In this article, several applications of nanomaterials in food packaging and food safety are reviewed, including: polymer/clay nanocomposites as high barrier packaging materials, silver nanoparticles as potent antimicrobial agents, and nanosensors and nanomaterial-based assays for the detection of food-relevant analytes (gasses, small organic molecules and food-borne pathogens). In addition to covering the technical aspects of these topics, the current commercial status and understanding of health implications of these technologies are also discussed. These applications were chosen because they do not involve direct addition of nanoparticles to consumed foods, and thus are more likely to be marketed to the public in the short term.

Applications of nanotechnology in food packaging and food safety: Barrier materials, antimicrobials and sensors

"Nanoantibiotics": a new paradigm for treating infectious diseases using nanomaterials in the antibiotics resistant era.

Nanofluids, the fluid suspensions of nanomaterials, have shown many interesting properties, and the distinctive features offer unprecedented potential for many applications. This paper summarizes the recent progress on the study of nanofluids, such as the preparation methods, the evaluation methods for the stability of nanofluids, and the ways to enhance the stability for nanofluids, the stability mechanisms of nanofluids, and presents the broad range of current and future applications in various fields including energy and mechanical and biomedical fields. At last, the paper identifies the opportunities for future research.

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A review on nanofluids: preparation, stability mechanisms, and applications

The antibacterial effect of zinc oxide (ZnO) nanoparticles on Campylobacter jejuni was investigated for inhibition and inactivation of cell growth. The results showed that C. jejuni was extremely sensitive to treatment with ZnO nanoparticles. The MIC of ZnO nanoparticles for C. jejuni was determined to be 0.05 to 0.025 mg/ml, which is 8- to 16-fold lower than that for Salmonella enterica serovar Enteritidis and Escherichia coli O157:H7 (0.4 mg/ml). The action of ZnO nanoparticles against C. jejuni was determined to be bactericidal, not bacteriostatic. Scanning electron microscopy examination revealed that the majority of the cells transformed from spiral shapes into coccoid forms after exposure to 0.5 mg/ml of ZnO nanoparticles for 16 h, which is consistent with the morphological changes of C. jejuni under other stress conditions. These coccoid cells were found by ethidium monoazide-quantitative PCR (EMA-qPCR) to have a certain level of membrane leakage. To address the molecular basis of ZnO nanoparticle action, a large set of genes involved in cell stress response, motility, pathogenesis, and toxin production were selected for a gene expression study. Reverse transcription-quantitative PCR (RT-qPCR) showed that in response to treatment with ZnO nanoparticles, the expression levels of two oxidative stress genes (katA and ahpC) and a general stress response gene (dnaK) were increased 52-, 7-, and 17-fold, respectively. These results suggest that the antibacterial mechanism of ZnO nanoparticles is most likely due to disruption of the cell membrane and oxidative stress in Campylobacter.

Antibacterial Activity and Mechanism of Action of Zinc Oxide Nanoparticles against Campylobacter jejuni

Nanoparticles (NPs) of copper oxide (CuO), zinc oxide (ZnO) and especially nanosilver are intentionally used to fight the undesirable growth of bacteria, fungi and algae. Release of these NPs from consumer and household products into waste streams and further into the environment may, however, pose threat to the ‘non-target’ organisms, such as natural microbes and aquatic organisms. This review summarizes the recent research on (eco)toxicity of silver (Ag), CuO and ZnO NPs. Organism-wise it focuses on key test species used for the analysis of ecotoxicological hazard. For comparison, the toxic effects of studied NPs toward mammalian cells in vitro were addressed. Altogether 317 L(E)C50 or minimal inhibitory concentrations (MIC) values were obtained for algae, crustaceans, fish, bacteria, yeast, nematodes, protozoa and mammalian cell lines. As a rule, crustaceans, algae and fish proved most sensitive to the studied NPs. The median L(E)C50 values of Ag NPs, CuO NPs and ZnO NPs (mg/L) were 0.01, 2.1 and 2.3 for crustaceans; 0.36, 2.8 and 0.08 for algae; and 1.36, 100 and 3.0 for fish, respectively. Surprisingly, the NPs were less toxic to bacteria than to aquatic organisms: the median MIC values for bacteria were 7.1, 200 and 500 mg/L for Ag, CuO and ZnO NPs, respectively. In comparison, the respective median L(E)C50 values for mammalian cells were 11.3, 25 and 43 mg/L. Thus, the toxic range of all the three metal-containing NPs to target- and non-target organisms overlaps, indicating that the leaching of biocidal NPs from consumer products should be addressed.

https://link.springer.com/content/pdf/10.1007%2Fs00204-013-1079-4.pdf

Toxicity of Ag, CuO and ZnO nanoparticles to selected environmentally relevant test organisms and mammalian cells in vitro: a critical review

Aims: To investigate antibacterial activities of zinc oxide nanoparticles (ZnO NP) and their mode of action against an important foodborne pathogen, Escherichia coli O157:H7.

