Signal self-enhancement by coordinated assembly of gold nanoparticles enables accurate one-step-immunoassays

Trends and challenges in electroanalytical biosensing methodologies for infectious viral diseases

Viral pandemic diseases have disruptive global consequences leading to millions of deaths and a severe impact on the global economy. Inadequate preventative protocols have led to an overwhelming demand for intensive care leading to uncontrollable burdens and even breakdown of healthcare sectors across many countries. The rapid detection of viral disease helps in the understanding of the relevant intricacies, helping to tackle infection with improved guidelines. Portable biosensor devices offer promising solutions by facilitating on-site detection of viral pathogens. This review summarizes the latest innovative strategies reported using electroanalytical methods for the screening of viral antigens. The structural components of viruses and their categories are presented followed by the various recognition elements and transduction techniques involved in biosensors. Core sections focus on biosensors reported for viral genomic detection(DNA and RNA) and antigenic capsid protein. Strategies for addressing the challenges of electroanalytical biosensing of viral components are also presented. The advantages, and disadvantages of biorecognition elements and nanozymes for the detection of viral disease are highlighted. Such technical insights will help researchers working in chemistry, and biochemistry as well as clinicians working in medical diagnostics.

One-step-immunoassay of procalcitonin enables rapid and accurate diagnosis of bacterial infection

Procalcitonin (PCT) (i.e. a precursor of calcitonin) attracts much attention as a reliable biomarker of bacterial infections because its concentration increases rapidly in the blood when bacterial infections occur in the body. Sepsis may occur due to indiscriminate and vigorous proliferation of infectious bacteria, and accordingly early diagnosis and treatment of bacterial infection are of crucial importance. However, current diagnostic methods for sepsis suffer from long assay time, multiple and complex assay steps, inaccuracy, and requirement of analytical equipments. The goal of this study is to develop an advanced one-step-immunoassay that enables quick and accurate diagnosis of sepsis through measuring the PCT concentration in patient sera, which is based on self-enhancement of optical detection signals from large gold particles (i.e. clusters of gold nanoparticles) that are formed on the agglomerates of PCT-bound 3-dimensional (3D) probes. The 3D probe is constructed through attaching polyclonal anti-PCT antibodies (IgGs) to the surface of a modified hepatitis B virus (HBV) capsid, where both tandem repeats of the B domain of Staphylococcal protein A (SPA_B) and the hexa-histidine tag are inserted into each HBV core protein (i.e. subunit of HBV capsid). That is, anti-PCT IgGs are attached via strong interaction between the Fc region and surface-exposed SPA_B. Furthermore, hook effect-free and PCT concentration-dependent optical signals were consistently generated by adding both bovine serum albumin (BSA) and nickel ions to patient sera and also by optimally adjusting the 3D probe concentration. Compared to conventional chemiluminescent microparticle immunoassay (CMIA) showing poor linearity of detection signals, this novel immunoassay accurately detected PCT with good linearity between PCT concentrations and optical signals in a wide range of PCT concentrations (0.05–200 ng mL⁻¹) and also showed a sufficiently low limit of detection, resulting in 100% sensitivity and 100% specificity when tested with 30 sepsis patients and 30 healthy individuals.

An advanced one-step-immunoassay enables quick and accurate diagnosis of sepsis with generation of clear optical signals in assay solution, which is based on sensitive detection of procalcitonin in patient sera.

