Rapid detection of the neonicotinoid insecticide imidacloprid using a quenchbody assay

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.

Development of a bioluminescence resonance energy transfer Quenchbody sensor for the detection of organophosphorus pesticides in water bodies

Rapid and precise quantification of organophosphorus pesticides (OPPs) in environmental water bodies is crucial for evaluating ecological risks and safeguarding human health. Traditional instrumental methods are complex, time-consuming, and expensive, while enzyme-based biosensors suffer from instability and require a constant supply of substrates. Hence, there is an urgent need for a fast, simple, and sensitive biosensor for OPPs. In this study, we developed a novel non-enzymatic biosensor for the detection of methyl parathion (MP) by employing the bioluminescence resonance energy transfer (BRET) Q-body strategy. Optimizing the spacer arm and screening fluorescent dyes identified the R6G BRET MP Q-body sensor with the best performance. Key parameters affecting the sensor's detection performance were optimized by using single-factor experiments. Under optimal conditions, the detection exhibited a detection limit of 5.09 ng·mL-1 and a linear range of 16.21-848.81 ng·mL-1. The sensor's accuracy was validated using standard recovery experiments, yielding a recovery rate of 84.47 %-102.08 % with a standard deviation of 1.93 %-9.25 %. The detection results of actual water samples demonstrate that this fast, simple, and highly sensitive BRET Q-body sensor holds great promise for practical water quality monitoring.

A breakthrough of immunoassay format for hapten: recent insights into noncompetitive immunoassays to detect small molecules

Immunoassay based on the antibodies specific for targets has advantages of high sensitivity, simplicity and low cost, therefore it has received more attention in recent years, especially for the rapid detection of small molecule chemicals present in foods, diagnostics and environments. However, limited by low molecular weight and only one antigenic determinant existed, immunoassays for these small molecule chemicals, namely hapten substances, were commonly performed in a competitive immunoassay format, whose sensitivities were obviously lower than the sandwich enzyme-linked immunosorbent assay generally adaptable for the protein targets. In order to break through the bottleneck of detection format, researchers have designed and established several novel noncompetitive immunoassays for the haptens in the past few years. In this review, we focused on the four representative types of noncompetitive immunoassay formats and described their characteristics and applications in rapid detection of small molecules. Meanwhile, a systematic discussion on the current technologies challenges and the possible solutions were also summarized. This review aims to provide an updated overview of the current state-of-the-art in noncompetitive immunoassay for small molecules, and inspire the development of novel designs for small molecule detection.

Efficient and rapid linker optimization with heterodimeric coiled coils improves the response of fluorescent biosensors comprising antibodies and protein M

We developed a coiled Q-probe (CQ-probe), a fluorescent probe containing a coiled-coil peptide pair E4/K4, to convert antibodies into biosensors for homogeneous immunoassays. This probe consists of an antibody-binding protein, protein M (PM) with the E4 peptide and the K4 peptide with a fluorescent dye. Compared to PM Q-probes, which are generated by modifying the C-terminus of PM with a fluorescent dye, CQ-probe variants with various linkers are easy to prepare and therefore enable the establishment of biosensors with a significant fluorescence response by localizing the fluorescent dye at the optimal position for quenching and antigen-dependent release. The fluorescence changes of biosensors converted from anti-BGP, anti-cortisol, and anti-testosterone antibodies using the rhodamine 6G (or TAMRA)-labeled CQ-probe upon antigen addition were 13 (or 2.6), 9.7 (or 1.5), and 2.1 (or 1.2) times larger than that of the biosensors converted using the PM Q-probe. Furthermore, the CQ-probe converted anti-digoxin IgG into a functional biosensor, whereas the PM Q-probe/antibody complex showed an insufficient response. This technology exhibits a promising capacity to convert antibodies into high-response biosensors, which are expected to be applied in a wide range of fields, including clinical diagnosis, environmental surveys, food analysis, and biological research.

