Abstract
Integrating multi-responsive polymers such as microgels onto optical fiber tips, in a controlled fashion, enables unprecedented functionalities to Lab-on-fiber optrodes. The creation of a uniform microgel monolayer with a specific coverage factor is crucial for enhancing the probes responsivity to a pre-defined target parameter. Here we report a reliable fabrication strategy, based on the dip coating technique, for the controlled realization of microgel monolayer onto unconventional substrates, such as the optical fiber tip. The latter was previously covered by a plasmonic nanostructure to make it sensitive to superficial environment changes. Microgels have been prepared using specific Poly(N-isopropylacrylamide)-based monomers that enable bulky size changes in response to both temperature and pH variations. The formation of the microgel monolayer is efficiently controlled through the selection of suitable operating pH, temperature and concentration of particle dispersions used during the dipping procedure. The effect of each parameter has been evaluated, and the validity of our procedure is confirmed by means of both morphological and optical characterizations. We demonstrate that when the coverage factor exceeds 90%, the probe responsivity to microgels swelling/collapsing is significantly improved. Our study opens new paradigms for the development of engineered microgels assisted Lab-on-Fiber probes for biochemical applications.
Highlights
Lab-on-fiber (LOF) optrodes enable physical, chemical and biological measurements approaches where the interaction between the parameter to be measured and the light takes place either within the optical fiber itself (Lab-in-fiber) or within a structure which is totally integrated around (Lab-around-fiber) or onto the fiber tip (Lab-on-tip) [1,2]
The strategy adopted in this work is based on our previous observations concerning the effect of MGs concentrations on the resulting film properties; larger concentrations give rise to films characterized by higher degrees of uniformity, density, and compactness. By taking this into account, here we first investigate the effect of temperature and physical (temperature) and chemical (pH) for finding the optimum combination of parameters guaranteeing the maximum coverage factor
The method allows the deposition of an active monolayer with a specific coverage factor, preventing particles aggregation, which mostly lead to weak process repeatability and random response
Summary
Lab-on-fiber (LOF) optrodes enable physical, chemical and biological measurements approaches where the interaction between the parameter to be measured and the light takes place either within the optical fiber itself (Lab-in-fiber) or within a structure which is totally integrated around (Lab-around-fiber) or onto the fiber tip (Lab-on-tip) [1,2]. For example, provide a platform where it is possible to realize nanostructures, ranging from semiconductor photonic crystals to plasmonic devices compatible with the fiber dimensions, which precisely confine highly concentrated optical fields and facilitate the interaction of these fields with local physical, chemical and biological variations [3,4]. In this way, fiber-coupled spectroscopic measurements can be performed within the fiber optrode itself, providing information about superficial environment changes even at sub-wavelength scale [5,6]. We have found that, by changing MGs concentration, it is possible to control the limit of detection, tune the working range as well as the response time of the probe, giving rise to advanced optrodes which can be reconfigured depending on the specific application [11]
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