MTL Annual Research Report 2011

Figure 1: Scheme of the microworm fabrication process. The bare AAO template (a) is first conformally coated with the iCVD hydrogel layer (b). The optode solution is filled in the pores of the template (c) and the excess optode and the hydrogel layer are etched away (d). A final hydrogel layer is deposited on both sides of the template to cap the optode (e). As the final step, the membrane is dipped in HCl solution to etch the AAO template and release the microworms (f).

The development of biosensors is considered a focal subject for clinical applications. The main efforts are being addressed towards in-vivo continuous monitoring of different analytes. Implantation of nanoparticles, consisting of an optode embedded in a polymer, for minimally invasive physiological monitoring has been already tested ^[1] . Nevertheless, the small size of the probes also results in them diffusing rapidly away from the desired location. In this work, we present a novel method to fabricate cylindrical-shape sensors (microworms). Microworms combine a long axis (tens of microns), which provides a higher hydrodynamic radius to prevent diffusion, with a nanostructured shell, which facilitates the diffusion of the analyte inside the cylinder to interact with a specific optode. The fabrication of the microworm sensors, using an anodic aluminum oxide (AAO) membrane as template, is depicted in Figure 1. The biocompatible hydrogel thin layer (50 nm) is deposited on the inner walls of the membrane by initiated chemical vapor deposition (iCVD). iCVD is a solvent-free polymerization method, which yields conformal coatings ^[2] with a full retention of functionality ^[3] . Therefore, the optode is fully encapsulated in the hydrogel layer to study its performance as sensor. These microworms can be implanted under the skin to monitor multiple types of ions and molecules by tracking the changes in the fluorescence signal. Recently, a sensor for in-vivo monitoring of sodium has been successfully created ^[4] . In addition, the latest investigations are being focused on the fabrication of microworm sensors for glucose detection.