Molecularly Imprinted Polymers: Novel Affinity-Based Detection for Sensor Development of Fulvic Acid

Fulvic acid (FA) is a water-soluble molecule belonging to the group of organic compounds called humic substances, which are derived from the decomposition of organic matter. Known for its significance in soil fertility and nutrient availability, it is considered a water pollutant due to its ability to become precursor for the formation of toxic halogenated disinfection by-products and complexes with heavy metals in soil. Several methods have been developed to remove this in water, such as coagulation and adsorption methods, but the efficiency is significantly affected by different factors such as the solubility, size, and concentration of the molecule.

Molecularly imprinted polymers (MIPs) are synthetic polymers that show promising properties to become an adsorbent for the removal of FA in water. MIPs exhibit robustness even in high pH and high temperature conditions and high selectivity for the target even in the presence of matrix interferers; they are also reusable, and their synthesis is simple and straightforward. This study explored the formulation of MIPs specific for FA using methacrylic acid, methacrylamide, and acrylamide as functional monomers.

Prior to MIP synthesis, this study employed the functionalization of silica gel with chitosan, followed by the immobilization of FA as the target and humic acid (HA) as the control molecule on the functionalized silica gel. Verification was performed through a series of FT-IR analyses conducted to ensure accuracy and consistency in the processes. The MIP’s selectivity was tested using HA, the control molecule. After the three-hour contact time with triplicate samples of FA and HA separately, the initial and final concentrations of MIP were analyzed using UV-Vis spectroscopy at a 190-400 nm range.

The 30 ppm MIP solution exhibited 65% FA recovery versus 1.69% HA recovery, proving the selectivity of the synthesized MIP towards the target. This paper could lay the groundwork for future researchers aiming to advance the development of a similar sensor or other innovations.