Screening and characterization of lactic acid bacteria and fermentation of gamma-aminobutyric acid-enriched bamboo shoots.

In order to produce fermented bamboo shoots with functional properties, two strains of lactic acid bacteria were selected for inoculation and fermentation. One strain, Lactiplantibacillus plantarum R1, exhibited prominent potential probiotic properties (including gastrointestinal condition tolerance, adhesion ability, antimicrobial ability, and antibiotic resistance), while the other, Levilactobacillus brevis R2, demonstrated the capability of high γ-aminobutyric acid (GABA) production (913.99 ± 14.2 mg/L). The synergistic inoculation of both strains during bamboo shoot fermentation led to a remarkable increase in GABA content (382.31 ± 12.17 mg/kg), surpassing that of naturally fermented bamboo shoots by more than 4.5 times and outperforming mono-inoculated fermentation. Simultaneously, the nitrite content was maintained at a safe level (5.96 ± 1.81 mg/kg). Besides, inoculated fermented bamboo shoots exhibited an increased crude fiber content (16.58 ± 0.04 g/100 g) and reduced fat content (0.39 ± 0.02 g/100 g). Sensory evaluation results indicated a high overall acceptability for the synergistically inoculated fermented bamboo shoots. This study may provide a strategy for the safe and rapid fermentation of bamboo shoots and lay the groundwork for the development of functional vegetable products enriched with GABA.

Resveratrol Enhances Anticancer Effects of Silybin on HepG2 Cells and H22 Tumor-bearing Mice via Inducing G2/M Phase Arrest and Increasing Bax/Bcl-2 Ratio.

BACKGROUND: Silybin, a major flavonoid extracted from the seeds of milk thistle, has a strong hepatoprotective but weak anti-hepatoma activity. Screening another natural ingredient and combining it with silybin is expected to improve the anti-hepatoma efficacy of silybin. OBJECTIVE: The objective of this study was to investigate the synergistic anti-hepatoma effect of resveratrol and silybin on HepG2 cells and H22 tumor-bearing mice in hepatocellular carcinoma (HCC) in vitro and in vivo, respectively. METHODS: Cell viability, scratch wound, clone formation, cell apoptosis, cell cycle, and western blot analysis of HepG2 cells were used to investigate the synergistic effects in vitro of the combination resveratrol with silybin. Growth rates, tumor weights, organ indexes, and histological pathological examination in H22 tumor-bearing mice were used to investigate the synergistic effects in vivo. RESULTS: The combination of resveratrol (50 µg/mL) and silybin (100 µg/mL) significantly suppressed cell viability, whose combination index (CI) was 1.63 (>1.15), indicating the best synergism. The combination exhibited the synergistic effect in blocking the migration and proliferative capacity of HepG2 cells in the measurement in vitro. In particular, resveratrol enhanced the upregulation of Bcl-2 expression and the downregulation of Bax expression with a concurrent increase in the Bax/Bcl-2 ratio. The combination of resveratrol (50 mg/kg) and silybin (100 mg/kg) reduced the tumor weight, inhibited the growth rate, increased the organ indexes, and destroyed the tumor tissue morphology in H22 tumor-bearing mice. CONCLUSION: Resveratrol was found to exhibit synergistic anti-cancer effects with silybin on HepG2 cells and H22 tumor-bearing mice.

Transcriptomic and metabolomic analyses to study the key role by which Ralstonia insidiosa induces Listeria monocytogenes to form suspended aggregates.

