Optofluidic device for ultra-sensitive detection of proteins using surface-enhanced Raman spectroscopy

An optofluidic device is reported in this paper that can highly improve the robustness of surface-enhanced Raman scattering (SERS) detection and provide fingerprint information of proteins with a concentration in the nanogram per liter range within minutes. Moreover, the conformational change of protein can also be obtained using this device. Fabricated by standard photolithography processes, the optofluidic device has a step microfluidic–nanofluidic structure, which provides robust SERS detection. The sensitivity of the device is investigated using insulin and albumin as target analytes at a concentration of 0.9 ng/L. The ability to detect conformational changes of proteins using this technology is also shown by probing these analytes before and after their denaturation.     

Vertically aligned multi-walled CNT arrays coated by gold nanoparticles for surface-enhanced Raman scattering

A unique substrate for surface-enhanced Raman scattering on vertical multi-walled carbon nanotube (MWCNT) arrays coated by Au nanoparticles was reported. The vertically aligned MWCNT arrays were prepared by thermal chemical vapor deposition at temperature of 720 °C, and then coated by gold nanoparticles by sputtering. The possible mechanisms for the SERS sensitivity were discussed. Raman spectroscopy experiments for detecting Rhodamine6G were carried on and some obvious Raman peaks were observed and analyzed.     

Fabrication of gold nanoparticle pattern using imprinted hydrogen silsesquioxane pattern for surface-enhanced Raman scattering

This is the first report of surface-enhanced Raman scattering (SERS) substrate fabrication using a combination of imprinted hydrogen silsesquioxane (HSQ: HSiO_3/2) patterns and self-assembly of gold nanoparticles (AuNPs). To assemble the AuNPs inside the imprinted HSQ pattern, it is important to understand the interactions between AuNPs and AuNPs, and those between AuNPs and HSQ. The authors investigated the effects HSQ surface charges on the self-assembly of AuNPs. It was found that the negatively charged AuNPs were successfully assembled according to the geometry of the negatively charged HSQ pattern. In addition, it was shown that the SERS substrate fabricated from an HSQ consisting of an inorganic polymer was suitable for organic chemical analysis, by comparing it with a substrate fabricated using an organic polymer.     

A droplet-based microfluidic platform for rapid immobilization of quantum dots on individual magnetic microbeads

Quantum dots (QDs) provide opportunities for the development of bioassays, biosensors, and drug delivery strategies. Decoration of the surface of QDs offers unique functions such as resistance to non-specific adsorption, selective binding to target molecules, and cellular uptake. The quality of decoration has substantial impact on the functionality of modified QDs. Single-phase microfluidic devices have been demonstrated for decorating QDs with biological molecules. The device substrate can serve as a solid-phase reaction platform, with a limitation being difficulty in the realization of reproducible decoration at high density of coverage of QDs. Magnetic beads (MBs) have been explored as an alternative form of solid-phase reaction platform for decorating QDs. As one example, controlled decoration to achieve unusually high density can be realized by first coating MBs with QDs, followed by the addition of molecules such as DNA oligonucleotides. Uniformity and high density of coatings on QDs have been obtained using MBs for solid-phase reactions in bulk solution, with the further advantage that the MBs offer simplification of procedural steps such as purification. This study explores the use of a droplet microfluidic platform to achieve solid-phase decoration of MBs with QDs, offering control of local reaction conditions beyond that available in bulk solution reactions. A microchannel network with a two-junction in-series configuration was designed and optimized to co-encapsulate one single 1 µm MB and many QDs into individual droplets. The microdroplet became the reaction vessel, and enhanced conjugation through the confined environment and fast mixing. A high density of QDs was coated onto the surface of single MB even when using a low concentration of QDs. This approach quickly produced decorated MBs, and significantly reduced QD waste, ameliorating the need to remove excess QDs. The methodology offers a degree of precision to control conjugation processes that cannot be attained in bulk synthesis methods. The proposed droplet microfluidic design can be widely adopted for nanomaterial synthesis using solid-phase assays.     

