The objective of this study was to investigate the combined effect of thermosonication (TS) and pulsed electric fields (PEF) against Saccharomyces cerevisiae in Chinese rice wine. The effectiveness of standalone TS treatment (35 °C, 750  W, 120 min) on the inactivation of S. cerevisiae was insignificant (0.76 log CFU/mL). However, 2.88 log CFU/mL of S. cerevisiae were inactivated when the standalone PEF treatment with moderate conditions (35 °C, 12 kV/cm, 120 μs) was applied. The combination of TS and PEF had an additive effect on the inactivation of S. cerevisiae, and the sequence applied (TS-PEF or PEF-TS) markedly influenced the inactivation results (P < 0.05). In particular, the microbial inactivation by TS-PEF (3.72 log CFU/mL) was higher than that by PEF-TS (3.48 log CFU/mL); this result indicates that PEF were able to restrain the effect of TS. On the other hand, TEM micrographs of S. cerevisiae after the different treatments showed that the combined techniques resulted in more severe disruptions on cells. Higher cytoplasmic shrinkage and more intracellular material leakage were observed from the TEM observations of the cells treated by TS-PEF. These results may serve as a reference of the potential application of the combined treatment TS-PEF for microbial inactivation in Chinese rice wine.

•Aptamer biosensor for BPA based on label-free electrochemical determination.•Simple and easy to use for small size molecules assays.•GNPs/GR nanocomposites were used as effective sensing platform.•Method demonstrated successful quantification of BPA in milk samples.A simple and label-free electrochemical aptasensor for bisphenol A (BPA) determination was developed based on gold nanoparticles dotted graphene (GNPs/GR) nanocomposite film modified glassy carbon electrode (GCE). The electrochemical probe of ferricyanide was used to investigate the interactions between aptamer and BPA. The resulting GNPs/GR layer exhibited good current response for BPA detection. The highly conductive and biocompatible nanostructure of GNPs/GR nanocomposite was characterised by atomic force microscope (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The peak current change (ΔI) of ferricyanide was linear with the concentration of BPA in the range from 0.01 μM to 10 μM with the detection limit of 5 nM. The proposed aptasensor is rapid, convenient and low-cost for effective sensing of BPA. Particularly, the aptasensor was applied successfully to determine BPA in milk products, and the average recovery was 105%.

Pulsed electric field (PEF) is a promising nonthermal food preservation technology that is based on the use of electric field to eradicate spoilage and pathogenic microorganisms in food products. The effect of various biological factors on the transmembrane potential of different microorganisms (Staphyloccocus aureus, Escherichia coli DH5α, and Saccharomyces cerevisiae) was investigated by means of both numerical simulation and experimental method. The PEF resistance of different microorganisms in grape juice was compared by applying field strength of 12–24 kV/cm, treatment time of 30–180 μs, and an initial temperature of 30 ºC. The results showed that S. cerevisiae exhibited the least resistance to PEF treatment, E. coli DH5α the second, and S. aureus the third. The simulation results indicated that larger cells like S. cerevisiae presented the higher values of transmembrane potential and induced field strength around the cells compared to E. coli DH5α and S. aureus, which led to a less resistance to PEF treatment. The effect of cell orientation on the induced transmembrane potential was very slight (1.67 % for E. coli DH5α and 3.43 % for S. cerevisiae). The thicker cell membrane caused concentrated electric field in the cell membrane, which enhanced the sensitivity of microorganism to PEF treatment. However, both transmembrane potential and electric field strength decreased with the thickness of cell wall increasing. According to both experimental and simulation results, it was evident that there was significant difference in the inactivation rate between different microorganisms, which could be largely attributed to the biological factors of different microorganisms.

A novel carbon composite electrode has been fabricated using ionic liquid n-octylpyridinum hexafluorophosphate (OPFP) and single-walled carbon nanotube (SWCNT). This electrode combined the advantages of ionic liquid and SWCNT as well as the characteristics of the “bulk” composite electrodes. Compared with the commercial glassy carbon electrode (GCE) and the ionic liquid–graphite (IL-G) composite electrode, the ionic liquid–SWCNT (IL-SWCNT) composite electrode exhibited remarkable increase in the electron transfer rate for electroactive compound and significant decrease in the overpotential for the oxidation of nitrite. Based on the enhanced electrocatalytic activity for the oxidation of nitrite, a wide linear range from 1.0 μM to 12.0 mM with a low detection limit of 0.1 μM was obtained. Furthermore, the IL-SWCNT electrode was applied to determine nitrite levels in milk samples. Experimental results showed that the proposed electrode could be used as an effective and sensitive sensor for the determination of nitrite.

Herein, we present a simple electrochemical tetracycline (TET) aptasensor with multi-walled carbon nanotubes (MWCNTs) modification. MWCNTs were dropped on the glassy carbon electrode (GCE) to immobilize the anti-TET aptamer and to construct the aptasensor. The stepwise assembly process of the aptasensor was characterized by cyclic voltammetry. Results demonstrated that the peak currents of Fe(CN)63−/Fe(CN)64− redox pair decreased due to the formation of anti-TET/TET complexes on the modified electrode. The optimization of the loading amount of MWCNTs, the incubating conditions of aptamer and the detection time of TET were investigated in details. Under optimal conditions, the peak currents change obtained by DPV increased linearly with the increasing TET concentrations in the range from 1 × 10−8 M to 5 × 10−5 M with a linear coefficiency of 0.995. This electrochemical aptasensor has a detection limit of 5 × 10−9 M and was successfully applied to the determination of TET in spiked milk samples.

