Evaluation of anti-A/Udorn/307/1972 antibody specificity to influenza A/H3N2 viruses using an evanescent-field coupled waveguide-mode sensor

Diagnostic techniques for critical respiratory infections: Update on current methods

Respiratory infections, whether chronic or acute, are frequent in both children and adults and result in an economic burden in health care systems. In particular, for an immunocompromised patient, respiratory infection leads to acute hypoxemic respiratory failure, a leading cause of intensive care unit (ICU) admission. Most respiratory infections are caused by bacteria, viruses, parasites, smoking, or air pollution. Over the last two decades, considerable improvements have been made in understanding and identifying respiratory infections. Various biosensing techniques have been developed with a range of targets to identify the infection at earlier stages. Recently, nanomaterials have been effectively applied to improve biosensors and their analytical performances. This review discusses recent biosensor developments for identifying respiratory infections caused by viruses and bacteria assisted by different types of nanomaterials and target molecules.

Biosensing epidemic and pandemic respiratory viruses: Internet of Things with Gaussian noise channel algorithmic model

The current world condition is dire due to epidemics and pandemics as a result of novel viruses, such as influenza and the coronavirus, causing acute respiratory syndrome. To overcome these critical situations, the current research seeks to generate a common surveillance system with the assistance of a controlled Internet of Things operated under a Gaussian noise channel. To create the model system, a study with an analysis of H1N1 influenza virus determination on an interdigitated electrode (IDE) sensor was validated by current-volt measurements. The preliminary data were generated using hemagglutinin as the target against gold-conjugated aptamer/antibody as the probe, with the transmission pattern showing consistency with the Gaussian noise channel algorithm. A good fit with the algorithmic values was found, displaying a similar pattern to that output from the IDE, indicating reliability. This study can be a model for the surveillance of varied pathogens, including the emergence and reemergence of novel strains.

Enhancing erythrocyte-influenza virus specificity by glycan-conjugated gold nanoparticle: Validation of hemagglutination by aptamer and neuraminidases

This study demonstrated the terminated sialo-sugar chains (Neu5Acα2,6Gal and Neu5Acα2,3Gal)-mediated specificity enhancement of influenza virus and chicken red blood cell (RBC) by hemagglutination assay. These glycan chains were immobilized on the gold nanoparticle (GNP) to withhold the higher numbers. With the preliminary optimization, a clear button formation with 0.5% RBC was visualized. On the other hand, intact B/Tokio/53/99 with 750 nM hemagglutinin (HA) displayed a nice hemagglutination. The interference on the specificity of RBC and influenza virus was observed by anti-influenza aptamer at the concentration 31 nM; however, there is no hemagglutination prevention was noticed in the presence of complementary aptamer sequences. Spiking GNP-conjugated Neu5Acα2,6Gal or Neu5Acα2,3Gal or a mixture of these two to the reaction promoted the hemagglutination to 63-folds higher with 12 nM virus, whereas under the same condition the heat-inactivated viruses were lost the hemagglutination. Neuraminidases from Clostridium perfringens and Arthrobacter ureafaciens at 0.0025 neuraminidase units are able to abolish the hemagglutination. Other enzymes, Glycopeptidase F (Elizabethkingia meningoseptica) and Endoglycosidase H (Streptomyces plicatus) did not show the changes with agglutination. Obviously, sialyl-Gal-terminated glycan-conjugated GNP amendment has enhanced the specificity of erythrocyte-influenza virus and able to be controlled by aptamer or neuraminidases.

