Laser-assisted thermal imprinting of glass guided mode resonant (GMR) optical filter

Laser-assisted thermal imprinting of glass nanostructures is demonstrated. Compare to the existing thermal imprinting, this method significantly reduced the contact imprinting time. The quality of the replicated glass nanostructures revealed by field emission scanning electron microscope ( SEM) and atomic force microscope ( AFM) exhibited a very smooth surface finish that closely matched the profile of the silicon mold. As proof-of-concept, the utility of laser-assisted, imprinted glass nanostructures as guided-mode resonant (GMR ) optical filter was evaluated. The peak spectral values obtained were satisfactory; which yielded an average FWHM and PWV of 4.6 nm and 691.39 nm respectively

Glassy Carbon: A Promising Material for Micro- and Nanomanufacturing

When certain polymers are heat-treated beyond their degradation temperature in the absence of oxygen, they pass through a semi-solid phase, followed by the loss of heteroatoms and the formation of a solid carbon material composed of a three-dimensional graphenic network, known as glassy (or glass-like) carbon. The thermochemical decomposition of polymers, or generally of any organic material, is defined as pyrolysis. Glassy carbon is used in various large-scale industrial applications and has proven its versatility in miniaturized devices. In this article, micro and nano-scale glassy carbon devices manufactured by (i) pyrolysis of specialized pre-patterned polymers and (ii) direct machining or etching of glassy carbon, with their respective applications, are reviewed. The prospects of the use of glassy carbon in the next-generation devices based on the material’s history and development, distinct features compared to other elemental carbon forms, and some large-scale processes that paved the way to the state-of-the-art, are evaluated. Selected support techniques such as the methods used for surface modification, and major characterization tools are briefly discussed. Barring historical aspects, this review mainly covers the advances in glassy carbon device research from the last five years (2013–2018). The goal is to provide a common platform to carbon material scientists, micro/nanomanufacturing experts, and microsystem engineers to stimulate glassy carbon device research

Design of microfluidic multiplex cartridge for point of care diagnostics

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonA simple, but innovative microfluidic Lab-on-a-chip (LOC) device which is broadly applicable in point of care diagnostics of biological pathogens was designed, fabricated and assembled utilising explicit microfluidic techniques. The purpose of this design was to develop a cartridge with the capability to perform multiplex DNA amplification reactions on a single device. To achieve this outcome, conventional laboratory protocols for sample preparation; involving DNA extraction, purification and elution were miniaturized to suit this lab-on-a-chip device of 75mm X 50mm cross-sectional area. The extraction process was carried out in a uniquely designed microchamber embedded with chitosan membrane that binds DNA at pH 5.0 and elutes when a different solution at pH 9.0 flows through. Likewise, purification protocol that occurs in the designed waste reservoir is very significant in biomedical field because it is concerned with waste treatment and cartridge disposability, was performed with a super absorbent powder that converts liquid to a gel like substance. This powder is known as sodium polyacrylate, which is also they treated with anti-bacterial chemicals to prevent environmental contamination. Furthermore, this process also employed the use of a passive valve for a precise fluid handling operation involving flow regulation from extraction to waste reservoir. In order to achieve the intended multiplexing function a multiplexer was created to distribute flow simultaneously through a bifurcated network of channels connected to six similar amplification microchambers. Prior to fabrication, computational fluid dynamics (CFD) simulation was utilized at flowrates less than 10μL/s as the means to test the effectiveness of each design components and also to specifically deduct empirical values that can be analyzed to improve or understand the relationship between the fluid and geometrical constraints of the microfluidic modular elements. The device produced was a hybrid cartridge composed of PDMS and glass which is the most widely used materials microfluidics research due to their low cost and simplicity of fabrication by soft lithography technique. The choice of material also took into account the various physical and chemical properties advantages and disadvantages in their bio-medical applications. Such properties include but not limited to surface energy that determines the wetting fluid characteristics, biocompatibility, optical transparency. Subsequently, after a prototype cartridge was developed fluid flow experimentation using liquid coloured dye was used on the fully fabricated cartridge to test the efficacy of its microfluidic functionalities before expensive DNA amplification reagents were utilised at similar flowrates to the CFD simulations. This gave rise to comparison between similar and dissimilar flow Peculiarities in the microfluidic circuit of both experiments. The final experiment was performed with the aid of a recent molecular technique in DNA amplification known as of RPA kit (recombinase polymerase amplification reaction). It involved performing two main reaction experiments; first, was the positive experiment that bears the sample DNA and the latter, negative that served as the control without DNA. In the end, quantitative analysis of results was done using an agarose gel that showed 143 base pairs, for the positive samples, thus validating the amplification experiment

Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome

Fabrication of Glass Microchannel via Glass Imprinting using a Vitreous Carbon Stamp for Flow Focusing Droplet Generator

This study reports a cost-effective method of replicating glass microfluidic chips using a vitreous carbon (VC) stamp. A glass replica with the required microfluidic microstructures was synthesized without etching. The replication method uses a VC stamp fabricated by combining thermal replication using a furan-based, thermally-curable polymer with carbonization. To test the feasibility of this method, a flow focusing droplet generator with flow-focusing and channel widths of 50 µm and 100 µm, respectively, was successfully fabricated in a soda-lime glass substrate. Deviation between the geometries of the initial shape and the vitreous carbon mold occurred because of shrinkage during the carbonization process, however this effect could be predicted and compensated for. Finally, the monodispersity of the droplets generated by the fabricated microfluidic device was evaluated