Ralstonia insidiosa can survive in a wide range of aqueous environments, including food processing areas, and is harmful to humans. It can induce Listeria monocytogenes to form suspended aggregates, resulting from the co-aggregation of two bacteria, which allows for more persistent survival and increases the risk of L. monocytogenes contamination. In our study, different groups of aggregates were analyzed and compared using Illumina RNA sequencing technology. These included R. insidiosa under normal and barren nutrient conditions and in the presence or absence of L. monocytogenes as a way to screen for differentially expressed genes (DEGs) in the process of aggregate formation. In addition, sterile supernatants of R. insidiosa were analyzed under different nutrient conditions using metabolomics to investigate the effect of nutrient-poor conditions on metabolite production by R. insidiosa. We also undertook a combined analysis of transcriptome and metabolome data to further investigate the induction effect of R. insidiosa on L. monocytogenes in a barren environment. The results of the functional annotation analysis on the surface of DEGs and qPCR showed that under nutrient-poor conditions, the acdx, puuE, and acs genes of R. insidiosa were significantly upregulated in biosynthetic processes such as carbon metabolism, metabolic pathways, and biosynthesis of secondary metabolites, with Log2FC reaching 4.39, 3.96, and 3.95 respectively. In contrast, the Log2FC of cydA, cyoB, and rpsJ in oxidative phosphorylation and ribosomal pathways reached 3.74, 3.87, and 4.25, respectively. Thirty-one key components were identified while screening for differential metabolites, which mainly included amino acids and their metabolites, enriched to the pathways of biosynthesis of amino acids, phenylalanine metabolism, and methionine metabolism. Of these, aminomalonic acid and Proximicin B were the special components of R. insidiosa that were metabolized under nutrient-poor conditions.

The inhibitory mechanism of 2-amino-3,8-dimethylimidazo [4,5-f] quinoxaline (MeIQx) formation by ultraviolet-gallic acid (UV-GA) during the oil-frying process of squid.

The inhibitory effect of ultraviolet-gallic acid (UV-GA) on carbonyl valence and intermediates and precursors of 2-amino-3,8-dimethylimidazo [4,5-f] quinoxaline (MeIQx) was investigated to futher clarify the inhibitory mechanism for safety control the quality of oil-fried squid. Ultraviolet C-treated gallic acid (UVC-GA) and ultraviolet B-treated gallic acid (UVB-GA) were produced by ultraviolet 225 nm of band C and 300 nm of band B, respectively. The MeIQx contents in oil-fried squid were significantly higher, and UVC-GA and UVB-GA could significantly inhibit the MeIQx formation and the formation rates of carbonyl valence and precursors (threonine (Thr), creatinine, and glucose). The UVB-GA inhibited formaldehyde formation, while UVC-GA significantly reduced the formaldehyde, acetaldehyde, and 2,5-dimethyl pyrazine contents. In conculsion, UV-GA reduced carbonyl produced from the lipid oxidation to further weaken the catalysis of carbonyl, rendering the MeIQx precursor degrading into the intermediates during Strecker degradation. Thus, the MeIQx formation was inhibited.

Microbial diversity and functional genes of red vinasse acid based on metagenome analysis.

Red vinasse acid has a distinct flavor and a vivid red color that are directly tied to the intricate metabolic activities of microorganisms that produce it. In this study, metagenomic technology was used to mine its functional genes and examine the microbial diversity of red vinasse acid. The findings revealed the identification of 2,609 species, 782 genera, and 63 phyla of microorganisms, and the dominant genus was Lactobacillus. Amino acid metabolism and carbohydrate metabolism were significant activities among the 16,093 and 49,652 genes that were annotated in the evolutionary genealogy of genes: Non-supervised Orthologous Groups (eggNOG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, respectively. In gluconeogenesis, red vinasse acid encodes 194 genes controlling the transporter protein systems of different sugars and has key enzyme genes that catalyze the conversion of intracellular sugars into glycolytic intermediates. In amino acid flavor formation, red vinasse acid contains 32 control genes for branched-chain aminotransferase (BCAT), 27 control genes for aromatic-amino-acid transaminase (ArAT), 60 control genes for keto acid invertase, 123 control genes for alcohol/aldehyde dehydrogenase, and 27 control genes for acetyl esterase, which have the basis for the formation of strong flavor substances from amino acids.

Biosynthesis of Platinum Nanoparticles with Cordyceps Flower Extract: Characterization, Antioxidant Activity and Antibacterial Activity.

