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.