Ultrasensitive and Highly Selective Detection of Staphylococcus aureus at the Single-Cell Level Using Bacteria-Imprinted Polymer and Vancomycin-Conjugated MnO2 Nanozyme.

Pathogenic bacterial infections, even at extremely low concentrations, pose significant threats to human health. However, the challenge persists in achieving high-sensitivity bacterial detection, particularly in complex samples. Herein, we present a novel sandwich-type electrochemical sensor utilizing bacteria-imprinted polymer (BIP) coupled with vancomycin-conjugated MnO2 nanozyme (Van@BSA-MnO2) for the ultrasensitive detection of pathogenic bacteria, exemplified by Staphylococcus aureus (S. aureus). The BIP, in situ prepared on the electrode surface, acts as a highly specific capture probe by replicating the surface features of S. aureus. Vancomycin (Van), known for its affinity to bacterial cell walls, is conjugated with a Bovine serum albumin (BSA)-templated MnO2 nanozyme through EDC/NHS chemistry. The resulting Van@BSA-MnO2 complex, serving as a detection probe, provides an efficient catalytic platform for signal amplification. Upon binding with the captured S. aureus, the Van@BSA-MnO2 complex catalyzes a substrate reaction, generating a current signal proportional to the target bacterial concentration. The sensor displays remarkable sensitivity, capable of detecting a single bacterial cell in a phosphate buffer solution. Even in complex milk matrices, it maintains outstanding performance, identifying S. aureus at concentrations as low as 10 CFU mL-1 without requiring intricate sample pretreatment. Moreover, the sensor demonstrates excellent selectivity, particularly in distinguishing target S. aureus from interfering bacteria of the same genus at concentrations 100-fold higher. This innovative method, employing entirely synthetic materials, provides a versatile and low-cost detection platform for Gram-positive bacteria. In comparison to existing nanozyme-based bacterial sensors with biological recognition materials, our assay offers distinct advantages, including enhanced sensitivity, ease of preparation, and cost-effectiveness, thereby holding significant promise for applications in food safety and environmental monitoring.

Dual Synthetic Receptor-Based Sandwich Electrochemical Sensor for Highly Selective and Ultrasensitive Detection of Pathogenic Bacteria at the Single-Cell Level.

Sensitive and rapid detection of pathogenic bacteria is essential for effective source control and prevention of microbial infectious diseases. However, it remains a substantial challenge to rapidly detect bacteria at the single-cell level. Herein, we present an electrochemical sandwich sensor for highly selective and ultrasensitive detection of a single bacterial cell based on dual recognition by the bacteria-imprinted polymer film (BIF) and aptamer. The BIF was used as the capture probe, which was in situ fabricated on the electrode surface within 15 min via electropolymerization. The aptamer and electroactive 6-(Ferrocenyl)hexanethiol cofunctionalized gold nanoparticles (Au@Fc-Apt) were employed as the signal probe. Once the target bacteria were anchored on the BIF-modified electrode, the Au@Fc-Apt was further specifically bound to the bacteria, generating enhanced current signals for ultrasensitive detection of Staphylococcus aureus down to a single cell in phosphate buffer solution. Even in the complex milk samples, the sensor could detect as low as 10 CFU mL-1 of S. aureus without any complicated pretreatment except for 10-fold dilution. Moreover, the current response to the target bacteria was hardly affected by the coexisting multiple interfering bacteria, whose number is 30 times higher than the target, demonstrating the excellent selectivity of the sensor. Compared with most reported sandwich-type electrochemical sensors, this assay is more sensitive and more rapid, requiring less time (1.5 h) for the sensing interface construction. By virtue of its sensitivity, rapidity, selectivity, and cost-effectiveness, the sensor can serve as a universal detection platform for monitoring pathogenic bacteria in fields of food/public safety.

Reusable and universal impedimetric sensing platform for the rapid and sensitive detection of pathogenic bacteria based on bacteria-imprinted polythiophene film.