Methods and Results:  ZnO NP with sizes of 70 nm and concentrations of 0, 3, 6 and 12 mmol l−1 and NP-free solutions were used in antimicrobial tests against E. coli O157:H7. ZnO NP showed increasing inhibitory effects on the growth of E. coli O157:H7 as the concentrations of ZnO NP increased. A complete inhibition of microbial growth was achieved at the concentration level of 12 mmol l−1 or higher. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy were used to characterize the changes of morphology and cellular compositions of bacterial cells treated with ZnO NP and study the mode of action of ZnO NP against E. coli O157:H7. The intensity of lipid and protein bands in the Raman spectra of bacterial cells increased after exposure to ZnO NP, while no significant changes in nucleic acid bands were observed.

Conclusions:  ZnO NP were found to have antibacterial activity against E. coli O157:H7. The inhibitory effects increase as the concentration of ZnO NP increased. Results indicate that ZnO NP may distort and damage bacterial cell membrane, resulting in a leakage of intracellular contents and eventually the death of bacterial cells.

Significance and Impact of the Study:  These results suggest that ZnO NP could potentially be used as an effective antibacterial agent to protect agricultural and food safety.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2672.2009.04303.x

Antibacterial activities of zinc oxide nanoparticles against Escherichia coli O157:H7.

Antifungal activity of zinc oxide nanoparticles against Botrytis cinerea and Penicillium expansum

Vibrational spectroscopic characteristics of melamine, cyanuric acid, and melamine cyanurate were measured using surface-enhanced Raman spectroscopy (SERS) coupled with gold nanosubstrates. Trace amounts of melamine and its analogues (cyanuric acid and melamine cyanurate) were characterized and quantified quickly and accurately by SERS in combination with partial least squares (PLS) analysis. Based on the relationship between the Raman intensity of the most prominent peak at around 676 cm−1 and log values of melamine concentrations, the limit of detection (LOD) of SERS for melamine was estimated to be 2.6 × 10−7 mol L−1 (∼33 ppb). An approximately 3 × 104 fold of enhancement factor for SERS signals of melamine on gold nanosubstrates was obtained. This result was based upon the comparison of the peak at around 676 cm−1 in the SERS spectra with that of normal Raman spectra of melamine in aqueous solutions. SERS spectra of cyanuric acid acquired from its solid form differ significantly from this compound in an aqueous solution, indicating a possible keto-enol isomerization reaction of cyanuric acid in water. When equal amounts of melamine and cyanuric acid were added together, spoke-like crystals of melamine cyanurate formed instantly, which could be measured and characterized by SERS. This study demonstrates that SERS could provide a fast and ultra-sensitive tool for detection and characterization of melamine and its derivative compounds in aqueous solutions.

A new approach to measure melamine, cyanuric acid, and melamine cyanurate using surface enhanced Raman spectroscopy coupled with gold nanosubstrates

Detection of Bacillus spores is of considerable importance to the food industry since they can survive standard processing procedures and sanitation treatments. Surface enhanced Raman spectroscopy (SERS) coupled with gold SERS-active substrates was used to detect and discriminate among five Bacillus spores (B. cereus ATCC 13061, B. cereus ATCC 10876, B. cereus sp., B. subtilis sp., and B. stearothermophilus sp.). Tremendously enhanced Raman signals of Bacillus spores deposited onto the gold substrates were detected, allowing the limit of detection (LOD) of SERS to reach the level of a single spore. Distinct spectral differences were observed between different Bacillus spores. Hierarchical cluster analysis (HCA) and principle component analysis (PCA) show clear data segregations at the species level between five Bacillus spores. Principle component (PC) values indicate that the Raman shift range between 900 and 1200 cm−1 contributed significantly to the total data variance in the PCA results. In particular, a prominent band of dipicolinic acid (DPA) was observed at 998 cm−1 and served as a biomarker for bacterial spores. This study demonstrates that SERS coupled with gold nanosubstrates is able to detect and discriminate single Bacillus spores non-destructively and with minimum sample preparation. SERS method is a promising tool for rapid, ultra-sensitive, and selective detection of bacterial spores, potentially in foods and other complex biological matrices.

Yang Liu

Papers

Antibacterial activities of zinc oxide nanoparticles against Escherichia coli O157:H7.

Antifungal activity of zinc oxide nanoparticles against Botrytis cinerea and Penicillium expansum

A new approach to measure melamine, cyanuric acid, and melamine cyanurate using surface enhanced Raman spectroscopy coupled with gold nanosubstrates

Detecting single Bacillus spores by surface enhanced Raman spectroscopy

Numerical study of heterogeneous porosity in gas diffusion layers of high-temperature proton-exchange membrane fuel cells