Microbial biosensor for Salmonella using anti-bacterial antibodies isolated from human serum

Research progress in the detection of common foodborne hazardous substances based on functional nucleic acids biosensors

With the further improvement of food safety requirements, the development of fast, highly sensitive, and portable methods for the determination of foodborne hazardous substances has become a new trend in the food industry. In recent years, biosensors and platforms based on functional nucleic acids, along with a range of signal amplification devices and methods, have been established to enable rapid and sensitive determination of specific substances in samples, opening up a new avenue of analysis and detection. In this paper, functional nucleic acid types including aptamers, deoxyribozymes, and G-quadruplexes which are commonly used in the detection of food source pollutants are introduced. Signal amplification elements include quantum dots, noble metal nanoparticles, magnetic nanoparticles, DNA walkers, and DNA logic gates. Signal amplification technologies including nucleic acid isothermal amplification, hybridization chain reaction, catalytic hairpin assembly, biological barcodes, and microfluidic system are combined with functional nucleic acids sensors and applied to the detection of many foodborne hazardous substances, such as foodborne pathogens, mycotoxins, residual antibiotics, residual pesticides, industrial pollutants, heavy metals, and allergens. Finally, the potential opportunities and broad prospects of functional nucleic acids biosensors in the field of food analysis are discussed.

Defect-Passivated Photosensor Based on Cesium Lead Bromide (CsPbBr3) Perovskite Quantum Dots for Microbial Detection

A defect-passivated photosensor based on cesium lead bromide (CsPbBr3) perovskite quantum dots (QD) was fabricated using parylene films, and the photosensor was applied for the microbial detection. The CsPbBr3 perovskite QDs were synthesized to be homogeneous in size under thermodynamic control, and the perovskite QD-based photosensor was fabricated using MoS2 flakes as the electron transfer layer. In this work, a parylene film with functional groups was deposited on a photosensor for physical protection (waterproof) and defect (halide vacancy) passivation of the perovskite QD. As the first effect of the parylene film, the physical protection of the perovskite QD from water was estimated by comparing the photosensor performance after incubation in water. As the second effect of the parylene, the interaction between the functional groups of the parylene film and the halide vacancies of the perovskite QDs was investigated through the bandgap, crystal structure, and trap-state density analysis. Additionally, density functional theory analysis on Mulliken charges, lattice parameters, and Gibbs free energy demonstrated the effect of the defect passivation by parylene films. Finally, the parylene-passivated QD-based photosensor was applied to the detection of two kinds of food-poisoning and gastroduodenal disease bacteria (Listeria monocytogenes and Helicobacter pylori).

Immunoaffinity biosensors for the detection of SARS-CoV-1 using screened Fv-antibodies from an autodisplayed Fv-antibody library

The detection of severe acute respiratory syndrome coronavirus (SARS-CoV-1) was demonstrated using screened Fv-antibodies for SPR biosensor and impedance spectrometry. The Fv-antibody library was first prepared on the outer membrane of E. coli using autodisplay technology and the Fv-variants (clones) with a specific affinity toward the SARS-CoV-1 spike protein (SP) were screened using magnetic beads immobilized with the SP. Upon screening the Fv-antibody library, two target Fv-variants (clones) with a specific binding affinity toward the SARS-CoV-1 SP were determined and the Fv-antibodies on two clones were named "Anti-SP1" (with CDR3 amino acid sequence: 1GRTTG5NDRPD11Y) and "Anti-SP2" (with CDR3 amino acid sequence: 1CLRQA5GTADD11V). The binding affinities of the two screened Fv-variants (clones) were analyzed using flow cytometry and the binding constants (KD) were estimated to be 80.5 ± 3.6 nM for Anti-SP1 and 45.6 ± 8.9 nM for Anti-SP2 (n = 3). In addition, the Fv-antibody including three CDR regions (CDR1, CDR2, and CDR3) and frame regions (FRs) between the CDR regions was expressed as a fusion protein (Mw. 40.6 kDa) with a green fluorescent protein (GFP) and the KD values of the expressed Fv-antibodies toward the SP estimated to be 15.3 ± 1.5 nM for Anti-SP1 (n = 3) and 16.3 ± 1.7 nM for Anti-SP2 (n = 3). Finally, the expressed Fv-antibodies screened against SARS-CoV-1 SP (Anti-SP1 and Anti-SP2) were applied for the detection of SARS-CoV-1. Consequently, the detection of SARS-CoV-1 was demonstrated to be feasible using the SPR biosensor and impedance spectrometry utilizing the immobilized Fv-antibodies against the SARS-CoV-1 SP.

One-step immunoassay based on filtration for detection of food poisoning-related bacteria

A one-step immunoassay based on filtration was presented, which used microbeads for target analyte detection and filters with appropriate pore sizes to distinguish the complexity of target analyte and microbeads. For effective bacterial detection, the microbead size and the filter's pore size must be optimized. The optimal concentrations of the enzyme (urease) and antibody were determined at the maximum absorbance change, that is, the maximum pH change. The pH change was measured using a field-effect transistor (FET). The correlation between pH change and threshold voltage was estimated to be 21.7 mV/pH, and the correlation between pH change and the source-drain current was estimated to be -379 nA/pH. For the one-step immunoassay, antibodies against target bacteria were isolated from horse serum by filtration, and these antibodies were estimated to have a sufficiently high specificity to overcome cross-reactivity among five types of food poisoning-related bacteria: Escherichia coli O157, Salmonella typhimurium, Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus. Finally, the FET-based one-step immunoassay was demonstrated for five types of food poisoning-related bacteria in human serum.

