Microorganisms recognition and quantification by lectin adsorptive affinity impedance

Lectin-based screen-printed gold electrodes are reported for the impedimetric label-free detection of bacteria. The selective interaction of lectins with carbohydrate components from microorganisms surface was used as the recognition principle for their detection and identification. Electrochemical impedance spectroscopy (EIS) was employed for the direct label-free transduction of the bacteria–lectin binding. Biotinylated Concanavalin A (Con A) and Escherichia coli were used for the evaluation of the lectin–bacteria complex formation. This complex was formed in solution, and then adsorbed onto the gold SPE surface. No bacteria immobilization was observed on the sensor prepared in the absence of ConA, demonstrating the absence of non-specific bacteria adsorption onto the gold SPE. On the contrary, the changes in electron transfer resistance allowed monitoring of E. coli–biotinylated Con A complex formation without any amplification step. Experimental variables such as the biotinylated-Con A concentration and the bacteria–lectin incubation time were optimized. The electron transfer resistance varied linearly with the logarithmic value of E. coli concentration over four orders of magnitude, 5.0 × 103 and 5.0 × 107 cfu mL−1. The selectivity of the approach was evaluated by checking the impedimetric responses of gold SPE modified with the complexes formed between nine lectins and three different bacteria (E. coli, Staphylococcus aureus and Mycobacterium phlei). Different response profiles were found when the different lectins were used as recognition elements. principal component analysis (PCA) allowed classification and distinction among bacteria. Finally, electrochemical monitoring of β-galactosidase activity for the surface attached bacteria was demonstrated to be useful to distinguish between E. coli and S. aureus, which exhibit a similar affinity towards biotinylated-Con A.