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

Paper-based sensors: affordable, versatile, and emerging analyte detection platforms

Paper-based sensors, often referred to as paper-based analytical devices (PADs), stand as a transformative technology in the field of analytical chemistry. They offer an affordable, versatile, and accessible solution for diverse analyte detection. These sensors harness the unique properties of paper substrates to provide a cost-effective and adaptable platform for rapid analyte detection, spanning chemical species, biomolecules, and pathogens. This review highlights the key attributes that make paper-based sensors an attractive choice for analyte detection. PADs demonstrate their versatility by accommodating a wide range of analytes, from ions and gases to proteins, nucleic acids, and more, with customizable designs for specific applications. Their user-friendly operation and minimal infrastructure requirements suit point-of-care diagnostics, environmental monitoring, food safety, and more. This review also explores various fabrication methods such as inkjet printing, wax printing, screen printing, dip coating, and photolithography. Incorporating nanomaterials and biorecognition elements promises even more sophisticated and sensitive applications.

Optimization of flow path parameters for enhanced sensitivity lateral flow devices

Lateral flow devices (LFDs) or lateral flow tests (LFTs) are one of the most widely used biosensor platforms for point-of-care (POC) diagnostics. The basic LFD design has remained largely unchanged since its first appearance, and this has limited LFD use in clinical applications due to a general lack of analytical sensitivity. We report here a comprehensive study of the use of laser-patterned geometric control barriers that influence the flow dynamics within an LFD, with the specific aim of enhancing LFD sensitivity and lowering the limit of detection (LOD). This control of sample flow produces an increase in the time available for optimizing the binding kinetics of the implemented assay. The geometric modification to the flow path is in the form of a constriction that is produced by depositing a photo-sensitive polymer onto the nitrocellulose membrane which when polymerized, creates impermeable barrier walls through the depth of the membrane. Both the position of the constriction within the flow path and the number of constrictions allow for an increase in the sensitivity because of a slower overall flow rate within the test and a larger volume of sample per unit width of the test line. For these high sensitivity LFDs (HS-LFD), through optimization of the constriction position and addition of a second constriction we attained a 62% increase in test line color intensity for the detection of procalcitonin (PCT) and were also able to lower the LOD from 10 ng/mL to 1 ng/mL. In addition, of relevance for future commercial exploitation, this also significantly decreases the antibody consumption per device leading to reduced costs for test production. We have further tested our HS-LFD with contrived human samples, validating its application for future clinical use.

Challenges and limits of mechanical stability in 3D direct laser writing

Direct laser writing is an effective technique for fabrication of complex 3D polymer networks using ultrashort laser pulses. Practically, it remains a challenge to design and fabricate high performance materials with different functions that possess a combination of high strength, substantial ductility, and tailored functionality, in particular for small feature sizes. To date, it is difficult to obtain a time-resolved microscopic picture of the printing process in operando. To close this gap, we herewith present a molecular dynamics simulation approach to model direct laser writing and investigate the effect of writing condition and aspect ratio on the mechanical properties of the printed polymer network. We show that writing conditions provide a possibility to tune the mechanical properties and an optimum writing condition can be applied to fabricate structures with improved mechanical properties. We reveal that beyond the writing parameters, aspect ratio plays an important role to tune the stiffness of the printed structures.

Direct laser writing is an effective technique for fabrication of complex 3D polymer networks using ultrashort laser pulses but to date it is difficult to obtain a time-resolved microscopic picture of the printing process in operando. Here, the use molecular dynamics simulation to model direct laser writing and investigate the effect of writing condition and aspect ratio on the mechanical properties of the printed polymer network.

Semi-quantitative detection of inflammatory biomarkers using a laser-patterned multiplexed lateral flow device

Inflammatory markers including C-reactive protein (CRP) and procalcitonin (PCT) have been shown to be useful biomarkers to improve triage speed and prevent the inappropriate use of antibiotics for infections such as pneumonia. Here, we present a novel and exciting solution to guide the administration of antibiotic treatment via rapid, semi-quantitative and multiplexed detection of CRP and PCT using an advanced lateral flow device (LFD) designed to have multiple parallel flow-paths, produced via the precise laser-based partitioning of the single flow-path of a standard LFD. Each flow-path within this multiplexed LFD has a unique detection capability which permits tailored detection of CRP within a predefined cut-off range (20 μg/mL - 100 μg/mL) and PCT above a pre-defined threshold (0.5 ng/mL). We demonstrate the use of this LFD in the successful detection of CRP and PCT semi-quantitatively within spiked human serum samples. This multiplexed near-patient assay has potential for development into a rapid triage and treatment of patients with suspected pneumonia.

