Inhibition-based biosensor for cyanide detection – a preliminary study

INTRODUCTION: The acute toxicity of cyanide along with its continue industrial use makes this substance of environmental concern [1]. Titration, spectrophotometry and ISE are the standard detection methods. However, they are complex and need sample pre-treatment [2]. To overcome these, another approach is using biosensors. To this end, we developed a disposable inhibition-based biosensor with a multi-heme nitrite reductase (ccNiR) coupled to graphite leads. MATERIALS AND METHODS: Electrochemical measurements were carried out in a conventional electrochemical cell, composed by a three-electrode system. The reference was an Ag/AgCl electrode, and the counter electrode was a Pt wire. The working electrode (WE) was in-house made using a graphite lead with the ccNiR (from bacteria D. desulfuricans ATCC 27774; stored in 0.05 M phosphate buffer, pH 7.6) immobilised by drop cast at the WE surface. The electrochemical technique used was square wave voltammetry. Electrochemical cells contained 0.1 M KCl in 0.1 M Tris–HCl buffer (pH 7.6) as supporting electrolyte. Dissolved oxygen was removed by a biochemical system (GOx, catalase and glucose). DISCUSSION AND CONCLUSIONS: In Figure 1 we can observe the decrease in catalytic activity due to the presence of cyanide. The biosensor dynamic range comprises the maximum value imposed by the European Union, 1.92 µM (98/83/EC directive), which does not happen with other cyanide biosensors [3]. Furthermore, a graphite lead cost 0.35€ and each of them can be split, allowing a very low-cost biosensor. Given that enzyme inhibition is reversible [4], the sensor can be used more than one time, if we optimise the enzyme immobilisation method.