Development of surface enhanced Raman spectroscopic silicon substrate microprobes for the investigation of subcutaneous lipid chemistry

Silicon substrate surface enhanced Raman spectroscopic microprobes (50 mum x 700 mum) are used to monitor the lipolysis of model sebum mixtures by Propionibacterium acnes (P. acnes). These bacteria produce a lipase that hydrolyzes triglycerides into their parent fatty acids. The roughened metal surfaces of these probes are first characterized by their fractal dimensions to assess surface-enhanced Raman activity before committing them to experiments. The fractal dimension is calculated using extended focus light reflectance microscopy. The technique is easily implemented and offers a nondestructive alternative SEM imaging.; Sebaceous lipids and fatty acids have characteristic SERS signals that make them resolvable in complex mixtures. The acids adsorb as their carboxylate. The symmetric carboxylate stretch (ca. 1390 cm-1) can be used as a diagnostic tool to indicate the presence of fatty acids in the system. The bacterial lipolysis is followed in a skin pore phantom. The phantom consists of a purpose-built syringe pump operating at physiological flow rates coupled to a 300 mum i.d. capillary. The silicon support allows tip flexibility that makes these probes ideal for insertion into small structures. P. acnes are immobilized on the inner walls of the capillary. The triglycerides are hydrolyzed as they are pumped through the phantom. The transformation is followed in vitro as changes in the SERS caused by lipolysis of triglyceride to free fatty acids.