基于微球均匀排布的外泌体检测微流控芯片

基于微机电系统(MEMS)微纳加工工艺和聚二甲基硅氧烷(PDMS)软刻蚀技术设计制造了一种外泌体检测芯片,芯片内部包含排列整齐的微柱阵列,用于实现微球在芯片内的均匀排布。利用该芯片成功实现了对外泌体的定量测定,检测下限可达到10~4个/m L,拟合函数的确定系数R~2为0. 996 5。与现有的芯片相比,芯片结构简单,响应快,可重现性好,避免了对外加场的依赖,有着一定的临床应用前景。     

Implementation of substrates for surface-enhanced Raman spectroscopy for continuous analysis in an optofluidic device

The fabrication of substrates for surface-enhanced Raman spectroscopy (SERS), which offer high enhancement factors as well as spatially homogeneous distribution of the enhancement, plays an important role for expanding the surface-enhanced Raman spectroscopy to a powerful quantitative and non-invasive measurement technique. In this paper, a method for the fabrication of capable SERS-active substrates by laser treatment of gold films supported on glass with single 351?nm UV-laser pulses is presented. Resulting nanometer scaled structures show enhancement factors of up to 10⁶ with very high spatial reproducibility for a monolayer of benzenethiol. A method for integration of these substrates into PDMS microchannels is shown. A technique for the generation of a simple mold master for PDMS replication is presented. Rhodamine 6G is used as model system to demonstrate continuous measurements on a solid SERS-active substrate in a microchannel. The label-free detection of the biological molecule albumin is improved by an order of magnitude.     

多层纳米银／壳聚糖膜用于芘的表面增强拉曼测定

多环芳烃类物质的高疏水性质使得其在金属表面吸附能力差,从而拉曼增强信号弱。该文针对此问题,制备了以壳聚糖为骨架,纳米银颗粒为热点的多层纳米银／壳聚糖复合膜表面拉曼增强基底,成功用于芘的表面增强拉曼检测。由于壳聚糖本身的富集作用,目标分子被吸附、富集于银纳米颗粒形成拉曼热点,可检测0．01μmol／L的芘。     

一种用于有机磷农药检测的微流控传感器

成功制作出一种用于检测有机磷农药的聚二甲基硅氧烷(PDMS)微流控传感器,该传感器集成了光纤和用于固定有机磷水解酶的SU-8圆柱.检测原理基于反应产物对光的吸收,不同浓度有机磷农药的实验结果显示:该传感器的线性相关系数为0.9934.实验结果展示了一种将酶固定在微流沟道的简单方法.简单的制备工艺和便携式的器件为集成化的...     

A microfluidic platform for electrical detection of DNA hybridization

Current methods used for detection of DNA hybridization involve the use of DNA microarrays which require overnight incubation times along with bulky and expensive fluorescent scanners. Here, we demonstrate electrical detection of DNA hybridization in an oligonucleotide functionalized microfluidic channel. We use microchannels functionalized with DNA probes integrated with electrodes for measuring conductance across the channel. As beads conjugated with the target DNA passing through the channel are captured on the surface, we are able to electrically detect changes in resistance due to bead capture. Our assay can be completed in less than an hour using less than a microliter of reagent, and has the potential for extensive multiplexing. Such a device can be useful as a handheld platform in a clinical setting where one would need to rapidly genotype a small number of genes rapidly.     

Utilization of nanoparticles in microfluidic systems for optical detection

An increasing interest has been shown in microfluidic systems due to their properties including low consumption of reagents, short analysis time and easy integration. However, despite of these advantages over conventional methods, some limitations in sensitivity and selectivity still exist in microfluidic systems. Recently advancements in nanotechnology offer some new approaches for the detection of target analytes with high sensitivity and selectivity. As a result, it is an appropriate method to enhance the detection sensitivity through a combination between microfluidic system and nanotechnology. Optical detection is a dominant technique in microfluidics because of its noninvasive nature and easy coupling. Numerous studies that integrate optical microfluidic system with nanotechnology have been reported in recent years. Therefore, optical microfluidic systems in combination with nanomaterials (NMs) are reviewed in our work. We illustrate the functions of different NMs in optical microfluidic systems and the efforts of different researchers to improve the performance of devices. After the introduction of different nanoparticle-based optical detection methods, challenges and future directions in the development of nanoparticle-based optical detection schemes in microfluidics have also been discussed.     

A one-step microfluidic approach for controllable preparation of nanoparticle-coated patchy microparticles

In this work, we describe a one-step microfluidic method for fabricating nanoparticle-coated patchy particles. Janus droplets composed of curable phase and non-curable phase were produced via a co-axial microfluidic device first. Nanoparticles were dispersed into the continuous phase or the non-curable phase to realize the surface coating of the curable phase. The curable phase was then polymerized by UV light and nanoparticle-coated patchy particles were obtained. The SEM characterization shows that the particles are monodispersed with nanoparticle selectively distributed on the convex or concave surface. The dispersity, size and shape of the particles could be easily controlled by changing the microfluidic flow parameters. Three different types of nanoparticles were successfully used to synthesize the patchy particles to demonstrate the validity of the method.     

