Pomegranate-Inspired Silica Nanotags Enable Sensitive Dual-Modal Detection of Rabies Virus Nucleoprotein

A sensitive fluoroimmunoassay for quantitative detection of imidacloprid based on quantum dot-streptavidin conjugate

Imidacloprid (IMI), the most commonly used neonicotinoid, is widely present in both the environment and agro-products due to extensive and prolonged application, posing potential risks to ecological security and human health. This study introduced a sensitive and rapid fluorescence-linked immunosorbent assay, employing Quantum Dot-Streptavidin conjugate (QDs-SA-FLISA), for efficient monitoring of IMI residues in agro-products. Under optimized conditions, the QDs-SA-FLISA exhibited a half-maximal inhibition concentration (IC50) of 1.70 ng/mL and a limit of detection (LOD, IC20) of 0.5 ng/mL. Investigation into the sensitivity enhancement effect of the QDs-SA revealed that the sensitivity (IC50) of the QDs-SA-FLISA was 7.3 times higher than that of ELISA. The recoveries and relative standard deviation (RSD) ranged from 81.7 to 118.1 % and 0.5-9.4 %, respectively, for IMI in brown rice, tomato and pear. There was no significant difference in IMI residues obtained between QDs-SA-FLISA and UHPLC-MS/MS. Thus, the QDs-SA-FLISA represents a reliable approach for the quantitative determination of IMI in agro-products.

Simple dual-readout immunosensor based on phosphate-triggered and potassium permanganate for visual detection of fenitrothion

Multicolor-based visual immunosensor is a promising tool for rapid analysis without the use of bulky instruments. Herein, an anti-fenitrothion nanobody-alkaline phosphatase fusion protein (VHHjd8-ALP) was employed to develop a multicolor visual immunosensor (MVIS) and a ratiometric fluorescence MVIS (RFMVIS, respectively). After one-step competitive immunoassay, the VHHjd8-ALP bound to microplate catalyzed phenyl phosphate disodium salt (ArP) into phenol. Under high alkaline condition (pH 12), the phenol reduced KMnO4 to intermediate (K2MnO4) and further to MnO2 in alkaline condition (pH 12), accompanied by a visible color transition of purple-green-yellow, which can be used for semiquantitative visual analysis or qualitative detection by measuring RGB value. RFMVIS was proposed on the basis of MVIS to further improve sensitivity. The CdTe quantum dot and fluorescein were used as signal probes to develop the fluorescent immunosensor. The CdTe dots with red emission (644 nm) was quenched by oxidation of KMnO4, whereas the fluorescein with green emission (520 nm) remained constant, accompanied by a fluorescent color transition of green-yellow-red. By measuring the ratio of the fluorescence intensity (I644/I520), the ratiometric fluorescence immunosensor was developed for qualitative analysis. The two visual immunosensors were sensitive and simple, and they showed good accuracy and practicability in the recovery test, thus are ideal tools for rapid screening.

Identification and Detection of Intracellular Reactive Sulfur Species Using a Reaction-Mediated Dual-Recognition Strategy

Reactive sulfur species (RSS) are emerging as a potential key gasotransmitter in diverse physiological processes linking two signaling molecules H2S and SO2. However, the exact roles of H2S and SO2 remain unclear. A major hurdle is the shortage of accurate and robust approaches for sensing of H2S and SO2 in biological systems. Herein, we report a reaction-mediated dual-recognition strategy-based nanosensor, silver nanoparticles (AgNPs)-loaded MIL-101 (Fe) (ALM) hybrids, for the simultaneous detection of H2S and SO2 in a living cell. Upon exposure to H2S, AgNPs can be oxidized to form Ag2S, causing a decrease of surface enhanced Raman spectroscopy (SERS) signals of p,p'-dimercaptoazobenzene. Moreover, SO2 reacts with the amino moiety of MIL-101 to form charge-transfer complexes, resulting in an increment of fluorescent (FL) intensity. The ALM with dual-modal signals can simultaneously analyze H2S and SO2 at a concentration as low as 2.8 × 10-6 and 0.003 μM, respectively. Most importantly, the ALM sensing platform enables targeting mitochondria and detection multiple RSS simultaneously in living cells under external stimulation, as well as displays indiscernible crosstalk between SERS and FL signals, which is very beneficial for the comprehension of physiological issues related with RSS.

