Optical Microbubble Resonators as Emerging Tools for Environmental Sensing: the "Safe Water" Project

In the last decades, the rapid growth of the world population and the increase in industrial and agricultural activities have contributed to a continuous depletion of the water resources quality, endangering the health of individual citizens especially when water is destined for human consumption. As highlighted in recent European directives on the quality and monitoring of the water environments (EU 2013/39, EU 2015/495 and EU 2018/840), particular attention is paid to emerging microcontaminants (EMCs such as drugs, hormones, personal care and life-style products), which, even if present in traces in the aqueous matrices, are poorly biodegradable and difficult to remove through conventional treatment processes [1,2]. Then, once these contaminants are entered within these aqueous matrices, they remain there and their presence can cause known or suspected adverse ecological and/or human health effects [3]. Therefore, it becomes essential to have an analytical method that can detect the presence of these pollutants at low concentrations. Based on the synergy among different competences of the consortium partners in the field of chemistry, electronics, photonics, microfluidics, the aim of the SAFE WATER project is the realization of a new portable optical instrument for in situ and multiplexing detection of different EMCs. The core of the device consists in the use of whispering gallery mode (WGM) optical microbubble resonators (OMBRs), considered as a localized swelling induced in a silica microcapillary by a suitable fabrication process [4]. These hollow-core resonant microcavities support the exclusive properties of the WGM resonators (i.e.: small mode volumes, high Q factor values, typically > 107 in air, high analytical sensitivity and extremely low limit of detection LOD up to pg/L) with an embedded microfuidics and their sensing principle is generally based on a label-free strategy [5]. The achievement of this innovative monitoring system requires the realization of the following objectives: i) development of an OMBR matrix, integrated on a chip, as an optical transduction element capable of detecting the selected EMCs in parallel; ii) development of chemical/biochemical functionalization protocols in order to modify the OMBR inner surface using highly specific chemical biochemical receptors for the selected EMCs; iii) development of the microfluidic circuit for mixing and sending the liquid sample with its chemical reagents to the OMBR matrix; iv) development of the optoelectronic system for interrogation of the OMBR matrix and for data processing and management. In this presentation the general aspects of the project and its progress will be presented and discussed. References: [1] R. D. Richardson et al. Anal. Chem., 2016, 88, 546-582. [2]R. Meffe et al. Sci. Total Environ., 2014, 481, 280-295. [3] L. Araujo et al. J. Environ. Hum., 2014, 1, 32-38. [4] S. Berneschi et al. Opt. Lett., 2011, 36, 3521-3523. [5] Z. Guo et al. Opt. Express, 2019, 27, 12424-12435.