Quenchbodies That Enable One-Pot Detection of Antigens: A Structural Perspective

Quenchbody (Q-body) is a unique, reagentless, fluorescent antibody whose fluorescent intensity increases in an antigen-concentration-dependent manner. Q-body-based homogeneous immunoassay is superior to conventional immunoassays as it does not require multiple immobilization, reaction, and washing steps. In fact, simply mixing the Q-body and the sample containing the antigen enables the detection of the target antigen. To date, various Q-bodies have been developed to detect biomarkers of interest, including haptens, peptides, proteins, and cells. This review sought to describe the principle of Q-body-based immunoassay and the use of Q-body for various immunoassays. In particular, the Q-bodies were classified from a structural perspective to provide useful information for designing Q-bodies with an appropriate objective.

Generation of a Recombinant scFv against Deoxycholic Acid and Its Conversion to a Quenchbody for One-Step Immunoassay

Development of a rapid detection method for deoxycholic acid (DCA) is crucial for its diagnosis in the early stages of inflammation and cancer. In this study, we expressed a soluble recombinant anti-DCA single-chain variable fragment (scFv) in Escherichia coli. To convert scFv into a Quenchbody (Q-body), we labeled scFv using commercially available maleimide-linked fluorophores. The TAMRA-C5-maleimide-conjugated Q-body showed the highest response within a few minutes of DCA addition, indicating its applicability as a wash-free immunoassay probe for onsite DCA detection.

Neuron-Inspired Nanofluidic Biosensors for Highly Sensitive and Selective Imidacloprid Detection

Pesticides have caused concerns about food safety due to their residual effects in vegetables and fruits. Imidacloprid, as the frequently used neonicotinoid pesticide, could harm cardiovascular and respiratory function and cause reproductive toxicity in humans. Therefore, reliable methods for portable, selective, and rapid detection are desirable to develop. Herein, we report a neuron-inspired nanofluidic biosensor based on a tyrosine-modified artificial nanochannel for sensitively detecting imidacloprid. The functional tyrosine is modified on the outer surface of porous anodic aluminum oxide to rapidly capture imidacloprid through π-π interactions and hydrogen bonds. The integrated nanofluidic biosensor has a wide concentration range from 10-8 to 10-4 g/mL with an ultralow detection limit of 6.28 × 10-9 g/mL, which outperforms the state-of-the-art sensors. This work provides a new perspective on detecting imidacloprid residues as well as other hazardous pesticide residues in environmental and food samples.

The Dawn of a New Era: Targeting the "Undruggables" with Antibody-Based Therapeutics

The high selectivity and affinity of antibodies toward their antigens have made them a highly valuable tool in disease therapy, diagnosis, and basic research. A plethora of chemical and genetic approaches have been devised to make antibodies accessible to more "undruggable" targets and equipped with new functions of illustrating or regulating biological processes more precisely. In this Review, in addition to introducing how naked antibodies and various antibody conjugates (such as antibody-drug conjugates, antibody-oligonucleotide conjugates, antibody-enzyme conjugates, etc.) work in therapeutic applications, special attention has been paid to how chemistry tools have helped to optimize the therapeutic outcome (i.e., with enhanced efficacy and reduced side effects) or facilitate the multifunctionalization of antibodies, with a focus on emerging fields such as targeted protein degradation, real-time live-cell imaging, catalytic labeling or decaging with spatiotemporal control as well as the engagement of antibodies inside cells. With advances in modern chemistry and biotechnology, well-designed antibodies and their derivatives via size miniaturization or multifunctionalization together with efficient delivery systems have emerged, which have gradually improved our understanding of important biological processes and paved the way to pursue novel targets for potential treatments of various diseases.