Convenient method of producing cyclic single-chain Fv antibodies by split-intein-mediated protein ligation and chaperone co-expression

Single-chain Fv (scFv) is a recombinant antibody in which the variable regions of the heavy chain (VH) and light chain (VL) are connected by a short flexible polypeptide linker. Compared with monoclonal antibodies, scFvs have the advantages of low-cost production using Escherichia coli and easy genetic manipulation. ScFvs are, therefore, regarded as useful modules for producing next-generation medical antibodies. The practical use of scFvs has been limited due to their aggregation propensity mediated by interchain VH-VL interactions. To overcome this problem, we recently reported a cyclic scFv whose N-terminus and C-terminus were connected by sortase A-mediated ligation. Preparation of cyclic scFv is, however, a time-consuming process. To accelerate the application study of cyclic scFv, we developed a method to produce cyclic scFv by the combined use of a protein ligation technique based on protein trans-splicing reaction (PTS) by split intein and a chaperone co-expression system. This method allows for the preparation of active cyclic scFv from the cytoplasm of E. coli. The present method was applied to the production of cyclic 73MuL9-scFv, a GA-pyridine antibody, as a kind of advanced glycation end-product. These findings are expected to evoke further application study of cyclic scFv.

A changing trend in diagnostic methods of Influenza A (H3N2) virus in human: a review

The influenza virus is classified into four types A, B, C, and D, but type A and B are responsible for major illnesses in people with influenza A being the only virus responsible for flu pandemics due to the presence of two surface proteins called hemagglutinin (H) and neuraminidase (N) on the virus. The two subtypes of influenza A virus, H1N1 and H3N2, have been known to cause many flu pandemics. Both subtypes change genetically and antigenically to produce variants (clades and subclades, also know as groups and subgroups). H3N2 tends to change rapidly, both genetically and antigenically whereas that of H1N1 generally tends to have smaller changes. Influenza A (H3N2) viruses have evolved to form many separate, genetically different clades that continue to co-circulate. Influenza A(H3N2) viruses have caused significant deaths as per WHO report. The review describes methods for detection of influenza A(H3N2) viruses by conventional serological methods as well as the advanced methods of molecular biology and biosensors. All these methods are based on different parameters and have different targets but the goal is to improve specificity and increase sensitivity. Amongst the molecular methods, real-time polymerase chain reaction (RT-PCR) is considered a gold standard test due to its many advantages whereas a number of other molecular methods are time-consuming, complex to perform or lack specificity. The review also considers bio-sensing methods for simple, rapid, highly sensitive, and specific detection of H3N2. The classification and principle of various H3N2 biosensors are also discussed.

Preparation of single-chain Fv antibodies in the cytoplasm of Escherichia coli by simplified and systematic chaperone optimization

A single-chain variable fragment (scFv) antibody is a recombinant protein in which a peptide linker connects the variable regions of the heavy chain and light chain. Due to its smaller molecular size, an scFv can be expressed using Escherichia coli. The presence of two disulphide bonds in the molecule often prevents expression of correctly folded scFv in the E. coli cytoplasm, making a refolding process necessary to regenerate scFv activity. The refolding process is time-consuming and requires large amounts of expensive reagents, such as guanidine hydrochloride, l-arginine and glutathione. Here, to conveniently obtain scFv proteins, we devised a simple and systematic method to optimize the co-expression of chaperone proteins and to combine them with specially engineered E. coli strains that permit the formation of stable disulphide bonds within the cytoplasm. Several scFv proteins were successfully obtained in a soluble form from E. coli cytoplasm. Thermal denaturation experiments and/or surface plasmon resonance measurements revealed that the thus-obtained scFvs possessed a stable tertiary structure and antigen-binding activity. The combined use of engineered E. coli with the simplified and systematic chaperone optimization can be useful for the production of scFv proteins.

