Low‚ÄövÑv´cost 3D printed devices for in field environmental monitoring

The goal of environmental monitoring is to assess the quality of the environment over time and prevent potential risks to the ecosystem and human health around the world. Since the excess or deficiency of soil and water components can cause contaminated and/or unbalanced systems, they should be carefully monitored and managed. Many knowledge gaps continue to significantly limit the development of application and monitoring devices to improve the accuracy, affordability, and usability of monitoring programmes. Choosing proper analytical methods from a vast array of them is a prerequisite that is dependent on the analysis request, but it is also critical to follow standard procedure. When using advanced laboratory techniques, the initial phase of the analysis is sample preparation, which involves removing interfering components and enriching the target analyte to detectable levels. the sample preparation is time-consuming and labour-expensive, and it comes with a high risk of analyte loss, sample contamination and/or degradation. 3D printing techniques, which are accessible and affordable, have the ability to fabricate highly complex devices with high levels of integration and automation to create portable and compact devices known as \lab on a chip\". This includes those that allow analysis of non-treated samples for environmental analysis saving time and money and eliminating the risks associated with sample pretreatment and importantly providing analytical results almost immediately. This thesis focuses on a novel and smart method of integrating functional parts into hundreds of microfluidic devices in a single run demonstrating the potential for small-scale manufacturing of user-friendly devices for direct environmental analysis in-field. Chapter 1 offers an overview of the analytical method for analysing environmental samples. It begins with discussion of laboratory instruments used for soil and water analysis by various spectrophotometric techniques such as Inductively coupled plasma mass spectrometry (ICP-MS) atomic absorption spectroscopy (AAS) x-ray fluorescence (XRF) etc as well as a brief introduction to the electrode pH meter. This is followed by an overview of portable techniques focusing on various microfluidic fabrication approaches such as polydimethylsiloxane (PDMS) paper-based analytical devices (˜í¬¿PADs) and 3D printing. The principles applications benefits and drawbacks of the current types of 3D print technologies such as Stereolithography (SLA) Fused deposition modelling (FDM) Inkjet 3D printing (i3DP) any many more for microfluidic fabrication are comprehensively discussed as well as their suitability for complex and integrated microfluidic manufacturing. In Chapter 2 a porous structure was integrated between two chambers of a single-material 3D printed device exploiting a phenomenon that occurs at the interface between the build and support material of a poly jet printer. The porous structure was used as a diffusionbased filter to isolate particulate matter (larger than 15 ˜í¬¿m) of the sample which enabled the device to be used for colourimetric detection. The application was for Fe3+ quantification in soil slurry and river water using a simple sample-in/answer-out method with no sample preparation steps. The Fe3\\(^+\\) concentration indicated close agreement (95%) between the infield device and Sector Field inductively coupled plasma - mass spectrometry (ICP-MS). This demonstrates the potential of the 3D printed device for portable affordable and userfriendly in-field analysis. In Chapter 3 the effects of various thicknesses (100 to 500 ˜í¬¿m) and printing orientations (0¬¨‚àû to 90¬¨‚àû) on the porosity and the physical properties of printed porous structure made in chapter 1 were investigated. It was discovered that the pore size varied with fabrication degree suggesting that the structure's characteristics gradually changed from 0¬¨‚àû with no pores to highly porous at 90¬¨‚àû. More specifically a 150 ˜í¬¿m structure printed at 90¬¨‚àûorientation isolated particles as small as 15 ˜í¬¿m in size while a structure printed at 30orientation removed particles as large as 45 ˜í¬¿m. Furthermore using voltage structures thicker than 500 ˜í¬¿m were able to filter particles as small as 1 ˜í¬¿m. Scanning electron microscopy (SEM) fluorescent and light microscopy results revealed that structures printed in 150 ˜í¬¿m and thicker have more dimensional accuracy and close to CAD software-based designs with significantly higher stability. Based on the results of the previous chapters Chapter 4 describes an integrated fluidic device that could withstand moderate hand pressure for particulate removal and measurement of pH. The device's utility was demonstrated for in-field colourimetric pH measurements within 1 min demonstrating the potential for rapid and low-cost in-field analysis. The pH indicator is placed in the device and the pH is determined by converting images captured with a smartphone camera to a chromaticity diagram in the International Commission on Illumination (CIE) 1931 colour space and comparing it to calibration standards. The 3D printed devices are capable of filtering particulate matter from the sample before mixing with an indicator avoiding optical interferences. Different environmental samples with a wide pH range (3-10) can be measured rapidly within 1 min. In addition to above one hundred thirty-six devices could be printed in 136 minutes with a print time of about 1 minute and a cost of $0.6 each demonstrating the potential for lowcost small-scale manufacturing of POC devices."