A Critical Review of Protein Conjugation Strategies for Environmental Applications: Challenges and Opportunities

Functional proteins combine molecular recognition, catalytic activity, and structural tunability, supporting applications in pollutant transformation, sensing, resource recovery, and disinfection. However, practical performance can be limited by deactivation and difficulties in recovering and reusing free proteins under operating conditions. Immobilizing proteins onto solid substrates can improve recovery and reuse, although the effects on stability and activity depend on the preparation; performance depends on protein loading, attachment site, structural integrity, functional-site accessibility, and the surrounding microenvironment. Site-specific conjugation can reduce attachment heterogeneity when a unique or selectively exposed handle is available; preserving structure and function also depends on the immobilization conditions. In this review, we frame protein immobilization as interfacial engineering and examine how chemical covalent conjugation, including both site-directed strategies and random coupling, governs function retention across four representative classes of environmentally relevant proteins: catalytic, sensing, separation, and antimicrobial. For each class, we connect molecular-level conjugation chemistry to macroscopic performance, evaluating how linkage site, conjugation strategy, spacer design, and support chemistry influence the activity, selectivity, and stability of immobilized proteins. Finally, we outline pathways toward robust protein–material interfaces and discuss remaining limitations. This review provides a rational design framework for developing selective, efficient, and sustainable protein-enabled technologies for environmental applications. We anticipate that it will inspire interdisciplinary collaboration among researchers in protein engineering and material design to address pressing environmental challenges.