Construction of ratiometric Si-Mn:ZnSe nanoparticles for the immunoassay of SARS-CoV-2 spike protein

Advances in rapid point-of-care virus testing

Outbreaks of viral diseases seriously jeopardize people's health and cause huge economic losses. At the same time, virology provides a new perspective for biology, molecular biology and cancer research, and it is important to study the discovered viruses with potential applications. Therefore, the development of immediate and rapid viral detection methods for the prevention and treatment of viral diseases as well as the study of viruses has attracted extensive attention from scientists. With the continuous progress of science and technology, especially in the field of bioanalysis, a series of new detection techniques have been applied to the on-site rapid detection of viruses, which has become a powerful approach for human beings to fight against viruses. In this paper, the latest research progress of rapid point-of-care detection of viral nucleic acids, antigens and antibodies is presented. In addition, the advantages and disadvantages of these technologies are discussed from the perspective of practical application requirements. Finally, the problems and challenges faced by rapid viral detection methods and their development prospects are discussed.

Ultrasensitive Ratiometric Fluorescence Bioassay for Accurate Detection of Covid-19-Specific Nucleocapsid Protein in Clinical Serum Samples Using Modified Cleavable Mesoporous SiO2 Satellite-Enriched Carbon Dots

Due to the presence of various autofluorescent compounds in biological samples like serum and the photobleaching of organic fluorophores, fluorescence sensing has limited practical applicability. This study describes the development of an improved ratiometric fluorescence assay to determine the nucleocapsid protein (N protein), one of the most conserved biomarkers of Covid-19 in spiked and serum samples using highly stable buffer-based near IR-dual emission carbon dots (CDs) encapsulated into the cavities of cleavable silica nanocapsule (SNCs) nanocomposite. The cavities of cleavable silica nanocapsules (SNCs) and the formed core-shell CDs@ SNCs were used as a superior reservoir of fluorescent markers produced by cohydrolyzing tetraethyl orthosilicate and diiminosilane linker, which held hundreds of CDs in silica shell frameworks. The SiO2 nanocomposite was modified with an N protein antibody that specifically paired to the receptor binding region of the Cov-19 spike protein subunit. CDs were taken out of SNCs by NaBH4 reduction, and the released CDs exhibited dual emission at 475 and 675 nm when excited at 400 nm. Ratiometric detection is completed over a binding-induced, concentration-dependent immuno-affinity of the N protein that drives the fluorescence quenching phenomenon between the CDs as fluorophore and the AuNPs as quencher. As the N protein concentration increased, the intensity of the red emission (675 nm) dropped, whereas the intensity of the green emission (475 nm) already remained constant, which is due to sandwich immunoassays of CDs around AuNPs. Using the exceptional fluorescent characteristics of CDs and the high selectivity of nanocomposite functionalized with N-protein antibody, the developed assay efficiently eliminates the autofluorescence background interference of serum samples. The fluorescence ratio (I475/I675) provides a limit of detection of 2 pg mL-1 over a linear range of 0.01 to 5 ng mL-1 and exhibits an amplified sensitivity of 54 times compared to conventional immunoassay using CDs as fluorescent labels. With one-step signal amplification and requiring small sample quantities (only 20 μL), this sensing platform can be effectively used for the accurate detection of N protein, and no cross-reactivity is detected in the presence of different interfering agents.

One-step-one-pot hydrothermally derived metal-organic-framework-nanohybrids for integrated point-of-care diagnostics of SARS-CoV-2 viral antigen/pseudovirus utilizing electrochemical biosensor chip

The COVID-19 pandemic has become a global catastrophe, affecting the health and economy of the human community. It is required to mitigate the impact of pandemics by developing rapid molecular diagnostics for SARS-CoV-2 virus detection. In this context, developing a rapid point-of-care (POC) diagnostic test is a holistic approach to the prevention of COVID-19. In this context, this study aims at presenting a real-time, biosensor chip for improved molecular diagnostics including recombinant SARS-CoV-2 spike glycoprotein and SARS-CoV-2 pseudovirus detection based on one-step-one-pot hydrothermally derived CoFeBDCNH₂-CoFe₂O₄ MOF-nanohybrids. This study was tested on a PalmSens-EmStat Go POC device, showing a limit of detection (LOD) for recombinant SARS-CoV-2 spike glycoprotein of 6.68 fg/mL and 6.20 fg/mL in buffer and 10% serum-containing media, respectively. To validate virus detection in the POC platform, an electrochemical instrument (CHI6116E) was used to perform dose dependent studies under similar experimental conditions to the handheld device. The results obtained from these studies were comparable indicating the capability and high detection electrochemical performance of MOF nanocomposite derived from one-step-one-pot hydrothermal synthesis for SARS-CoV-2 detection for the first time. Further, the performance of the sensor was tested in the presence of Omicron BA.2 and wild-type D614G pseudoviruses.

