Dual substrate sensor platform for rapid detection and differentiation of coliforms.

In the present work, we modified and improved the previously developed sensor platform (based on screen-printed carbon electrode) for rapid detection and quantification of coliforms. The second substrate (L-alanyl-p-nitroanilide) was included in the sensor platform, which produced the second cathodic voltammetric peak at the new potential (-113 mV) in the defined potential range (-600 to 400 mV). The 106 CFU/mL of 5 different groups of coliforms in 3 h of incubation produced electrochemical signals equal to 960 µA, 970 µA, 988 µA, 950 µA, 956 µA and 920 µA respectively. After 3 h of incubation the two strains of Gram-positive bacteria with concentration of 106 CFU/mL produced voltammetric signals equal to --80 µA and- 200 µA (due to high /-150 µA/ capacitive/background current) respectively. No voltammetric peak occurred with Gram-positive bacteria at the potential equal to -113 mV. The voltammetric signals produced at the new potential range were specific for coliforms.

Novel sensor platform for rapid detection and quantification of coliforms on food contact surfaces.

In this paper, a novel sensor platform based on screen printed carbon electrode coated by graphene modified polyacrylamide gel (GR/PAAGC) was developed and implemented for sampling, detection and enumeration of coliform bacteria (coliforms) on food contact surfaces. The optimized formula of polyacrylamide (PAA) and agar-agar increased the adhesive properties of the gel, being crucial for the coliforms recovery, attached to food contact surfaces. The 6-Chloro-3-indoxyl-ß-D-galactopyranoside (6-CIGP) was used as a new electrochemical reporter for ß-D-galactosidase activity. The released 6,6'-Dichloro-Indigo (6-DI) was directly detected by GR/PAAGC sensor. The presence of Isopropyl-ß-D-thiogalactopyranoside (IPTG) and n-Octyl-ß-D-thiogalactopyranoside (OBDG) in the gel contributed to reduction of the detection time. The addition of graphene enhanced the voltammetric signal and increased the conductivity of PAA gel. The anodic and cathodic peaks of the released product were directly proportional to the concentration of coliforms. Bacterial cell concentrations ranging from 1.6log10CFU/mL to 6.6log10CFU/mL were detected. Well-shaped, sharp voltammetric curves were generated within 3 h. Redox peaks exhibited good sensitivity with detection limits (LOD) < 0.6log10CFU/mL. After series of optimization experiments, coliforms ranging from 0.6log10CFU/cm2 to 6.610CFU/cm2 on stainless steel surfaces have been detected within 30 min with a LOD of 0.1log10CFU/cm2. The developed rapid, sensitive, reproducible and specific sensor successfully applied for single detection as well as for real-time monitoring of growth of coliform bacteria on stainless steel surfaces during food processing.