The aim of this work is to develop a green route for platinum nanoparticles (PtNPs) biosynthesized using Cordyceps flower extract and to evaluate their antioxidant activity and antibacterial activity. Different characterization techniques were utilized to characterize the biosynthetic PtNPs. The results showed that PtNPs were spherical particles covered with Cordyceps flower extract. The average particle size of PtNPs in Dynamic Light Scattering was 84.67 ± 5.28 nm, while that of PtNPs in Transmission Electron Microscope was 13.34 ± 4.06 nm. Antioxidant activity of PtNPs was evaluated by DPPH free radical scavenging ability test. The results showed that the antioxidant activity was positively correlated with the concentration of PtNPs, the DPPH scavenging efficiency of PtNPs (0.50-125.00 µg/mL) was 27.77-44.00%. In addition, the morphological changes of four kinds of bacteria (Escherichia coli, Salmonella typhimurium, Bacillus subtilis, Staphylococcus aureus) exposed to PtNPs were observed by scanning electron microscope. The results showed that the antibacterial activity of PtNPs against Gram-negative bacteria was stronger than that of Gram-positive bacteria.

Clinical Application of Early Warning Scoring Based on BiLSTM-Attention in Emergency Obstetric Preexamination and Triage.

Maternity is a special category of population and the criteria for emergency prescreening cannot be directly applied to adults. Therefore, a set of criteria for grading maternal conditions should be established. In this paper, we have combined the semantic analysis technique of BiLSTM-Attention neural network and fuzzy defect risk assessment method, to develop a hybrid approach, to preprocess the text of emergency obstetric prescreening information. Furthermore, we have used word2vec to characterize the word embedding vector and highlight the features related to the degree of defects of emergency obstetric prescreening information through the attention mechanism and obtain the semantic feature vector of the warning information. BiLSTM-Attention neural network has the dual advantages of extracting bidirectional semantic information and giving weight to important judgment information which has effectively improved the semantic understanding accuracy. Experimental tests and application analysis show that the judgment model which is based on proposed method has accurately classified and graded the defects of emergency obstetric prescreening alerts. Additionally, the accuracy and microaverage value are used as evaluation indexes.

Involvement of phase II enzymes and efflux transporters in the metabolism and absorption of naringin, hesperidin and their aglycones in rats.

This study examined the effects of phase II metabolism and efflux transportation on the bioavailability of naringin, hesperidin, and their aglycones (naringenin and hesperetin) in rats. Results indicated naringin and hesperidin have a lower oral bioavailability than their aglycones. Of all the phase II enzymes tested, UDP-glucuronosyltransferase (UGT) 1A1, UGT1A2, UGT1A3, UGT1A7 and SULT sulfotransferase (SULT) 1B1 were of minor importance regarding the phase II metabolism of naringenin and hesperetin in the small intestine. Naringin, hesperidin, and their aglycones were all extensively metabolised in the liver. Naringin and hesperidin were more extensively transported by efflux transporters compared to their aglycones. Significant correlations between phase II enzymes and efflux transporters were detected. In conclusion, more extensive metabolism of naringin and hesperidin than their aglycones in the small intestine, and the interplay of phase II enzymes and efflux transporters in the small intestine explain the lower relative oral bioavailability of naringin and hesperidin than their aglycones.

Gene Analysis of Listeria monocytogenes Suspended Aggregates Induced by Ralstonia insidiosa Cell-Free Supernatants under Nutrient-Poor Environments.

Listeria monocytogenes is a zoonotic food-borne pathogen. The production of food-borne pathogenic bacteria aggregates is considered to be a way to improve their resistance and persistence in the food chain. Ralstonia insidiosa has been shown to induce L. monocytogenes to form suspended aggregates, but induction mechanisms remain unclear. In the study, the effect of R. insidiosa cell-free supernatants cultured in 10% TSB medium (10% RIS) on the formation of L. monocytogenes suspended aggregates was evaluated. Next, the Illumina RNA sequencing was used to compare the transcriptional profiles of L. monocytogenes in 10% TSB medium with and without 10% RIS to identify differentially expressed genes (DEGs). The result of functional annotation analysis of DEGs indicated that these genes mainly participate in two component system, bacterial chemotaxis and flagellar assembly. Then the reaction network of L. monocytogenes suspended aggregates with the presence of 10% RIS was summarized. The gene-deletion strain of L. monocytogenes was constructed by homologous recombination. The result showed that cheA and cheY are key genes in the formation of suspended aggregates. This research is the preliminary verification of suspended aggregates' RNA sequencing and is helpful to analyze the aggregation mechanisms of food-borne pathogenic bacteria from a new perspective.

