Highly Chemiluminescent Magnetic Beads for Label-Free Sensing of 2,4,6-Trinitrotoluene

Until now, despite the great success acquired in scientific research and commercial applications, magnetic beads (MBs) have been used for nothing more than a carrier in most cases in bioassays. In this work, highly chemiluminescent magnetic beads containing N-(4-aminobutyl)-N-ethyl isoluminol (ABEI) and Co²⁺ (Co²⁺/ABEI/MBs) were first synthesized via a facile strategy. ABEI and Co²⁺ were grafted onto the surface of carboxylated MBs by virtue of a carboxyl group and electrostatic interaction. The as-prepared Co²⁺/ABEI/MBs exhibited good paramagnetic properties, satisfactory stability, and intense chemiluminescence (CL) emission when reacted with H₂O₂, which was more than 150 times that of ABEI functionalized MBs. Furthermore, it was found that 2,4,6-trinitrotoluene (TNT) aptamer could attach to the surface of Co²⁺/ABEI/MBs via electrostatic interaction and coordination interaction between TNT aptamer and Co²⁺, leading to a decrease in CL intensity due to the catalytic site Co²⁺ being blocked by the aptamer. In the presence of TNT, TNT would bind strongly with TNT aptamer and detach from the surface of Co²⁺/ABEI/MBs, resulting in partial restoration of the CL signal. Accordingly, label-free aptasensor was developed for the determination of TNT in the range of 0.05-25 ng/mL with a detection limit of 17 pg/mL. This work demonstrates that Co²⁺/ABEI/MBs are easily connected with recognition biomolecules, which are not only magnetic carriers but also direct sensing interfaces with excellent CL activity. It provides a novel CL interface with a magnetic property which easily separates analytes from the sample matrix to construct label-free bioassays.