Modular graphene mediator film-based electrochemical pocket device for chlorpyrifos determination

Laser-induced 2D/0D graphene-nanoceria freestanding paper-based films for on-site hydrogen peroxide monitoring in no-touch disinfection treatments

A one-shot CO2 laser-based strategy to generate conductive reduced graphene oxide (rGO) decorated with nanoceria (nCe) is proposed. The 2D/0D rGO-nCe films, integrated as catalytic sensing layers in paper-based sensors, were employed for on-site monitoring of indoor fogging treatments against Listeria monocytogenes (Lm), a ubiquitous pathogenic bacterium. The rGO-nCe laser-assisted synthesis was optimized to preserve the rGO film morphological and electron-transfer features and simultaneously integrate catalytic nCe. The films were characterized by microscopical (SEM), spectroscopical (EDX, Raman, and FTIR), and electrochemical techniques. The most performing film was integrated into a nitrocellulose substrate, and the complete sensor was assembled via a combination of xurography and stencil printing. The rGO-nCe sensor's catalytic activity was proved toward the detection of H2O2, obtaining sensitive determination (LOD = 0.3 µM) and an extended linear range (0.5-1500 µM). Eventually, the rGO-nCe sensor was challenged for the real-time continuous monitoring of hydrogen peroxide aerosol during no-touch fogging treatment conducted following the EU's recommendation for biocidal product use. Treatment effectiveness was proved toward three Lm strains characterized by different origins, i.e., type strain ATCC 7644, clinical strain 338, and food strain 641/6II. The sensor allows for discrimination and quantification treatments at different environmental biocidal amounts and fogging times, and correlates with the microbiological inhibition, promoting the proposed sensor as a useful tool to modulate and monitor no-touch treatments.

Enhanced Electron Transfer Efficiency of Fructose Dehydrogenase onto Roll-to-Roll Thermal Stamped Laser-Patterned Reduced Graphene Oxide Films

Herein, a strategy to stamp laser-produced reduced graphene oxide (rGO) onto flexible polymers using only office-grade tools, namely, roll-to-roll thermal stamping, is proposed, proving for the first time its effectiveness for direct bioelectrocatalysis. This straightforward, scalable, and low-cost approach allows us to overcome the limits of the integration of laser-induced rGO-films in bioanalytical devices. Laser-produced rGO has been thermally stamped (TS) onto different polymeric substrates (PET, PVC, and EVA) using a simple roll-laminator; the obtained TS-rGO films have been compared with the native rGO (untransferred) via morphochemical and electrochemical characterization. Particularly, the direct electron transfer (DET) reaction between fructose dehydrogenase (FDH) and TS-rGO transducers has been investigated, with respect to the influence of the amount of enzyme on the catalytic process. Remarkable differences have been observed among TS-rGO transducers; PET proved to be the elective substrate to support the transfer of the laser-induced rGO, allowing the preservation of the morphochemical features of the native material and returning a reduced capacitive current. Noteworthily, TS-rGOs ensure superior electrocatalysis using a very low amount of FDH units (15 mU). Eventually, TS-rGO-based third-generation complete enzymatic biosensors were fabricated via low-cost benchtop technologies. TS-rGOPET exhibited bioanalytical performances superior to the native rGO, allowing a sensitive (0.0289 μA cm-2 μM-1) and reproducible (RSD = 3%, n = 3) d-fructose determination at the nanomolar level (LOD = 0.2 μM). TS-rGO exploitability as a point-of-need device was proved via the monitoring of d-fructose during banana (Musa acuminata) postharvest ripening, returning accurate (recoveries 110-90%; relative error -13/+1%) and reproducible (RSD ≤ 7%; n = 3) data.