Individual and combined toxicity of imidacloprid and two seed dressing insecticides on collembolans Folsomia candida

The aim of this study was to examine the chronic toxicity of imidacloprid (IMI), clothianidin (CLO) and fipronil (FIP) as a single exposure, as well as binary mixtures of IMI with CLO or FIP toward collembolans Folsomia candida, which are fauna present in the soil. Chronic toxicity assays were performed following an ISO guideline in a Tropical Artificial Soil (TAS), and the influence on the number and growth of the juveniles produced were determined. The range of nominal concentrations used in the tests with the individual compounds was 0.08-1.28 mg/kg (IMI), 0.079-1.264 mg/kg (FIP) and 0.007-0.112 mg/kg (CLO), whereas the mixture assays were performed with half the value used in the tests with individual compounds. Based upon single exposures, IMI produced a similar impact of reducing reproduction by 50% (EC₅₀ ranging from 0.74 to 0.85 mg/kg) compared to FIP (EC₅₀ = 0.78 mg/kg), whereas CLO was the most toxic to F. candida (EC₅₀ = 0.08 mg/kg). Their mixtures generally resulted in a diminished effect on reproduction, as evidenced by the higher EC₅₀ values. In contrast, in the case of the IMI+FIP combination at high concentrations at the EC₅₀ level, a synergistic effect on toxicity was observed. The single exposure to the three insecticides and the mixture of IMI-FIP also decreased the size of generated juveniles, which was evidenced by the reduction in the proportion of large juveniles and increased proportion of small juveniles. However, both binary mixtures (IMI-FIP and IMI-CLO) presented antagonistic effects as evidenced by less than expected reductions in growth. Data on the toxic effects of IMI in a mixture with other seed dressing insecticides to collembolans provides useful information to environmental risk assessors by diminishing the uncertainties on the ecological risk of exposure to pesticides, enabling soil management degradation by utilizing multiple insecticides.

VH-Based Mini Q-Body: A Novel Quench-Based Immunosensor

Quenchbodies (Q-bodies), a type of biosensor, are antibodies labeled with a fluorescent dye near the antigen recognition site. In the absence of an antigen, the dye is quenched by tryptophans in the antibody sequence; however, in its presence, the dye is displaced and therefore de-quenched. Although scFv and Fab are mainly used to create Q-bodies, this is the first report where a single-domain heavy chain V_H from a semi-synthetic human antibody library formed the basis. To create a proof of concept "mini Q-body", a human anti-lysozyme single-domain V_H antibody C3 was used. Mini Q-bodies were successfully developed using seven dyes. Different responses were observed depending on the dye and linker length; it was concluded that the optimal linker length for the TAMRA dye was C5, and rhodamine 6G was identified as the dye with the largest de-quenching response. Three single-domain antibodies with sequences similar to that of the C3 antibody were chosen, and the results confirmed the applicability of this method in developing mini Q-bodies. In summary, mini Q-bodies are an easy-to-use and time-saving method for detecting proteins.

Small-Molecule Modulated Affinity-Tunable Semisynthetic Protein Switches

Engineered protein switches have been widely applied in cell-based protein sensors and point-of-care diagnosis for the rapid and simple analysis of a wide variety of proteins, metabolites, nucleic acids, and enzymatic activities. Currently, these protein switches are based on two main types of switching mechanisms to transduce the target binding event to a quantitative signal, through a change in the optical properties of fluorescent molecules and the activation of enzymatic activities. In this paper, we introduce a new affinity-tunable protein switch strategy in which the binding of a small-molecule target with the protein activates the streptavidin-biotin interaction to generate a readout signal. In the absence of a target, the biotinylated protein switch forms a closed conformation where the biotin is positioned in close proximity to the protein, imposing a large steric hindrance to prevent the effective binding with streptavidin. In the presence of the target molecule, this steric hindrance is removed, thereby exposing the biotin for streptavidin binding to produce strong fluorescent signals. With this modular sensing concept, various sulfonamide, methotrexate, and trimethoprim drugs can be selectively detected on the cell surface of native and genetically engineered cells using different fluorescent dyes and detection techniques.

