-driven microfluidics for cancer cells manipulation.