Cyclization of Single-Chain Fv Antibodies Markedly Suppressed Their Characteristic Aggregation Mediated by Inter-Chain VH-VL Interactions

Single-chain Fv (scFv) antibodies are recombinant proteins in which the variable regions of the heavy chain (VH) and light chain (VL) are connected by a short flexible polypeptide linker. ScFvs have the advantages of easy genetic manipulation and low-cost production using Escherichia coli compared with monoclonal antibodies, and are thus expected to be utilized as next-generation medical antibodies. However, the practical use of scFvs has been limited due to low homogeneity caused by their aggregation propensity mediated by inter-chain VH-VL interactions. Because the interactions between the VH and VL domains of antibodies are generally weak, individual scFvs are assumed to be in equilibrium between a closed state and an open state, in which the VH and VL domains are assembled and disassembled, respectively. This dynamic feature of scFvs triggers the formation of dimer, trimer, and larger aggregates caused by the inter-chain VH-VL interactions. To overcome this problem, the N-terminus and C-terminus were herein connected by sortase A-mediated ligation to produce a cyclic scFv. Open-closed dynamics and aggregation were markedly suppressed in the cyclic scFv, as judged from dynamic light scattering and high-speed atomic force microscopy analyses. Surface plasmon resonance and differential scanning fluorometry analysis revealed that neither the affinity for antigen nor the thermal stability was disrupted by the scFv cyclization. Generality was confirmed by applying the present method to several scFv proteins. Based on these results, cyclic scFvs are expected to be widely utilized in industrial and therapeutic applications.

Gold Nanorod Integrated Electrochemical Sensing for Hyperglycaemia on Interdigitated Electrode

Gestational diabetes (hyperglycaemia) is an elevated blood sugar level diagnosed during the period of pregnancy and affects the baby's health. Hyperglycaemia has been found within the gestational weeks between 24 and 28, and the foetus has also the possibility of getting out prior to this test frame; it causes excessive birth weight, early birth, low-blood sugar level, respiratory distress syndrome, and type-2 diabetes to the mother. It creates a mandatory situation to identify the hyperglycaemia at least during the pregnancy weeks from 18 to 20. Further, a continuous monitoring of the level of glucose is necessary for the proper delivery. In this work, a method is introduced for glucose detection at 0.06 mg/mL, assisted by gold nanorod (GNR)-conjugated glucose oxidase (GOx) on interdigitated electrode sensor. In the absence of GNR, GOx shows the limit of glucose detection to be 0.25 mg/mL. Moreover, with GOx-GNR the reactions of all the glucose concentrations have recorded higher levels of the current from the baseline. With the specificity analysis, it was found that the glucose only reacts with GOx-GNR and discriminates other sugars efficiently. This method of detection is useful to diagnose and continuously monitor the glucose level during the pregnancy period.

Amine-Aldehyde Chemical Conjugation on a Potassium Hydroxide-Treated Polystyrene ELISA Surface for Nanosensing an HIV-p24 Antigen

The enzyme-linked immunosorbent assay (ELISA) has been widely used for disease surveillance and drug screening due to its relatively higher accuracy and sensitivity. Fine-tuning the ELISA is mandatory to elevate the specific detection of biomolecules at a lower abundance. Towards this end, higher molecular capture on the polystyrene (PS) ELISA surface is crucial for efficient detection, and it could be attained by immobilizing the molecules in the correct orientation. It is highly challenging to immobilize protein molecules in a well-aligned manner on an ELISA surface due to charge variations. We employed a 3-(aminopropyl) triethoxysilane (APTES)- and glutaraldehyde (GLU)-coupled PS surface chemical strategy to demonstrate the high performance with ELISA. A potassium hydroxide treatment followed by an equal ratio of 1% APTES and GLU attachment was found to be optimal, and a longer incubation with GLU favored maximum sensitivity. p24 is a vital early secreting antigen for diagnosing human immunodeficiency virus (HIV), and it has been used for efficient detection with the above chemistry. Three different procedures were followed, and they led to the improved detection of the HIV-p24 antigen at 1 nM, which is a 30-fold higher level compared to a conventional ELISA surface. The surface chemical functionalization shown here also displays a higher specificity with human serum and HIV-TAT. The above approach with the designed surface chemistry could also be recommended for disease diagnosis on other sensing surfaces involving the interaction of the probe and the analyte in heterogeneous test samples.

