Laser direct-write technique for enabling novel functionalities in paper-based devices

Lead Research Organisation: University of Southampton
Department Name: Optoelectronics Research Centre


This project focusses on the use of a laser-based direct-write (LDW) technique developed within our group for creation of novel microfluidic devices in porous substrates such as paper. The proprietary technique involves local deposition of a photo-polymer onto a porous substrate at pre-defined locations, and its subsequent polymerisation by exposure from a laser source to form hydrophobic structures that define and demarcate the fluidic flow path and therefore the fluidic device in the porous substrate. The focus of this project is to further explore the usefulness of this LDW technique in improving the performance of laser-patterned microfluidics devices through incorporation of additional functionalities that can allow for the use of such devices in real world point-of-care scenarios. The primary objectives of the project is to develop approaches that use 'smart optically-triggered gates', laser-patterned within a paper-based microfluidic device to implement the following: improvements in sensitivity of the device, quantitative measurements of either a single or multiple biomarkers, detection of multiple biomarkers within a single device and finally, simplification of the sample preparation step - all of which are highly desired for diagnostic applications.

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509747/1 30/09/2016 29/09/2021
1953579 Studentship EP/N509747/1 27/09/2017 29/09/2021 Panagiotis Galanis
Description In the work funded through this award we present a relatively simple approach that allows in-line filtration of various constituents of a liquid analyte. This work was accomplished using a laser-based direct-write technique that allows the fabrication of porous barriers, which enable in-line filtration within a paper-based microfluidic device. The barriers were produced within porous substrates, namely nitrocellulose membranes, via local deposition of an acrylate-based negative photo-polymer that was subsequently polymerised by exposure from a laser source (fibre coupled continuous wave at 405 nm with maximum power of 60 mW). Adjustment of the photo-polymer deposition parameters determines the porosity of the barriers, which, when carefully designed and integrated within a fluidic channel, can act as filters that enable either complete blocking, selective flow or controlled separation of particles of different sizes within a fluid travelling through the channel. We have successfully identified the fabrication parameters for the creation of barriers that allow the filtration of two different types of particles, Au-nanoparticles with sizes of 40, 100 and 200 nm and latex microbeads with sizes of 200 nm and 1 µm, dispersed within an aqueous solution. We also report the use of a variable-porosity barrier for selective separation of latex microbeads from Au-nanoparticles, thereby showing the usefulness of this technique for enabling in-line filtration in such paper-based microfluidic devices and also provides an exciting potential route for sample preparation which is important for clinical tests.
Additionally, in this award we report the use of the same technique of the local photo-polymer deposition for the fabrication of 3D microfluidic paper-based analytical devices (3D-µPADs) where the sample flows in both the lateral and vertical directions through multiple stacked layers of porous materials. This method is based again on the local acrylate-based negative photo-polymer deposition (deposition speed 30 mm/s) on a porous cellulose paper substrate followed by the subsequent exposure to a laser source, to stack several layers of cellulose paper and make 3D multilayer µPADs. With this technique, we provide a pathway to eliminate the limitations that other reported methods have during the fabrication of µPADs such as the need for multiple sophisticated alignments within adjoining layers and the use of additional tools to ensure adequate contact between the layers. In this study, we demonstrate the usefulness of our four layer 3D-µPAD for simultaneous detection of three analytes, namely BSA, glucose, nitrite spiked in artificial urine and also the pH of the tested sample, through single step colorimetric assays with the lower detectable values found at 0.4 mg/ml for BSA, 14.5 µg/ml for glucose and 2.5 µg/ml for nitrite. Our 3D-µPAD fabrication methodology can also be adapted in more complex analytical assays where multiple steps are needed for applications in point-of-care diagnostics.
Furthermore, through this award we report the use of the same laser-based patterning technique in the creation of paper-based flow-through filters that when combined with a traditional lateral flow device provide an alternative pathway for the detection of a pre-determined analyte over a wide concentration range. The laser-patterned approach was used to create photo-polymer structures that alter the porosity of the paper to produce porous flow-through filters, with controllable values of porosity. When located at the front end of a lateral flow device the flow-through filters were shown to block particles (of known sizes of 200 nm, 500 nm, 1000 nm and 3000 nm) that exceed the effective pore size of the filter while allowing smaller particles to flow through onto a lateral flow channel. The analyte detection is based on the use of a size-exclusive filter that retains a complex (>3 µm is size) formed by the binding of the target analyte with two antibodies each of which is tagged with different-sized labels (40 nm Au-nanoparticles and 3 µm latex beads), and which is larger than the effective pore size of the filter. This method was tested for the detection of C-reactive protein in a broad concentration range from 10 ng/ml to 100,000 ng/ml with a limit-of-detection found at 13 ng/ml and unlike other reported methods used for analyte detection, with this technique we are able to counter the Hook effect which is a limiting factor in many lateral flow assays.
Finally, in this award we explore the capability to incorporate a light responsive hydrogel in our paper-based devices. However, up to date we encounter several problems with the most important one being the poor responsivity of the light activated material upon exposure to light of certain wavelength.
Exploitation Route We believe that with the outcome of this funding we make one step forward and improve the functionality of paper-based devices for point-of-care diagnostic testing. The work of in-line filtration provides a simple, easy and inexpensive pathway for sample preparation where the separation of a complex sample to its various constituents is needed. This filtration method can be easily used in clinical diagnostics for the separation of plasma from whole human blood which is highly desired due to the fact that plasma is used for the detection of many diseases.
Furthermore, the reported method of 3D-µPADs can also be used for clinical diagnostics where the multiplex detection of various analytes within the same sample is needed. In this reported method we present only the results of a single step colorimetric assay for three given analytes, however it can be developed to detect any other analyte or even perform complex assays where mixing of different compounds is needed.
Last but not least, the developed flow-through filtration method can de used for the detection of various analytes in a broad concentration range, which is clinically significant as the different levels of certain analytes (e.g. CRP) are associated with different risk levels of diseases. Additionally, the reported method has the potential to be used as a tool to improve the performance (e.g. by increasing the sensitivity) of lateral flow assays.
Sectors Pharmaceuticals and Medical Biotechnology