Effects of Nisin, Cecropin, and Penthorum chinense Pursh on the Intestinal Microbiome of Common Carp (Cyprinus carpio).

Following a ban on antibiotic use in the feed industry, trials on the effects of various immunostimulants (prebiotics, probiotics, antimicrobial peptides [AMPs], and herbs) on the survival, growth, immunity, and disease control of farmed fish in aquaculture are being rapidly conducted. The wide variety of microbes with roles in nutrition, metabolism, and immunity in the fish intestine is the primary factor affecting the fermentability and functionality of dietary immunostimulants. For this reason, the dynamic interactions between immunostimulants and the intestinal microbiome may influence fish health. In this study, the effects of two agriculturally important AMPs (nisin and cecropin) and one herb (Penthorum chinense) on the gut microbiome of common carp were investigated, using 16S rDNA high-throughput sequencing. The results suggest that all three substances can alter the richness, diversity, and composition of the intestinal microbiota of common carp. P. chinense had a similar effect on the gut microbiota of common carp to that of nisin, and both promoted more striking changes in the gut microbiota community than did cecropin. The relative abundance of Proteobacteria was lower in the nisin and P. chinense groups than in the control and cecropin groups. The relative abundance of Bacteroidetes in the nisin, cecropin, and P. chinense groups was markedly increased, compared with that of the control group. Additionally, nisin, cecropin, and P. chinense showed obvious anti-inflammatory effects on the fish intestine, which was reflected by significantly increasing the expression levels of two anti-inflammatory cytokines IL-10 and TGF-ß. Some digestive enzyme activities in the fish intestine were also significantly enhanced by supplementing these three substances in feeds.

Inhibitory effects of fermented Ougan (Citrus reticulata cv. Suavissima) juice on high-fat diet-induced obesity associated with white adipose tissue browning and gut microbiota modulation in mice.

In this study, Ougan juice (OJ) and lactic acid bacteria fermented Ougan juice (FOJ) were investigated individually for their capability of preventing obesity in high-fat diet (HFD)-fed C57BL/6J mice. After being administered with OJ or FOJ for 10 weeks, the body weight gain, hyperlipidemia, and gut microbiota dysbiosis of HFD-fed mice were examined. The results showed that OJ or FOJ supplementation inhibited weight gain, lowered fat accumulation, reduced liver steatosis, improved glucose homeostasis and insulin sensitivity, increased brown adipose tissue (BAT) activity, and promoted white adipose tissue (WAT) browning. Both OJ and FOJ additions increased the diversity of gut microbiota. OJ reduced the relative abundance of phylum Erysipelatoclostridiaceae and genus Erysipelatoclostridium and remarkably increased SCFA-producing bacteria Blautia, while FOJ reduced the ratio of Firmicutes to Bacteroidetes and enhanced the relative abundance of family Lactobacillaceae. Spearman's correlation analysis revealed that Akkermansia, Dubosiella, and Muribaculaceae were significantly negatively correlated with obesity-related indexes. In general, FOJ exhibited a better inhibitory effect on obesity than OJ, and the possible inhibitory mechanism lies in promoting WAT browning and increasing intestinal probiotics. This study provides the guidance for developing fermented Ougan juice as an obesity-inhibiting functional food.

Formation of Multispecies Biofilms and Their Resistance to Disinfectants in Food Processing Environments: A Review.

