Nanomaterial-Supported Enzymes for Water Purification and Monitoring in Point-of-Use Water Supply Systems.

Abstract

Increasing pollution of global water sources and challenges in rapid detection and treatment of the wide range of contaminants pose considerable burdens on public health. The issue is particularly critical in rural areas, where building of centralized water treatment systems and pipe infrastructure to connect dispersed populations is not always practical. Point-of-use (POU) water supply systems provide cost-effective and energy-efficient approaches to store, treat, and monitor the quality of water. Currently available POU systems have limited success in dealing with the portfolio of emerging contaminants, particularly those present at trace concentrations. A site-to-site variation in contaminant species and concentrations also requires versatile POU systems to detect and treat contaminants and provide on-demand clean water. Among different technologies for developing rapid and sensitive water purification processes and sensors, enzymes offer one of the potential solutions because of their strong activity and selectivity toward chemical substrates. Many enzyme-nanomaterial composites have recently been developed that enhance enzymes' stability and activity and expand their functionality, thus facilitating the application of nanosupported enzymes in advanced POU systems. In this Account, we highlight the strengths and limitations of nanosupported enzymes for their potential applications in POU systems for water treatment as well as detection of contaminants, even at trace levels. We first summarize the mechanisms by which silica, carbon, and metallic nanosupports improve enzyme stability, selectivity, and catalysis. The unique immobilization properties and potential advantages of novel bioderived nanosupports over non-bioderived nanomaterials are emphasized. We illustrate prospective applications of nanosupported enzymes in POU systems with different roles: water purification, disinfection, and contaminant sensing. For each type of application, nanosupported enzymes offer higher performance than free enzymes. Nanosupports prolong enzymes' lifetimes and improve the rates of contaminant removal by concentrating contaminants near the enzymes. Nanosupports also stabilize antimicrobial enzymes while facilitating their attachment to bacterial surfaces, thereby increasing their potential uses for disinfection and prevention of biofouling in water purification and storage devices. As enzyme-based electrochemical sensors rely on electrochemical reactions of enzymatically generated species, the ability of conductive nanosupports to enhance enzyme activity and stability and to promote transfer of electrons onto the electrode greatly improves the sensitivity and durability of electroenzymatic contaminant sensors. Despite the promising results in laboratory settings, the application of nanosupported enzymes in real-world POU systems requires the implementation of multiple enzyme combinations and strategies for minimizing health risks associated with unintended releases of nanomaterials. Finally, we identify multidisciplinary research gaps in the development of nanosupported enzyme treatment systems and provide frameworks for the early adopters to make informed decisions on whether and how to use such POU systems.