Interfacing the enzyme multiheme cytochrome c nitrite reductase with pencil lead electrodes: Towards a disposable biosensor for cyanide surveillance in the environment

The present study reports a novel voltammetric biosensor for cyanide based on its inhibitory effect on cytochrome c nitrite reductase (ccNiR). Interestingly, the earlier development of a point-of-care test for nitrite based on the direct electrochemistry of ccNiR has shown that the cyanide inhibition depends on the type of carbon material employed as transducer (Monteiro et al., 2019). In this work, commercial graphite pencil leads were employed in the construction of both working and pseudo-reference electrodes, with ccNiR being simply drop casted onto the former. In this way, we produced a functional and fully integrated voltammetric biosensor for nitrite quantification that also allows to observe a decrease in the catalytic current due to cyanide addition. Under turnover conditions, the biosensor showed a linear response with the logarithm of cyanide concentration in the 5-76 mu M (cyclic voltammetry) and 1-40 mu M (square-wave voltammetry) ranges, with a sensitivity of 20-25% ln [cyanide mu M] 1 and a detection limit of 0.86-4.4 mu M. The application of the pencil lead as a putative pseudo-reference was very promising, since the potentials profile matched those observed with a true reference electrode (Ag/AgCl). Overall, the direct electron transfer between ccNiR and a pencil lead electrode was demonstrated for the first time, with cyanide-induced inhibition being easily monitored, paving the way for the employment of these lowcost bioelectrodes as cyanide probes for on-site surveillance of aquatic environments.

Automated summary

This study presents a novel voltammetric biosensor for cyanide detection based on the inhibitory effect on cytochrome c nitrite reductase. Using commercial graphite pencil leads for electrode construction, the biosensor demonstrated a linear response to cyanide concentration with a sensitivity of 20-25% ln [cyanide mu M]^-1, paving the way for lowcost bioelectrodes as cyanide probes for on-site surveillance of aquatic environments.