Recent advances in surface chemical modifications of paper-based analytical platforms

Recently, paper-based analytical devices (PADs) have gained significant interest in the fields of analytical and bioanalytical chemistry. Being able to meet the criteria for smart and sustainable analytical devices, particularly cost-effectiveness, user-friendliness, fast analysis, and portability, PADs have proven valuable for point-of-care diagnostics, environmental monitoring, food safety inspection, and illicit drug detection. The main reason for the popularity of PADs is that they are based on papers as smart solid substrates, which exhibit unique chemical and physical properties. The PADs' flexibility allows for easy sample loading and surface modifications, enabling tailored performance. Various approaches have been developed to modify the surfaces of PADs to endow them with specific properties. The overreaching goal of this review is to provide, after a brief introduction to the types, chemistry, and properties of paper, a comprehensive examination of the most successful approaches used to modify PADs with organic, inorganic, organic-inorganic hybrid, and biological materials for a variety of (bio) chemical analytes. Furthermore, it offers a deep understanding of the interface between PADs and the (nano) materials. It elucidates how incorporating different materials onto the paper substrate influences the performance and sensitivity of PADs in detecting target analytes. It discusses the sustainability criteria fulfilled during the preparation of PADs and the current challenges related to their commercialization potential. Finally, it outlines future research directions, highlighting the need to address current challenges and suggesting avenues for further advancements in the field of PADs.