Programmable delay in paper-based devices using laser direct writing

Demand for low-cost alternatives to conventional medical diagnostic tools has been the driving force that has spurred significant developments in the diagnostics field. Paper-based fluidics, proposed by the Whitesides’ group in 2007 has been regarded as one such alternative, and consequently, this field has been progressing rapidly and a range of paper-based fluidic devices that implement different assays have since been demonstrated. Research into the development of methodologies that control, and in particular delay the flow of fluids in these devices is an urgently needed requirement that would enable greater functionalities in such paper-based devices.In this work, to control fluid-flow, we report the use of a new approach that is based on the laser-based photo-polymerisation technique that we have reported earlier for the creation of fluidic patterns (channels/wells) in paper. The delay or slowing down, of the fluid-flow in a fluidic channel is achieved via the introduction of barriers aligned across the direction of the fluid-flow – in a fashion similar to how speed-bumps enable traffic-calming control on a road. The schematic in Figure 1a shows how the delay can be introduced via the creation/insertion of barriers which are solid and impermeable and by controlling the ‘depth’ of the solid/impregnable barriers (Figure 1) to allow for controlled leakage of the fluids under the barriers. The control over the depth of the barriers is obtained by simply adjusting the laser-writing parameters such as the output power and writing/scanning speed. We observe that solid/impregnable barriers of various depths decrease the fluid flow by a rate that is proportional to their depth. Having patterned these barriers at pre-defined locations in the fluidic channel, using a pulsed laser operating at 266nm (20Hz, 10ns) we have achieved flow-delays with a time span ranging from few minutes to over an hour. We have also performed a study to understand the influence of the number of barriers and their position on the flow-delay, and this is shown in Figure 2.Since the channels and flow-delay barriers can be written via a common laser-writing procedure, this technique has a distinct advantage over certain other methods that require specialist operating environments, or custom-designed equipment to enable both these aspects. We believe this rapid and versatile technique is therefore suited for fabrication of ‘sample-in-read-out’ type automated paper-based microfluidic devices that can implement single/multistep analytical assays

The rotation strategy in high-level European soccer teams

The purpose of the present study was to examine the rotation strategy in high-level soccer teams during a sequence of three games per week (1st domestic, 2nd European and 3rd domestic). Data were collected during the 2014-15, 2015-16, 2016-17 and 2017-18 competitive season for the soccer teams that were qualified in the quarter finals of the Champions League. Regression analysis showed that when a large number of players participated in the initial list for the three games, more points in the domestic league were lost. Similarly, increasing the changes of players in the initial list between the 1st and the 3rd game and between the 2nd and the 3rd game a negative effect on the domestic league was observed. In contrast, a positive effect of the number of changes of players in the starting line between the 1st and the 2nd game, regarding the total points won, was found. As the average time of the substitutes participated in the game increases in all three games, the total points of the teams are reduced. The biggest time of changes in the 2nd game had a negative impact on the points of European games. In order to achieve a more efficient rotation, coaches should have a qualitative and competitive roster of players. Furthermore, coaches should try to apply different tactics in previous matches in order, as many players as possible, to maintain high levels of homogeneity and competing readiness

Laser-printed fluidic channels for the manufacture of multiplexed paper-based diagnostic sensors

Paper-based microfluidics is a rapidly progressing inter-disciplinary technology driven by the need for low-cost alternatives to conventional point-of-care diagnostic tools. For transport of reagents/analytes, such devices often consist of interconnected hydrophilic fluid-flow channels that are demarcated by hydrophobic barrier walls that extend through the thickness of the paper. Here, we present a laser-based fabrication procedure that uses laser-induced polymerisation of a photopolymer to produce the required fluidic channels in paper or other porous materials. Experimental results showed that the structures successfully guide the flow of fluids and also allow containment of fluids in wells, and hence the technique is suitable for fabrication of paper-based microfluidic devices.&amp; more...<br/

Laser direct write techniques for the fabrication of paper-based diagnostic devices

