A Label-Free Optical Interferometric Biosensor for Comparing Antibody Interaction with Folic Acid Derivatives Based on Gelatin and Dextran

Folic acid plays a critical role in cellular metabolism, including DNA synthesis and cell division. Understanding its interactions with antibodies is essential for creating diagnostic platforms and therapeutic systems. The effectiveness of these interactions depends on the carrier used for folic acid, which is often a protein like bovine serum albumin, ovalbumin, or keyhole limpet hemocyanin. Polymers such as dextran and gelatin are emerging as promising alternatives. This study compares the interaction of antibodies with folic acid conjugates based on dextran and gelatin using an updated label-free optical biosensor employing spectral interferometry. This method evaluates the influence of carrier structure on interaction kinetics and specificity, identifying optimal materials for various applications.
Conjugates of folic acid with gelatin and dextran were synthesized using carbodiimide chemistry. Gelatin conjugates were prepared by reacting folic acid with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, followed by incubation with gelatin. The product was purified through precipitation and washing cycles. Dextran conjugates were synthesized similarly, replacing gelatin with dextran. A biosensor chip surface was modified with folic acid–gelatin conjugate, and antibodies specific to folic acid were immobilized. Conjugates of folic acid–gelatin or folic acid–dextran were introduced in a competitive binding assay, and interaction dynamics were monitored using spectral interferometry.
The folic acid–gelatin conjugate demonstrated weak interaction at low concentrations and low desorption rates, making it suitable for mimicking complex biological systems where nonspecific interactions and limited accessibility of binding sites are relevant. In contrast, the folic acid–dextran conjugate exhibited higher binding efficiency, specificity, and stability due to enhanced accessibility of folic acid and reduced nonspecific interactions. The biosensor enabled real-time monitoring of these interactions, providing detailed profiles for each conjugate. Folic acid–gelatin is advantageous for systems involving complex biological interactions, while folic acid–dextran offers high specificity and faster binding kinetics.
Folic acid–gelatin and folic acid–dextran conjugates exhibit distinct interaction profiles with antibodies. Gelatin conjugates are suited for systems with nonspecific binding, whereas dextran conjugates provide higher specificity and stability. The experimental results showed that the label-free biosensing with spectral correlation interferometry is a powerful approach for evaluating conjugate interactions and identifying suitable materials for biomedical applications.