Red Spectral Shift in Sensitive Colorimetric Detection of Tuberculosis by ESAT-6 Antigen-Antibody Complex: a New Strategy with Gold Nanoparticle

Tuberculosis (TB) is a highly contagious life-threatening disease caused by the bacterial pathogen Mycobacterium tuberculosis. ESAT-6, an abundant early secretory antigenic target protein by M. tuberculosis, found to play a vital role in virulence. Developing a friendly method for the detection of ESAT-6 at the lower concentration facilitates to treat TB at an earlier stage and helps to control the spreading of disease. Herein, a new single-step approach was designed and was done by pre-mixing ESAT-6 and antibody before being added to the gold nanoparticle (GNP) followed by the salt-induced aggregation. We could attain the detection limit of 1.25 pM, showing the aggregation of GNP and the red spectral shift. Further, a higher specificity was demonstrated with the lack of electrostatic biofouling by ESAT-6 on GNP and retained the dispersed GNP in the presence of 10-kDa culture filtrate protein from M. tuberculosis. The required precise antibody concentration for this assay was found to be 60 nM. The increment in the antibody concentration from 75 nM drastically diminishes the sensitivity to ~ 680-fold, due to the crowding effect. With this assay, we attested the suitability of colorimetric assay for efficiently detecting the smaller-sized protein.

Production of Single-Chain Fv Antibodies Specific for GA-Pyridine, an Advanced Glycation End-Product (AGE), with Reduced Inter-Domain Motion

Due to their lower production cost compared with monoclonal antibodies, single-chain variable fragments (scFvs) have potential for use in several applications, such as for diagnosis and treatment of a range of diseases, and as sensor elements. However, the usefulness of scFvs is limited by inhomogeneity through the formation of dimers, trimers, and larger oligomers. The scFv protein is assumed to be in equilibrium between the closed and open states formed by assembly or disassembly of VH and VL domains. Therefore, the production of an scFv with equilibrium biased to the closed state would be critical to overcome the problem in inhomogeneity of scFv for industrial or therapeutic applications. In this study, we obtained scFv clones stable against GA-pyridine, an advanced glycation end-product (AGE), by using a combination of a phage display system and random mutagenesis. Executing the bio-panning at 37 °C markedly improved the stability of scFvs. We further evaluated the radius of gyration by small-angle X-ray scattering (SAXS), obtained compact clones, and also visualized open.

Detection of antibodies against hepatitis B virus surface antigen and hepatitis C virus core antigen in plasma with a waveguide-mode sensor

In large-scale disasters, such as huge significant earthquakes, on-site examination for blood typing and infectious disease screening will be very helpful to save lives of victims who need surgical treatment and/or blood transfusion. However, physical damage, such as building collapse, electric power failure and traffic blockage, disrupts the capacity of the medical system. Portable diagnostic devices are useful in such cases of emergency. In this study, we evaluated a waveguide-mode sensor for detection of anti-hepatitis virus antibodies. First, we examined whether we can detect antigen-antibody interaction on a sensor chip immobilized hepatitis B virus surface (HBs) antigen and hepatitis C virus (HCV) core antigen using monoclonal mouse antibodies for HBs antigen and HCV core antigen. We obtained significant changes in the reflectance spectra, which indicate specific antigen-antibody interaction for anti-HBs antibody and anti-HCV antibody. Next, we examined the effect of horseradish peroxidase-conjugated secondary antibody using aminoethyl carbazole as the peroxidase substrate and found that the colorimetric reaction increases detection sensitivity for anti-HBs antibody more than 300 times. Finally, we successfully detected anti-HBs antibody in human blood samples with an enhancing method using a peroxidase reaction. Thus, a portable device utilizing a waveguide-mode sensor may be applied to on-site blood testing in emergency settings.

