Voltammetric nanodiamond-coated screen-printed immunosensor for the determination of a peanut allergen in commercial food products

Groundnuts, like peanuts, are commonly integrated into the Mediterranean dietary pattern, and their consumption has been recommended worldwide. However, reported cases of peanut allergy have increased and, therefore, commercial food tracking is essential, since in extreme cases peanut intake causes anaphylaxis. Efficient detection of peanut traces in food samples can be achieved using electrochemical immunosensors that benefit from their advantageous features such as high selectivity and sensitivity, low cost, and rapid detection. Because disposable screen-printed electrodes can be connected to portable devices, they can be used for in situ allergen analysis.

In the present work, a voltammetric immunosensor was developed to quantify a major peanut allergen, Ara h 1, using screen-printed carbon electrodes (SPCE) as transducers. Distinct carbon-based nanomaterials were tested, and nanodiamonds were selected for the nanostructuration of the transducer’s surface. A sandwich-type immunoassay was performed on the nanodiamond-coated SPCEs using an alkaline phosphatase-labelled detection antibody and a mixture containing an enzymatic substrate (3-indoxyl phosphate) and silver nitrate. The immunological interaction was detected through the (linear sweep) voltammetric stripping of the enzymatically deposited silver. A linear concentration range was established between 25 and 500 ng·mL⁻¹ (i_p = (0.027 ± 0.001) [Ara h 1] + (1.41 ± 0.31), r = 0.994, n = 5), with a sensitivity of 0.342 µA·mL·ng^-1·cm^-2. The limits of detection (LOD) and quantification (LOQ) were 0.78 and 2.6 ng·mL⁻¹, respectively. Other allergens, non-target proteins and food product ingredients were tested to assess the selectivity of the immunosensor. Its applicability was evaluated by analysing a set of breakfast cereals, cookies, and energetic and cereal bars.