Electrochemical Immunosensor for the Determination of Nuclear Matrix Protein 22 in Urine Using Carboxylated MWCNTs and Zeolitic Imidazolate Framework Modified with AgNPs

Nuclear matrix protein 22 (NMP22) is considered one of the noninvasive biological indications in the urine that has recently captured extensive clinical attention for bladder cancer screening and surveillance. Hence, it is imperative to create a straightforward, sensitive, and precise NMP22 assay. As a type of carbon nanomaterial, carboxylated multiwalled carbon nanotubes (CMWCNTs) exhibit exceptional electrical conductivity and abundant carboxyl groups. The silver nanoparticles and zeolitic imidazolate frameworks-8 composite (AgNPs-ZIF-8), which is a three-dimensional material, possess a wide surface area, acceptable electrical conductivity, and satisfactory biocompatibility. More importantly, it can also immobilize NMP22 antibodies in striking amounts via the Ag–NH2 bonds. Along these lines, in this work, AgNPs were decorated on ZIF-8 and modified on the glassy carbon electrode together with CMWCNTs. The comparative advantages of carbon nanotubes, metal–organic frameworks, and AgNPs were successfully combined to develop an electrochemical immunosensor with superior sensitivity and reliability for the detection of NMP22 in urine. It should be mentioned that the immunosensor not only has a wide linear range (10–2 to 105 pg mL–1) and a low detection limit (8.8 fg mL–1, S/N = 3) but also exhibits robust precision, excellent selectivity, and desirable stability. Aside from that, the immunosensor was effectively utilized to detect human urine samples, demonstrating an excellent performance.