Isolation of a human SARS-CoV-2 neutralizing antibody from a synthetic phage library and its conversion to fluorescent biosensors

Since late 2019, the outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the resultant spread of COVID-19 have given rise to a worldwide health crisis that is posing great challenges to public health and clinical treatment, in addition to serving as a formidable threat to the global economy. To obtain an effective tool to prevent and diagnose viral infections, we attempted to obtain human antibody fragments that can effectively neutralize viral infection and be utilized for rapid virus detection. To this end, several human monoclonal antibodies were isolated by bio-panning a phage-displayed human antibody library, Tomlinson I. The selected clones were demonstrated to bind to the S1 domain of the spike glycoprotein of SARS-CoV-2. Moreover, clone A7 in Fab and IgG formats were found to effectively neutralize the binding of S protein to angiotensin-converting enzyme 2 in the low nM range. In addition, this clone was successfully converted to quench-based fluorescent immunosensors (Quenchbodies) that allowed antigen detection within a few minutes, with the help of a handy fluorometer.

Creation of a quick and sensitive fluorescent immunosensor for detecting the mineralocorticoid steroid hormone aldosterone

Aldosterone (ALD) is a steroid hormone secreted by the zona glomerulosa of the adrenal cortex that mainly acts on the kidney to regulate sodium ion and water reabsorption. Detection of ALD plays an important role in the diagnosis of primary aldosteronism in patients with hypertension. For the first time, the gene encoding the anti-ALD antibody, A2E11, was successfully cloned and analyzed using phage display technology. The antibody had an affinity of 2.5 nM against ALD, and after binding to ALD, it reached saturation within 5 s. Using this antibody, a Quenchbody (Q-body) was constructed by labeling the N-termini of heavy and light chains of the antigen-binding fragment of A2E11 with the fluorescent dye ATTO520 to detect ALD based on the principle of photoinduced electron transfer. The sensor detected ALD in 2 min, and the limit of detection was 24.1 pg/mL with a wide detection range from 24.1 pg/mL to 10 µg/mL and a half-maximal effective concentration of 42.3 ng/mL. At the highest concentration of ALD in the assay, the fluorescence intensity increased by 5.0-fold compared to the original fluorescence intensity of the Q-body solution. The Q-body could be applied to analyze 50% of human serum without a significant influence of the matrix. The recoveries of ALD in spiked serum samples with the Q-body assay were confirmed to range from 90.3% to 98.2%, suggesting their potential applications in the diagnosis of diseases, such as essential hypertension.

Recombinant antibodies and their use for food immunoanalysis

Antibodies are widely employed as biorecognition elements for the detection of a plethora of compounds including food and environmental contaminants, biomarkers, or illicit drugs. They are also applied in therapeutics for the treatment of several disorders. Recent recommendations from the EU on animal protection and the replacement of animal-derived antibodies by non-animal-derived ones have raised a great controversy in the scientific community. The application of recombinant antibodies is expected to achieve a high growth rate in the years to come thanks to their versatility and beneficial characteristics in comparison to monoclonal and polyclonal antibodies, such as stability in harsh conditions, small size, relatively low production costs, and batch-to-batch reproducibility. This review describes the characteristics, advantages, and disadvantages of recombinant antibodies including antigen-binding fragments (Fab), single-chain fragment variable (scFv), and single-domain antibodies (VHH) and their application in food analysis with especial emphasis on the analysis of biotoxins, antibiotics, pesticides, and foodborne pathogens. Although the wide application of recombinant antibodies has been hampered by a number of challenges, this review demonstrates their potential for the sensitive, selective, and rapid detection of food contaminants.

Intra Q-body: an antibody-based fluorogenic probe for intracellular proteins that allows live cell imaging and sorting

Although intracellular biomarkers can be imaged with fluorescent dye(s)-labeled antibodies, the use of such probes for precise imaging of intracellular biomarkers in living cells remains challenging due to background noise from unbound probes. Herein, we describe the development of a conditionally active Fab-type Quenchbody (Q-body) probe derived from a monoclonal antibody (DO-1) with the ability to both target and spatiotemporally visualize intracellular p53 in living cells with low background signal. p53 is a key tumor suppressor and validated biomarker for cancer diagnostics and therapeutics. The Q-body displayed up to 27-fold p53 level-dependent fluorescence enhancement in vitro with a limit of detection of 0.72 nM. In fixed and live cells, 8.3- and 8.4-fold enhancement was respectively observed. Furthermore, we demonstrate live-cell sorting based on p53 expression. This study provides the first evidence of the feasibility and applicability of Q-body probes for the live-cell imaging of intrinsically intracellular proteins and opens a novel avenue for research and diagnostic applications on intracellular target-based live-cell sorting.

