Foodborne illnesses are a growing concern for the food industry and consumers, with millions of cases reported every year. Consequently, there is a critical need to develop rapid, sensitive, and inexpensive techniques for pathogen detection in order to mitigate this problem. However, current pathogen detection strategies mainly include time-consuming laboratory methods and highly trained personnel. Electrochemical in-field biosensors offer a rapid, low-cost alternative to laboratory techniques, but the electrodes used in these biosensors require expensive nanomaterials to increase their sensitivity, such as noble metals (e.g., platinum, gold) or carbon nanomaterials (e.g., carbon nanotubes, or graphene). Herein, we report the fabrication of a highly sensitive and label-free laser-induced graphene (LIG) electrode that is subsequently functionalized with antibodies to electrochemically quantify the foodborne pathogen Salmonella enterica serovar Typhimurium. The LIG electrodes were produced by laser induction on polyimide film in ambient conditions, and hence circumvent the need for hightemperature, vacuum environment, and metal seed catalysts commonly associated with graphene-based electrodes fabricated via chemical vapor deposition processes. After functionalization with Salmonella-antibodies, the LIG biosensors were able to detect live Salmonella in chicken broth across a wide linear range (25 to 10 5 CFU mL -1 ) and with a low detection limit (13 ± 7 CFU mL -1 ; n = 3, mean ± standard deviation). These results were acquired with an average response time of 22 minutes without the need for sample preconcentration or redox labeling techniques. Moreover, these LIG immunosensors displayed high selectivity as demonstrated by non-significant response to other bacteria strains. These results demonstrate how LIG-based electrodes can be used for electrochemical immunosensing in general and, more specifically, could be used as a viable option for rapid, low-cost pathogen detection in food processing facilities before contaminated foods reach the consumer.
The integration of microfluidics
and electrochemical cells is at
the forefront of emerging sensors and energy systems; however, a fabrication
scheme that can create both the microfluidics and electrochemical
cells in a scalable fashion is still lacking. We present a one-step,
mask-free process to create, pattern, and tune laser-induced graphene
(LIG) with a ubiquitous CO2 laser. The laser parameters
are adjusted to create LIG with different electrical conductivity,
surface morphology, and surface wettability without the need for postchemical
modification. Such definitive control over material properties enables
the creation of LIG-based integrated open microfluidics and electrochemical
sensors that are capable of dividing a single water sample along four
multifurcating paths to three ion selective electrodes (ISEs) for
potassium (K+), nitrate (NO3
–), and ammonium (NH4
+) monitoring and to an
enzymatic pesticide sensor for organophosphate pesticide (parathion)
monitoring. The ISEs displayed near-Nernstian sensitivities and low
limits of detection (LODs) (10–5.01 M, 10–5.07 M, and 10–4.89 M for the K+, NO3
–, and NH4
+ ISEs,
respectively) while the pesticide sensor exhibited the lowest LOD
(15.4 pM) for an electrochemical parathion sensor to date. LIG was
also specifically patterned and tuned to create a high-performance
electrochemical micro supercapacitor (MSC) capable of improving the
power density by 2 orders of magnitude compared to a Li-based thin-film
battery and the energy density by 3 orders of magnitude compared to
a commercial electrolytic capacitor. Hence, this tunable fabrication
approach to LIG is expected to enable a wide range of real-time, point-of-use
health and environmental sensors as well as energy storage/harvesting
modules.
Currently, improvement of food preservation has been a substantial challenge for industries to increase shelf-life of products and to maintain food quality during storage. These goals are often tied to the sustainable tendency for use of eco-friendly packaging to store these products without loss of the packaging features. Therefore, the aim of this study was to produce biodegradable antimicrobial films by the incorporation of nisin Z peptide under different concentrations (0 %, 5 %, 10 %, 15 % and 20 % wt.) into hydroxypropylmethylcellulose (HPMC) matrices. The active film properties were evaluated in terms of their antimicrobial capacity in vitro, mechanical performance and microscopic characteristics. Hence, active films containing 10 % (wt.) of nisin Z and control films were placed in contact with sliced mozzarella cheese for eight days, and microbiological growth was monitored during storage. Nisin Z’s antimicrobial effects were observed against the Gram-positive microorganisms such as Staphylococcus aureus and Listeria innocua, regardless if the compound was free as a suspension or incorporated into HPMC matrices. However, the expected low action of nisin Z against Gram-negative bacteria, as reported in literature, was not observed since Salmonella enterica Choleraesuis’s growth was inhibited. Moreover, active films with added nisin Z (10 % wt.) were more effective than the control film to inhibit mesophilic microorganisms in mozzarella cheese during 8 days of storage. The mechanical properties of the films were not influenced by nisin Z incorporation, since the addition of the compound enhanced the active function without the loss of mechanical properties required for a good food packaging. These results suggest that biodegradable films produced by nisin Z addition into HPMC matrix are an excellent biomaterial for mozzarella cheese preservation.
The objective of this work was to develop gluten-free cookies and savory fried pies using tannin-rich sorghum (Sorghum bicolor) flour, to evaluate their in vitro starch digestibility, and to verify how knowledge of sorghum benefits may contribute to the sensory acceptability of both products. The contents of rapidly digestible starch, slowly digestible starch, and resistant starch were determined. Sensory acceptance was evaluated in two sessions: one without information on sorghum benefits to human health; and another where this information was presented. The resistant starch and slowly digestible starch contents of the cookies (5.07 and 16.22%, respectively) were about twice those of the savory fried pies (2.54 and 8.89%, respectively), whereas the opposite was observed for the rapidly digestible starch contents (9.89 and 19.65%, respectively). The cookies and savory fried pies were sensorially accepted, with a significant increase in the means of the sensory scores after the information on sorghum benefits was disclosed. Therefore, gluten-free cookies and savory fried pies prepared with tannin sorghum flour have a great commercial potential, shown by the good sensory acceptance and by the slowly digestible starch and resistant starch contents of these products.
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