Graphene-based functional electrochemical sensors for the detection of chlorpyrifos in water and food samples: a review

Prolonged and excessive use of chlorpyrifos (CPS) has caused severe pollution, particularly in crops, vegetables, fruits, and water sources. As a result, CPS is detected in various food and water samples using conventional methods. However, its applications are limited due to size, portability, cost, etc. In this regard, electrochemical sensors are preferred for CPS detection due to their high sensitivity, reliability, rapid, on-site detection, and user-friendly. Notably, graphene-based electrochemical sensors have gained more attention due to their unique physiochemical and electrochemical properties. It shows high sensitivity, selectivity, and quick response because of its high surface area and high conductivity. In this review, we have discussed an overview of three graphene-based different functional electrochemical sensors such as electroanalytical sensors, bio-electrochemical sensors, and photoelectrochemical sensors used to detect CPS in food and water samples. Furthermore, the fabrication and operation of these electrochemical sensors using various materials (low band gap material, nanomaterials, enzymes, antibodies, DNA, aptamers, and so on) and electrochemical techniques (CV, DPV, EIS, SWV etc.) are discussed. The study found that the electrical signal was reduced with increasing CPS concentration. This is due to the blocking of active sites, reduced redox reaction, impedance, irreversible reactions, etc. In addition, acetylcholinesterase-coupled sensors are more sensitive and stable than others. Also, it can be further improved by fabricating with low band gap nanomaterials. Despite their advantages, these sensors have significant drawbacks, such as low reusability, repeatability, stability, and high cost. Therefore, further research is required to overcome such limitations.

One-Step Laser Nanostructuration of Reduced Graphene Oxide Films Embedding Metal Nanoparticles for Sensing Applications

The combination of two-dimensional materials and metal nanoparticles (MNPs) allows the fabrication of novel nanocomposites with unique physical/chemical properties exploitable in high-performance smart devices and biosensing strategies. Current methods to obtain graphene-based films decorated with noble MNPs are cumbersome, poorly reproducible, and difficult to scale up. Herein, we propose a straightforward, versatile, surfactant-free, and single-step technique to produce reduced graphene oxide (rGO) conductive films integrating "naked" noble MNPs. This method relies on the instantaneous laser-induced co-reduction of graphene oxide and metal cations, resulting in highly exfoliated rGO nanosheets embedding gold, silver, and platinum NPs. The production procedure has been optimized, and the obtained nanomaterials are fully characterized; the hybrid nanosheets have been easily transferred onto lab-made screen-printed electrodes preserving their nanoarchitecture. The Au@rGO-, Ag@rGO-, and Pt@rGO-based electrodes have been challenged to detect caffeic acid, nitrite, and hydrogen peroxide in model solutions and real samples. The sensors yielded quantitative responses (R² ≥ 0.997) with sub-micromolar limits of detections (LODs ≤ 0.6 μM) for all the analytes, allowing accurate quantification in samples (recoveries ≥ 90%; RSD ≤ 14.8%, n = 3). This single-step protocol which requires low cost and minimal equipment will allow the fabrication of free-standing, MNP-embedded rGO films integrable into a variety of scalable smart devices and biosensors.

Properties of a Novel Salmonella Phage L66 and Its Application Based on Electrochemical Sensor-Combined AuNPs to Detect Salmonella

Salmonella is widespread in nature and poses a significant threat to human health and safety. Phage is considered as a new tool for the control of food-borne pathogens. In this study, Salmonella phage L66 (phage L66) was isolated from sewage by using Salmonella Typhimurium ATCC 14028 as the host bacterium, and its basic properties were obtained by biological and bioinformatics analysis. Phage L66 had a broad host spectrum, with an optimal infection complex of 0.1 and an optimal adsorption rate of 90.06%. It also exhibited thermal stability between 30 °C~60 °C and pH stability pH from 3 to 12, and the average lysis amount was 46 PFU/cell. The genome sequence analysis showed that the genome length of phage L66 was 157,675 bp and the average GC content was 46.13%. It was predicted to contain 209 genes, 97 of which were annotated with known functions based on the evolutionary analysis, and phage L66 was attributed to the Kuttervirus genus. Subsequently, an electrochemical sensor using phage L66 as a recognition factor was developed and the working electrode GDE-AuNPs-MPA-Phage L66 was prepared by layer-by-layer assembly for the detection of Salmonella. The slope of the impedance was 0.9985 within the scope from 20 to 2 × 10⁷ CFU/mL of bacterial concentration. The minimum detection limit of the method was 13 CFU/mL, and the average spiked recovery rate was 102.3% with a relative standard deviation of 5.16%. The specificity and stability of this sensor were excellent, and it can be applied for the rapid detection of Salmonella in various foods. It provides a phage-based electrochemical biosensor for the detection of pathogenic bacteria.