Passion fruit-inspired dendritic mesoporous silica nanospheres-enriched quantum dots coupled with magnetism-controllable aptasensor enable sensitive detection of ochratoxin A in food products

Ochratoxin A (OTA) is a powerful mycotoxin present in a variety of food products, and its detection is important for human health. Here, a fluorescent aptasensor is reported for sensitive OTA determination. Specifically, the surface of bio-inspired passion fruit-like dendritic mesoporous silica nanospheres-enriched quantum dots (MSNQs-apt) was first modified with the OTA aptamer as the recognition unit and fluorescence emitter, while the aptamer-complementary DNA (MNPs-cDNA) was linked with the magnetic nanoparticles (MNPs) as the separation element. In the range of 2.56 pg/mL to 8 ng/mL, the proposed aptasensor exhibited satisfactory linearity and a detection limit of 1.402 pg/mL. The developed aptasensor achieved recoveries of 90.98-103.20% and 94.33-107.57 % in red wine and wheat flour samples, respectively. By simply replacing the aptamer, this aptasensor can be easily extended to detection of other analytes, suggesting its potential as a universal detection platform for mycotoxins in food products.

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.

The application of nanoparticles in point-of-care testing (POCT) immunoassays

The Covid-19 pandemic has led to greater recognition of the importance of the fast and timely detection of pathogens. Recent advances in point-of-care testing (POCT) technology have shown promising results for rapid diagnosis. Immunoassays are among the most extensive POCT assays, in which specific labels are used to indicate and amplify the immune signal. Nanoparticles (NPs) are above the rest because of their versatile properties. Much work has been devoted to NPs to find more efficient immunoassays. Herein, we comprehensively describe NP-based immunoassays with a focus on particle species and their specific applications. This review describes immunoassays along with key concepts surrounding their preparation and bioconjugation to show their defining role in immunosensors. The specific mechanisms, microfluidic immunoassays, electrochemical immunoassays (ELCAs), immunochromatographic assays (ICAs), enzyme-linked immunosorbent assays (ELISA), and microarrays are covered herein. For each mechanism, a working explanation of the appropriate background theory and formalism is articulated before examining the biosensing and related point-of-care (POC) utility. Given their maturity, some specific applications using different nanomaterials are discussed in more detail. Finally, we outline future challenges and perspectives to give a brief guideline for the development of appropriate platforms.

Nanosphere Structures Using Various Materials: A Strategy for Signal Amplification for Virus Sensing

Nanomaterials have been explored in the sensing research field in the last decades. Mainly, 3D nanomaterials have played a vital role in advancing biomedical applications, and less attention was given to their application in the field of biosensors for pathogenic virus detection. The versatility and tunability of a wide range of nanomaterials contributed to the development of a rapid, portable biosensor platform. In this review, we discuss 3D nanospheres, one of the classes of nanostructured materials with a homogeneous and dense matrix wherein a guest substance is carried within the matrix or on its surface. This review is segmented based on the type of nanosphere and their elaborative application in various sensing techniques. We emphasize the concept of signal amplification strategies using different nanosphere structures constructed from a polymer, carbon, silica, and metal-organic framework (MOF) for rendering high-level sensitivity of virus detection. We also briefly elaborate on some challenges related to the further development of nanosphere-based biosensors, including the toxicity issue of the used nanomaterial and the commercialization hurdle.

CRISPR-empowered hybridization chain reaction amplification for an attomolar electrochemical sensor

Rapid pathogen screening holds the key against certain viral infections, especially in an overwhelming pandemic. Herein, a CRISPR-empowered electrochemical biosensor was designed for the ultrasensitive detection of the avian influenza A (H7N9) virus gene sequence. Combining the CRISPR/Cas system, a signal-amplification strategy and a high-conductivity sensing substrate, the developed biosensor showed an ultrawide dynamic range, an ultralow detection limit, and excellent selectivity for H7N9 detection, providing a potential sensing platform for the simple, fast, sensitive, and on-site detection of infectious diseases.

