A Facile Method for Detection of Substituted Salicylic Acids Using Pyrenesulfonamide‐Terminated Self‐Assembled Monolayers on Silicon Oxide Surfaces

Abstract

Self-assembled monolayers (SAMs) of alkylsilanes (e.g., alkyltrialkoxysilanes and alkyltrichlorosilanes) on Si/SiO 2 surfaces have received a great deal of attention in a variety of research areas potentially because the SAMs improve the fundamental understanding of interfacial phenomena and develop many technological applications, such as fieldeffect transistor, catalysis, microarray, non-biofouling coating, and (bio)analytical devices. 1 In the field of chemo/biosensors, immobilization of receptors on surfaces enables the functional and structural understanding of the molecular interactions between receptors and analytes and usually provides rapid response times, easy-to-use testing procedures, and high potential for the reuse of materials. 2 For example, a number of protein functions were successfully investigated through the immobilization of over 10 000 proteins on a Si/SiO 2 surface. 3 Mrksich and coworkers quantitatively evaluated the effect of three different inhibitors of the non-receptor tyrosine kinase, c-Src by immobilizing a 9-mer peptide on a gold surface, thus shedding light on the dynamics of enzyme-substrate interactions and the applications in drug discovery. 4 Moreover, immobilized metal-ion affinity chromatography (IMAC) is often used for the analysis of analytes and the purification of proteins. 5 Salicylic acids (o-hydroxybenzoic acids) play a pivotal role in the metabolism and physiology of living organisms. 6 They are also widely used in pharmaceuticals, cosmetics, medical diagnosis, food technology, and environmental monitoring. 7 For example, in plants, salicylic acid is involved in the regulation of defenses against pathogens and insects and affects a number of physiological processes such as fruit yield, seed germination, protein synthesis, and nutrient uptake. 8 In addition, salicylic acid is an aromatic organic compound, which may cause allergic contact dermatitis, one of the most prevalent forms of immunotoxicity found in humans. 9 Consequently, monitoring and quantita-tive determination of salicylic acids in aqueous solutions is important. 2,10 Moreover, for detailed studies on their function and physiological properties and effects, it is necessary to be able to selectively recognize each derivative.Recently, we have successfully demonstrated the molecular recognition between salicylic acids and pyrene derivatives in solution by fluorescence measurement. Briefly, selective recognition was achieved using intermolecular interactions, including π-π interactions and multi-hydrogen bonds, and intramolecular hydrogen bonding between the phenolic O-H group and the adjacent C O group. 11 More interestingly, the association constant for the binding event was affected by the substituents of both the pyrene and salicylic acid moieties. For example, pyrene-1-butylsulfonamide has different association constant values with various salicylic acid derivatives: 2.83 × 10 4 M −1 for 3,5dinitrosalicylic acid, 9.07 × 10 3 M −1 for 5-nitirosalicylic acid, and 5.32 × 10 3 M −1 for 5-iodosalicylic ac...