Carbon-based thick films for electrochemical detection of neonicotinoid insecticides

Abstract

Neonicotinoids (NNIs) are water-soluble, toxic, widespread-used systemic insecticides commonly found in the environment. Integrated electrochemical sensors enable the rapid on-site detection of NNIs in aqueous samples by analysing the reduction of the NNI's nitro functional group on the working electrode. We have investigated graphite (G), glassy carbon (GC) and carbon black (CB) thick films as working electrodes for the electrochemical detection of the NNI imidacloprid (IMD). Up to 35-μm-thick films of G, GC and CB on alumina were prepared by screen printing and subsequent firing at 850 °C in argon. G had the largest grain size, the roughest surface, and the lowest sheet resistance of 6.9 Ω/sq. GC and CB had a smoother surface, while their sheet resistances were up to 27 Ω/sq. All three films showed a reversible response to the Fe(CN)₆^3−/4− redox probe with G having the highest electrochemically active surface area and the highest heterogeneous electron transfer rate constant. In the IMD solution with neutral pH, G, GC and CB exhibited characteristic reduction peak at −1.1 V and a re-oxidation peak at +0.2 V. An additional adsorption cathodic peak was observed with CB, indicating a significantly higher affinity of CB for IMD adsorption. With LODs under 1 μM, the G, GC and CB pristine thick films exhibiting great potential for the sensitive detection of IMD.