Limitations of the pH sensitive probe seminapthorhodafluor
Shanahan, Rachel A.
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By incorporating proteinaceous 'drugs', such as cytokines and growth factors, into biodegradable polymers (BP), one can deliver these to sustain and accelerate wound repair. However, as the BP degrades, the local, microscopic 'pH' within the BP, near the drugs could change significantly and adversely affect the drug (e.g., denature it). What is the local pH surrounding a protein within such a BP? A popular method in determining the pH of such a system involves the use of a pH-responsive probe and an aqueous buffer calibration curve. Is this method reliable? In the current research we have studied the effects of tethering, buffer ionic strength, and solvent polarity on the pH probe SNARF-1. Thin films of poly (D,L-lactic-co-glycolic acid) (PLGA), poly (-L-lactic acid) (PLLA), poly (glycolic acid), and polyethylene glycol (PEG) were fabricated and doped with SNARF-1. An aqueous buffer calibration curve was then used to determine the pH within the thin films. To explore the local pH surrounding a protein we have covalently attached a pH-responsive fluorescent probe (seminaphthorhodafluror, SNARF) to a model protein (human serum albumin, HSA). The fluorescence response from the SNARF-HSA provides an estimate on the local 'pH' surrounding the HSA. Results from these studies illustrate SNARF's limitations.