Enhanced affinity of C18 and L-lactyl co-modified silica particles toward chlorogenic acid for sensing applications

Porous silica offers high surface area and chemical stability, making it ideal for chemical sensing applications. Its surface can be easily modified with functional groups to tailor molecular interactions, especially in aqueous environments. Alkyl-modified silica, widely used in chromatography, also shows promise for sensing due to its tunable hydrophobicity. Raman spectroscopy enables label-free, water-compatible detection, however often requires relatively high analyte concentrations. Modified silica surfaces may overcome this disadvantage by concentrating analytes in the detection area. Thus, simple, tunable platforms based on functionalized silica could offer an effective alternative to complex systems like SERS or molecular imprinting. We modified porous silica with various acyl groups (C3, C6, C9, C18) and D-/L-lactyl groups via amide bond formation following the introduction of aminopropyl groups. Elemental analysis was used to estimate the degree of modification, and residual amino groups were acetylated to suppress nonspecific interactions. We evaluated the interactions between the modified silica and chlorogenic acid in aqueous solutions using confocal Raman microscopy. We found that interaction strength was influenced by acyl chain length; higher C18 content reduced binding, likely due to limited accessibility of surface silanol groups. While D- or L-lactyl modification alone had minimal impact, co-modification with C18 and L-lactyl groups produced a synergistic enhancement, consistent with combined chiral and hydrophilic effects. Silica co-modified at a 1:1 molar ratio (40 % total modification) achieved ∼50-fold enrichment of chlorogenic acid compared with unmodified silica. Co-modification of porous silica with hydrophobic and chiral hydrophilic groups enables efficient enrichment of chlorogenic acid in aqueous environments, sufficient for direct detection by confocal Raman microscopy without SERS enhancement. This simple, tunable platform could be extended to other small bioactive molecules and applied to complex matrices such as taste sensing.