The rapid and sensitive detection of pathogenic bacteria is highly demanded for early warning of infectious disease epidemics and protection of human health. Herein, a reusable and universal impedimetric sensing platform based on a bacteria-imprinted polythiophene film (BIF) is proposed for the rapid and sensitive detection of pathogenic bacteria using Staphylococcus aureus (S. aureus) as a model analyte. Monomer screening among four 3-substituted thiophenes was first performed based on the imprinting factor, and 3-thiopheneethanol (TE) was eventually selected. The BIF as a recognition layer was quickly deposited in an environmentally friendly process on a glassy carbon electrode via electro-copolymerization of the S. aureus template and TE monomer followed by in situ template removal. Upon rebinding of S. aureus on the BIF, the impedance increased. Under optimal conditions, the BIF-based sensor can quantitatively detect S. aureus in a wide linear range of 10 to 107 CFU mL-1 with a low detection limit of 4 CFU mL-1. Additionally, the sensor exhibits excellent selectivity, capable of identifying S. aureus from multi-bacterial strain mixtures. It also demonstrates applicability in the analysis of real lettuce and shrimp samples with good recoveries. Most significantly, the BIF sensing interface can be reused up to five times with good signal retention. Compared with most reported methods, this sensor is more rapid with a much shorter total assay time of 30 min, including the BIF preparation, bacterial rebinding, and impedance detection. This assay may hold great potential to help in the rapid, sensitive, and label-free detection of pathogenic bacteria in fields of food safety and public health.

Microwave Heating Characteristics on Lipid Quality in Sterilized Rainbow Trout (Oncorhynchus mykiss) Using Designed Heating Processing.

The aim of this study was to simulate microwave heating characteristics to investigate the lipid quality in rainbow trout, including the impact of the heating rate, maximum temperature, and thermal processing level on the extent of lipid oxidation and on the fatty acid extraction coefficient. Increasing F0 from 3 to 6 min improved fatty acid retention at high heating rates but led to a decrease in the measured results at low heating rates. Elevated thermal processing levels and maximum temperatures were observed to intensify the oxidation. At F0 = 3 min, an increase in maximum temperature led to an increase in the total lipid extraction coefficient but a decrease in the fatty acid extraction coefficient. However, an increase in maximum temperature resulted in a decrease in both extraction coefficients when F0 was 6 min. The coefficient spectra of fatty acid extraction obtained from the microwave and traditional heat treatments showed nonparallel trends, confirming the presence of non-thermal effects during microwave thermal processing. In conclusion, compared to conventional heat treatment methods, microwave processing has significant potential for enhancing the lipid quality of ready-to-eat rainbow trout products and effectively reducing production costs.

Effects of high-temperature short-time processing on nutrition quality of Pacific saury (Cololabis saira) using extracted fatty acids as the indicator.

Microwave thermal processing is a promising technology to greatly improve product quality by achieving high-temperature short-time (HTST) processing for solid foods. And the non-thermal effect of microwave fields on nutritional quality is a major public concern. To distinguish the non-thermal effect of microwave fields, the thermal effect of HTST processing should be revealed first. The objective of this study was to investigate the effects of different HTST processing on quality of Pacific saury fillets using extracted fatty acids as the indicator. A self-developed thermal processing system was used to conduct the HTST processing with different heating rate (5.48-18.30°C/min), maximum heating temperature (123, 133 °C), and thermal processing level (F 0 = 3.0 min, 6.0 min). Results showed that the extraction coefficient of lipids and fatty acids decreased with increasing heating rates, which implied less thermal damage of fish tissue, while higher thermal processing level increased these extraction coefficients. However, higher maximum processing temperature caused serious thermal damage of fatty acids, especially for PUFAs. Furthermore, changing pattern of each fatty acid during different HTST processing was revealed, which provided fundamental data for designing microwave thermal processing and exploring microwave non-thermal effects.

Studying the non-thermal effects of microwave on amino acids in sterilized rainbow trout (Oncorhynchus mykiss) fillets using a double side approximating method.

The aim of this study was to investigate the impact of microwave non-thermal effects on thermal sensitive amino acids in rainbow trout (Oncorhynchus mykiss) fillets. To distinguish non-thermal effects from thermal effects occurring simultaneously, a Double Side Approximating Method (DSAM) derived from computational mathematics was developed. Two corresponding water bath treatments were designed for each microwave processing to approximate the time-temperature profiles at the hot and cold spots of the microwave processed samples while maintaining a comparable thermal intensity (F0). The microwave non-thermal effects on amino acids were determined by comparing the amount of each of 22 amino acids between the microwave processed and the two corresponding water bath treated rainbow trout fillets. The results indicated that the DSAM was successfully implemented, as the amino acid contents' order curve in the microwave processed samples was clearly exceeded the boundary formed by the two corresponding water bath treated samples. This finding confirmed the occurrence of microwave non-thermal effects on amino acids. The non-thermal effect resulted in a notable increase in the quantity of most amino acids, while it reduced the content of Lys and Hyp. Longer microwave processing times intensified these effects, while higher thermal processing intensities resulted in more damage to each amino acid.

