Applications of Microfluidics in Liquid Crystal-Based Biosensors

Liquid crystals (LCs) with stimuli-responsive configuration transition and optical anisotropic properties have attracted enormous interest in the development of simple and label-free biosensors. The combination of microfluidics and the LCs offers great advantages over traditional LC-based biosensors including small sample consumption, fast analysis and low cost. Moreover, microfluidic techniques provide a promising tool to fabricate uniform and reproducible LC-based sensing platforms. In this review, we emphasize the recent development of microfluidics in the fabrication and integration of LC-based biosensors, including LC planar sensing platforms and LC droplets. Fabrication and integration of LC-based planar platforms with microfluidics for biosensing applications are first introduced. The generation and entrapment of monodisperse LC droplets with different microfluidic structures, as well as their applications in the detection of chemical and biological species, are then summarized. Finally, the challenges and future perspectives of the development of LC-based microfluidic biosensors are proposed. This review will promote the understanding of microfluidic techniques in LC-based biosensors and facilitate the development of LC-based microfluidic biosensing devices with high performance.

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Demonstration of a Label-Free and Low-Cost Optical Cavity-Based Biosensor Using Streptavidin and C-Reactive Protein

Biosensors ◽

10.3390/bios11010004 ◽

2020 ◽

Vol 11 (1) ◽

pp. 4

Author(s):

Donggee Rho ◽

Seunghyun Kim

Keyword(s):

Limit Of Detection ◽

Point Of Care ◽

Low Cost ◽

Optical Cavity ◽

Sample Volume ◽

Small Sample ◽

Label Free ◽

C Reactive Protein ◽

Reactive Protein ◽

Cavity Structure

An optical cavity-based biosensor (OCB) has been developed for point-of-care (POC) applications. This label-free biosensor employs low-cost components and simple fabrication processes to lower the overall cost while achieving high sensitivity using a differential detection method. To experimentally demonstrate its limit of detection (LOD), we conducted biosensing experiments with streptavidin and C-reactive protein (CRP). The optical cavity structure was optimized further for better sensitivity and easier fluid control. We utilized the polymer swelling property to fine-tune the optical cavity width, which significantly improved the success rate to produce measurable samples. Four different concentrations of streptavidin were tested in triplicate, and the LOD of the OCB was determined to be 1.35 nM. The OCB also successfully detected three different concentrations of human CRP using biotinylated CRP antibody. The LOD for CRP detection was 377 pM. All measurements were done using a small sample volume of 15 µL within 30 min. By reducing the sensing area, improving the functionalization and passivation processes, and increasing the sample volume, the LOD of the OCB are estimated to be reduced further to the femto-molar range. Overall, the demonstrated capability of the OCB in the present work shows great potential to be used as a promising POC biosensor.

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Integrating high-performing electrochemical transducers in lateral flow assay

Analytical and Bioanalytical Chemistry ◽

10.1007/s00216-021-03301-y ◽

2021 ◽

Author(s):

Antonia Perju ◽

Nongnoot Wongkaew

Keyword(s):

High Performance ◽

Point Of Care ◽

Low Cost ◽

High Sensitivity ◽

Lateral Flow ◽

Analytical Performance ◽

Label Free ◽

High Performing ◽

Lateral Flow Assays ◽

Electrochemical Transducers

AbstractLateral flow assays (LFAs) are the best-performing and best-known point-of-care tests worldwide. Over the last decade, they have experienced an increasing interest by researchers towards improving their analytical performance while maintaining their robust assay platform. Commercially, visual and optical detection strategies dominate, but it is especially the research on integrating electrochemical (EC) approaches that may have a chance to significantly improve an LFA’s performance that is needed in order to detect analytes reliably at lower concentrations than currently possible. In fact, EC-LFAs offer advantages in terms of quantitative determination, low-cost, high sensitivity, and even simple, label-free strategies. Here, the various configurations of EC-LFAs published are summarized and critically evaluated. In short, most of them rely on applying conventional transducers, e.g., screen-printed electrode, to ensure reliability of the assay, and additional advances are afforded by the beneficial features of nanomaterials. It is predicted that these will be further implemented in EC-LFAs as high-performance transducers. Considering the low cost of point-of-care devices, it becomes even more important to also identify strategies that efficiently integrate nanomaterials into EC-LFAs in a high-throughput manner while maintaining their favorable analytical performance.