We report on the use of laser direct-write techniques for the fabrication of point-of-care paper-based diagnostic sensors. These include laser-based deposition, laser ablation and laser-induced photo-polymerisation.Firstly, Laser Induced Forward Transfer (LIFT) was employed to deposit biomolecules from a donor film onto paper receivers. Paper was chosen as the ideal receiver because of its inherent properties which make it an efficient and suitable platform for point-of-care diagnostic sensors. Both enzyme-tagged and untagged antibodies were LIFT-printed and their viability was confirmed via a colorimetric enzyme-linked immunosorbent assay (ELISA).Secondly, we report on the laser-based structuring of paper-based fluidic devices. Laser-scanning the paper defines the areas that will be polymerised, thus creating barriers that keep the liquid solutions contained. Complicated devices are easy to fabricate and the flexibility of this technique allows for unique patterns, making it appropriate for rapid prototyping but also for large-scale production. Furthermore, the laser patterning technique allows control of the depth or degree of polymerisation, thereby allowing the liquid to wick through but also imposition of flow delays.Finally, the use of lasers for the fabrication of a 'master' which can be used for casting a PDMS mould for applications in micro-contact printing. The combination of the above mentioned techniques represent the platform technology for the rapid, precise and versatile laser-based fabrication of diagnostic point-of-care sensors

Improved sensitivity and limit-of-detection of lateral flow devices using spatial constrictions of the flow-path

Excel file contains data for the graphs presented in: Katis, I. et al. (2018). Improved sensitivity and limit-of-detection of lateral flow devices using spatial constrictions of the flow-path. Biosensors &amp; Bioelectronics, 113, 95-100.</span

Laser direct-write for fabrication of three-dimensional paper-based devices

We report the use of a laser-based direct-write (LDW) technique that allows the design and fabrication of three-dimensional (3D) structures within a paper substrate that enables implementation of multi-step analytical assays via a 3D protocol. The technique is based on laser-induced photo-polymerisation, and through adjustment of the laser writing parameters such as the laser power and scan speed we can control the depths of hydrophobic barriers that are formed within a substrate which, when carefully designed and integrated, produce 3D flow paths. So far, we have successfully used this depth-variable patterning protocol for stacking and sealing of multi-layer substrates, for assembly of backing layers for two-dimensional (2D) lateral flow devices and finally for fabrication of 3D devices. Since the 3D flow paths can also be formed via a single laser-writing process by controlling the patterning parameters, this is a distinct improvement over other methods that require multiple complicated and repetitive assembly procedures. This technique is therefore suitable for cheap, rapid and large-scale fabrication of 3D paper-based microfluidic devices