Effects of Microwave Pasteurization on the Quality and Shelf-Life of Low-Sodium and Intermediate-Moisture Pacific Saury (Cololabis saira).

The objective of this study was to investigate the effects of microwave pasteurization on the quality and shelf-life of low-sodium and intermediate-moisture Pacific saury. Microwave pasteurization was used to process low-sodium (1.07% ± 0.06%) and intermediate-moisture saury (moisture content 30% ± 2%, water activity 0.810 ± 0.010) to produce high-quality ready-to-eat food stored at room temperature. Retort pasteurization with the same thermal processing level of F90 = 10 min was used for comparison. Results showed that microwave pasteurization had significantly (p < 0.001) shorter processing times (9.23 ± 0.19 min) compared with traditional retort pasteurization (17.43 ± 0.32 min). The cook value (C) and thiobarbituric acid (TBARS) content of microwave-pasteurized saury were significantly lower than that of retort-pasteurized saury (p < 0.05). With more microbial inactivation, microwave pasteurization brought better overall texture than retort processing. After 7 days of storage at 37 °C, the total plate count (TPC) and TBARS of microwave pasteurized saury still met the edible standard, while the TPC of retort pasteurized saury no longer did. These results showed that the combined processing of microwave pasteurization and mild drying (Aw < 0.85) could produce high-quality ready-to-eat saury products. These results indicate a new methodology for producing high-quality products stored at room temperature.

Colloidal SERS measurement of enrofloxacin with petaloid nanostructure clusters formed by terminal deoxynucleotidyl transferase catalyzed cytosine-constituted ssDNA.

We developed petal-like plasmonic nanoparticle (PLNP) clusters-based colloidal SERS method for enrofloxacin (EnFX) detection. PLNPs were synthesized by the regulation of single-stranded DNA composed of homo-cytosine deoxynucleotides (hC) catalyzed by terminal deoxynucleotidyl transferase. SERS hot spots were created via the agglomeration process of PLNPs by adding an inorganic salt potassium iodide solution, in which EnFX molecules were attached to the negatively charged PLNPs surface by electrostatic interactions. This approach enabled direct in situ detection of antibiotic residues, achieving a limit of detection (LOD) of 1.15 µg/kg for EnFX. The spiked recoveries of the SERS method were approximately 92.7% to 107.2% and the RSDs ranged from 1.05% to 7.8%, indicating that the method can be applied to actual sample detection. This colloidal SERS measurement platform would be very promising in various applications, especially in real-time and on-site food safety screening owing to its rapidness, simplicity, and sensitivity.

Unlocking the Potential of Microwave Sterilization Technology in Ready-to-Eat Imitation Crab Meat Production.

Microwave sterilization is a novel potential sterilization technology to improve food quality. An industrial microwave sterilization system was used to sterilize imitation crab meat under thermal processing intensity F0 = 1, 2, 3. The characteristics of the microwave process, such as heating rate, processing time, and C100, were calculated. In addition, the quality of processed imitation crab meat was investigated. Compared with the conventional retort method, microwave sterilization significantly shortened the processing time of imitation crab meat by 63.71% to 72.45%. Under the same thermal processing intensity, microwave sterilization has demonstrated better results than retort sterilization in terms of water-holding capacity, color, and texture. Furthermore, microwave-treated imitation crab meat ingredients had a greater capacity to bind water molecules and obtained a more appropriate secondary protein structure. In addition, microwave technology can better preserve the unsaturated fatty acids (UFA) of imitation crab meat, which are 9.14%, 1.19%, and 0.32% higher than the traditional method at F0 = 1, 2, 3. The results would provide useful data for the subsequent research and development of ready-to-eat surimi products.

Quality changes of duck meat during thermal sterilization processing caused by microwave, stepwise retort, and general retort heating.

