Advances in polymeric nanosensor technology for biological analysis

Abstract

Polymeric nanosensors are a next-generation sensing technology with the promise to improve the way that scientists, engineers, and healthcare professionals collect analyte data. They have a diameter on the order of 100 nanometers, a polyethylene glycol based lipid coating for biocompatibility, and they utilize luminescence techniques for signal transduction which allows for remote and non-invasive sensor read-outs. This makes them ideal for complex in vitro and in vivo applications in biological environments where the currently available sensor technology falls short. However, being an emerging technology, more research and development is needed to address several current limitations. This thesis presents advancements in polymeric nanosensor technology in three key areas of need: (1) attachment strategies and range control methods in enzyme-based detection mechanisms (2) tools for dynamic range control and extension for ionophore-based detection mechanisms, and (3) methods for background noise elimination. These areas of need are addressed through three reports of technological innovation. The first details a novel method for attaching glucose oxidase to polymeric nanosensors through a biotin/avidin approach, with broader implications for any type of enzyme-based (biomolecule-detecting) polymeric nanosensor. It also demonstrates three methods increasing the apparent enzyme activity associated with each nanoparticle and therefore shifting the response range toward lower glucose concentrations: by tuning the amount of biotin groups on the nanosensor surface, by adjusting the amount of biotinylated-glucose oxidase used during synthesis, and by adjusting the amount of avidin linkers used during synthesis. More biotin groups on the nanosensor surface and more biotinylated-glucose oxidase during synthesis both led to lower response ranges, while an optimal amount of avidin (0.22 mg) lead to the lowest response range. The second report details two designs for dual indicator use in ionophore-based (ion-detecting) polymeric nanosensors with supporting theoretical response models for each. This tool is shown control the sensor LogEC50 over 1.5 orders of magnitude and expand the total range span by 47%. The third report details a bulk optode membrane sensor that incorporates persistent luminescent microparticles into an ionophore-based mechanism for sodium detection. The signal from this ‘glow sensor’ can avoid background noise from biological autofluorescence by programming a delay in between sensor excitation and signal collection. The sensor is also shown to reversibly respond to sodium with a response range of 2.4 – 414 mM sodium and a LogEC50 of 52 mM sodium, with selectivity coefficients of -2.2 and -3.3 over the potentially interfering cations potassium and lithium, respectively, and with a shelf-life of at least 14 days. These three developments solve key issues and help push polymeric-nanosensors toward application in real-world settings.