This paper describes the development of a "diffusion-to-surface" ratiometric graphene electrosensor for the selective detection of live cells and pathogens that highly express mannose-binding proteins (MBPs). MBPs have been implicated in many pathological processes and are identified on specific types of bacteria. Consequently, MBPs are a promising biomarker for targeted disease diagnosis and therapy. Here, we develop a unique electrosensor that features a ratiometric voltammetric signal for the selective probing of MBPs. Self-assembly of mannosyl anthraquinone (AQ) to a graphene oxide-decorated screen-printed electrode produces the sensor with an inherent surface-controlled voltammetric signal. Subsequently, addition of a redox probe (RP) imparts the system with a diffusion-controlled current, thus enabling a ratiometric sensing rationale for which AQ serves as a reference. While the reference current is hardly compromised by adding analytes, RP exhibits a concentration-dependent current quenching on addition of mannose-selective lectins over other proteins. Importantly, this ratiometric electrosensor has proven to be applicable for the ratiometric probing of alternatively activated macrophages and a Gram-negative bacterium highly expressing MBPs, but shows minimal response to a series of control live cells and bacteria without mannose receptor expression.
Keywords: anthraquinone; bacteria; cell; electrochemistry; graphene; sensor.