Laser-direct-write methods for fabrication of paper-based medical diagnostic sensors

We demonstrate the use of laser-based direct-write methods, namely laser-induced forward transfer and laser-induced photo-polymerization as printing and patterning tools for the fabrication of paper-based fluidic sensors that enable affordable point-of-care medical diagnostics

Rapid and mask-less laser-processing technique for the fabrication of microstructures in polydimethylsiloxane

We report a rapid laser-based method for structuring polydimethylsiloxane (PDMS) on the micron-scale. This mask-less method uses a digital multi-mirror device as a spatial light modulator to produce a given spatial intensity pattern to create arbitrarily shaped structures via either ablation or multi-photon photo-polymerisation in a master substrate, which is subsequently used to cast the complementary patterns in PDMS. This patterned PDMS mould was then used for micro-contact printing of ink and biological molecules

Nanofabrication technologies: high-throughput for tomorrow's metadevices

Fabrication fundamentals1. Serial versus parallel? Most are currently fabricated by serial writing….2. Additive or subtractive?3. Feature size required.4. One-off demonstration (journal paper) or volume production (in the shops by next Christmas…)5. What material?6. Cost….(+ normalise to 150mm diameter wafer)7. Time to fabricat

Laser manufacturing for multi-analyte paper-based diagnostic sensors

We present here our work on the fabrication of paper-based multiplexed diagnostic sensors, using direct-write laser-based processes (Laser Induced Forward Transfer and photo-polymerisation), for the detection of glucose and proteins (BSA)

Engineering fluidic delays in paper-based devices using laser direct-writing

We report the use of a new laser-based direct-write technique that allows programmable and timed fluid delivery in channels within a paper substrate which enables implementation of multi-step analytical assays. 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 depth and/or the porosity of hydrophobic barriers which, when fabricated in the fluid path, produce controllable fluid delay. We have patterned these flow delaying barriers at pre-defined locations in the fluidic channels using either a continuous wave laser at 405nm, or a pulsed laser operating at 266nm. Using this delay patterning protocol we generated flow delays spanning from minutes to over an hour. Since the channels and flow delay barriers can be written via a common laser-writing process, this is a distinct improvement over other methods that require specialist operating environments, or custom-designed equipment. This technique can therefore be used for rapid fabrication of paper-based microfluidic devices that can perform single or multistep analytical assays

Rapid prototyping of microfluidic channels in nitrocellulose using laser-direct-write patterning

The demand for low-cost alternatives to conventional point-of-care (POC) diagnostic tools has led to significant developments in the field of microfluidics in porous paper. Several approaches have already been reported for fabricating fluidic devices in such materials, which include photolithography, inkjet printing, printing of wax, plasma oxidation, laser-cutting, and shaping. Nitrocellulose is a particularly important material that is routinely used in lateral-flow type medical diagnostic tests used in POC environments. Here, we report the patterning of microfluidic structures in porous nitrocellulose through a simple laser-direct-write (LDW) procedure, which relies on light-induced photo-polymerisation of a photopolymer previously impregnated in the nitrocellulose membranes. During the subsequent development step, the un-polymerised photopolymer is removed, while the polymerized structures remain. These resulting hydrophobic structures extend throughout the thickness of the nitrocellulose and form the barrier-walls of the interconnected hydrophilic fluidic patterns they demarcate. Analysis showed that these structures can contain and guide the flow of liquids without any leakage, and hence this technique can be used to produce an array of microfluidic devices for many applications such as clinical diagnostics and analytical chemistry. Our results show that the smallest dimensions that can be achieved for hydrophobic barrier-walls and microfluidic channels using this method are ~ 60 µm and ~ 100 µm respectively, both of which are the smallest values reported so far for fabrication of nitrocellulose-based microfluidic devices. In addition, the process steps for this LDW process are compatible for roll-to-roll processing, which would lead to device production on a commercial-scale

Direct-write laser techniques for the manufacture of multiplexed paper-based diagnostic sensors

The ever-present need for affordable and reliable devices for health monitoring has led to a significant growth over the past few years in the development and applications of paper-based point-of-care diagnostics that operate with minimal reagent volumes, are portable and need no special training or equipment for their use. We present here our work on the fabrication of multiplexed paper-based diagnostic sensors for the detection of glucose and bovine serum albumin (BSA) using lasers-based methods. Our use of lasers for the fabrication of the devices is justified by the versatility, speed of production, and cost, all of which are of critical importance for mass-market applications. A laser direct-write process, Laser-Induced Forward Transfer (LIFT), was used to print the reagents and biological molecules on paper substrates that facilitate the sensing of the specific analytes. A second laser-based process was also implemented to create hydrophobic walls and barriers in paper and membrane substrates, which define the wells and channels that can guide biological and chemical solutions through the paper devices. A pulsed KrF excimer laser operating at 248 nm was used for LIFT and a continuous wave laser at 405 nm was used for patterning of the paper. The small dimensions of the structures produced (~100 µm) and the precise and low-volume (nl) deposition of materials by these processes enable the miniaturisation of these devices ensuring the minimal use of reagents. We have quantified the speed and cost of our laser-based methods and believe they can be up-scaled for mass production

Laser-polymerised 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.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. The patterns can be produced rapidly using simple low power c.w. laser sources at a writing speed of order 1 ms-1 and we have successfully demonstrated techniques for controlled delay, forward biased and multiplexed flow of several different fluids. We show our early results for diagnostic paper-based sensors for the detection of glucose and bovine serum albumin (BSA) using colorometric readout, which we believe makes the technique especially useful for mass-market applications, particularly in developing world situations where simplicity, cheapness and ready availability are the key parameters

Laser-direct-write technique for rapid prototyping of multiplexed paper-based diagnostic sensors

The demand for low-cost alternatives to conventional point-of-care diagnostic tools has led to significant developments in the field of paper-based diagnostics, and several methods, which include photolithography, inkjet printing, wax printing etc., have been reported for the fabrication of fluidic devices in porous materials such as paper. Here, we present a simple, laser-based direct-write procedure, which relies on light-induced photo-polymerisation of a photopolymer previously impregnated in the porous substrates for fabrication of the user-defined fluidic patterns within such substrates. During the subsequent development step, the un-polymerised photopolymer is washed-out; however, the hydrophobic polymerized structures that remain in the substrate, and extend throughout its thickness define the barrier-walls of the hydrophilic fluidic patterns they demarcate. These structures contain and guide liquids without any leakage, thus validating the feasibility of using this technique in the production of microfluidic devices. Our results show that for cellulose paper, the minimum widths the hydrophobic barrier-walls should have to successfully contain fluids is ~ 120 µm, and similarly, the minimum dimensions a fluidic channel can have to guide fluids is ~ 80 µm, both of which are the smallest values reported so far. These patterns can be produced rapidly via scanning of a low power continuous-wave laser at speeds of the order of one meter per second and we have successfully implemented it in patterning a range of porous materials including nitrocellulose membranes, glass fibre filter and polyvinylidene fluoride. To further validate the applicability of these laser-patterned devices as sensors, we have demonstrated their use for a range of colorimetric assays including the detection of glucose, protein and nitrite, and also an enzyme-linked immunosorbent assay for detection of C-reactive protein. Finally, we have quantified the speed and cost of our laser-based method and believe that it is suited to up-scaling for mass production

Laser engineering of various porous materials for fabrication of paper-based microfluidic devices

We report the successful demonstration of a laser-based direct-write technique for patterning of various porous materials in order to fabricate more diversified and multifunctional paper-based microfluidic devices that find applications in affordable point-of-care medical diagnostics