Shape- and Size-Controlled Synthesis of Silver Nanoparticles Using Aloe vera Plant Extract and Their Antimicrobial Activity

Biogenic synthesis of silver nanoparticles (AgNP) was performed at room temperature using Aloe vera plant extract in the presence of ammoniacal silver nitrate as a metal salt precursor. The formation of AgNP was monitored by UV-visible spectroscopy at different time intervals. The shape and size of the synthesized particle were visualized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. These results were confirmed by X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses and further supported by surface-enhanced Raman spectroscopy/Raman scattering (SERS) study. UV-visible spectrum has shown a sharp peak at 420 nm and further evidenced by FTIR peak profile (at 1587.6, 1386.4, and 1076 cm^-1 with corresponding compounds). The main band position with SERS was noticed at 1594 cm^-1 (C-C stretching vibration). When samples were heated under microwave radiation, AgNP with octahedron shapes with 5-50 nm were found and this method can be one of the easier ways to synthesis anisotropic AgNP, in which the plant extract plays a vital role to regulate the size and shape of the nanoparticles. Enhanced antibacterial effects (two- to fourfold) were observed in the case of Aloe vera plant protected AgNP than the routinely synthesized antibiotic drugs. Shape and size-controlled synthesis of silver nanoparticles using Aloe vera plant extract.

Biotin-Streptavidin Competition Mediates Sensitive Detection of Biomolecules in Enzyme Linked Immunosorbent Assay

Enzyme Linked Immunosorbent Assay (ELISA) is the gold standard assay for detecting and identifying biomolecules using antibodies as the probe. Improving ELISA is crucial for detecting disease-causing agents and facilitating diagnosis at the early stages of disease. Biotinylated antibody and streptavidin-conjugated horse radish peroxide (streptavidin-HRP) often are used with ELISA to enhance the detection of various kinds of targets. In the present study, we used a competition-based strategy in which we pre-mixed free biotin with streptavidin-HRP to generate high-performance system, as free biotin occupies some of the biotin binding sites on streptavidin, thereby providing more chances for streptavidin-HRP to bind with biotinylated antibody. ESAT-6, which is a protein secreted early during tuberculosis infection, was used as the model target. We found that 8 fM of free biotin mixed with streptavidin-HRP anchored the higher detection level of ESAT-6 by four-fold compared with detection without free biotin (only streptavidin-HRP), and the limit of detection of the new method was 250 pM. These results suggest that biotin-streptavidin competition can be used to improve the diagnosis of analytes in other types of sensors.

Aptamer-based 'point-of-care testing'

Aptamers are single-stranded oligonucleotides that can be artificially generated by a method called Systematic evolution of ligands by exponential enrichment (SELEX). The generated aptamers have been assessed for high-performance sensing applications due to their appealing characteristics. With either aptamers alone or complementing with antibodies, several high sensitive and portable sensors have been demonstrated for use in 'point-of-care testing'. Due to their high suitability and flexibility, aptamers are conjugated with nanostructures and utilized in field applications. Moreover, aptamers are more amenable to chemical modifications, making them capable of utilization with most developed sensors. In this overview, we discuss novel, portable, and aptamer-based sensing strategies that are suitable for 'point-of-care testing'.

A Point-of-Care Immunosensor for Human Chorionic Gonadotropin in Clinical Urine Samples Using a Cuneated Polysilicon Nanogap Lab-on-Chip