A label-free capacitive immunosensor based on quartz crystal Au electrode was developed for rapid and sensitive detection of Escherichia coli O157:H7. The immunosensor was fabricated by immobilizing affinity-purified anti-E. coli O157:H7 antibodies onto self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA) on the surface of a quartz crystal Au electrode. Bacteria suspended in solution became attached to the immobilized antibodies when the immunosensor was tested in liquid samples. The change in capacitance caused by the bacteria was directly measured by an electrochemical detector. An equivalent circuit was introduced to simulate the capacitive immunosensor. The immunosensor was evaluated for E. coli O157:H7 detection in pure culture and inoculated food samples. The experimental results indicated that the capacitance change was linearly correlated with the cell concentration of E. coli O157:H7. The immunosensor was able to discriminate between cellular concentrations of 102–105 cfu mL−1 and has applications in detecting pathogens in food samples. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were also employed to characterize the stepwise assembly of the immunosensor.

Aptamer with small molecular weight, simple structure, and easy synthesis, which can be used repeatedly and preserved for long time, has important applications in biosensor field. This article describes several commonly used methods for fixing aptamer onto the sensor surfaces, including the gold-sulfur self-assembled monolayer, covalent bond, biotin/avidin affinity, complementary nucleic acid chain connection, as well as current research progress and the characteristics of each method. Development of aptasensors with wide detection range, low detection limit, short detection time, and capability of detection of multitargets will certainly facilitate its application in food quality and safety testing, disease diagnosis, drug analysis, environment monitoring, etc.

Nonspecific interactions between immobilized biomolecules and interfering proteins significantly impede biosensor development and commercialization. Advances in bioinformatics and computer technology have facilitated a greater understanding of biological interactions. We employed two different protein–protein docking programs to simulate the nonspecific interaction between ampicillin antibody and potential interfering proteins (human serum albumin and ovalbumin). To evaluate the contact and probability of association with the active site of the antibody, different amino acid chains from human serum albumin (HSA) and ovalbumin (OVA) were modeled in the simulation. In addition, a well-known specific immune complex, lysozyme and lysozyme antibody, was simulated for comparison. The results demonstrated that the cluster density of nonspecific interactions was smaller than the specific interaction between lysozyme and antibody, and that the dock scores were scattered. However, the active site of ampicillin antibody was prone to nonspecific protein interactions. The strength of interaction was different for specific binding and nonspecific binding. These results provide a platform for detecting the probability of nonspecific interactions and for improving methods of biosensor detection construction with reduced nonspecific adsorption.

As a potential pandemic threat to human health, there has been an urgent need for rapid detection of the highly pathogenic avian influenza (AI) H5N1 virus. In this study, magnetic nanobeads amplification based quartz crystal microbalance (QCM) immunosensor was developed as a new method and application for AI H5N1 virus detection. Polyclonal antibodies against AI H5N1 virus surface antigen HA (Hemagglutinin) were immobilized on the gold surface of the QCM crystal through self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHDA). Target H5N1 viruses were then captured by the immobilized antibodies, resulting in a change in the frequency. Magnetic nanobeads (diameter, 30 nm) coated with anti-H5 antibodies were used for further amplification of the binding reaction between antibody and antigen (virus). Both bindings of target H5N1 viruses and magnetic nanobeads onto the crystal surface were further confirmed by environmental scanning electron microscopy (ESEM). The QCM immunosensor could detect the H5N1 virus at a titer higher than 0.0128 HA unit within 2 h. The nanobeads amplification resulted in much better detection signal for target virus with lower titers. The response of the antibody–antigen (virus) interaction was shown to be virus titer-dependent, and a linear correlation between the logarithmic number of H5N1 virus titers and frequency shift was found from 0.128 to 12.8 HA unit. No significant interference was observed from non-target subtypes such as AI subtypes H3N2, H2N2, and H4N8. The immunosensor was evaluated using chicken tracheal swab samples. This research demonstrated that the magnetic nanobeads amplification based QCM immunosensor has a great potential to be an alternative method for rapid, sensitive, and specific detection of AI virus H5N1 in agricultural, food, environmental and clinical samples.

•Influence of hitting ball and tray were investigated to optimize acoustic device.•Indicator MI1 was more appropriate to determine firmness compared with f2m.•Linear regression and artificial neural network were used to build firmness models.•Increase of nodes in hidden layer of ANN did not improve models performance much.Firmness can be used to indicate ripeness of many agro-products, usually determined by acoustic impulse method nondestructively. An acoustic device was developed after investigating the influence of hitting ball and fruit tray on spectrum. Three firmness indices such as f2m, MI1 (index of the first order moment) and MI2 (index of the second order moment) were proposed to correlate with firmness of watermelon. Significant correlation was found out between firmness and these indices using linear regressive model and nonlinear model of artificial neutral network (ANN). It was concluded the linear model was more suitable than nonlinear model using ANN because of little difference of correlation coefficients. Although more computations needed, index MI1 was considered more precisely to use as firmness indices than f2m in the case of splitting peaks with almost the same amplitude around the first resonant frequency.