Integration of biosensors into digital microfluidics: Impact of hydrophilic surface of biosensors on droplet manipulation

Impact of nanotechnology on conventional and artificial intelligence-based biosensing strategies for the detection of viruses

Recent years have witnessed the emergence of several viruses and other pathogens. Some of these infectious diseases have spread globally, resulting in pandemics. Although biosensors of various types have been utilized for virus detection, their limited sensitivity remains an issue. Therefore, the development of better diagnostic tools that facilitate the more efficient detection of viruses and other pathogens has become important. Nanotechnology has been recognized as a powerful tool for the detection of viruses, and it is expected to change the landscape of virus detection and analysis. Recently, nanomaterials have gained enormous attention for their value in improving biosensor performance owing to their high surface-to-volume ratio and quantum size effects. This article reviews the impact of nanotechnology on the design, development, and performance of sensors for the detection of viruses. Special attention has been paid to nanoscale materials, various types of nanobiosensors, the internet of medical things, and artificial intelligence-based viral diagnostic techniques.

On-chip-based electrochemical biosensor for the sensitive and label-free detection of Cryptosporidium

Cryptosporidium, an intestinal protozoan pathogen, is one of the leading causes of death in children and diarrhea in healthy adults. Detection of Cryptosporidium has become a high priority to prevent potential outbreaks. In this paper, a simple, easy to fabricate, and cost-effective on-chip-based electrochemical biosensor has been developed for the sensitive and label-free detection of Cryptosporidium oocysts in water samples. The sensor was fabricated using standard lithography using a mask with a 3-electrode design and modified by self-assembling a hybrid of a thiolated protein/G and the specific anti-Cryptosporidium monoclonal antibodies (IgG3). The electrochemical impedance spectroscopy (EIS) was employed to quantitate C. parvum in the range of 0 to 300 oocysts, with a detection limit of approximately 20 oocysts/5 µL. The high sensitivity and specificity of the developed label-free electrochemical biosensor suggest that this novel platform is a significant step towards the development of fast, real-time, inexpensive and label-free sensing tool for early warning and immediate on-site detection of C. parvum oocysts in water samples, as compared to the traditional methods (such as PCR and microscopy). Furthermore, under optimized conditions, this label-free biosensor can be extended to detect other analytes and biomarkers for environmental and biomedical analyses.

Comprehensive review of conventional and state-of-the-art detection methods of Cryptosporidium

Cryptosporidium is a critical waterborne protozoan pathogen found in water resources that have been a major cause of death and serious illnesses worldwide, costing millions of dollars annually for its detection and treatment. Over the past several decades, substantial efforts have been made towards developing techniques for the detection of Cryptosporidium. Early diagnostic techniques were established based on the existing tools in laboratories, such as microscopes. Advancements in fluorescence microscopy, immunological, and molecular techniques have led to the development of several kits for the detection of Cryptosporidium spp. However, these methods have several limitations, such as long processing times, large sample volumes, the requirement for bulky and expensive laboratory tools, and the high cost of reagents. There is an urgent need to improve these existing techniques and develop low-cost, portable and rapid detection tools for applications in the water quality industry. In this review, we compare recent advances in nanotechnology, biosensing and microfluidics that have facilitated the development of sophisticated tools for the detection of Cryptosporidium spp.Finally, we highlight the advantages and disadvantages, of these state-of-the-art detection methods compared to current analytical methodologies and discuss the need for future developments to improve such methods for detecting Cryptosporidium in the water supply chain to enable real-time and on-site monitoring in water resources and remote areas.

