Affinity capture surface carboxyl-functionalized MoS₂ sheets to enhance the sensitivity of surface plasmon resonance immunosensors

The development of functionalized molybdenum disulfide (MoS₂) has led to a new trend in the biosensing field, owing to its high sensitivity and bio-affinity characteristics with regards to the simple synthesis of carboxyl-functionalized MoS₂ nanocomposites. In this study, we used monochloroacetic acid (MCA) to successfully modify carboxyl-MoS₂. The efficiency of this MCA modification method showed a higher -COOH group content of 30.1%, mainly due to chlorine atoms occupying the MoS2 sulfur vacancy to allow for the formation of a strong bonding effect. This then enhanced the surface area of -COOH and improved the formation of covalent bonds between proteins. We demonstrated that MoS₂-COOH-based surface plasmon resonance (SPR) chips can provide excellent sensitivity and high affinity for immunoassay biomolecules detected in a low sample volume of 20 μl. With respect to the shifts of the SPR angles of the chips, the high binding affinity at a BSA concentration of 14.5 nM for a MoS₂-COOH chip, a MoS₂ chip and a traditional SPR chip are 4.69 m° 2.49 m° and 1.53 m° respectively. In addition, the MoS₂-COOH chip could amplify the SPR angle response by 3.1 folds and enhance the high association rate of ka by 212 folds compared to MoS₂ and traditional SPR chips. The results thus obtained revealed that the overall affinity binding value, K_A, of the MoS₂-COOH chip can be significantly enhanced by up to ∼ 6.5 folds that of the MoS₂ chip. In summary, the excellent binding affinity, biocompatible and high sensitivity suggest the potential of the clinical application of this MoS₂-COOH-based SPR chip detection method for in vitro diagnostic and point-of-care testing devices.