Nanomaterials for virus sensing and tracking

The effect of the on-going COVID-19 pandemic on global healthcare systems has underlined the importance of timely and cost-effective point-of-care diagnosis of viruses. The need for ultrasensitive easy-to-use platforms has culminated in an increased interest for rapid response equipment-free alternatives to conventional diagnostic methods such as polymerase chain reaction, western-blot assay, etc. Furthermore, the poor stability and the bleaching behavior of several contemporary fluorescent reporters is a major obstacle in understanding the mechanism of viral infection thus retarding drug screening and development. Owing to their extraordinary surface-to-volume ratio as well as their quantum confinement and charge transfer properties, nanomaterials are desirable additives to sensing and imaging systems to amplify their signal response as well as temporal resolution. Their large surface area promotes biomolecular integration as well as efficacious signal transduction. Due to their hole mobility, photostability, resistance to photobleaching, and intense brightness, nanomaterials have a considerable edge over organic dyes for single virus tracking. This paper reviews the state-of-the-art of combining carbon-allotrope, inorganic and organic-based nanomaterials with virus sensing and tracking methods, starting with the impact of human pathogenic viruses on the society. We address how different nanomaterials can be used in various virus sensing platforms (e.g. lab-on-a-chip, paper, and smartphone-based point-of-care systems) as well as in virus tracking applications. We discuss the enormous potential for the use of nanomaterials as simple, versatile, and affordable tools for detecting and tracing viruses infectious to humans, animals, plants as well as bacteria. We present latest examples in this direction by emphasizing major advantages and limitations.

Dual-Mode Immunosensor for Electrochemiluminescence Resonance Energy Transfer and Electrochemical Detection of Rabies Virus Glycoprotein Based on Ru(bpy)32+-Loaded Dendritic Mesoporous Silica Nanoparticles

Rabies is a serious zoonotic disease in almost all warm-blooded animals and causes fatal encephalitis. The detection of rabies virus (RABV) is critical and remains a significant challenge. Herein, an electrochemiluminescence resonance energy transfer (ECL-RET) and electrochemical (EC) dual-mode immunosensor was developed for highly sensitive detection of RABV glycoprotein. Dendritic mesoporous silica nanoparticles (DMSNs) were employed to load Ru(bpy)₃²⁺ and to obtain ECL probes (Ru@DMSNs). Ru@DMSNs were decorated on the electrode surface, followed by the modification of the RABV antibody (Ab₁). RABV was specifically recognized and captured by Ab₁, causing the decline of the ECL signal due to the obstruction of electron transfer. Additionally, manganese oxide nanoparticles (MnO_x) modified with Ab₂ can further quench the ECL signal of Ru@DMSNs via the RET between Ru@DMSNs and MnO_x. Meanwhile, MnO_x can catalyze the oxidation of o-phenylenediamine (o-PD), generating a significant differential pulse voltammetry (DPV) signal as a second signal to monitor RABV glycoprotein concentration. Consequently, an immunosensor was developed to achieve dual-signal detection of RABV and improve reliability. Under the optimal conditions, detection ranges of 0.10 pg·mL^-1 to 10 ng·mL^-1 for ECL (with an 88 fg·mL^-1 detection limit) and 1 pg·mL^-1 to 2 ng·mL^-1 for EC (with a 0.1 pg·mL^-1 detection limit) were obtained for RABV detection. The reliability of this immunoassay was validated by eight brain tissue samples. The results were found to be compatible with the results of the real-time reverse transcription-polymerase chain reaction (RT-PCR) assay, indicating the potential applicability of this method for RABV diagnosis.

Patterned Liquid-Infused Nanocoating Integrating a Sensitive Bacterial Sensing Ability to an Antibacterial Surface

The slippery liquid-infused surfaces show a great antibacterial property. However, most liquid-infused surfaces cannot detect whether or not the unknown aqueous samples contain microorganisms. Therefore, it is highly necessary but a challenge to integrate bacterial sensing capability into antibacterial surface. In this work, we prepared a slippery patterned liquid-infused nanocoating on the glass substrate for integrating bacterial sensing capability into the bacterial repellence surface. Dendritic mesoporous silica nanoparticles (DMSNs) with a suitable particle size of ca. 128 nm were employed as a building block to fabricate the multifunctional nanocoating with a superhydrophilic microwell and hydrophobic periphery by a dip-coating strategy, hydrophobic treatment, photomask-mediated plasma etching, and liquid infusion. Dendritic porous silica nanoparticles (DPSNs) with a larger particle size of ca. 260 nm were uniformly loaded with Au nanoparticles (NPs), providing large surface area for the modification of Raman reporter (4-mercaptobenzoic acid (4-MBA)) and aptamer. Thus, as a Raman tag, the formed DPSNs-Au-MBA-aptamer could achieve sensitive surface-enhanced Raman spectroscopy (SERS) detection of target bacteria. Combined with the Raman tag, the patterned liquid-infused nanocoating not only completely repelled bacteria on the hydrophobic area but also enabled sensitive SERS detection of Staphylococcus aureus in a very low sample volume (1 μL) with a low detection limit of 2.6 colony formation units (CFU)/mL on the antibody-modified superhydrophilic microwell. This research provided a novel and reliable strategy to construct a multifunctional nanocoating with microbial repellence and sensing capabilities.

