Label-Free Electrochemical Aptasensor for the Detection of the 3-O-C₁₂-HSL Quorum-Sensing Molecule in <i>Pseudomonas aeruginosa</i>

Pseudomonas aeruginosa, an opportunistic Gram-negative bacterium, is one of the main sources of infections in healthcare environments, making its detection very important. N-3-oxo-dodecanoyl L-homoserine lactone (3-O-C12-HSL) is a characteristic molecule of quorum sensing—a form of cell-to-cell communication between bacteria—in P. aeruginosa. Its detection can allow the determination of the bacterial population. In this study, the development of the first electrochemical aptasensor for the detection of 3-O-C12-HSL is reported. A carbon-based screen-printed electrode modified with gold nanoparticles proved to be the best platform for the aptasensor. Each step in the fabrication of the aptasensor (i.e., gold nanoparticles’ deposition, aptamer immobilization, incubation with the analyte) was optimized and characterized using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Different redox probes in solution were evaluated, the best results being obtained in the presence of [Fe(CN)6]4−/[Fe(CN)6]3−. The binding affinity of 106.7 nM for the immobilized thiol-terminated aptamer was determined using surface plasmon resonance. The quantification of 3-O-C12-HSL was performed by using the electrochemical signal of the redox probe before and after incubation with the analyte. The aptasensor exhibited a logarithmic range from 0.5 to 30 µM, with a limit of detection of 145 ng mL−1 (0.5 µM). The aptasensor was successfully applied for the analysis of real samples (e.g., spiked urine samples, spiked microbiological growth media, and microbiological cultures)

Specific electrochemical sensor for cadmium detection: Comparison between monolayer and multilayer functionalization

Selective and sensitive cadmium sensors were prepared by functionalizing glassy carbon electrodes (GCE) using the electrochemical reduction of p-benzoic acid diazonium salts according to either a multilayer or a monolayer coating process. Such modified electrodes were then post-functionalized with 1,2-bis-[o-aminophenylthio]ethane (APTE) or its monoprotected derivative leading to specific Cd2+ electrochemical sensors. The step by step preparation of the electrodes as well as the ability of the immobilized receptor to complex Cd2+ was investigated by XPS and Raman spectroscopy. The detection and quantification of cadmium was performed in two steps: the preconcentration of Cd2+ ions by complexation with immobilized APTE and the analysis by Linear Sweep Stripping Voltammetry (LSSV). More importantly, multilayer versus monolayer grafting has a strong influence on the sensor performances. Whereas calibration curves typical of an equilibrium process were obtained for sensors realized with multilayer organic films, sensors with a monolayer organic film led to linear calibration curves, in the same concentration range. Finally, the monolayer sensor gave a lower limit of detection (LOD) and highlighted better selectivity than unmodified electrode