ABSTRACT: In food processing environments, various microorganisms can adhere and aggregate on the surface of equipment, resulting in the formation of multispecies biofilms. Complex interactions among microorganisms may affect the formation of multispecies biofilms and resistance to disinfectants, which are food safety and quality concerns. This article reviews the various interactions among microorganisms in multispecies biofilms, including competitive, cooperative, and neutral interactions. Then, the preliminary mechanisms underlying the formation of multispecies biofilms are discussed in relation to factors, such as quorum-sensing signal molecules, extracellular polymeric substances, and biofilm-regulated genes. Finally, the resistance mechanisms of common contaminating microorganisms to disinfectants in food processing environments are also summarized. This review is expected to facilitate a better understanding of interspecies interactions and provide some implications for the control of multispecies biofilms in food processing.

Immunomodulatory activity of puerarin in RAW264.7 macrophages and cyclophosphamide-induced immunosuppression mice.

CONTEXT: Puerarin, a natural isoflavone extracted from Radix puerariae, is famous for treating various cardiovascular and cerebrovascular diseases. However, little is known about its direct immunomodulatory activity. OBJECTIVE: This study was designed to investigate the in vitro and in vivo immunomodulatory effects of Radix puerariae by using the murine monocyte-macrophage cell line RAW264.7 and immunosuppressed cyclophosphamide-induced mice. METHODS: MTT and neutral red phagocytosis assays were conducted to evaluate the in vitro immunomodulatory activities of puerarin on cell viability and phagocytosis by measuring the proliferation, phagocytic, nitric oxide (NO) ability, and TNF-α production ability of stimulated and lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Immunosuppressed cyclophosphamide-induced mice were used to evaluate the in vivo immunomodulatory activities of puerarin by measuring IL-4 and IFN-γ, the serum half hemolysis value, spleen and thymus index, and proliferation assay for splenic lymphocytes. RESULTS AND DISCUSSION: Results showed that puerarin improves immunomodulatory activity by increasing cell proliferation, cell phagocytosis, and NO secretion in RAW264.7 macrophages and reduces the abnormal immunologic activity by decreasing cell phagocytosis and NO secretion in LPS-stimulated RAW264.7 macrophages. In addition, puerarin enhanced the immunologic activity of cyclophosphamide-induced immunosuppression mice by increasing the secretion of NO, IFN-γ, and IL-4, the serum half hemolysis value (HC50), the spleen and thymus index, and proliferation for splenic lymphocytes. CONCLUSION: Puerarin exhibited an upregulated immunomodulatory effect on RAW264.7 macrophages and immunosuppression mice. In addition, puerarin had a downregulated immunomodulatory effect on RAW264.7 macrophages. The results suggest that puerarin could be a promising immunomodulator to assist in the treatment of tumors.

Biotransformation of two citrus flavanones by lactic acid bacteria in chemical defined medium.

Microbial processes are being developed to transform flavonoid glycosides to varieties of metabolites with higher bioavailability. The aim of this study was to determine the metabolic activity and survival of five lactic acid bacteria (LAB) stains (L. rhamnosus LRa05, L. casei LC89, L. plantarum N13, L. acidophilus LA85, and L. brevis LB01) in two different citrus flavanone standards (hesperetin-7-O-rutinoside and naringenin-7-O-rutinoside). The enzymatic activity, metabolites, antioxidant activities, and α-glucosidase inhibition property in the two standards were also investigated before and after incubated with LAB. The medium contained standards permitted survival of the five LAB stains. All strains exhibited ß-glucosidase activity. Of the five LAB strains tested, just L. plantarum N13 and L. brevis LB01 have the ability to metabolize hesperetin-7-O-rutinoside, only L. plantarum N13, L. acidophilus LA85, and L. brevis LB01 could metabolize naringenin-7-O-rutinoside, moreover, L. acidophilus LA85l was the strain with the highest biotransformation ratio of naringenin-7-O-rutinoside. L. acidophilus LA85 and L. plantarum N13 can degrade naringenin-7-O-rutinoside into naringenin. L. brevis LB01 can degrade hesperetin-7-O-rutinoside into hesperetin, 3-(4'-hydroxyphenyl)-2-propenoic acid, 3-(3'-hydroxy-4'-methoxyphenyl)hydracrylic acid, and 3-(4'-hydroxyphenyl)propionic acid. Incubation of L. acidophilus LA85 in naringenin-7-O-rutinoside solution supposed no apparent influence in the biological activities that tested. L. acidophilus LA85 may potentially contribute to the bioavailability of citrus flavanones, and to be applied as functional cultures to obtain more bioavailable and bioactive metabolites in food products or in the human gastrointestinal tract.