Portable on-chip colorimetric biosensing platform integrated with a smartphone for label/PCR-free detection of Cryptosporidium RNA

Cryptosporidium, a protozoan pathogen, is a leading threat to public health and the economy. Herein, we report the development of a portable, colorimetric biosensing platform for the sensitive, selective and label/PCR-free detection of Cryptosporidium RNA using oligonucleotides modified gold nanoparticles (AuNPs). A pair of specific thiolated oligonucleotides, complementary to adjacent sequences on Cryptosporidium RNA, were attached to AuNPs. The need for expensive laboratory-based equipment was eliminated by performing the colorimetric assay on a micro-fabricated chip in a 3D-printed holder assembly. A smartphone camera was used to capture an image of the color change for quantitative analysis. The detection was based on the aggregation of the gold nanoparticles due to the hybridization between the complementary Cryptosporidium RNA and the oligonucleotides immobilized on the AuNPs surface. In the complementary RNA's presence, a distinctive color change of the AuNPs (from red to blue) was observed by the naked eye. However, in the presence of non-complementary RNA, no color change was observed. The sensing platform showed wide linear responses between 5 and 100 µM with a low detection limit of 5 µM of Cryptosporidium RNA. Additionally, the sensor developed here can provide information about different Cryptosporidium species present in water resources. This cost-effective, easy-to-use, portable and smartphone integrated on-chip colorimetric biosensor has great potential to be used for real-time and portable POC pathogen monitoring and molecular diagnostics.

Progress of Microfluidic Continuous Separation Techniques for Micro-/Nanoscale Bioparticles

Separation of micro- and nano-sized biological particles, such as cells, proteins, and nucleotides, is at the heart of most biochemical sensing/analysis, including in vitro biosensing, diagnostics, drug development, proteomics, and genomics. However, most of the conventional particle separation techniques are based on membrane filtration techniques, whose efficiency is limited by membrane characteristics, such as pore size, porosity, surface charge density, or biocompatibility, which results in a reduction in the separation efficiency of bioparticles of various sizes and types. In addition, since other conventional separation methods, such as centrifugation, chromatography, and precipitation, are difficult to perform in a continuous manner, requiring multiple preparation steps with a relatively large minimum sample volume is necessary for stable bioprocessing. Recently, microfluidic engineering enables more efficient separation in a continuous flow with rapid processing of small volumes of rare biological samples, such as DNA, proteins, viruses, exosomes, and even cells. In this paper, we present a comprehensive review of the recent advances in microfluidic separation of micro-/nano-sized bioparticles by summarizing the physical principles behind the separation system and practical examples of biomedical applications.

Coplanar Electrowetting-Induced Droplet Detachment from Radially Symmetric Electrodes

This work demonstrates electrowetting-induced droplet detachment in air from coplanar electrodes using a single voltage pulse. It also presents two models to predict when this detachment will occur. Previous works approximated the minimum energy for detachment based on (i) adhesion work at the solid-liquid interface and (ii) interfacial energy changes along all three interfaces in the system. This investigation updates those models to include changes in gravitational potential energy during detachment and provides validation by testing predicted detachment thresholds against experimental observations. Droplets of varying volume were ejected from electrowetting devices with (i) radially symmetric four-part coplanar electrodes and (ii) single electrodes with a ground wire inserted directly into the droplet. All experiments were performed in air. Incorporation of gravitational potential energy improves predictions for critical electrowetting number and captures the observed increase in applied voltage required with increased droplet volume. These new models will be of particular benefit in three-dimensional digital microfluidics applications that manipulate droplets in air.

Development and Study of Biocompatible Polyurethane-Based Polymer-Metallic Nanocomposites

INTRODUCTION

In this work we selected components, developed technology and studied a number of parameters of polymer nanocomposite materials, remembering that the material would have high optical and good mechanical characteristics, good sorption ability in order to ensure high value of the optical signal for a short time while maintaining the initial geometric shape. In addition, if this nanocomposite is used for medicine and biology (biocompatible or biocidal materials or the creation of a sensor based on it), the material must be non-toxic and/or biocompatible. We study the creation of polymer nanocomposites which may be applied as biocompatible materials with new functional parameters.

MATERIAL AND METHODS

A number of polymer nanocomposites based on various urethane-acrylate monomers and nanoparticles of gold, silicon oxides, zinc and/or titanium oxides are obtained, their mechanical (microhardness) properties and wettability (contact angle) are studied. The set of required, biology-related properties of these materials, such as toxicity and sorption of microorganisms are also investigated in order to prove their possible applicability.