3D microfluidic cloth-based analytical devices on a single piece of cloth by one-step laser hydrophilicity modification

In this work, we report for the first time a simple and robust method for constructing a 3D microfluidic analytical device on a single piece of hydrophobic cotton cloth. Specifically, laser scanning technology was applied to process hydrophilic regions at the top and bottom of a single piece of hydrophobic cloth. Symmetrical hydrophilic regions at the bottom and top constituted vertical microfluidic channels, and asymmetrical hydrophilic regions constituted transverse flow channels. Liquid flow velocity in 3D cloth-based microchannels can be adjusted flexibly by modifying laser parameters, and programmable laser scanning can be utilized to process 3D microfluidic devices with various patterns. Single-piece 3D cloth-based microfluidic devices formed via this method can be used in many fields such as information encryption and anti-counterfeiting, multi-liquid printing and liquid mixing dilution. Compared to traditional processing methods of 3D cloth-based microfluidic devices, the laser scanning method eliminates multiple complex and repetitive assembly processes, which is a significant advance in this research area. This processing method provides a new option for fast and large-scale manufacturing of 3D cloth-based microfluidic analysis devices for point-of-care testing application in undeveloped regions/countries.

Increasing the packing density of assays in paper-based microfluidic devices

Paper-based devices have a wide range of applications in point-of-care diagnostics, environmental analysis, and food monitoring. Paper-based devices can be deployed to resource-limited countries and remote settings in developed countries. Paper-based point-of-care devices can provide access to diagnostic assays without significant user training to perform the tests accurately and timely. The market penetration of paper-based assays requires decreased device fabrication costs, including larger packing density of assays (i.e., closely packed features) and minimization of assay reagents. In this review, we discuss fabrication methods that allow for increasing packing density and generating closely packed features in paper-based devices. To ensure that the paper-based device is low-cost, advanced fabrication methods have been developed for the mass production of closely packed assays. These emerging methods will enable minimizing the volume of required samples (e.g., liquid biopsies) and reagents in paper-based microfluidic devices.

A rapid diagnostic test for human Visceral Leishmaniasis using novel Leishmania antigens in a Laser Direct-Write Lateral Flow Device

Visceral Leishmaniasis (VL) causes high morbidity and mortality in low-to-middle-income countries worldwide. In this study, we used Laser Direct-Write (LDW) technology to develop a new Lateral Flow Device (LFD) with double-channel geometry on a low-cost paper platform as a rapid and accurate serodiagnostic assay for human VL. This Duplex VL-LFD was based on a laser-patterned microfluidic device using two recombinant Leishmania proteins, β-tubulin and LiHyp1, as novel diagnostic antigens. The VL-LFD assay was tested with blood/serum samples from patients diagnosed with VL, Tegumentary Leishmaniasis, Leishmaniasis of unknown identity, other parasitic diseases with similar clinical symptoms, i.e. Leprosy Disease and Chagas Disease, and blood from healthy donors, and compared in parallel with commercial rK39 IT-LEISH^® Kit. Clinical diagnosis and real-time Polymerase Chain Reaction assay were used as reference standards. VL-LFD Sensitivity (S ± 95% Confidence Intervals (CI)) of 90.9 (78.9-100) and Specificity (Sp ± 95% CI) of 98.7 (96.1-100) outperformed the IT-LEISH^® Kit [S = 77.3 (59.8-94.8), Sp = 94.7 (89.6-99.8)]. This is the first study reporting successful development of an LFD assay using the LDW technology and the VL-LFD warrants comparative testing in larger patient cohorts and in areas with endemic VL in order to improve diagnosis and disease management.

Three-dimensional paper based platform for automatically running multiple assays in a single step

Paper based assays are paving the way to automated, simplified, robust and cost-effective point of care testing (POCT). We propose a method for fabricating three dimensional (3D) microfluidic paper based analytical devices (μPADs) via combining thin adhesive films and paper folding, which avoids the use of cellulose powders and the complex folding sequence and simultaneously permits assays in several layers. To demonstrate the effectiveness of this approach, a 3DμPADs was designed to conduct more assays on a small footprint, allowing dual colorimetric and electrochemical detections. More importantly, we further developed a 3D platform for implementing automated and multiplexed ELISA in parallel, since ELISA, a routine and standard laboratory method, has rarely been used in practical analyses outside of the laboratory. In this configuration, complex and multistep diagnostic assays can be carried out with the addition of the sample and buffer in a simple fashion. Using Troponin I as model, the device showed a broad dynamic range of detection with a detection limit of 0.35 ng/mL. Thus, the developed platforms allow for various assays to be cost-effectively carried out on a single 3D device, showing great potential in an academic setting and point of care testing under resource-poor conditions.