Investigation and risk assessment of dibutyl phthalate in a typical region by a high-throughput dual-signal immunoassay

The systematic investigation and risk assessment of dibutyl phthalate (DBP) were performed using an ultrasensitive dual-signal immunoassay in Zhenjiang, Jiangsu Province. In this study, C-dots@H-MnO₂ nanohybrid were synthesized and labelled on the secondary antibody to generate fluorometric and colorimetric signals. Attributed to the efficient catalysis of carbon dots (C-dots) and the high C-dots loading of hollow manganese (IV) oxide (H-MnO₂), the excellent sensitivity and low detection limits (0.243 and 0.692 μg/L respectively) were produced. Based on the proposed method, 25 water and 119 beverage samples were investigated. DBP was found in all water samples and 65.5% of beverage samples, with the concentrations varying in 16.5-32.1 μg/L and 0-553 μg/L, respectively. In addition, the mean concentration (22.9 μg/L) in waters was decreased significantly compared with that detected in 2016 (43.5 μg/L) by our Lab. For beverages, a similar phenomenon was observed by the measured concentrations from coffee. Furthermore, the potential ecological risks of DBP were evaluated, the results indicated that human activities had caused serious pollution and high risks to the local aquatic ecosystem. On the other hand, the results of health risk assessment suggested that DBP in beverages might not cause obvious side effects to local residents.

The Emerging Roles of Silver nanoparticles to Target Viral Life-Cycle and Detect Viral Pathogens

Along the line of recent vaccine advancements, new antiviral therapeutics are compelling to combat viral infection‐related public health crises. Several properties of silver nanoparticles (AgNPs) such as low level of cytotoxicity, ease of tunability of the AgNPs in the ultra‐small nanoscale size and shape through different convenient bottom‐up chemistry approaches, high penetration of the composite with drug formulations into host cells has made AgNPs, a promising candidate for developing antivirals. In this review, we have highlighted the recent advancements in the AgNPs based nano‐formulations to target cellular mechanisms of viral propagation, immune modulation of the host, and the ability to synergistically enhance the activity of existing antiviral drugs. On the other hand, we have discussed the recent advancements on AgNPs based detection of viral pathogens from clinical samples using inherent physicochemical properties. This article will provide an overview of our current knowledge on AgNPs based formulations that has promising potential for developing a counteractive strategy against emerging and existing viruses.

A CRISPR/Cas12a-Mediated Dual-Mode Electrochemical Biosensor for Polymerase Chain Reaction-Free Detection of Genetically Modified Soybean

A clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a-mediated dual-mode electrochemical biosensor without polymerase chain reaction (PCR) amplification was designed for sensitive and reliable detection of genetically modified soybean SHZD32-1. A functionalized composite bionanomaterial Fe3O4@AuNPs/DNA-Fc&Ru was synthesized as the signal unit, while a characteristic gene fragment of SHZD32-1 was chosen as the target DNA (tDNA). When Cas12a, crRNA, and tDNA were present simultaneously, a ternary complex Cas12a-crRNA-tDNA was formed, and the nonspecific cleavage ability of the CRISPR/Cas12a system toward single-stranded DNA was activated. Thus, the single-stranded DNA-Fc in the signal unit was cleaved, resulting in the decrease in the fast scan voltammetric (FSV) signal from ferrocene (Fc) and the increase in the electrochemiluminescence (ECL) signal from ruthenium complex (Ru) inhibited by Fc. The linear range was 1-107 fmol/L for ECL and 10-108 fmol/L for FSV, and the limit of detection (LOD) was 0.3 fmol/L for ECL and 3 fmol/L for FSV. Accuracy, precision, stability, selectivity, and reliability were all satisfied. In addition, PCR-free detection could be completed in an hour at room temperature without requiring complicated operation and sample processing, showing great potential in the field detection of genetically modified crops.