RESULTS AND DISCUSSION

The composition of the samples influences their microhardness and the value of contact angle, which means that varying with the monomer and the metallic, oxide nanoparticles composition, we could change these parameters. Besides it, the set of required, biology-related properties of these materials, such as toxicity and sorption of microorganisms were also investigated in order to prove their possible applicability. It was shown that the materials are non-toxic, the adhesion of microorganisms on their surface also could be varied by changing their composition.

CONCLUSION

The presented polymer nanocomposites with different compositions of monomer and the presence of nanoparticles in them are prospective material for a possible bio-application as it is biocompatible, not toxic. The sorption of microorganism could be varied depending on the type of bacterias, the monomer composition, and nanoparticles.

Highly Flexible and Ultraprecise Manipulation of Light-Levitated Femtoliter/Picoliter Droplets

Ultraprecise manipulation of the droplets at the microscale is a promising paradigm for broad implications in reagent transport and element analysis, but the existing strategies still suffer from cross-contamination or the miscellaneous auxiliaries. Inspired by the levitation, we develop a method for excellently manipulating levitated femtoliter/picoliter droplets by a single focused laser. We show that the unique light-induced vapor flow in association with the interface morphology is responsible for creation and manipulation of levitated droplets. In particular, we demonstrate that the levitated droplets formed by this light method show extraordinary motility. The highly accurate two-dimensional labyrinth movement of the levitated droplets with designed trajectories above the free surface is easily realized by scanning the light. These results demonstrate that a single focused light can function as an "optical baton" to enable us to construct a wide variety of the long-sought precise manipulation systems for bioassays, pharmacy, and chemosynthesis.

Droplet Mechanical Hand Based on Anisotropic Water Adhesion of Hydrophobic-Superhydrophobic Patterned Surfaces

Superhydrophobic copper surfaces patterned with non-round hydrophobic areas were fabricated by a combination of through-mask chemical oxidation and fluorocarbon film deposition techniques. The anisotropic sliding resistance of droplets on typical non-round hydrophobic patterns such as semicircle, V-shape, and line segment hydrophobic patterns was observed. The dependence of sliding anisotropy on the pattern shape and dimensions was investigated. Results showed that the experimental sliding resistance was in good agreement with the calculated data using a classical drag-resistance model (Furmidge equation). By taking advantage of the anisotropic sliding resistance, these patterned surfaces can be used as droplet mechanical hands to capture, transfer, mix, and release in situ micro droplets by simply moving the surfaces in different directions. A droplet pinned on a non-round hydrophobic pattern can be captured by lifting a surface with another non-round hydrophobic pattern in a large-sliding-resistance direction after touching it, while the captured droplet can be released in situ with nearly no mass loss by horizontally moving the surface in the low-sliding-resistance direction. The lossless droplet manipulations using hydrophobic/superhydrophobic patterned surfaces have advantages of being low in cost and easy to operate and may have great promising applications to high throughput drug screening, molecular detection, and other lab-on-chip devices.

Label-Free Capacitive Biosensor for Detection of Cryptosporidium

Cryptosporidium, an intestinal protozoan pathogen, is one of the leading causes of diarrhea in healthy adults and death in children. Detection of Cryptosporidium oocysts has become a high priority to prevent potential outbreaks. In this paper, a label-free interdigitated-based capacitive biosensor has been introduced for the detection of Cryptosporidium oocysts in water samples. Specific anti-Cryptosporidium monoclonal antibodies (IgG3) were covalently immobilized onto interdigitated gold electrodes as the capture probes, and bovine serum albumin was used to avoid non-specific adsorption. The immobilization of the antibodies was confirmed by measuring the change in the contact angle. The detection was achieved by measuring the relative change in the capacitive/dielectric properties due to the formation of Cryptosporidium-antibody complex. The biosensor has been tested for different concentrations of Cryptosporidium. The results show that the biosensor developed can accurately distinguish different numbers of captured cells and densities on the surface of the biosensor. The number of Cryptosporidium oocysts captured on the electrode surface was confirmed using a fluorescein isothiocyanate (FITC) immunofluorescence assay. The response from the developed biosensor has been mainly dependent on the concentration of Cryptosporidium under optimized conditions. The biosensor showed a linear detection range between 15 and 153 cells/mm² and a detection limit of 40 cells/mm². The label-free capacitive biosensor developed has a great potential for detecting Cryptosporidium in environmental water samples. Furthermore, under optimized conditions, this label-free biosensor can be extended for detection of other biomarkers for biomedical and environmental analyses.