Microinjection molded disposable microfluidic lab-on-a-chip for efficient detection of agglutination

Previous diagnosing methods based on agglutination have a limitation in view of emergency and point-of-care diagnoses due to the requirement of large scale equipments and much agglutination time. In this paper, we propose a low cost microfluidic lab-on-a-chip for more efficient detection of agglutination. In the present lab-on-a-chip, two inlet microwells, flow guiding microchannels, chaotic micromixer and reaction microwell are fully integrated. Mold inserts for the lab-on-a-chip were manufactured by UV photolithography and nickel electroplating process. The complete lab-on-a-chip was realized by the microinjection molding of cyclic olefin copolymer and the subsequent thermal bonding. The improved serpentine laminating micromixer, developed by our group, integrated in the lab-on-a-chip showed the high-level of chaotic mixing, thereby enabling us to get a reliable mixing of sample and reagent. The performance of the fabricated lab-on-a-chip was demonstrated by agglutination experiments with simulated bloods of 10 μl and simulated sera of 10 μl. The results of agglutination inside the reaction microwell were clearly read by means of the level of light transmission. The present microfluidic lab-on-a-chip could be widely applied to various clinical diagnostics based on agglutination tests.     

Fabrication of multilayer systems combining microfluidic andmicrooptical elements for fluorescence detection

This paper presents the fabrication of a microchemical chip for the detection of fluorescence species in microfluidics. The microfluidic network is wet-etched in a Borofloat 33 (Pyrex) glass wafer and sealed by means of a second wafer. Unlike other similar chemical systems, the detection system is realized with the help of microfabrication techniques and directly deposited on both sides of the microchemical chip. The detection system is composed of the combination of refractive microlens arrays and chromium aperture arrays. The microfluidic channels are 60 μm wide and 25 μm deep. The utilization of elliptical microlens arrays to reduce aberration effects and the integration of an intermediate (between the two bonded wafers) aluminum aperture array are also presented. The elliptical microlenses have a major axis of 400 μm and a minor axis of 350 μm. The circular microlens diameters range from 280 to 300 μm. The apertures deposited on the outer chip surfaces are etched in a 3000-Å-thick chromium layer, whereas the intermediate aperture layer is etched in a 1000-Å-thick aluminum layer. The overall thickness of this microchemical system is less than 1.6 mm. The wet-etching process and new bonding procedures are discussed. Moreover, we present the successful detection of a 10-nM Cy5 solution with a signal-to-noise ratio (SNR) of 21 dB by means of this system     

An integrated microfluidic system for fast, automatic detection of C-reactive protein

C-reactive protein (CRP) is a well-known inflammation marker in human beings. This study reports a new microfluidic system for fast, automatic detection of CRP. It contains pneumatic micropumps, a vortex-type micromixer, a pneumatic micro-injector and several microvalves to automatically perform the entire protocol for CRP detection. This includes sample/reagent transportation, incubation between the target CRP and a CRP-specific aptamer, washing processes, and the chemiluminescence development process. In addition, the chemiluminescence signal is measured by using a custom-made optical system which consists of a photomultiplier tube, a portable air compressor and eight electronic magnet valves to quantify the concentration of CRP. When compared to previous works, not only can this new microfluidic system automatically perform the entire process via a new integrated micro-injector and new micropumps, but a new CRP-specific DNA aptamer with a higher affinity and specificity is also used for CRP measurement. Experimental data show that the developed system can automatically complete the entire protocol within 30 min with a detection limit of 0.0125 mg/L, which is superior to previous published results. Moreover, this study also measures CRP concentration from clinical samples to verify the performance of the developed microfluidic system. The results indicate that the measured CRP concentrations from human serums are consistent with those using a benchtop system. The developed system can also detect CRP concentrations from human whole blood without any external sample pretreatment process. This microfluidic system may be promising for point-of-care applications for CRP detection in the future.     