The quality changes of duck meat during thermal sterilization using microwave, stepwise retort and general retort heating were evaluated. Results showed that compared with stepwise retort and general retort, duck meat subjected to microwave showed significantly higher gumminess, chewiness, cohesiveness and resilience as well as glutamic acid, lysine and total amino acids. Low-field NMR revealed that the relative content of immobilized water after microwave and stepwise retort treatment was significantly higher than that after general retort treatment. The relative content of 1-octen-3-ol with characteristic mushroom aroma was significantly higher with microwave and stepwise retort heating than with general retort heating, while 2-pentyl-furan with poor taste was only detected with general retort heating. The muscle bundles subjected to microwave were neatly arranged, similar to those with no thermal sterilization. Overall, the meat quality after three thermal sterilization treatment was microwave > stepwise retort > general retort.

Fishing unfunctionalized SERS tags with DNA hydrogel network generated by ligation-rolling circle amplification for simple and ultrasensitive detection of kanamycin.

Simple assay format-based SERS methods for sensitive target substance analysis is of great significance for the development of on-site monitoring biosensors. Herein, taking the typical antibacterial kanamycin (KANA) as a subject, a simple, highly sensitive and specific SERS aptasensor was developed by manipulating DNA hydrogel network to fish plasmonic core-shell nanoparticles. A competitive binding mode of aptamer, ligation-rolling circle amplification (L-RCA), gap-containing Au@Au nanoparticles (GCNPs) with embedded Raman reporters were integrated into the sensor. In the presence of KANA, the double stranded DNA (dsDNA) structure of the aptamer was disrupted, and the released primers were used to construct two kinds of circularized padlock probes (CPPs) which were partially complementary. DNA hydrogel network was formed through the intertwining and self-assembly of two RCA-generated single stranded DNA (ssDNA) chains, during which GCNPs and magnetic beads (MBs) were entangled and incorporated. Finally, KANA quantification was successfully achieved through the quantification of the DNA hydrogel. Overall, this novel SERS aptasensor realized a simple and ultrasensitive quantification of KANA down to 2.3 fM, plus excellent selectivity, and precision even for real food samples. In view of innovative fusion across L-RCA-based DNA hydrogel and SERS technique, the proposed method has promising potential for application in on-site detection and quantification of trace food contaminants.

Rapid, sensitive and label-free detection of pathogenic bacteria using a bacteria-imprinted conducting polymer film-based electrochemical sensor.

The rapid and sensitive detection of pathogenic bacteria is very important for timely prevention and treatment of foodborne disease. Here, a bacteria-imprinted conductive poly(3-thiopheneacetic acid) (BICP) film-based impedimetric sensor was developed for the rapid, sensitive and label-free detection of staphylococcus aureus (S. aureus). The BICP film preparation was very convenient and eco-friendly, which was in situ deposited on gold electrode surface without the use of toxic organic solvents and cross-linkers. The process of imprinting and recognition were characterized by electrochemical technique and scanning electron microscope. The BICP had a novel structure without cocci-shaped cavities formed in the poly(3-thiopheneacetic acid) (PTAA) matrices. To obtain the optimal sensing performance, a set of factors affecting the imprinting and recognition were investigated. Under the optimized conditions, an extremely rapid recognition within 10 min, a very low limit of detection (LOD) of 2 CFU/mL, and wide linear range from 10 to 108 CFU/mL were achieved by the BICP film-based impedimetric sensor. The sensor also demonstrated high selectivity, and good universality and repeatability. Furthermore, the feasibility of its application has also been demonstrated in the analysis of real milk samples. This sensor offered a simple and universal method for rapid, sensitive, and selective detection of pathogenic bacteria, which could hold great potentials in fields like food safety.

Frequency Distribution in Domestic Microwave Ovens and Its Influence on Heating Pattern.

In this study, snapshots of operating frequency profiles of domestic microwave ovens were collected to reveal the extent of microwave frequency variations under different operation conditions. A computer simulation model was developed based on the finite difference time domain method to analyze the influence of the shifting frequency on heating patterns of foods in a microwave oven. The results showed that the operating frequencies of empty and loaded domestic microwave ovens varied widely even among ovens of the same model purchased on the same date. Each microwave oven had its unique characteristic operating frequencies, which were also affected by the location and shape of the load. The simulated heating patterns of a gellan gel model food when heated on a rotary plate agreed well with the experimental results, which supported the reliability of the developed simulation model. Simulation indicated that the heating patterns of a stationary model food load changed with the varying operating frequency. However, the heating pattern of a rotary model food load was not sensitive to microwave frequencies due to the severe edge heating overshadowing the effects of the frequency variations.