Sense–Analyze–Respond–Actuate (SARA) Paradigm: Proof of Concept System Spanning Nanoscale and Macroscale Actuation for Detection of Escherichia coli in Aqueous Media

Abstract

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).

One-Step Fabrication of Stimuli-Responsive Chitosan-Platinum Brushes for Listeria monocytogenes Detection

“…Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods, as described by Hills et al [ 15 ] and Giacobassi et al [ 16 ], were used as noted. A three-electrode system with a platinum auxiliary electrode and an Ag/AgCl reference electrode at room temperature was used with a CHI 600E potentiostat analyzer.…”

“…These calibration curves consisted of the change in impedance (Δ ) (Ohm) vs. the concentration of cells (log CFU mL −1 ) at fixed cutoff frequencies as noted. The limit of detection (LOD) was calculated using the 3σ method, and the analytical sensitivity was determined by the slope of the linear portion of the calibration curve (R 2 > 0.98) at a fixed frequency [ 16 ]. Analysis with the presence of interferents (food components and other bacteria) was assessed to determine the selectivity for target bacteria.…”

“…It has also been shown that chitosan exerts multifunctional forces on bacteria such as hydrophobic, hydrogen bond, and electrostatic interactions that are complementary and can reinforce each other [ 14 ]. This property combined with the pH stimulus–response is thus shown to be beneficial for sensing bacteria; this study has demonstrated that the actuation of chitosan (pH stimulus) [ 15 ] and PNIPAAm (poly(N-isopropylacrylamide, a temperature-responsive polymer) [ 16 ] brushes can improve bacteria detection in complex aqueous media by increasing the probability of target–receptor interaction as a result of microscale structural changes. These previous works demonstrated that actuation of brushes with bacteria capture while brushes were in the extended state followed by brush collapse improve sensing performance (i.e., signal to noise ratio) [ 16 ].…”

Prevalence of Escherichia coli and Antibiotic-Resistant Bacteria During Fresh Produce Production (Romaine Lettuce) Using Municipal Wastewater Effluents

“…This study was carried out with an initial E. coli concentration that exceeded regulatory requirements in order to track the fate and prevalence of E. coli and ARB throughout the entire system (foliage, soil, and leachate) during cultivation and post-harvest storage, and also to demonstrate the worst-case scenario in the event of high E. coli levels in irrigation water. Recent reviews have addressed the technological challenges of implementing these federal guidelines for the specific case of alternative water sources (e.g., treated wastewater and brackish water; Markland et al, 2017;Rock et al, 2019) that would benefit with data-informed decision support tools being actively used to monitor microbial contamination (McLamore et al, 2019;Giacobassi et al, 2021).…”

Aptamers for Detection and Diagnostics (ADD) is a proposed mobile app acquiring optical data from conjugated quantum nanodots to identify molecules indicating presence of SARS-CoV-2 virus: Why public health and healthcare need smartphone sensors as a platform for early detection and prevention

“…Just because the user can detect the presence of mercury in drinking water does not mean that the user has another alternative source of drinking water in under-served or dystopian communities. Is it more or less psychologically debilitating to drink water or consume food if the user is cognizant that the water is contaminated with mercury 352 or the food is laced with bacteria 353 beyond the level of food safety?…”