Electrochemical One-Step Immunoassay Based on Switching Peptides and Pyrolyzed Carbon Electrodes

Switching peptides were designed to bind reversibly to the binding pocket of antibodies (IgG) by interacting with frame regions (FRs). These peptides can be quantitatively released when antigens bind to IgG. As FRs have conserved amino acid sequences, switching peptides can be used as antibodies for different antigens and different source animals. In this study, an electrochemical one-step immunoassay was conducted using switching peptides labeled with ferrocene for the quantitative measurement of analytes. For the effective amperometry of the switching peptides labeled with ferrocene, a pyrolyzed carbon electrode was prepared by pyrolysis of the parylene-C film. The feasibility of the pyrolyzed carbon electrode for the electrochemical one-step immunoassay was determined by analyzing its electrochemical properties, such as its low double-layer capacitance (C_dl), high electron transfer rate (k_app), and wide electrochemical window. In addition, the factors influencing the amperometry of switching peptides labeled with ferrocene were analyzed according to the hydrodynamic radius, the number of intrahydrogen bonds, dipole moments, and diffusion coefficients. Finally, the applicability of the electrochemical one-step immunoassay for the medical diagnosis of the human hepatitis B surface antigen (hHBsAg) was assessed.

ClearColi as a platform for untagged pneumococcal surface protein A production: cultivation strategy, bioreactor culture, and purification

Abstract

Several studies have searched for new antigens to produce pneumococcal vaccines that are more effective and could provide broader coverage, given the great number of serotypes causing pneumococcal diseases. One of the promising subunit vaccine candidates is untagged recombinant pneumococcal surface protein A (PspA4Pro), obtainable in high quantities using recombinant Escherichia coli as a microbial factory. However, lipopolysaccharides (LPS) present in E. coli cell extracts must be removed, in order to obtain the target protein at the required purity, which makes the downstream process more complex and expensive. Endotoxin-free E. coli strains, which synthesize a nontoxic mutant LPS, may offer a cost-effective alternative way to produce recombinant proteins for application as therapeutics. This paper presents an investigation of PspA4Pro production employing the endotoxin-free recombinant strain ClearColi® BL21(DE3) with different media (defined, auto-induction, and other complex media), temperatures (27, 32, and 37 °C), and inducers. In comparison to conventional E. coli cells in a defined medium, ClearColi presented similar PspA4Pro yields, with lower productivities. Complex medium formulations supplemented with salts favored PspA4Pro yields, titers, and ClearColi growth rates. Induction with isopropyl-β-d-thiogalactopyranoside (0.5 mM) and lactose (2.5 g/L) together in a defined medium at 32 °C, which appeared to be a promising cultivation strategy, was reproduced in 5 L bioreactor culture, leading to a yield of 146.0 mg PspA4Pro/g dry cell weight. After purification, the cell extract generated from ClearColi led to 98% purity PspA4Pro, which maintained secondary structure and biological function. ClearColi is a potential host for industrial recombinant protein production.

Key points

• ClearColi can produce as much PspA4Pro as conventional E. coli BL21(DE3) cells.

• 10.5 g PspA4Pro produced in ClearColi bioreactor culture using a defined medium.

• Functional PspA4Pro (98% of purity) was obtained in ClearColi bioreactor culture.

Capacitive biosensor based on vertically paired electrodes for the detection of SARS-CoV-2

Vertically paired electrodes (VPEs) with multiple electrode pairs were developed for the enhancement of capacitive measurements by optimizing the electrode gap and number of electrode pairs. The electrode was fabricated using a conductive polymer layer of PEDOT:PSS instead of Ag and Pt metal electrodes to increase the VPE fabrication yield because the PEDOT:PSS layer could be effectively etched using a reactive dry etching process. In this study, sensitivity enhancement was realized by decreasing the electrode gap and increasing the number of VPE electrode pairs. Such an increase in sensitivity according to the electrode gap and the number of electrode pairs was estimated using a model analyte for an immunoassay. Additionally, a computer simulation was performed using VPEs with different electrode gaps and numbers of VPE electrode pairs. Finally, VPEs with multiple electrode pairs were applied for SARS-CoV-2 nucleoprotein (NP) detection. The capacitive biosensor based on the VPE with immobilized anti-SARS-CoV-2 NP was applied for the specific detection of SARS-CoV-2 in viral cultures. Using viral cultures of SARS-CoV-2, SARS-CoV, MERS-CoV, and CoV-strain 229E, the limit of detection (LOD) was estimated to satisfy the cutoff value (dilution factor of 1/800) for the medical diagnosis of COVID-19, and the assay results from the capacitive biosensor were compared with commercial rapid kit based on a lateral flow immunoassay.

Rapid detection of Pseudomonas aeruginosa using a DNAzyme-based sensor

In the present study, a DNAzyme was screened in vitro through the use of a DNA library and crude extracellular mixture (CEM) of Pseudomonas aeruginosa. Following eight rounds of selection, a DNAzyme termed PAE-1 was obtained, which displayed high rates of cleavage with strong specificity. A fluorescent biosensor was designed for the detection of P. aeruginosa in combination with the DNAzyme. A detection limit as low as 1.2 cfu/ml was observed. Using proteases and filtration, it was determined that the target was a protein with a molecular weight of 10 kDa-50 kDa. The DNAzyme was combined with a polystyrene board to construct a simple indicator plate sensor which produced a color that identified the target within 10 min. The results were reliable when tap water and food samples were tested. The present study provides a novel experimental strategy for the development of sensors based on a DNAzyme to rapidly detect P. aeruginosa in the field.