Dendrimer precursors for nanomolar and picomolar real-time surface plasmon resonance/potentiometric chemical nerve agent sensing using electrochemically crosslinked ultrathin films

Nanomolar detection and specific recognition of pinacolyl methylphosphonate (PMP), a hydrolysis product and an analog of a relatively persistent class of toxic nerve agents, has been achieved. In addition, picomolar sensitivity is observed with methylphosphonic acid (MPA), an end-hydrolysis product for all organophosphate-based nerve agents. This is achieved using a combined surface plasmon resonance (SPR) and potentiometry setup. A modified polyamidoamine (PAMAM) carbazole/Cu²⁺ dendrimer, which is electrochemically crosslinked on a self-assembled monolayer (SAM) modified Au substrate, is used as an active sensing element for trapping the nerve-agent analogs. The ultrathin films have been used to study the anchoring of nerve agents via non-covalent interactions. The carbazole to amine ratio is optimized to ensure free primary amines are available to interact with the analyte and the Cu²⁺ ions present in the system, which further enhances the selectivity. The carbazole group on the periphery serves a dual purpose: crosslinking the dendrimers to form a conjugated network film, and generating the potentiometric response. The adsorption kinetics are monitored by using an in situ SPR/potentiometric setup. This technique not only offers a real-time dual detection of highly toxic nerve-agent analogs, but also shows viability for future sensor-device applications.