Unveiling polymer drying dynamics locally via a plasmonic lab-on-fiber probe

Understanding the drying process of polymer solutions is crucial for diverse fundamental research and practical applications. Despite the widely adopted physical, chemical, and optical techniques, monitoring the drying process of polymer solutions in situ with a high spatial resolution is still challenging. Here, we demonstrate a lab-on-fiber probe by functionalizing plasmonic nanostructures onto optical fiber tip. Taking advantage of the local sensitivity and real-time operation of the fiber probe, the drying dynamics of polymer solutions are locally unveiled in situ and only a small volume of sample is required. Through real-time mode tracking of the fiber probe, we infer local variations in dielectric constant and structural shrinkage of the polymer matrix during solvent evaporating which cannot be fully resolved before. A distinct turning point in spectral responses is observed attributed to the competition between the local refractive index increase and the array pitch reduction induced by polymer shrinkage. We further extract the dependence of the turning point on solution concentrations. Numerical analyses verify the experimental observations. The plasmonic lab-on-fiber provides a novel platform for exploring dynamic characteristics of versatile materials when local variations are interested.