A review of sorting, separation and isolation of cells and microbeads for biomedical applications: microfluidic approaches

We have reviewed the microfluidic approaches for cell/particle isolation and sorting, and extensively explained the mechanism behind each method.

Selective electrohydrodynamic concentration of waterborne parasites on a chip

Concentrating diluted samples is a key step to improve detection capabilities. The wise use of scaling laws shows the advantages of working with sub-microliter-sized samples. Rapid progress in MEMS technologies has driven the design of integrated platforms performing many biochemical operations. Here we report a new concentrator device based on electro-hydrodynamic forces which can be easily integrated into electrowetting-on-dielectric (EWOD) platforms. This approach is label-free and applicable to a wide range of micro-objects. The detection and analysis of two common waterborne parasites, Cryptosporidium and Giardia, is a perfect test case due to their global health relevance. By fully controlling the interplay of the various forces acting on the micron-sized Cryptosporidium parvum and Cryptosporidium muris oocysts, we show that it is possible to concentrate them on the side of a 10 μL initial drop and then extract them efficiently from a droplet of a few hundred nanoliters. We performed a finite element modeling of the forces acting on the parasites' oocysts to optimize the electrodes' shapes. We obtained state-of-the-art concentration factors of 12 ± 0.4 times and 2 to 4 times in the sub-region of the drop and the extracted droplet, respectively, with an efficiency of 70 ± 6%. Furthermore, this device had the ability to selectively concentrate parasites of different species out of a mix. We demonstrated this by segregating C. parvum oocysts from either Giardia lamblia cysts or its related species, C. muris oocysts.

Detection of contaminants in water supply: A review on state-of-the-art monitoring technologies and their applications

Water monitoring technologies are widely used for contaminants detection in wide variety of water ecology applications such as water treatment plant and water distribution system. A tremendous amount of research has been conducted over the past decades to develop robust and efficient techniques of contaminants detection with minimum operating cost and energy. Recent developments in spectroscopic techniques and biosensor approach have improved the detection sensitivities, quantitatively and qualitatively. The availability of in-situ measurements and multiple detection analyses has expanded the water monitoring applications in various advanced techniques including successful establishment in hand-held sensing devices which improves portability in real-time basis for the detection of contaminant, such as microorganisms, pesticides, heavy metal ions, inorganic and organic components. This paper intends to review the developments in water quality monitoring technologies for the detection of biological and chemical contaminants in accordance with instrumental limitations. Particularly, this review focuses on the most recently developed techniques for water contaminant detection applications. Several recommendations and prospective views on the developments in water quality assessments will also be included.

Portable device for the detection of colorimetric assays

In this work, a low-cost, portable device is developed to detect colorimetric assays for in-field and point-of-care (POC) analysis. The device can rapidly detect both pH values and nitrite concentrations of five different samples, simultaneously. After mixing samples with specific reagents, a high-resolution digital camera collects a picture of the sample, and a single-board computer processes the image in real time to identify the hue-saturation-value coordinates of the image. An internal light source reduces the effect of any ambient light so the device can accurately determine the corresponding pH values or nitrite concentrations. The device was purposefully designed to be low-cost, yet versatile, and the accuracy of the results have been compared to those from a conventional method. The results obtained for pH values have a mean standard deviation of 0.03 and a correlation coefficient R2 of 0.998. The detection of nitrites is between concentrations of 0.4-1.6 mg l-1, with a low detection limit of 0.2 mg l-1, and has a mean standard deviation of 0.073 and an R2 value of 0.999. The results represent great potential of the proposed portable device as an excellent analytical tool for POC colorimetric analysis and offer broad accessibility in resource-limited settings.