Human chorionic gonadotropin (hCG), a glycoprotein hormone secreted from the placenta, is a key molecule that indicates pregnancy. Here, we have designed a cost-effective, label-free, in situ point-of-care (POC) immunosensor to estimate hCG using a cuneated 25 nm polysilicon nanogap electrode. A tiny chip with the dimensions of 20.5 × 12.5 mm was fabricated using conventional lithography and size expansion techniques. Furthermore, the sensing surface was functionalized by (3-aminopropyl)triethoxysilane and quantitatively measured the variations in hCG levels from clinically obtained human urine samples. The dielectric properties of the present sensor are shown with a capacitance above 40 nF for samples from pregnant women; it was lower with samples from non-pregnant women. Furthermore, it has been proven that our sensor has a wide linear range of detection, as a sensitivity of 835.88 μA mIU^-1 ml^-2 cm^-2 was attained, and the detection limit was 0.28 mIU/ml (27.78 pg/ml). The dissociation constant K_d of the specific antigen binding to the anti-hCG was calculated as 2.23 ± 0.66 mIU, and the maximum number of binding sites per antigen was B_max = 22.54 ± 1.46 mIU. The sensing system shown here, with a narrow nanogap, is suitable for high-throughput POC diagnosis, and a single injection can obtain triplicate data or parallel analyses of different targets.

Colorimetric detection of influenza A virus using antibody-functionalized gold nanoparticles

Early and accurate diagnosis is considered the key issue to prevent the further spread of viruses and facilitate influenza therapy. Herein, we report a colorimetric immunosensor for influenza A virus (IAV) based on gold nanoparticles (AuNPs) modified with monoclonal anti-hemagglutinin antibody (mAb). The immunosensor allows for a fast, simple, and selective detection of IAV. In this assay, influenza-specific antibodies are conjugated to AuNPs to create mAb-AuNP probes. Since IAV has multiple recognition sites for probes on the surface, the mAb-AuNP probes can be specifically arranged on the virus surface due to their very specific antigen recognition. In this case, this aggregation of the mAb-AuNP probes produces a red shift in the absorption spectrum due to plasmon coupling between adjacent AuNPs, and it can be detected with the naked eye as a color change from red to purple and quantified with the absorption spectral measurements. The aggregate formation is also confirmed with transmission electron microscopy (TEM) imaging and dynamic light scattering (DLS). Under the optimal conditions, the present immunoassay can sensitively measure H3N2 IAV (A/Brisbane/10/2007) with a detection limit of 7.8 hemagglutination units (HAU). This proposed immunosensor revealed high specificity, accuracy, and good stability. Notably, it is a single-step detection using AuNP probes and UV-vis spectrophotometer for readout, and no additional amplification, e.g., enzymatic, is needed to read the result. This assay depends on an ordered AuNP structure covering the virus surface and can be applied to any virus pathogen by incorporating the appropriate pathogen-specific antibody.

Neuraminidase-producing oral mitis group streptococci potentially contribute to influenza viral infection and reduction in antiviral efficacy of zanamivir

Influenza is a serious respiratory disease among immunocompromised individuals, such as the elderly, and its prevention is an urgent social issue. Influenza viruses rely on neuraminidase (NA) activity to release progeny viruses from infected cells and spreading the infection. NA is, therefore, an important target of anti-influenza drugs. A causal relationship between bacteria and influenza virus infection has not yet been established, however, a positive correlation between them has been reported. Thus, in this study, we examined the biological effects of oral mitis group streptococci, which are predominant constituents of human oral florae, on the release of influenza viruses. Among them, Streptococcus oralis ATCC 10557 and Streptococcus mitis ATCC 6249 were found to exhibit NA activity and their culture supernatants promoted the release of influenza virus and cell-to-cell spread of the infection. In addition, culture supernatants of these NA-producing oral bacteria increased viral M1 protein expression levels and cellular ERK activation. These effects were not observed with culture supernatants of Streptococcus sanguinis ATCC 10556 which lacks the ability to produce NA. Although the NA inhibitor zanamivir suppressed the release of progeny viruses from the infected cells, the viral release was restored upon the addition of culture supernatants of NA-producing S. oralis ATCC 10557 or S. mitis ATCC 6249. These findings suggest that an increase in the number of NA-producing oral bacteria could elevate the risk of and exacerbate the influenza infection, hampering the efficacy of viral NA inhibitor drugs.