Search

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.

A recently developed blood typing diagnostic based on a polyester thread substrate has shown great promise for use in medical emergencies and in impoverished regions. The device is easy to use and transport, while also being inexpensive, accurate, and rapid. This study used a fluorescent confocal microscope to delve deeper into how red blood cells were behaving within the polyester thread-based diagnostic at the cellular level, and how plasma separation could be made to visibly occur on the thread, making it possible to identify blood type in a single step. Red blood cells were stained and the plasma phase dyed with fluorescent compounds to enable them to be visualised under the confocal microscope at high magnification. The mechanisms uncovered were in surprising contrast with those found for a similar, paper-based method. Red blood cell aggregates did not flow over each other within the thread substrate as expected, but suffered from a restriction to their flow which resulted in the chromatographic separation of the RBCs from the liquid phase of the blood. It is hoped that these results will lead to the optimisation of the method to enable more accurate and sensitive detection, increasing the range of blood systems that can be detected usc Refereed/Peer-reviewed

Cellulose paper specimens with and without surface modification were compared in order to study their physicochemical compatibility with quantum dots (QDs) for biochemical sensing applications. Silane and chitosan modification methods were applied. The distribution of QDs deposited on untreated paper and papers modified with silane and chitosan were investigated in order to understand the interaction between QDs and fibre. Modified papers were shown to significantly reduce the undesirable redistribution of QDs during paper drying. The retention ability and thermal resistance of QDs to the loss of fluorescence on modified papers were also studied for the purpose of determining the most suitable paper surface modification for developing QD-Paper-based analytical devices (QD-PADs). Furthermore, chitosan-modified paper was used to design QD-PADs to quantify glucose concentration in aqueous samples; the quenching effect of the enzymatic product on the fluorescent emission of QDs was used as the indicator system. The change of fluorescence of QDs was measured by a simple in-house constructed fluorescence imaging system. The detection limit of glucose was 5 mg/dL, which is comparable with other reported paper sensors for detection of glucose. Refereed/Peer-reviewed