Foodborne pathogens are a major concern for public health. We demonstrate for the first time a partially automated sensing system for rapid (~17 min), label-free impedimetric detection of Escherichia coli spp. in food samples (vegetable broth) and hydroponic media (aeroponic lettuce system) based on temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) nanobrushes. This proof of concept (PoC) for the Sense-Analyze-Respond-Actuate (SARA) paradigm uses a biomimetic nanostructure that is analyzed and actuated with a smartphone. The bio-inspired soft material and sensing mechanism is inspired by binary symbiotic systems found in nature, where low concentrations of bacteria are captured from complex matrices by brush actuation driven by concentration gradients at the tissue surface. To mimic this natural actuation system, carbon-metal nanohybrid sensors were fabricated as the transducer layer, and coated with PNIPAAm nanobrushes. The most effective coating and actuation protocol for E. coli detection at various temperatures above/below the critical solution temperature of PNIPAAm was determined using a series of electrochemical experiments. After analyzing nanobrush actuation in stagnant media, we developed a flow through system using a series of pumps that are triggered by electrochemical events at the surface of the biosensor. SARA PoC may be viewed as a cyber-physical system that actuates nanomaterials using smartphone-based electroanalytical testing of samples. This study demonstrates thermal actuation of polymer nanobrushes to detect (sense) bacteria using a cyber-physical systems (CPS) approach. This PoC may catalyze the development of smart sensors capable of actuation at the nanoscale (stimulus-response polymer) and macroscale (non-microfluidic pumping).

Nanoencapsulation can provide a means to effectively deliver antimicrobial compounds and enhance the safety of fresh produce. However, to date there are no studies which directly compares how different nanoencapsulation systems affect fresh produce safety and quality. This study compared the effects on quality and safety of fresh-cut lettuce treated with free and nanoencapsulated natural antimicrobial, cinnamon bark extract (CBE). A challenge study compared antimicrobial efficacy of 3 different nanoencapsulated CBE systems. The most effective antimicrobial treatment against Listeria monocytogenes was chitosan-co-poly-N-isopropylacrylamide (chitosan-PNIPAAM) encapsulated CBE, with a reduction on bacterial load up to 2 log CFU/g (P < 0.05) compared to the other encapsulation systems when fresh-cut lettuce was stored at 5 °C and 10 °C for 15 d. Subsequently, chitosan-PNIPAAM-CBE nanoparticles (20, 40, and 80 mg/mL) were compared to a control and free CBE (400, 800, and 1600 μg/mL) for its effects on fresh-cut lettuce quality over 15 d at 5 °C. By the 10th day, the most effective antimicrobial concentration was 80 mg/mL for chitosan-PNIPAAM-CBE, up to 2 log CFU/g reduction (P < 0.05), compared with the other treatments. There was no significant difference between control and treated samples up to day 10 for the quality attributes evaluated. Chitosan-PNIPAAM-CBE nanoparticles effectively inhibited spoilage microorganisms' growth and extended fresh-cut lettuce shelf-life. Overall, nanoencapsulation provided a method to effectively deliver essential oil and enhanced produce safety, while creating little to no detrimental quality changes on the fresh-cut lettuce.

Figure 5: Bode plots for A) PNIPAAm-ConA and B) PNIPAAm-Anti-GroEL antibody modified electrodes exposed to various concentrations of E. coli O157:H7 (CFU mL -1 ) in vegetable broth. Insets show the exploded view over the frequency range of 1-3.5 Hz. Nyquist plots for C) PNIPAAm-ConA modified electrodes and D) PNIPAAm-Anti-GroEL antibody modified electrodes exposed to various concentration of E. coli O157:H7 (CFU mL -1 ) in vegetable broth. Calibration curves at 1 Hz for E) PNIPAAm-ConA and F) PNIPAAm-Anti-GroEL antibody modified electrodes exposed to E. coli O157:H7 in vegetable broth over their respective linear ranges.Foodborne pathogens are a major concern for the health and safety of the public. Escherichia coli spp. are some of the most common foodborne bacteria. Conventional methods for detecting E. coli are time-consuming and require highly trained personnel and laboratories. Therefore, More rapid, sensitive, and reliable methods are needed for pathogen detection in food products to ensure public health.To develop a sensing mechanism for rapid, label-free detection of E. coli spp. in food samples using temperatureresponsiveness of poly(N-isopropylacrylmide) (PNIPAAm) brushes. This bio-inspired soft material and sensing mechanism resembles natural bacteria-host symbiotic systems where low concentrations of bacteria in complex matrices are selectively captured.