Design of paper sensors for biochemical applications

Paper-based analytical devices have attracted wide interest from researchers and commercial developers for various biomedical and chemical applications. The potential of paper-based analytical platform to deliver affordable, reliable and user-friendly diagnostic devices for people living in less-industrialized countries and remote regions has become increasingly clear. The motivation of this research project is to develop robust and reproducible paper-based sensors, and to explore new strategies to enhance the capability of paper-based sensors as diagnostic platforms. Most current paper-based diagnostic devices designed for developing areas have focused on affordable, sensitive, specific and rapid (ASSR) features; however, for utilization in developing areas, paper devices are not easily operated by non-professional and untrained personnel, and do not fulfil the requirements of being user-friendly, equipment-free or with minimum equipment and delivered to end-users (UED). Therefore, the utilization of various technologies to develop ASSR and UED paper devices is the ultimate goal of this project. This thesis reports four paper sensor design studies, which represent two different development stages of the paper sensor. One is sensor design at a relatively mature development stage, which requires attention to the feasibility of commercialization of the sensor; the other is sensor design at an early development stage, which focuses on the potential for increasing the functionalities of the sensor. Although at different stages of sensor development, affordable, sensitive, specific, rapid, user-friendly, equipment-free or with minimum equipment and delivered to end-users (ASSURED) features are the guideline for all the designs. The key point of the paper sensor developed at a relatively mature development stage is to ensure that the device is compatible with the point-of-care diagnostic market. At this stage, the UED features of the device are particularly important in order for it to gain acceptance by the end-users. The paper sensor developed at this stage in this thesis is integrated with world-wide smartphone technology. The device is rapidly read by a smartphone and easy for users to operate. With the help of smartphone technology, users can quickly and simply obtain the test results without the need of further interpretation. The results can also be stored and transmitted conveniently by users and other professionals. In addition, strategies for retaining the bio-stability of the paper sensor are proposed in order to enable the device to function reliably when delivered to users. Two feasible strategies, the addition of additives and freeze drying, are reported in this project to improve the longevity of the paper sensors. The other studies carried out at the early stage of sensor development emphasize the improvement of the functionalities and enhancing the capabilities of paper sensors as diagnostic platforms. Specifically, the excellent properties of quantum dot nanoparticles and biomolecules are introduced to paper devices using paper modification strategies in this project. Cost-effective modification strategies are utilized in these studies, making the devices affordable and easily-accessible. The devices with add-in properties demonstrated high sensitivity and selectivity for sensing applications. The stability of these paper devices was proven to be maintained over a period of time. However, this part of the preliminary trials is appropriate for laboratory applications and will need to be enhanced to suit the original motivation of paper devices for field settings and remote areas. The applications performed by the sensor design in this project make the test immediately and reliably available to users. The sensor design studies explored in this project establish the ASSURED platform which shows great potential for use in resource-limited settings. These studies also show enormous potential for integration with future work, which would strongly drive the development of products for point-of-care, telemedicine and biochemical sensing.