Optofluidic Waveguides for the Label-Free Study of Silk Protein Aggregates

Methods for studying protein aggregation are crucial to understanding the associated disease pathologies and for functional biomaterial synthesis in nature and in the laboratory. The ideal measurement platform is low-volume, label-free, and noncontact, as well as easily integrated into continuous-flow microfluidic experiments to provide scalability. Current approaches realize only a subset of these requirements. Here, we demonstrate a new technique for studying protein aggregates and <i>in situ</i> aggregation within hollow-core photonic crystal fibers. These optofluidic waveguides allow us to perform continuous-flow microfluidic label-free analysis of silk fibroin protein in the form of preformed nanofibrillar aggregates and on the native protein as it undergoes aggregation <i>in situ</i> in the optofluidic waveguide. We demonstrate label-free ultraviolet absorbance measurements on both calibration-standard nanospheres and silk fibroin aggregates as well as monitoring the aggregation of native silk fibroin protein solution via simultaneous ultraviolet absorbance and intrinsic fluorescence measurements <i>in situ</i>. This technique forms a platform for the study of protein aggregation that is low volume, label-free, and optical, thereby providing a valuable optofluidic tool for a range of protein biophysics.