Single-Step, Optical Biosensors for the Rapid and Sensitive Detection of Bacterial and Viral Pathogens

Abstract

This dissertation discusses the development of inexpensive, easy-to-use, and field-deployable diagnostic techniques and devices for the early detection of various pathogens, commonly found in clinical samples and contaminated food and water. Infectious diseases account for about 90% of world health problems, killing approximately 14 million people annually, the majority of which reside in developing countries. In 2012, the World Health Organization (WHO) published data on the top 10 causes of death across the globe. Although communicable disease is a prevalent cause of fatality, both low-income and high-income countries, pathogen species and transmission are very different. Nearly 60% of deaths in developing countries are caused by food, water, air or blood-borne pathogens. The most prevalent illnesses are diarrheal disease, malaria, and HIV/AIDS. By contrast, the leading causes of death in developed countries (heart disease, cancer, and stroke) are not communicable and are often preventable. However, there is an increasing need for the development of rapid and accurate methods for pathogen identification in clinical samples, due to the growing prevalence of antibiotic-resistant strains. Incorrect, or unneeded antibiotic therapies result in the evolution of extremely aggressive nosocomial (hospital-acquired) infections, such as methicillin- (MRSA) and vancomycin-resistant Staphylococcus aureus (VRSA). The implementation of rapid, easy to use and cost-effective diagnostics will reduce the frequency of pathogen-related deaths in underdeveloped countries, and improve targeted antibiotic treatment in hospital settings, thus decreasing the potential development of more treatment-resistant "super bugs". This research includes novel techniques utilizing two major sensing modalities: serological (i.e. immunological), and nucleic acid amplification testing (NAATs). We first developed a highly sensitive (limit-of-detection = 100 CFU mL-1) particle immunoassay that takes advantage of elastic and inelastic light scatter phenomena, for optical detection of target antigens. This assay is performed upon a unique nanofibrous substrate that promotes multiplexing on a user-friendly platform. We then developed a novel technique, termed emulsion loop-mediated isothermal amplification (eLAMP), in which the target amplicon is detected in real-time, again utilizing light scattering detection and quantification. Both techniques require no sample pre-treatments, and can be combined with smartphone imaging for detection of targets in under 15 minutes. These methods have the potential to improve the speed and sensitivity of early pathogenic identification, thus leading to a reduction in preventative deaths and a decrease in global economic costs associated with infectious disease in clinical and other settings.