Development and characterization of a capillary-flow microfluidic device for nucleic acid detection

We have developed a capillary flow-driven microfluidic biosensor to meet the needs of diagnostics for resource-limited areas. The device combined elements of lateral flow assays and microfluidic technology resulting in a hybrid with benefits of both formats. The biosensor was achieved by bonding two pieces of polymethyl methacrylate with channels ablated by a CO₂ laser, and enclosing an absorbent pad. The channels were UV/ozone treated to increase hydrophilicity which enabled capillary flow. The absorbent pad allowed for continuous flow in the channels once filled. The application of biosensor was demonstrated by detection of DNA with a sandwich assay. The target DNA was hybridized with nucleic acid modified magnetic beads as well as Ru(bpy) ₃ ²⁺ doped silica nanoparticles. Fluorescent signals were quantified in a holder fabricated to fit in a fluorescent microtiter plate reader. The capillary flow microfluidic was capable to detect 1?pmol target. The assay format which features rapid analysis and does not require the use of pumps could allow for inexpensive point of care diagnostics in the future.     

A paper-based microfluidic Dot-ELISA system with smartphone for the detection of influenza A

An automated, portable, and integrated paper-based microfluidic system has been developed for influenza A detection with smartphone at point-of-care (POC) settings. The low-cost paper-based microfluidic chip consists of a reagent storage and reaction modules. The storage module, which consists of a couple of reagent chambers with dispensation channels, is responsible for reagent storage and release. The reaction module consists of an absorbent pad and a nitrocellulose (NC) membrane which is functionalized with specific monoclonal antibodies on a test and control spots for immunoassay detection. Microfluidic Dot-ELISA is performed when the dispensed reagent flows through the NC membrane at a controllable speed and reaches the absorbent pad because of the gravity and capillary force without active pumping. A smartphone is used to capture image from the NC membrane with its own camera and process the image with an intelligent algorithm of custom application software which is developed with Java. With a smartphone, the detection result can be displayed and transmitted to other medical agencies if necessary. Experimental results show that, compared with the traditional methods, more convenient and efficient influenza A detection can be achieved with the developed paper-based POC microfluidic chip with the assistance of smartphone.     

New production method of convex microlens arrays for integrated fluorescence microfluidic detection systems

A new method for producing microlens array with large sag heights is proposed for integrated fluorescence microfluidic detection systems. Three steps in this production technique are included for concave microlens array formations to be integrated into microfluidic systems. First, using the photoresist SU-8 to produce hexagonal microchannel array is required. Second, UV curable glue is injected into the hexagonal microchannel array. Third, the surplus glue is rotated by a spinner at high velocity and exposed to a UV lamp to harden the glue. The micro concave lens molds are then finished and ready to produce convex microlens in poly methsiloxane (PDMS) material. This convex microlens in PDMS can be used for detecting fluorescence in microfluidic channels because a convex microlens plays the light convergence role for optical fiber detection.

     

Thread-based microfluidic system for detection of rapid blood urea nitrogen in whole blood

This study develops a thread-based microfluidic device with variable volume injection capability and 3-dimensional (3D) detection electrodes for capillary electrophoresis electrochemical (CE–EC) detection of blood urea nitrogen (BUN) in whole blood. A poly methyl methacrylate (PMMA) substrate with concave 3D electrodes produced by the hot embossing method is used to enhance the sensing performance of the CE–EC system. Results show that the chip with 3D sensing electrodes exhibits a measured current response nine times higher and signal-to-noise ratio five times higher when compared to the peak responses obtained using a chip with conventional 2D sensing electrodes. In addition, the developed thread-based microfluidic system is capable of injecting variable sample volumes into the separation thread simply by wrapping the injection thread different numbers of times around the separation thread. The peak S/N ratio can be further enhanced with this simple approach. Results also indicate that the CE–EC system exhibits good linear dynamic range for detecting a urea sample in concentrations from 0.1 to 10.0 mM (R ² = 0.9848), which is suitable for adoption in detecting the BUN concentration in human blood (1.78–7.12 mM). Separation and detection of the ammonia ions converted from BUN in whole blood is successfully demonstrated in the present study, with the developed thread-based microfluidic system providing a low-cost, high-performance method for detecting BUN in human blood.     

New production method of convex microlens arrays for integrated fluorescence microfluidic detection systems

A new method for producing microlens array with large sag heights is proposed for integrated fluorescence microfluidic detection systems. Three steps in this production technique are included for concave microlens array formations to be integrated into microfluidic systems. First, using the photoresist SU-8 to produce hexagonal microchannel array is required. Second, UV curable glue is injected into the hexagonal microchannel array. Third, the surplus glue is rotated by a spinner at high velocity and exposed to a UV lamp to harden the glue. The micro concave lens molds are then finished and ready to produce convex microlens in poly methsiloxane (PDMS) material. This convex microlens in PDMS can be used for detecting fluorescence in microfluidic channels because a convex microlens plays the light convergence role for optical fiber detection.