Portable device for the detection of colorimetric assays

In this work, a low-cost, portable device is developed to detect colorimetric assays for in-field and point-of-care (POC) analysis. The device can rapidly detect both pH values and nitrite concentrations of five different samples, simultaneously. After mixing samples with specific reagents, a high-resolution digital camera collects a picture of the sample, and a single-board computer processes the image in real time to identify the hue-saturation-value coordinates of the image. An internal light source reduces the effect of any ambient light so the device can accurately determine the corresponding pH values or nitrite concentrations. The device was purposefully designed to be low-cost, yet versatile, and the accuracy of the results have been compared to those from a conventional method. The results obtained for pH values have a mean standard deviation of 0.03 and a correlation coefficient R² of 0.998. The detection of nitrites is between concentrations of 0.4-1.6 mg l^-1, with a low detection limit of 0.2 mg l^-1, and has a mean standard deviation of 0.073 and an R² value of 0.999. The results represent great potential of the proposed portable device as an excellent analytical tool for POC colorimetric analysis and offer broad accessibility in resource-limited settings.

An electrohydrodynamic technique for rapid mixing in stationary droplets on digital microfluidic platforms

This paper presents an electrohydrodynamic technique for rapid mixing of droplets in open and closed digital microfluidic (DMF) platforms. Mixing is performed by applying a high frequency AC voltage to the coplanar or parallel electrodes, inducing circulation zones inside the droplet which results in rapid mixing of the content. The advantages of the proposed method in comparison to conventional mixing methods that operate based on transporting the droplet back and forth and side to side include 1) a shorter mixing time (as fast as 0.25 s), 2) the use of a fewer number of electrodes, reducing the size of the chip, and 3) the stationary nature of the technique which reduces the chance of cross-contamination and surface biofouling. Mixing using the proposed method is performed to create a uniform mixture after merging a water droplet with another droplet containing either particles or dye. The results show that increasing the frequency, and or the amplitude of the applied voltage, enhances the mixing process. However, actuation with a very high frequency and voltage may result in shedding pico-liter satellite droplets. Therefore, for each frequency there is an effective range of the amplitude which provides rapid mixing and avoids shedding satellite droplets. Also, the increase in the gap height between the two plates (for the closed DMF platforms) significantly enhances the mixing efficiency due to the lower viscous effects. Effects of the addition of salts and DNA to the samples were also studied. The electrothermal effect decreased for these cases, which was solved by increasing the frequency of the applied voltage. To assure the high frequency actuation does not increase the sample temperature excessively, the temperature change was monitored using a thermal imaging camera and it was found that the increase in temperature is negligible.

A review of digital microfluidics as portable platforms for lab-on a-chip applications

Following the development of microfluidic systems, there has been a high tendency towards developing lab-on-a-chip devices for biochemical applications. A great deal of effort has been devoted to improve and advance these devices with the goal of performing complete sets of biochemical assays on the device and possibly developing portable platforms for point of care applications. Among the different microfluidic systems used for such a purpose, digital microfluidics (DMF) shows high flexibility and capability of performing multiplex and parallel biochemical operations, and hence, has been considered as a suitable candidate for lab-on-a-chip applications. In this review, we discuss the most recent advances in the DMF platforms, and evaluate the feasibility of developing multifunctional packages for performing complete sets of processes of biochemical assays, particularly for point-of-care applications. The progress in the development of DMF systems is reviewed from eight different aspects, including device fabrication, basic fluidic operations, automation, manipulation of biological samples, advanced operations, detection, biological applications, and finally, packaging and portability of the DMF devices. Success in developing the lab-on-a-chip DMF devices will be concluded based on the advances achieved in each of these aspects.