Interferometric optical sensors based on porous silicon grafted with styrenic moieties for highly enhanced VOC detection

The majority of volatile organic compounds (VOCs) are hazardous pollutants that pose significant risks to human health and the environment. Thus, the development of a smart sensing system for the early identification of VOCs would be in high demand, particularly those enabling rapid detection with high sensitivity and long-term stability. In this study, an interferometric optical sensor was rationally devised through the facile non-atmospheric thermolysis of polystyrene (PS) pre-loaded into a porous silicon (pSi) template prepared via electrochemical anodization. During the thermolysis, styrenic carbon fragments were covalently grafted onto the pore walls of pSi to form a PS-grafted pSi composite (pSi-PS). This composite was subsequently utilized as a scaffold for grafting poly(4-chlorostyrene) (PPCS) via a second thermolysis step, consequently yielding the double-grafted pSi composite (pSi-PS-PPCS). The obtained samples were subsequently employed as an interferometric optical sensor for the sensitive detection of various VOCs, including ethanol, isopropanol, isobutanol, n-hexane, methyl ethyl ketone (M. E. K.), and ethyl acetate. The sensitivity of the optical response to those VOCs exhibited the following order: n-hexane < ethanol < isopropanol < M. E. K. < isobutanol < ethyl acetate. Notably, the double-grafted pSi-PS-PPCS sensor exhibited significantly higher sensitivity than both pristine pSi and single-grafted pSi-PS. The highly enhanced sensitivity of pSi-PS-PPCS, particularly toward isobutanol and ethyl acetate vapors, was mainly attributed to strong intermolecular interactions (such as hydrophobic, hydrogen bonding effects and/or strong interplay of π–π interactions) between the VOC analytes and the chlorine-substituted phenyl moieties of the grafted PPCS.