Fabrication of paper devices via laser-heating-wax-printing for high-tech enzyme-linked immunosorbent assays with low-tech pen-type pH meter readout

In this work, a new method named laser-heating-wax-printing (LHWP) is described to fabricate paper devices for developing sensitive, affordable, user-friendly paper-based enzyme-linked immunosorbent assays (P-ELISAs) that initially use common pen-type pH meters for portable, quantitative readout. The LHWP enables a rapid patterning of wax in paper via one step of heating the wax layer coated on the paper surface using a mini-type CO₂ laser machine. Wax-patterned paper microzones created in this way are utilized to conduct the pen-type pH meter-based P-ELISAs with enzyme-loaded SiO₂ microbeads for highly efficient signal amplification of each antibody-antigen binding event. The results show that this new P-ELISA system is quantitatively sensitive to the concentrations of a model protein analyte in buffer samples ranging from 12.5 to 200 pg mL^-1, with a limit of detection of ca. 7.5 pg mL^-1 (3σ). Moreover, the satisfactory recovery results of assaying several human serum samples validate its feasibility for practical applications.

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

We report on the use of a laser-direct write (LDW) technique that allows the fabrication of lateral flow devices with enhanced sensitivity and limit of detection. This manufacturing technique comprises the dispensing of a liquid photopolymer at specific regions of a nitrocellulose membrane and its subsequent photopolymerisation to create impermeable walls inside the volume of the membrane. These polymerised structures are intentionally designed to create fluidic channels which are constricted over a specific length that spans the test zone within which the sample interacts with pre-deposited reagents. Experiments were conducted to show how these constrictions alter the fluid flow rate and the test zone area within the constricted channel geometries. The slower flow rate and smaller test zone area result in the increased sensitivity and lowered limit of detection for these devices. We have quantified these via the improved performance of a C-Reactive Protein (CRP) sandwich assay on our lateral flow devices with constricted flow paths which demonstrate an improvement in its sensitivity by 62x and in its limit of detection by 30x when compared to a standard lateral flow CRP device.

3D Printing of Artificial Blood Vessel: Study on Multi-Parameter Optimization Design for Vascular Molding Effect in Alginate and Gelatin

3D printing has emerged as one of the modern tissue engineering techniques that could potentially form scaffolds (with or without cells), which is useful in treating cardiovascular diseases. This technology has attracted extensive attention due to its possibility of curing disease in tissue engineering and organ regeneration. In this paper, we have developed a novel rotary forming device, prepared an alginate⁻gelatin solution for the fabrication of vessel-like structures, and further proposed a theoretical model to analyze the parameters of motion synchronization. Using this rotary forming device, we firstly establish a theoretical model to analyze the thickness under the different nozzle extrusion speeds, nozzle speeds, and servo motor speeds. Secondly, the experiments with alginate⁻gelatin solution are carried out to construct the vessel-like structures under all sorts of conditions. The experiment results show that the thickness cannot be adequately predicted by the theoretical model and the thickness can be controlled by changing the parameters. Finally, the optimized parameters of thickness have been adjusted to estimate the real thickness in 3D printing.

Multinozzle Multichannel Temperature Deposition System for Construction of a Blood Vessel

3D bioprinting is an emerging technology that drives us to construct the complicated tissues and organs consisting of various materials and cells, which has been in widespread use in tissue engineering and organ regeneration. However, the protection and accurate distribution of cells are the most urgent problems to achieve tissue and organ reconstruction. In this article, a multinozzle multichannel temperature deposition and manufacturing (MTDM) system is proposed to fabricate a blood vessel with heterogeneous materials and gradient hierarchical porous structures, which enables not only the reconstruction of a blood vessel with an accurate 3D model structure but also the capacity to distribute bioactive materials such as growth factors, nutrient substance, and so on. In addition, a coaxial focusing nozzle is proposed and designed to extrude the biomaterial and encapsulation material, which can protect the cell from damage. In the MTDM system, the tubular structure of a blood vessel was successfully fabricated with the different biomaterials, which proved that the MTDM system has a potential application prospect in tissue engineering and organ regeneration.