Fluorescence and Colorimetric Analysis of African Swine Fever Virus Based on the RPA-Assisted CRISPR/Cas12a Strategy

It is well-established that different detection modes are necessary for corresponding applications, which can effectively reduce matrix interference and improve the detection accuracy. Here, we reported a magnetic separation method based on recombinase polymerase amplification (RPA)-assisted clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a for dual-mode analysis of African swine fever virus (ASFV) genes, including colorimetry and fluorescence. The ASFV gene was selected as the initial RPA template to generate the amplicon. The RPA amplicon was then recognized by CRISPR-associated RNA (crRNA), activating the trans-cleavage activity of Cas12a and leading to the nonspecific cleavage of ssDNA as well as a significant release of alkaline phosphatase (ALP) in the ALP-ssDNA modified magnetic bead. The released ALP can catalyze para-nitrophenyl phosphate to generate para-nitrophenol, resulting in substantial changes in absorbance and fluorescence, both of which can be used for detection with the naked eye. This strategy allows the sensitive detection of ASFV DNA, with a 20 copies/mL detection limit; no cross-reactivity with other viruses was observed. A good linear relationship was obtained in serum. In addition, this sensor displayed 100% specificity and sensitivity for clinical sample analysis. This method integrates the high sensitivity of fluorescence with easy readout of colorimetry and enables a simple, low-cost, and highly sensitive dual-mode detection of viral nucleic acid, thereby providing a broad prospect for the practical application in the diagnosis of virus infection.

Fluorescent detection of emerging virus based on nanoparticles: From synthesis to application

The spread of COVID-19 has caused huge economic losses and irreversible social impact. Therefore, to successfully prevent the spread of the virus and solve public health problems, it is urgent to develop detection methods with high sensitivity and accuracy. However, existing detection methods are time-consuming, rely on instruments, and require skilled operators, making rapid detection challenging to implement. Biosensors based on fluorescent nanoparticles have attracted interest in the field of detection because of their advantages, such as high sensitivity, low detection limit, and simple result readout. In this review, we systematically describe the synthesis, intrinsic advantages, and applications of organic dye-doped fluorescent nanoparticles, metal nanoclusters, up-conversion particles, quantum dots, carbon dots, and others for virus detection. Furthermore, future research initiatives are highlighted, including green production of fluorescent nanoparticles with high quantum yield, speedy signal reading by integrating with intelligent information, and error reduction by coupling with numerous fluorescent nanoparticles.

Atomically dispersed Mn boosting photoelectrochemical SARS-CoV-2 spike protein immunosensing on carbon nitride

The sudden outbreak of coronavirus disease (COVID-19) triggered by SARS-CoV-2 infection has created a terrifying situation around the world. The spike protein of SARS-CoV-2 can act as an early biomarker for COVID-19. Therefore, controlling the spread of COVID-19 requires a low-cost, fast-response, and sensitive monitoring technique of spike protein. Herein, a photoelectrochemical (PEC) immunosensor for the detection of spike protein was constructed using the nanobody and an Mn (Ⅱ) modified graphitic carbon nitride (Mn/g-C₃N₄). The introduction of atomically dispersed Mn (Ⅱ) can accelerate the effective transfer and separation of photogenerated electron-hole pairs, which significantly boosts PEC performance of g-C₃N₄, thereby improving the detection sensitivity. As a recognition site, nanobody can achieve high-affinity binding to the spike protein, leading to a high sensitivity. The linear detection range of the proposed PEC immunosensor was 75 fg mL^-1 to 150 pg mL^-1, and the limit of detection was calculated to be 1.22 fg mL^-1. This stable and feasible PEC immunosensor would be a promising diagnostic tool for sensitively detecting spike protein of SARS-CoV-2.

Increase the Surface PANI Occupancy of Electrospun PMMA/PANI Fibers: Effect of the Electrospinning Parameters on Surface Segregation

For preparing high-performance electrospun fibers with functional molecules that cannot cross-entangle themselves, such as conductive polymers, promoting the aggregation of functional molecules on the surface by surface segregation is a promising approach. In the present study, electrospun polymethyl methacrylate/polyaniline (PMMA/PANI) fibers were prepared under various conditions, including solution composition, applied voltage, tip-to-collector distance, temperature, humidity, and gas-phase solvent concentration, to examine the effects of the parameters on fiber morphology and surface segregation. The changes in fiber morphology and variations in the intensity of PANI and PMMA’s characteristic bands were investigated with scanning electron microscopy (SEM) and Raman spectroscopy. The results demonstrated that by changing the saturation difference and the viscosity, the amount of PMMA and PANI added significantly influenced whether surface segregation could occur. The effect of other investigated parameters on surface segregation was concluded to alter the molecular migratable time by affecting the jet flight time and the solvent volatilization rate. Among them, increasing the solvent concentration could significantly promote surface segregation without sacrificing morphological advantages. When the solvent concentration increased from 1.4 to 158 mg/m³, the Raman peak intensity ratio of PANI and PMMA increased from 2.91 to 5.05, while the fiber diameter remained essentially constant.