Whole genome sequencing and genome annotation of Dermacoccus abyssi strain HZAU 226 isolated from spoiled eggs.

Dermacoccus abyssi strain HZAU 226 is a spoilage bacterium isolated from eggs. So far, there are still few genomic resources available on the Dermacoccus abyssi. Here, we reported the complete genome sequence of Dermacoccus abyssi strain HZAU 226. High-quality DNA was extracted using the Qiagen kit, then single-molecule sequencing was performed by GridION sequencer. The raw data was quality-controlled and assembled to obtain the final genome, which consisted of a complete genome of 2,992,060 bp circular chromosome and a 64,524 bp plasmid. The structural and functional annotations of the genome were achieved through the analysis of different available databases, including antibiotic resistance genes, secondary metabolite synthesis genes and stress-related genes. Meanwhile, comparative genomic analyses of the strains were also performed. This is the first report on the complete genome of Dermacoccus abyssi, which will provide genomic resources for the study of spoilage bacteria in eggs.

Enhancement of S-adenosylmethionine production by deleting thrB gene and overexpressing SAM2 gene in Bacillus amyloliquefaciens.

OBJECTIVES: To improve the S-adenosylmethionine (SAM) production in methionine-free medium, effects of deleting genes of SAM decarboxylase (speD) and homoserine kinase (thrB) on SAM titers were investigated, and the SAM synthetase gene (SAM2) was also overexpressed. RESULTS: In B. amyloliquefaciens HSAM2, deleting speD to block the SAM utilization pathway significantly reduced the SAM titer. After knockout of thrB to block the branched pathway, the resulted mutant HSAM4 produced 143.93 mg/L SAM, increasing by 42% than HSAM2. Further plasmid-based expression of SAM2 improved the SAM titer to 226.92 mg/L, and final optimization of key fermentation parameters resulted in the maximum SAM titer of 412.01 mg/L in flasks batch fermentation. CONCLUSIONS: Deleting thrB and overexpressing SAM2 gene were efficient for enhanced SAM production in B. amyloliquefaciens. The maximum SAM titer in flasks batch fermentation was much higher than that of previous reports.

Transcriptome Analysis of Gene Expression in Dermacoccus abyssi HZAU 226 under Lysozyme Stress.

Lysozyme acts as a kind of cationic antimicrobial protein and effectively hydrolyzes bacterial peptidoglycan to have a bactericidal effect, which also plays an important role in protecting eggs from microbial contamination. Dermacoccus abyssi HZAU 226, a Gram-positive bacterium isolated from spoiled eggs, has egg white and lysozyme tolerance, but its survival mechanism is unknown, especially from a transcriptomics point of view. In this study, the high lysozyme tolerance of D. abyssi HZAU 226 was characterized by three independent experiments, and then the Illumina RNA-seq was used to compare the transcriptional profiles of this strain in Luria-Bertani (LB) medium with and without 5 mg/mL lysozyme to identify differentially expressed genes (DEGs); 1024 DEGs were identified by expression analysis, including 544 up-regulated genes and 480 down-regulated genes in response to lysozyme treatment. The functional annotation analysis results of DEGs showed that these genes were mainly involved in glutathione biosynthesis and metabolism, ion transport, energy metabolism pathways, and peptidoglycan biosynthesis. This study is the first report of bacterial-related lysozyme RNA-seq, and our results help in understanding the lysozyme-tolerance mechanism of bacteria from a new perspective and provide transcriptome resources for subsequent research in related fields.

