Electrochemical detection of gram-negative bacteria through mastoparan-capped magnetic nanoparticle.

The increasing number of multidrug resistance microorganisms is an alarming threat, and their rapid detection is essential to prevent nosocomial, foodborne, or waterborne infections. Many peptides derived from the venom of wasp Synoeca surinama have antimicrobial activity against Gram-positive and Gram-negative bacteria. Synoeca-MP, an antimicrobial peptide (AMP) from mastoparan family, seems to increase bacterial membrane permeability, promoting cytotoxicity and membrane disruption. Here Synoeca-MP was evaluated as biorecognition element tethered over chitosan-coated magnetic nanoparticles (Fe3O4-Chit). The transducing layer of the biosensor was developed from the self-assembling of 4-mercaptobenzoic acid (4-MBA) monolayer onto gold substrate. Atomic force microscopy (AFM) analyses confirmed the biointeraction between AMP and different pathogens membranes. The fabrication and performance of the biosensing assembly were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Detection of Enterococcus faecalis (G+), Klebsiella pneumoniae (G-), Pseudomonas aeruginosa (G-), and Candida tropicalis was assessed in a recognition range from 101 to 105 CFU.mL-1. An instrumental limit of detection of 10 CFU.mL-1 was obtained for each specimen. However, the device presented a preferential selectivity towards Gram-negative bacteria. The proposed biosensor is a sensitive, fast, and straightforward platform for microbial detection in aqueous samples, envisaged for environmental monitoring applications.

Concanavalin A differentiates gram-positive bacteria through hierarchized nanostructured transducer.

Biosensors are pre-prepared diagnostic devices composed of at least one biological probe. These devices are envisaged for the practical identification of specific targets of microbiological interest. In recent years, the use of narrow-specific probes such as lectins has been proven to distinguish bacteria and glycoproteins based on their superficial glycomic pattern. For instance, Concanavalin A is a carbohydrate-binding lectin indicated as a narrow-specific biological probe for Gram-negative bacteria. As a drawback, Gram-positive bacteria are frequently overlooked from lectin-based biosensing studies because their identification results in low resolution and overlapped signals. In this work, the authors explore the effect that platform nanostructuration has over the electrochemical response of ConA-based platforms constructed for bacterial detection; one is formed of chitosan-capped magnetic nanoparticles, and another is composed of gold nanoparticle-decorated magnetic nanoparticles. The biosensing platforms were characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) as a function of bacterial concentration. Our results show that probe-target interaction causes variations in the electrical responses of nanostructured transducers. Moreover, the association of gold nanoparticles to magnetic nanoparticles resulted in an electrical enhancement capable of overcoming low resolution and overlapping Gram-positive identification. Both platforms attained a limit of detection of 10 ° CFU mL-1, which is useful for water analyses and sanitation concerns, where low CFU mL-1 are always expected. Although both platforms were able to detect Gram-negative bacteria, Gram-positives were only correctly differentiated by the gold nanoparticle-decorated magnetic nanoparticles, thus demonstrating the positive influence of hierarchically nanostructured platforms.