Laser-based printing and patterning for biological applications

1. IntroductionLaser direct-write methodologies are highly flexible, non-contact and serial pattern generation procedures that allow a user to create patterns either on the surface or in the volume of a material of choice through point-by-point scanning of the laser beam across the material work-piece. Pattern generation can be through either addition or subtraction of the material or through modifications to its physical properties, and the scale lengths typically range from nm-mm. Here we show the usefulness and versatility of such laser-based approaches for fabrication of paper-based sensors for medical diagnostics.2. Laser-based patterningPaper-based microfluidics has been a rapidly progressing inter-disciplinary technology driven by the need for low-cost alternatives to conventional point-of-care diagnostic tools since it was proposed by the Whitesides group in 2007 [1, 2]. For transport of reagents/analytes, such devices often consist of interconnected hydrophilic fluid-flow channels that are demarcated by hydrophobic barrier walls that extend through the thickness of the paper. Here, we present a laser-based fabrication procedure that uses laser-induced polymerisation of a photopolymer to produce the required fluidic channels in paper or other porous materials. Experimental results showed that the structures successfully guide the flow of fluids and also allow containment of fluids in wells, and hence the technique is suitable for fabrication of paper-based microfluidic devices.As shown in the schematic (Figure 1a), the process is conceptually simple. The minimum width for the hydrophobic barriers that successfully prevented fluid leakage was ~120 μm and the minimum width for the fluidic channels that can be formed was ~80 μm, the smallest reported so far for paper-based fluidic patterns. Some of the example devices are shown in Figure 1b-1e. The patterns can be produced rapidly using simple low power c.w. laser sources at a writing speed of order 1 m/s and we have also successfully demonstrated the use this technique for introduction of a range of additional functionalities such as controlled delay, three-dimensional flow and multiplexed flow of several different fluids.3. Laser-based printing With the end-goal of developing low-cost colorimetric point-of-care diagnostic sensors on paper, we also report our results on LIFT-printing of antibodies, both untagged and conjugated with the enzyme horseradish peroxidase (HRP). LIFT is an additive direct-write technique used commonly for depositing materials from a thin donor film onto a receiver substrate. The donor (a glycerol film containing the antibodies) is pre-deposited onto a carrier (a fused silica substrate) that is transparent to the incident laser light, and photons from the laser (KrF-excimer, 248nm, 1Hz, 10 ns, and maximum energy ~400mJ/pulse) provide the driving force that transfers a small volume of the donor onto the accepting receiver (paper). The viability of the untagged (target) antibodies post-transfer was validated by an indirect colorimetric Enzyme Linked Immunosorbent Assay. HRP-tagged antibody attaches specifically to the LIFT-printed target antibody and on addition of the corresponding chromogenic substrate, the printed pixels turn blue (Figure 2)

Towards AMR testing using paper-based diagnostic sensors

Overuse of broad spectrum antimicrobial agent means that resistance to them can evolve rapidly in microbe populations, and hence when a broad spectrum treatment is really crucial, it is less effective at saving the patient. Furthermore, once the bacteria become resistant, it can then exacerbate the prevalence of antibiotic resistance. Current routine empirical antibiotic therapy protocol involves laboratory based bacterial culture testing which can take up to 2-3 days. As a result, the only option available to the clinician is the treatment of the patient using an empirical antibiotic prescription. Such treatments can either prove to be ineffective, or potentially worsen the patient’s condition. However, if the specific microbe species causing an infection can be quickly identified earlier on, it will allow doctors to prescribe a specific targeted antimicrobial instead of using a broad spectrum antimicrobial. Therefore, early diagnosis and prompt correct antibiotic treatment is important for clinical recovery and prevention of this serious antibiotic resistance. In this work, we will present our preliminary results on the use of a laser-based fabrication technique in the development of paper-based diagnostic tests which are analogues of the commonly available pregnancy 'dipstick' testing kits, and which will allow the timely detection of multiple pathogens at the point-of-care, either in the clinic or in the community. These paper-based diagnostic sensors fabricated via our laser-based technology are cheap, easy-to-use and allow rapid testing of either pathogens or their antimicrobial resistance to antibiotics.<br/

Bacterial pathogen detection using laser-structured paper-based diagnostic sensors

Antimicrobial resistance has been recently identified by the World Health Organisation as a global threat and the need for novel diagnostic tools has been stressed. Current routine empirical antibiotic therapy protocol involves laboratory-based bacterial culture testing which can take up to 2-3 days. However, if the specific microbe species causing an infection can be quickly identified earlier on, it will allow doctors to prescribe a specific targeted antimicrobial instead of using a broad spectrum antimicrobial. In this work, we will present our preliminary results on the use of a laser-based fabrication technique of paper-based diagnostic tests via photo-polymerisation. The technique allows the creation of hydrophobic barriers through the whole thickness of the paper, and therefore the creation of fluidic channels and test zones in many different shapes, sizes and patterns. The laser-based direct-write procedure is non-contact, non-lithographic and mask-less and uses a low-power 405nm diode laser. The laser-structured paper can then be infused with chromogenic agars that allow the growth and detection of different bacteria. These devices are analogues of the commonly available agar plates and will allow the timely detection of multiple pathogens at the point-of-care. These paper-based diagnostic sensors fabricated via our laser-based technology are cheap, easy-to-use and allow rapid testing of either pathogens or their antimicrobial resistance to antibiotics