Abstract
In recent years， molecularly imprinted polymers have shown considerable promise in analytical detection and early diagnosis of diseases due to their high selectivity and specificity. Nevertheless， the practical implementation of these methods is still restricted by several intrinsic limitations associated with traditional synthesis approaches， including a strong reliance on organic solvents， poor recognition efficiency in aqueous media， and low adsorption capacity. To overcome these challenges， this study presents an innovative strategy that integrates superhydrophilic resin with graphene aerogel （GA）， resulting in successful fabrication of a superhydrophilic molecularly imprinted resin-GA composite （HMIR-GA） via surface in situ polymerization in water. The resulting HMIR-GA exhibited a significantly enhanced adsorption capacity and improved recognition performance in aqueous environments towards tumor biomarker. Characterization of the HMIR-GA was performed using Fourier transform infrared （FT-IR） spectroscopy， scanning electron microscopy （SEM）， nitrogen adsorption-desorption analysis， and contact angle measurements. FT-IR spectra revealed that the broad peak at 3 400 cm(-1) can be ascribed to the formation of -OH associations. The absorption peak at 1 724 cm(-1) corresponds to the stretching vibration peak of C=O on the surface of graphene oxide （GO）. The absorption peaks at 1 602 cm(-1) and 1 462 cm(-1) are assigned to the C=C stretching vibration peaks of resorcinol. During the reaction process， due to the reduction effect of ammonia water， the C=O on graphene oxide is reduced. The characteristic peak at 1 069 cm(-1) is induced by the stretching vibration of C-O-C， representing the formation by the reaction between resorcinol and hexamethylenetetramine. These characteristic peaks clearly demonstrate that the HMIR have been successfully incorporated into the graphene aerogel. The FT-IR results confirm the successful synthesis of HMIR-GA. SEM reveals that the surface of graphene oxide exhibits a wrinkled lamellar structure. In contrast， the fabricated HMIR-GA and superhydrophilic molecularly non-imprinted resin-GA composite （HNIR-GA） display a loose and porous architecture， indicating that the synthesized HMIR has been successfully grown onto the graphene aerogel. The porous structure is conducive to the rapid adsorption of 5-hydroxyindoleacetic acid （5-HIAA）， which is beneficial for enhancing the performance of relevant applications. The Brunauer-Emmett-Teller （BET） specific surface areas of HMIR-GA and HNIR-GA are 95.1 m²/g and 44.5 m²/g， respectively. The pore volumes are 0.31 cm³/g and 0.20 cm³/g， respectively. In comparison with HNIR-GA， HMIR-GA possesses a larger specific surface area and pore volume， which is conducive to enhancing its adsorption capacity for 5-HIAA. To evaluate the hydrophilicity of HMIR-GA and HNIR-GA， contact angle measurements were performed. The results showed that when water droplets were placed on the surfaces of these two materials， they rapidly spread and fully wetted the surfaces within 0.07 s， indicating that HMIR-GA and HNIR-GA exhibited superior hydrophilic properties. This enhanced hydrophilicity facilitates the effective adsorption and extraction of the tumor biomarker 5-HIAA from urine samples. Static and competitive adsorption experiments revealed that HMIR-GA has a strong affinity for 5-HIAA. The evaluation of adsorption kinetics was carried out by employing both the pseudo-first-order and pseudo-second-order models， indicating a better fit with the pseudo-second-order model （R²=0.999 3）， suggesting that chemisorption is the dominant mechanism. Furthermore， equilibrium adsorption data were analyzed using the following models-Langmuir， Freundlich， Temkin， and Dubinin-Radushkevich （D-R）. The best fit was achieved with the Freundlich isotherm model （R²≥0.985 2）， indicating multilayer adsorption on heterogeneous surfaces. A highly sensitive method for precise determination of 5-HIAA was established by employing HMIR-GA as a pipette tip solid-phase extraction adsorbent coupled with high performance liquid chromatography. The calibration curve exhibited excellent linearity across the mass concentration range of 0.02-40.0 μg/mL （r=0.999 8）. The limits of detection （LOD） and quantification （LOQ） were 3.7 ng/mL and 12.3 ng/mL， respectively， based on signal-to-noise ratios of 3 and 10. Method accuracy was verified through recovery tests at spiked mass concentrations of 0.1， 1.0， and 10.0 μg/mL， yielding recoveries between 75.7% and 92.5% with relative standard deviations （RSDs） below 3.4%. Precision assessments via intra-day and inter-day tests yielded RSDs of 2.9% and 4.1%， respectively （n=6）. Finally， the developed method was applied for the determination of 5-HIAA levels in real urine samples. This work not only provides a robust and environmentally friendly strategy for the fabrication of functionalized molecularly imprinted polymers but also shows great promise for clinical applications， offering crucial technical support for early diagnosis of gastroenteropancreatic neuroendocrine tumors.