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Feedback Delays for Ultrasensitive Sensing

Volume 1: 21st Biennial Conference on Mechanical Vibration and Noise, Parts A, B, and C ◽

10.1115/detc2007-35088 ◽

2007 ◽

Cited By ~ 1

Author(s):

Mohammed F. Daqaq ◽

Calvin Bradley ◽

Nader Jalili ◽

Khaled Alhazza

Keyword(s):

Low Cost ◽

Effective Means ◽

Sensitivity Enhancement ◽

Biological Species ◽

Label Free ◽

Enabling Technology ◽

Shift Method ◽

Cantilever Sensors ◽

Magnitude Sensitivity ◽

Frequency Variations

Nanomechanical Cantilever Sensors (NMCS) have recently emerged as an effective means for label-free chemical and biological species detection. Their high selectivity, low cost, and easy mass production make them an enabling technology for micro- and nanodetection techniques. Sensitivity constitutes one of the most desirable characteristics of NMCS. However, sensitivity of current NMCS is predominately limited by their size. In other words, smaller sensors are more sensitive than larger ones. The detection of ultra-small masses or frequency variations is therefore obstructed by the availability of more advanced fabrication techniques that are capable of manufacturing smaller and smaller sensors. Even in that case, other issues such as noise, damping, and measurement difficulties become more evident. Therefore, techniques for sensitivity enhancement should be studied and implemented to allow for accurate and precise detection of even smaller parameter variations. Along that line of reasoning, we propose a simple, but effective concept to enhance sensitivity of NMCS. The proposed methodology is based on utilizing feedback delays to create a limit-cycle response whose amplitude is ultra-sensitive to frequency variations. In this paper, we explain, analyze, and derive the equations that verify the proposed concept. We then experimentally implement the sensitivity enhancement technique on a macrocantilever beam and demonstrate more than two-orders-of-magnitude sensitivity enhancement over the frequency-shift method.

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Multifunctional, inexpensive, and reusable nanoparticle-printed biochip for cell manipulation and diagnosis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1621318114 ◽

2017 ◽

Vol 114 (8) ◽

pp. E1306-E1315 ◽

Cited By ~ 32

Author(s):

Rahim Esfandyarpour ◽

Matthew J. DiDonato ◽

Yuxin Yang ◽

Naside Gozde Durmus ◽

James S. Harris ◽

...

Keyword(s):

Point Of Care ◽

Developed Countries ◽

Biological Species ◽

Small Sample ◽

Clinical Diagnostics ◽

Cell Manipulation ◽

Label Free ◽

Cell Capture ◽

Species Sorting ◽

Isolation And Characterization

Isolation and characterization of rare cells and molecules from a heterogeneous population is of critical importance in diagnosis of common lethal diseases such as malaria, tuberculosis, HIV, and cancer. For the developing world, point-of-care (POC) diagnostics design must account for limited funds, modest public health infrastructure, and low power availability. To address these challenges, here we integrate microfluidics, electronics, and inkjet printing to build an ultra–low-cost, rapid, and miniaturized lab-on-a-chip (LOC) platform. This platform can perform label-free and rapid single-cell capture, efficient cellular manipulation, rare-cell isolation, selective analytical separation of biological species, sorting, concentration, positioning, enumeration, and characterization. The miniaturized format allows for small sample and reagent volumes. By keeping the electronics separate from microfluidic chips, the former can be reused and device lifetime is extended. Perhaps most notably, the device manufacturing is significantly less expensive, time-consuming, and complex than traditional LOC platforms, requiring only an inkjet printer rather than skilled personnel and clean-room facilities. Production only takes 20 min (vs. up to weeks) and $0.01—an unprecedented cost in clinical diagnostics. The platform works based on intrinsic physical characteristics of biomolecules (e.g., size and polarizability). We demonstrate biomedical applications and verify cell viability in our platform, whose multiplexing and integration of numerous steps and external analyses enhance its application in the clinic, including by nonspecialists. Through its massive cost reduction and usability we anticipate that our platform will enable greater access to diagnostic facilities in developed countries as well as POC diagnostics in resource-poor and developing countries.

