A novel hybrid patterning technique for micro and nanochannel fabrication by integrating hot embossing and inverse UV photolithography

Development of lab-on-chip biosensor for the detection of toxic heavy metals: A review

Recently, a decrease in water availability and quality has been raised due to rapid industrialization, unsustainable agricultural activities and anthropogenic activities. Heavy metals are considered significant pollutants in the water environment, cause environmental hazards and health effects to humans. For monitoring water contaminants utilized different conventional techniques. Still, they have some drawbacks, such as cost expensive, ecological issues, and processing time, requiring technicians and researchers to operate them effectively. Biosensors have become reasonable devices for screening and identifying environmental contaminants because of their different benefits contrasted with other detecting techniques. This review summarizes the toxic effect of heavy metal and their source, occurrence. A detailed discussion is provided on the heavy metal recognition materials for detecting heavy metals in wastewater. Lab on chip (LOC) is an emerging micro-electrical mechanical system (MEMS) device that intakes liquid and makes it move through the micro-channels, to accomplish fast, cost-effective and profoundly sensitive analysis with significant yield. LOC also provided a discussion on numerous laboratory functions on a single platform. This article attempts to discuss the detection of heavy metals using lab on a chip by suitable recognition materials. Further, the design and fabrication mechanism and their recognition abilities of LOC were also reviewed. The review mainly focuses on the application of LOC biosensors, pros, and cons, and suggests a roadmap towards future development to enhance the practical use in pollutant monitoring.

Surface Patterning of Closed Nanochannel Using VUV Light and Surface Evaluation by Streaming Current

In nanofluidics, surface control is a critical technology because nanospaces are surface-governed spaces as a consequence of their extremely high surface-to-volume ratio. Various surface patterning methods have been developed, including patterning on an open substrate and patterning using a liquid modifier in microchannels. However, the surface patterning of a closed nanochannel is difficult. In addition, the surface evaluation of closed nanochannels is difficult because of a lack of appropriate experimental tools. In this study, we verified the surface patterning of a closed nanochannel by vacuum ultraviolet (VUV) light and evaluated the surface using streaming-current measurements. First, the C₁₈ modification of closed nanochannels was confirmed by Laplace pressure measurements. In addition, no streaming-current signal was detected for the C₁₈-modified surface, confirming the successful modification of the nanochannel surface with C₁₈ groups. The C₁₈ groups were subsequently decomposed by VUV light, and the nanochannel surface became hydrophilic because of the presence of silanol groups. In streaming-current measurements, the current signals increased in amplitude with increasing VUV light irradiation time, indicating the decomposition of the C₁₈ groups on the closed nanochannel surfaces. Finally, hydrophilic/hydrophobic patterning by VUV light was performed in a nanochannel. Capillary filling experiments confirmed the presence of a hydrophilic/hydrophobic interface. Therefore, VUV patterning in a closed nanochannel was demonstrated, and the surface of a closed nanochannel was successfully evaluated using streaming-current measurements.

Fabrication of 2D silicon nano-mold by side etch lift-off method

Nano-imprint technology is a method of nano-pattern reproduction, has the characteristics of high resolution, high throughput, and low-cost. It can reduce the complexity and cost of the equipment while improving the resolution, which considered a promising industrial production technology. The key to nanoimprinting lies in the mold, and the quality of the mold directly determines the quality of the imprinted graphics. Here, a method for fabricating sub-100 nm concave 2D silicon nano-mold by side etch lift-off is proposed. The effects of different wet etching time and the metal deposition angle on the width of nanochannels were studied. The measurement result of dry etching shows that on the entire 4 inch silicon wafer, the width of the nanochannel varies by 4% and the depth by 2%. The width of the nanochannel between chips varies by 0.7%, and the depth variation is 1%. With this new method, high-precision and large-scale silicon nano-mold can be produced, which has great potential for realizing high-precision and low-cost manufacturing of nano devices.

Paper-Based Microfluidic Sensors for Onsite Environmental Detection: A Critical Review

A newly developed research topic, fabricated paper-based microfluidic sensors, was discussed in the field of low-cost environmental detection. Distinguished with the traditional dipstick or lateral-flow setups, these paper-based microfluidic sensors can serve as a tool for onsite quantitative and semi-quantitative measurements, without risks to cause environmental pollution. They have attracted increasing interest since the first easy-fabricated paper-based setup reported by Whitesides group in 2007. Most of the publications utilized paper-based sensors in clinical detection. In recent years, some groups started to use these sensors in environmental measurement, leading to precise, easy operation, low-cost, and eco-friendly methods for onsite detection. In this review, paper-based microfluidic sensors were briefly introduced, followed by literatures review and discussion for future perspectives.

Preparation of thermostable and compatible citrate-based polyesters for enhancing the ultraviolet shielding performance of thermoplastic resin

A new class of citrate-based polyesters with excellent ultraviolet absorption characteristic was synthesized as polymer additive to enhance ultraviolet shielding performance of PETG.