Differential Effects of Growth Medium Salinity on Biofilm Formation of Two Salmonella enterica Strains.

ABSTRACT: Salmonella enterica is a prominent foodborne pathogen, including diverse serotypes that are prolific biofilm formers. Its ability to form biofilm can be affected by multiple environmental factors. In this study, the effect of salinity on biofilm formation by S. enterica was evaluated by using two recently isolated strains of Salmonella serotypes Enteritidis and Newport. Although supplementing the growth medium with a low concentration (0.5 to 2%) of sodium chloride (NaCl) slightly enhanced biofilm formation for the strain S. enterica serovar Enteritidis 110, it sharply reduced or abolished biofilm formation by the strain S. enterica serovar Newport 193. This differential effect of salinity on S. enterica strains of different serotypes was poorly correlated with inhibition of planktonic growth but strongly correlated with cell motility. Examining genes known to affect biofilm formation showed that the expression of adrA, csgD, and fliC, which encode proteins required for surface adhesion and cell motility, was significantly downregulated with salinity increase in Salmonella Newport 193 but not in Salmonella Enteritidis 110. Therefore, it is plausible that the differential effect of salinity on biofilm formation by Salmonella Enteritidis 110 and Salmonella Newport 193 resulted from the differential regulation to genes required for cell adherence and motility.

A fluorescence immunoassay based on CdTe : Zn/ZnS quantum dots for the rapid detection of bacteria, taking Delftia tsuruhatensis CM'13 as an example.

A fluorescence immunoassay has been widely applied in different fields due to its high sensitivity, simple operations, and high accuracy. Quantum dots (QDs) are often selected as labels in a fluorescence immunoassay due to their high fluorescence, better stability, and biocompatibility. In this study, novel doped CdTe : Zn/ZnS QDs with stability and a high photoluminescence quantum yield (40.78%) were prepared by the water synthesis method and used as labels to conjugate with goat anti-rabbit IgG to establish a fluorescence immunoassay (FLISA) for bacteria compared to the traditional enzyme-linked immunosorbent assay (ELISA) based on the reaction between an antibody and an antigen. A good linear relationship between the fluorescence intensity and concentrations of D. tsuruhatensis CM13 was found when the concentrations were in the range of 103 CFU mL-1-108 CFU mL-1. The limit of detection (LOD) of D. tsuruhatensis CM13 was 1.25 × 103 CFU mL-1 by FLISA, which was about 80 times lower than the LOD obtained from ELISA (105 CFU mL-1). This indicated that our FLISA method has higher sensitivity than traditional ELISA, and the CdTe : Zn/ZnS QDs synthesized in this paper have good applications in the rapid sensitive detection of microorganisms.

Background Signal-Free Magnetic Bioassay for Food-Borne Pathogen and Residue of Veterinary Drug via Mn(VII)/Mn(II) Interconversion.

Paramagnetic ion-mediated sensors can greatly simplify current magnetic sensors for biochemical assays, but it remains challenging because of the limited sensitivity. Herein, we report a magnetic immunosensor relying on Mn(VII)/Mn(II) interconversion and the corresponding change in the low-field nuclear magnetic resonance (LF-NMR) of the transverse relaxation rate (R2). The fact that the NMR R2 of the water protons detected in Mn(II) aqueous solution is much stronger than Mn(VII) aqueous solution enables the modulation of the LF-NMR signal intensity of R2. By employing immunomagnetic separation and enzyme-catalyzed reaction, this Mn(VII)/Mn(II) interconversion allows the development of a background signal-free magnetic immunosensor with a high signal-to-background ratio that enables detection of ractopamine and Salmonella with high sensitivity (the limits of detection for ractopamine and Salmonella are 8.1 pg/mL and 20 cfu/mL, respectively). This Mn-mediated magnetic immunosensor not only retains the good stability but also greatly improves the sensitivity of conventional paramagnetic ion-mediated magnetic sensors, offering a promising platform for sensitive, stable, and convenient bioanalysis.