An electrochemical microsensor for osteopontin based on a molecularly imprinted layer and a built-in probe-functionalized acupuncture needle

Osteopontin (OPN) is an important biomarker for reflecting osteoarthritic inflammation and endochondral ossification. In the field of electroanalysis, OPN is a non-electroactive protein, which is usually detected by means of an outer probe or biolabel. Here, a novel microsensor that can directly electroanalyze OPN was constructed by coordinating a surface molecularly imprinted polymer (SMIP) with a built-in electroactive probe of poly(methylene blue) (pMB) on an acupuncture needle microelectrode (ANME). The OPN template can be reversibly anchored using 4-mercaptophenylboronic acid (4-MBPA) via a borate bond between phenylboronic acid and the external cis-diol of the glycoprotein. Methylene blue (MB) and dopamine (DA) were sequentially electropolymerized and grown around templates, which played pivotal roles in the detection signal from the built-in pMB through the imprinted nanocavities. After the recombination of OPN molecules with imprinted nanocavities, the current strength of built-in pMB could be impeded, producing a highly sensitive response. This microsensor shows a linear relationship with the concentration of OPN from 0.01 to 1000 ng mL^-1 with a detection limit of 3 pg mL^-1. The microsensor also exhibits high selectivity and stability, which is attributed to the recognizing ability of the imprinted nanocavities and the hindrance and anti-interference function of coated polydopamine (pDA). This strategy of preparing a sensor shows practical and scientific significance for functionalizing microelectrodes and constructing microsensors for non-electroactive glycoproteins. In the future, it will be fascinating to integrate this microsensor with the acupuncture technique.