Optical Patterning of Two-Dimensional Materials

Recent advances in the field of two-dimensional (2D) materials have led to new electronic and photonic devices enabled by their unique properties at atomic thickness. Structuring 2D materials into desired patterns on substrates is often an essential and foremost step for the optimum performance of the functional devices. In this regard, optical patterning of 2D materials has received enormous interest due to its advantages of high-throughput, site-specific, and on-demand fabrication. Recent years have witnessed scientific reports of a variety of optical techniques applicable to patterning 2D materials. In this minireview, we present the state-of-the-art optical patterning of 2D materials, including laser thinning, doping, phase transition, oxidation, and ablation. Several applications based on optically patterned 2D materials will be discussed as well. With further developments, optical patterning is expected to hold the key in pushing the frontiers of manufacturing and applications of 2D materials.

Non-lithographic nanofluidic channels with precisely controlled circular cross sections

Nanofluidic channels have received growing interest due to their potential for applications in the manipulation of nanometric objects, such as DNA, proteins, viruses, exosomes, and nanoparticles. Although significant advances in nanolithography-based fabrication techniques over the past few decades have allowed us to explore novel nanofluidic transport phenomena and unique applications, the development of new technologies enabling the low-cost preparation of nanochannels with controllable and reproducible shapes and dimensions is still lacking. Thus, we herein report the application of a nanofiber printed using a near-field electrospinning method as a sacrificial mold for the preparation of polydimethylsiloxane nanochannels with circular cross sections. Control of the size and shape of these nanochannels allowed the preparation of nanochannels with channel widths ranging from 70-368 nm and height-to-width ratios of 0.19-1.00. Capillary filling tests confirmed the excellent uniformity and reproducibility of the nanochannels. These results therefore are expected to inspire novel nanofluidic studies due to the simple and low-cost nature of this fabrication process, which allows precise control of the shape and dimensions of the circular cross section.

Selective Light-Induced Patterning of Carbon Nanotube/Silver Nanoparticle Composite To Produce Extremely Flexible Conductive Electrodes

Recently, highly flexible conductive features have been widely demanded for the development of various electronic applications, such as foldable displays, deformable lighting, disposable sensors, and flexible batteries. Herein, we report for the first time a selective photonic sintering-derived, highly reliable patterning approach for creating extremely flexible carbon nanotube (CNT)/silver nanoparticle (Ag NP) composite electrodes that can tolerate severe bending (20 000 cycles at a bending radius of 1 mm). The incorporation of CNTs into a Ag NP film can enhance not only the mechanical stability of electrodes but also the photonic-sintering efficiency when the composite is irradiated by intense pulsed light (IPL). Composite electrodes were patterned on various plastic substrates by a three-step process comprising coating, selective IPL irradiation, and wiping. A composite film selectively exposed to IPL could not be easily wiped from the substrate, because interfusion induced strong adhesion to the underlying polymer substrate. In contrast, a nonirradiated film adhered weakly to the substrate and was easily removed, enabling highly flexible patterned electrodes. The potential of our flexible electrode patterns was clearly demonstrated by fabricating a light-emitting diode circuit and a flexible transparent heater with unimpaired functionality under bending, rolling, and folding.

Diazoketo-functionalized POSS resists for high performance replica molds of ultraviolet-nanoimprint lithography

Novel polyhedral oligomeric silsesquioxane (POSS) resists, which are based on a new photo-crosslinking system via Wolff rearrangement, are developed as ideal replica mold materials for ultraviolet-nanoimprint lithography. These POSS resist materials are synthesized by incorporating diazoketo and hydroxyl groups into the POSS core. The resist materials have exhibited a variety of desirable properties as replica molds, such as high modulus, low shrinkage ratio, high transparency, low surface energy, and resistance to organic solvents. The resultant replica molds exhibit a high resolution patterning capacity. These economic fabrication methods of replica molds with high mechanical durability and good releasing properties are potentially useful for versatile applications in the area of mold-based lithography.

Unconventional micro-/nanofabrication technologies for hybrid-scale lab-on-a-chip

Micro-/nanofabrication-based lab-on-a-chip (LOC) technologies have recently been substantially advanced and have become widely used in various inter-/multidisciplinary research fields, including biological, (bio-)chemical, and biomedical fields. However, such hybrid-scale LOC devices are typically fabricated using microfabrication and nanofabrication processes in series, resulting in increased cost and time and low throughput issues. In this review, after briefly introducing the conventional micro-/nanofabrication technologies, we focus on unconventional micro-/nanofabrication technologies that allow us to produce either in situ micro-/nanoscale structures or master molds for additional replication processes to easily and conveniently create novel LOC devices with micro- or nanofluidic channel networks. In particular, microfabrication methods based on crack-assisted photolithography and carbon-microelectromechanical systems (C-MEMS) are described in detail because of their superior features from the viewpoint of the throughput, batch fabrication process, and mixed-scale channels/structures. In parallel with previously reported articles on conventional micro-/nanofabrication technologies, our review of unconventional micro-/nanofabrication technologies will provide a useful and practical fabrication guideline for future hybrid-scale LOC devices.