Viral antigen nanoparticles for discriminated and quantitative detection of different subtypes of anti-virus immunoglobulins

The aim of this study is to develop a novel method for the accurate diagnosis of the infection status of viral diseases, which requires discriminated and quantitative detection of different anti-virus immunoglubulin subtypes. Considering hepatitis A as a representative model disease, viral antigen nanoparticles (vAgNPs) were designed and synthesized by genetically presenting hepatitis A virus (HAV) antigens on the surface of human heavy chain ferritin (hFTH) nanoparticles to detect anti-HAV antibodies with discriminating immunoglobulin subtypes M and G (IgM and IgG, respectively). The vAgNPs also display multi-copies of hexa-histidine peptide (H6) on their surface to chemisorb gold ions (Au3+), which is vital for the autonomous generation of quantitatively meaningful detection signals. The quantitative level of anti-HAV IgM or IgG in 30 patient sera was successfully analyzed using the vAgNPs of HAV, which was performed through label-free one-step-immunoassay based on the self-enhancement of optical signals from gold nanoparticles clustered on the viral antigen nanoparticles. The diagnostic performance was compared with that of enzyme-linked immunosorbent assay (ELISA), which did not enable accurate quantitative assay due to the poor linearity between the antibody concentration and detection signal. Furthermore, these vAgNP-based immunoassays did not produce any false negative/positive signals, indicating 100% sensitivity and 100% specificity.

Click-conjugated photon-upconversion nanoparticles in an immunoassay for honeybee pathogen Melissococcus plutonius

European foulbrood (EFB) is an infectious disease affecting honeybee larvae caused by the bacterium Melissococcus plutonius. The enzyme-linked immunosorbent assay (ELISA) is the gold standard for antibody-based bacteria detection, however, its sensitivity is not high enough to reveal early-stage EFB infection. Photon-upconversion nanoparticles (UCNPs) are lanthanide-doped nanomaterials that emit light of shorter wavelength under near-infrared (NIR) excitation and thus avoid optical background interference. After conjugation with specific biorecognition molecules, UCNPs can be used as ultrasensitive labels in immunoassays. Here, we introduce a method for conjugation of UCNPs with streptavidin based on copper-free click chemistry, which involves surface modification of UCNPs with alkyne-modified bovine serum albumin (BSA) that prevents the non-specific binding and provides reactive groups for conjugation with streptavidin-azide. To develop a sandwich upconversion-linked immunosorbent assay (ULISA) for M. plutonius detection, we have prepared a rabbit polyclonal anti-Melissococcus antibody. The specific capture of the bacteria was followed by binding of biotinylated antibody and UCNP-BSA-streptavidin conjugate for a highly sensitive upconversion readout. The assay yielded an LOD of 340 CFU mL-1 with a wide working range up to 109 CFU mL-1, which is 400 times better than the LOD of the conventional ELISA. The practical applicability of the ULISA was successfully demonstrated by detecting M. plutonius in spiked real samples of bees, larvae and bottom hive debris. These results show a great potential of the assay for early diagnosis of EFB, which can prevent uncontrolled spreading of the infection and losses of honeybee colonies.

Performance of point-of-care diagnosis of AIDS: label-free one-step-immunoassay vs. lateral flow assay

The objective of this study is to develop an accurate, rapid, simple, and label-free assay technology that enables point-of-care diagnosis of AIDS. For this, 3-dimensional (3D) probes to sensitively detect anti-HIV antibodies were designed and synthesized by genetically presenting a HIV antigen (gp41) on the surface of engineered human ferritin nanoparticles. The 3D probes also present multi-copies of the hexa-histidine peptide (H₆) on their surface to chemisorb gold ions (Au³⁺), which is essential for the generation and self-enhancement of assay signals. The developed new assay technology (named "one-step-immunoassay") quickly produced clear optical signals through a simple and convenient one-step procedure. The diagnostic performance of the one-step-immunoassay was compared with that of the conventional lateral flow assay (LFA) using 30 AIDS patient and 20 healthy sera. The sensitivity of LFA was only 63% when a single antigen (gp41) was used but enhanced to 90% when three different antigens (gp41, p24, and gp120) were used together as the assay probes. In contrast, the one-step-immunoassay using only gp41 produced strong optical signals within 15 min without causing any false negative/positive signals, showing 100% sensitivity and 100% specificity and holding promising potential for clinical point-of-care diagnosis of AIDS.