Preparation of Anti-Aristolochic Acid I Monoclonal Antibody and Development of Chemiluminescent Immunoassay and Carbon Dot-Based Fluoroimmunoassay for Sensitive Detection of Aristolochic Acid I

Aristolochic acid (AA) toxicity has been shown in humans regarding carcinogenesis, nephrotoxicity, and mutagenicity. Monitoring the AA content in drug homologous and healthy foods is necessary for the health of humans. In this study, a monoclonal antibody (mAb) with high sensitivity for aristolochic acid I (AA-I) was prepared. Based on the obtained mAb, a chemiluminescent immunoassay (CLEIA) against AA-I was developed, which showed the 50% decrease in the RLU_max (IC₅₀) value of 1.8 ng/mL and the limit of detection (LOD) of 0.4 ng/mL. Carbon dots with red emission at 620 nm, namely rCDs, were synthesized and employed in conventional indirect competitive enzyme-linked immunosorbent assay (icELISA) to improve the assay sensitivity of a fluoroimmunoassay (FIA). Oxidized 3,3'',5,5''-tetramethylbenzidine dihydrochloride (oxTMB) can quench the emission of the rCDs through the inner-filter effect; therefore, the fluorescence intensity of rCDs can be regulated by the concentration of mAb. As a result, the assay sensitivity of FIA was improved by five-fold compared to CLEIA. A good relationship between the results of the proposed assays and the standard ultra-high performance liquid chromatography-triple quadrupole mass spectrometer (UPLC-QQQ-MS/MS) of real samples indicated good accuracy and practicability of CLEIA and FIA.

The Most Active Oxidase-Mimicking Mn2 O3 Nanozyme for Biosensor Signal Generation

Oxidase-mimicking nanozymes are more desirable than peroxidase-mimicking ones since H₂ O₂ can be omitted. However, only a few nanomaterials are known for oxidase-like activities. In this work, we compared the activity of Mn₂ O₃ , Mn₃ O₄ and MnO₂ and found that Mn₂ O₃ had the highest oxidase activity. Interestingly, the activity of Mn₂ O₃ was even inhibited by H₂ O₂ . The oxidase-like activity of Mn₂ O₃ was not much affected by the presence of proteins such as bovine serum albumin (BSA), but the physisorption of antibodies to Mn₂ O₃ was not strong enough to withstand the displacement by BSA. We then treated Mn₂ O₃ with 3-aminopropyltriethoxysilane to graft an amine group, which was used to conjugate antibodies using glutaraldehyde as a crosslinker. A one-step indirect competitive ELISA (icELISA) was developed for the detection of isocarbophos, and an IC₅₀ of 261.7 ng/mL was obtained, comparable with the results of the standard two-step assay using horseradish peroxidase (HRP)-labeled antibodies. This assay has the advantage of significant timesaving for rapid detection of large amounts of samples. This work has discovered a highly efficient oxidase-mimicking nanozyme useful for various nano- and analytical applications.

Synthesis of polystyrene-based fluorescent quantum dots nanolabel and its performance in H5N1 virus and SARS-CoV-2 antibody sensing

Quantum dots (QDs) based fluorescent nanobeads are considered as promising materials for next generation point-of-care diagnosis systems. In this study, we carried out, for the first time, the synthesis of QDs nanobeads using polystyrene (PS) nanobead as the template. QDs loading on PS nanobead surface in this method can be readily achieved by the use of polyelectrolyte, avoiding the time-consuming and uncontrollable silane reagents-involved functionalization procedure that conventional synthesis of silica-based QDs nanobeads often suffer from. Notably, the application of QDs nanobeads in suspension microarray for H5N1 virus detection leads to a sensitivity lower than 25 PFU/mL. In addition, QDs nanobead was also incorporated into lateral flow assay for SARS-CoV-2 antibody detection, leading to more than one order of magnitude detection sensitivity as compared to that of commercial one based on colloid gold.

DNAzyme Walker for Homogeneous Detection of Enterovirus EV71 and CVB3

When dealing with infectious pathogens, the risk of contamination or infection in the process of detecting them is nonnegligible. Separation-free detection will be beneficial in operation and safety. In this work, we proposed a DNAzyme walker for homogeneous and isothermal detection of enterovirus. The DNAzyme is divided into two inactivate subunits. When the subunit-conjugated antibody binds to the target virus, the activity of the DNAzyme recovers as a result of spatial proximity. The walker propels, and the fluorescence recovers. The final fluorescence intensity of the reaction mixture is related to the concentration of the target virus. The detection limit of this proposed method is 6.6 × 10⁴ copies/mL for EV71 and 4.3 × 10⁴ copies/mL for CVB3, respectively. Besides, this method was applied in detection of EV71 in clinical samples with a satisfactory result. The entire experiment is easy to operate, and the proposed method has great potential for practical use.

Effect of proteins on the oxidase-like activity of CeO2 nanozymes for immunoassays

Protein adsorption inhibits the oxidase-like activity of CeO₂ nanoparticles. Coating a partial shell of silica on CeO₂ and subsequent conjugation of antibodies allow highly sensitive and selective detection of fenitrothion.