Mixed-scale channel networks including Kingfisher-beak-shaped 3D microfunnels for efficient single particle entrapment

Reproducible research results for nanofluidics and their applications require viable fabrication technologies to produce nanochannels integrated with microchannels that can guide fluid flow and analytes into/out of the nanochannels. We present the simple fabrication of mixed-scale polydimethylsiloxane (PDMS) channel networks consisting of nanochannels and microchannels via a single molding process using a monolithic mixed-scale carbon mold. The monolithic carbon mold is fabricated by pyrolyzing a polymer mold patterned by photolithography. During pyrolysis, the polymer mold shrinks by ∼90%, which enables nanosized carbon molds to be produced without a complex nanofabrication process. Because of the good adhesion between the polymer mold and the Si substrate, non-uniform volume reduction occurs during pyrolysis resulting in the formation of curved carbon mold side walls. These curved side walls and the relatively low surface energy of the mold provide efficient demolding of the PDMS channel networks. In addition, the trigonal prismatic shape of the polymer is converted into to a Kingfisher-beak-shaped carbon structure due to the non-uniform volume reduction. The transformation of this mold architecture produces a PDMS Kingfisher-beak-shaped 3D microfunnel that connects the microchannel and the nanochannel smoothly. The smooth reduction in the cross-sectional area of the 3D microfunnels enables efficient single microparticle trapping at the nanochannel entrance; this is beneficial for studies of cell transfection.

Integrated optofluidic-microfluidic twin channels: toward diverse application of lab-on-a-chip systems

Optofluidics, which integrates microfluidics and micro-optical components, is crucial for optical sensing, fluorescence analysis, and cell detection. However, the realization of an integrated system from optofluidic manipulation and a microfluidic channel is often hampered by the lack of a universal substrate for achieving monolithic integration. In this study, we report on an integrated optofluidic-microfluidic twin channels chip fabricated by one-time exposure photolithography, in which the twin microchannels on both surfaces of the substrate were exactly aligned in the vertical direction. The twin microchannels can be controlled independently, meaning that fluids could flow through both microchannels simultaneously without interfering with each other. As representative examples, a tunable hydrogel microlens was integrated into the optofluidic channel by femtosecond laser direct writing, which responds to the salt solution concentration and could be used to detect the microstructure at different depths. The integration of such optofluidic and microfluidic channels provides an opportunity to apply optofluidic detection practically and may lead to great promise for the integration and miniaturization of Lab-on-a-Chip systems.

A novel 2D silicon nano-mold fabrication technique for linear nanochannels over a 4 inch diameter substrate

A novel low-cost 2D silicon nano-mold fabrication technique was developed based on Cu inclined-deposition and Ar⁺ (argon ion) etching. With this technique, sub-100 nm 2D (two dimensional) nano-channels can be etched economically over the whole area of a 4 inch n-type <100> silicon wafer. The fabricating process consists of only 4 steps, UV (Ultraviolet) lithography, inclined Cu deposition, Ar⁺ sputter etching, and photoresist & Cu removing. During this nano-mold fabrication process, we investigated the influence of the deposition angle on the width of the nano-channels and the effect of Ar⁺ etching time on their depth. Post-etching measurements showed the accuracy of the nanochannels over the whole area: the variation in width is 10%, in depth it is 11%. However, post-etching measurements also showed the accuracy of the nanochannels between chips: the variation in width is 2%, in depth it is 5%. With this newly developed technology, low-cost and large scale 2D nano-molds can be fabricated, which allows commercial manufacturing of nano-components over large areas.

Two dimensional PMMA nanofluidic device fabricated by hot embossing and oxygen plasma assisted thermal bonding methods

A method for obtaining a low-cost and high-replication precision two-dimensional (2D) nanofluidic device with a polymethyl methacrylate (PMMA) sheet is proposed. To improve the replication precision of the 2D PMMA nanochannels during the hot embossing process, the deformation of the PMMA sheet was analyzed by a numerical simulation method. The constants of the generalized Maxwell model used in the numerical simulation were calculated by experimental compressive creep curves based on previously established fitting formula. With optimized process parameters, 176 nm-wide and 180 nm-deep nanochannels were successfully replicated into the PMMA sheet with a replication precision of 98.2%. To thermal bond the 2D PMMA nanochannels with high bonding strength and low dimensional loss, the parameters of the oxygen plasma treatment and thermal bonding process were optimized. In order to measure the dimensional loss of 2D nanochannels after thermal bonding, a dimension loss evaluating method based on the nanoindentation experiments was proposed. According to the dimension loss evaluating method, the total dimensional loss of 2D nanochannels was 6 nm and 21 nm in width and depth, respectively. The tensile bonding strength of the 2D PMMA nanofluidic device was 0.57 MPa. The fluorescence images demonstrate that there was no blocking or leakage over the entire microchannels and nanochannels.

Micro structure fabrication with a simplified hot embossing method

A facile hot embossing method—low pressure hot embossing (LPHE)—is reported in this paper.