pH SENSING AND IMAGING WITH NANOPARTICLES AND IMPLANTABLE FILMS

pH is a very important parameter in biological systems. Monitoring pH in situ may provide useful information for studying pH regulated cellular events, diagnosing diseases and assessing treatment efficacy. Various strategies have been introduced for developing pH sensors. However, it is still challenging to monitor pH in biological systems with high specificity, especially through thick tissue. In this dissertation, we describe three types of pH sensors which are used to noninvasively monitor pH in living cells, monitor and map bacterial growth caused pH variation through thick tissue with minimal autofluorescence background. In Chapter 2, a pH nanosensor with high specificity and sensitivity is developed based on surface-enhanced Raman scattering by encapsulating 4-mercaptobezonic acid functionalized silver nanoparticles in a proton permeable silica shell. The performance of silica protected nanosensor against aggregation and biomolecular interference is investigated. The nanosensors are introduced to report intracellular pH in living macrophages. In Chapter 3, a pH sensor film is designed for monitoring pH variation on a surface through thick tissue in real time. The pH sensor film is composed of a film of upconverting nanoparticles which functions as a local light source and a thin layer of pH indicator which modulates the luminescence in a pH dependent way. Upconverting nanoparticles are excited by near infrared laser (980 nm) which allows high tissue penetration depth and avoids autofluorescence from tissue. The pH sensor film is applied to monitor bacterial growth caused pH decrease at the interface of sensor film and trypic soy agar in real time through 6 mm porcine tissue. In Chapter 4, a pH sensor film with the ability to image pH variation through thick tissue with high spatial resolution is designed utilizing X-ray radioluminescent particles as a local light source. pH calibration curves are generated by taking the ratio of peak intensity at 620 nm over that at 700 nm. By creating a localized reference region on the sensor film, the tissue effect on the ratio of the two peaks is adjusted. The pH sensor film is used to monitor bacterial growth and study antibiotic effect with millimeter of spatial resolution which is primarily determined by the width of the X-ray beam. Both upconverting luminescence and X-ray radioluminesce based pH sensors have the potential to revolutionize the ability to diagnose and assess treatment for implanted medical devices associated bacterial infection