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Highly Sensitive Electrochemical Aptasensor for Detecting the VEGF165 Tumor Marker with PANI/CNT Nanocomposites

Biosensors ◽

10.3390/bios11040114 ◽

2021 ◽

Vol 11 (4) ◽

pp. 114

Author(s):

Yunjeong Park ◽

Min-Sung Hong ◽

Woo-Hyuk Lee ◽

Jung-Gu Kim ◽

Kyunghoon Kim

Keyword(s):

Tumor Marker ◽

Limit Of Detection ◽

Biological Fluid ◽

Low Cost ◽

High Sensitivity ◽

Label Free ◽

Electrochemical Aptasensor ◽

Promising Tool ◽

Highly Sensitive ◽

Endothelial Growth Factor

Sensing targeted tumor markers with high sensitivity provides vital information for the fast diagnosis and treatment of cancer patients. A vascular endothelial growth factor (VEGF165) have recently emerged as a promising biomarker of tumor cells. The electrochemical aptasensor is a promising tool for detecting VEGF165 because of its advantages such as a low cost and quantitative analysis. To produce a sensitive and stable sensor electrode, nanocomposites based on polyaniline (PANI) and carbon nanotube (CNT) have potential, as they provide for easy fabrication, simple synthesis, have a large surface area, and are suitable in biological environments. Here, a label-free electrochemical aptasensor based on nanocomposites of CNT and PANI was prepared for detecting VEGF165 as a tumor marker. The nanocomposite was assembled with immobilized VEGF165 aptamer as a highly sensitive VEGF165 sensor. It exhibited stable and wide linear detection ranges from 0.5 pg/mL to 1 μg/mL, with a limit of detection of 0.4 pg/mL because of the complementary effect of PANI/CNT. The fabricated aptasensor also exhibited good stability in biological conditions, selectivity, and reproducibility after several measurement times after the dissociation process. Thus, it could be applied for the non-invasive determination of VEGF, in biological fluid diagnosis kits, or in an aptamer-based biosensor platform in the near future.

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Thin Films Sensor Devices for Mycotoxins Detection in Foods: Applications and Challenges

Chemosensors ◽

10.3390/chemosensors7010003 ◽

2019 ◽

Vol 7 (1) ◽

pp. 3 ◽

Cited By ~ 7

Author(s):

Andréia Santos ◽

Andreia Vaz ◽

Paula Rodrigues ◽

Ana Veloso ◽

Armando Venâncio ◽

...

Keyword(s):

Thin Film ◽

High Performance ◽

Large Scale ◽

Low Cost ◽

Animal Health ◽

High Sensitivity ◽

Enzyme Linked Immunosorbent Assay ◽

Film Sensor ◽

Fast Analysis ◽

Sensor Devices

Mycotoxins are a group of secondary metabolites produced by different species of filamentous fungi and pose serious threats to food safety due to their serious human and animal health impacts such as carcinogenic, teratogenic and hepatotoxic effects. Conventional methods for the detection of mycotoxins include gas chromatography and high-performance liquid chromatography coupled with mass spectrometry or other detectors (fluorescence or UV detection), thin layer chromatography and enzyme-linked immunosorbent assay. These techniques are generally straightforward and yield reliable results; however, they are time-consuming, require extensive preparation steps, use large-scale instruments, and consume large amounts of hazardous chemical reagents. Rapid detection of mycotoxins is becoming an increasingly important challenge for the food industry in order to effectively enforce regulations and ensure the safety of food and feed. In this sense, several studies have been done with the aim of developing strategies to detect mycotoxins using sensing devices that have high sensitivity and specificity, fast analysis, low cost and portability. The latter include the use of microarray chips, multiplex lateral flow, Surface Plasmon Resonance, Surface Enhanced Raman Scattering and biosensors using nanoparticles. In this perspective, thin film sensors have recently emerged as a good candidate technique to meet such requirements. This review summarizes the application and challenges of thin film sensor devices for detection of mycotoxins in food matrices.

