Integratable opto-microfluidic devices for sensitive detection of bio-analytes

The expensive fabrication of current optical microfluidic devices is a barrier to the successful implementation of these devices in low-cost, high-sensitivity biosensing systems. Organic photodiodes (OPDs) have great potential for application as photodetectors in integrated microfluidic devices due to their uncomplicated optical alignment, thin device architecture, precise control of the active area and simple device fabrication onto glass or polymer substrates. Recent developments in OPDs have resulted in new photoactive materials, such as poly[N-9´-heptadecanyl-2,7-carbazolealt- 5,5-(4´,7´-di-2-thienyl-2´,1´,3´-benzothiadiazole)] (PCDTBT), that have improved detectivity and stability. These unique optoelectronic characteristics enhance the detection sensitivity of OPD-integrated microfluidic biosensors while maintaining simple, inexpensive device fabrication. To realise point-of-care (POC) detection of bio-analytes, the complexity of optical instrumentation must be minimised. Chemiluminescence (CL) offers an attractive solution to microfluidic analyte detection because it precludes the use of excitation light sources and emission filters. However, the low intensity of light emitted from CL reactions demands the use of highly sensitive photodetectors. Therefore, investigations of strategies to enhance CL assays and the combination of CL with PCDTBT-based detectors are the motivating factors for this work. Additionally, the enrichment of target organisms using a high-efficiency recovery method provides a route to optically detect bio-analytes at concentrations as low as hundreds or tens of organisms in a sample. This doctoral thesis focuses on the following challenges: (i) demonstrate sensitive CL detection using a PCDTBT-based photodetector, (ii) investigate the integration of multiple OPDs in high-throughput microfluidic chips to realise multiplexed CL detection and (iii) explore methods for enhancing the sensitivity of opto-microfluidic detection. The progress made towards addressing these challenges is summarised below. Article I reported the design and fabrication of an integrated optical microfluidic device employing a PCDTBT-based photodetector. The response of the OPD to CL light was enhanced by optimising the thickness of the photoactive layer and the hole transport layer. The current-voltage response due to detection of a medically relevant protein analyte was characterised. Further demonstration of quantitative CL detection with the optimised OPD was conducted in Article II. The opto-microfluidic device was found to exhibit a linear response over four orders of magnitude, with a detection limit of approximately tens of picograms per millilitre and a detection sensitivity of approximately hundreds of picograms per millilitre. Moreover, high reproducibility and specificity to CL detection was observed, indicating the capability of the integrated OPD for POC applications. Article III developed a multiplexed CL detection platform by integrating multiple PCDTBT OPDs with a high-throughput microfluidic chip. The fabricated device is compatible with mass production methods. The analytical performance of the OPD pixel was characterised for the detection of individual waterborne pathogens. Article IV performed a series of parallel CL detection experiments to demonstrate the simultaneous detection of multiple waterborne pathogens in one water sample. Rapid multiplexed analysis and extension to complex samples were demonstrated. Article V investigated the enhancement of CL detection by incorporating standard gold nanoparticles into a simple, inexpensive opto-microfluidic device. The limit of detection for an environmentally relevant protein analyte was ∼200 times lower than previously reported CL sensors using other OPD designs. The remarkable stability and specific detectivity of the PCDTBT OPD was also characterised. Article VI presented a high-efficiency bio-analyte recovery system by incorporating multiple counter-flow filtration units. A high concentrating ratio was obtained with a short processing time. The filtration system showed recovery efficiencies above 80% for waterborne protozoa at environmentally realistic concentrations in real environmental water samples. A compact filter made of multiple counter-flow units arranged into a cascade-like structure is also shown. The separation of water particulates from the target protozoan organisms was addressed to enhance the recovery performance of conventionally used filters

Roadmap on printable electronic materials for next-generation sensors

The dissemination of sensors is key to realizing a sustainable, ‘intelligent’ world, where everyday objects and environments are equipped with sensing capabilities to advance the sustainability and quality of our lives—e.g., via smart homes, smart cities, smart healthcare, smart logistics, Industry 4.0, and precision agriculture. The realization of the full potential of these applications critically depends on the availability of easy-to-make, low-cost sensor technologies. Sensors based on printable electronic materials offer the ideal platform: they can be fabricated through simple methods (e.g., printing and coating) and are compatible with high-throughput roll-to-roll processing. Moreover, printable electronic materials often allow the fabrication of sensors on flexible/stretchable/biodegradable substrates, thereby enabling the deployment of sensors in unconventional settings. Fulfilling the promise of printable electronic materials for sensing will require materials and device innovations to enhance their ability to transduce external stimuli—light, ionizing radiation, pressure, strain, force, temperature, gas, vapours, humidity, and other chemical and biological analytes. This Roadmap brings together the viewpoints of experts in various printable sensing materials—and devices thereof—to provide insights into the status and outlook of the field. Alongside recent materials and device innovations, the roadmap discusses the key outstanding challenges pertaining to each printable sensing technology. Finally, the Roadmap points to promising directions to overcome these challenges and thus enable ubiquitous sensing for a sustainable, ‘intelligent’ world