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Hydrogel Patterns in Microfluidic Devices by Do-It-Yourself UV-Photolithography Suitable for Very Large-Scale Integration

Micromachines ◽

10.3390/mi11050479 ◽

2020 ◽

Vol 11 (5) ◽

pp. 479

Author(s):

Anthony Beck ◽

Franziska Obst ◽

Mathias Busek ◽

Stefan Grünzner ◽

Philipp Mehner ◽

...

Keyword(s):

Large Scale ◽

Low Cost ◽

Stimuli Responsive ◽

Single Chip ◽

Active Components ◽

Chemical Laboratory ◽

Fast Analysis ◽

Aspect Ratios ◽

Micro Patterning ◽

Do It Yourself

The interest in large-scale integrated (LSI) microfluidic systems that perform high-throughput biological and chemical laboratory investigations on a single chip is steadily growing. Such highly integrated Labs-on-a-Chip (LoC) provide fast analysis, high functionality, outstanding reproducibility at low cost per sample, and small demand of reagents. One LoC platform technology capable of LSI relies on specific intrinsically active polymers, the so-called stimuli-responsive hydrogels. Analogous to microelectronics, the active components of the chips can be realized by photolithographic micro-patterning of functional layers. The miniaturization potential and the integration degree of the microfluidic circuits depend on the capability of the photolithographic process to pattern hydrogel layers with high resolution, and they typically require expensive cleanroom equipment. Here, we propose, compare, and discuss a cost-efficient do-it-yourself (DIY) photolithographic set-up suitable to micro-pattern hydrogel-layers with a resolution as needed for very large-scale integrated (VLSI) microfluidics. The achievable structure dimensions are in the lower micrometer scale, down to a feature size of 20 µm with aspect ratios of 1:5 and maximum integration densities of 20,000 hydrogel patterns per cm². Furthermore, we demonstrate the effects of miniaturization on the efficiency of a hydrogel-based microreactor system by increasing the surface area to volume (SA:V) ratio of integrated bioactive hydrogels. We then determine and discuss a correlation between ultraviolet (UV) exposure time, cross-linking density of polymers, and the degree of immobilization of bioactive components.

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Image-based surface reconstruction in geomorphometry – merits, limits and developments of a promising tool for geoscientists

Earth Surface Dynamics Discussions ◽

10.5194/esurfd-3-1445-2015 ◽

2015 ◽

Vol 3 (4) ◽

pp. 1445-1508 ◽

Cited By ~ 17

Author(s):

A. Eltner ◽

A. Kaiser ◽

C. Castillo ◽

G. Rock ◽

F. Neugirg ◽

...

Keyword(s):

Structure From Motion ◽

High Performance ◽

Scientific Practice ◽

Low Cost ◽

Image Data ◽

Ground Truth ◽

Scale Invariant ◽

High Quality ◽

Promising Tool ◽

Wide Range

Abstract. Photogrammetry and geosciences are closely linked since the late 19th century. Today, a wide range of commercial and open-source software enable non-experts users to obtain high-quality 3-D datasets of the environment, which was formerly reserved to remote sensing experts, geodesists or owners of cost-intensive metric airborne imaging systems. Complex tridimensional geomorphological features can be easily reconstructed from images captured with consumer grade cameras. Furthermore, rapid developments in UAV technology allow for high quality aerial surveying and orthophotography generation at a relatively low-cost. The increasing computing capacities during the last decade, together with the development of high-performance digital sensors and the important software innovations developed by other fields of research (e.g. computer vision and visual perception) has extended the rigorous processing of stereoscopic image data to a 3-D point cloud generation from a series of non-calibrated images. Structure from motion methods offer algorithms, e.g. robust feature detectors like the scale-invariant feature transform for 2-D imagery, which allow for efficient and automatic orientation of large image sets without further data acquisition information. Nevertheless, the importance of carrying out correct fieldwork strategies, using proper camera settings, ground control points and ground truth for understanding the different sources of errors still need to be adapted in the common scientific practice. This review manuscript intends not only to summarize the present state of published research on structure-from-motion photogrammetry applications in geomorphometry, but also to give an overview of terms and fields of application, to quantify already achieved accuracies and used scales using different strategies, to evaluate possible stagnations of current developments and to identify key future challenges. It is our belief that the identification of common errors, "bad practices" and some other valuable information in already published articles, scientific reports and book chapters may help in guiding the future use of SfM photogrammetry in geosciences.

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