A fluorescent immunosensor that lights up tumor biomarker p53 in living cells was developed based on the Q-body technology. The technology was further applied to the live cell monitoring of p53 levels, and live cell sorting based on p53 expression.

Quench-Release-Based Fluorescent Immunosensor for the Rapid Detection of Tumor Necrosis Factor α

Tumor necrosis factor α (TNF-α) is used as a biomarker for the diagnosis of various inflammatory and autoimmune diseases. In recent years, numerous approaches have been used for the qualitative and quantitative analyses of TNF-α. However, these methods have several drawbacks, such as a tedious and time-consuming process, high pH and temperature sensitivity, and increased chances of denaturation in vitro. Quenchbody (Q-body) is a fluorescence immunoprobe that functions based on the principle of photoinduced electron transfer and has been successful in detecting various substances. In this study, we constructed two Q-bodies based on a therapeutic antibody, adalimumab, to rapidly detect human TNF-α. Both sensors could detect TNF-α within 5 min. The results showed that the limit of detection (LOD) of TNF-α was as low as 0.123 ng/mL with a half-maximal effective concentration (EC₅₀) of 25.0 ng/mL using the TAMRA-labeled Q-body, whereas the ATTO520-labeled Q-body had a LOD of 0.419 ng/mL with an EC₅₀ of 65.6 ng/mL, suggesting that the Q-bodies could rapidly detect TNF-α with reasonable sensitivity over a wide detection range. These biosensors will be useful tools for the detection and monitoring of inflammatory biomarkers.

LSPR immuno-sensing based on iso-Y nanopillars for highly sensitive and specific imidacloprid detection

Imidacloprid is the most widely used insecticide in agriculture and its intensive use over the last 30 years has caused a global concern due to its potentially toxic effects on the ecosystem. Considering the recent scientific interest in novel simple methods for imidacloprid analysis, we propose a label-free sensitive and specific localised surface plasmon resonance system for the detection of the insecticide based on 2D nanostructured metasurfaces with highly performing plasmonic properties. The specificity of the sensor proposed was achieved by covalent bio-functionalization of the metasurface using a smart and easy one-step procedure mediated by carbon disulphide. The biosensor produced was tested using a set of imidacloprid standard solutions showing a competitive limit of detection, lower than 1 ng mL^-1. Our novel nanosensing configuration represents a valid and reliable solution to realize low-cost portable POC tests as an alternative to the laborious and expensive methods traditionally used for insecticide detection.

Rapid conversion of IgG to biosensor using an antibody-binding protein-based probe

We successfully developed a fluorescent probe that can quickly convert full-length antibodies to Quenchbodies, which represent a type of fluorescent immunosensor with high binding affinity and specificity depending on the reaction of antigens and antibodies. An anti-testosterone IgG was successfully converted to an immunosensor that detects testosterone with a limit of detection (LOD) of 0.76 nM and concentration for 50% of maximal effect (EC₅₀) of 61.5 nM. Another IgG-based immunosensor detected ractopamine with an LOD of 15.5 pM and EC₅₀ of 48.6 nM.

Electrochemical Sensing of Neonicotinoids Using Laser-Induced Graphene

Neonicotinoids are the fastest-growing insecticide accounting for over 25% of the global pesticide market and are capable of controlling a range of pests that damage croplands, home yards/gardens, and golf course greens. However, widespread use has led to nontarget organism decline in pollinators, insects, and birds, while chronic, sublethal effects on humans are still largely unknown. Therefore, there is a need to understand how prevalent neonicotinoids are in the environment as there are currently no commercially available field-deployable sensors capable of measuring neonicotinoid concentrations in surface waters. Herein, we report the first example of a laser-induced graphene (LIG) platform that utilizes electrochemical sensing for neonicotinoid detection. These graphene-based sensors are created through a scalable direct-write laser fabrication process that converts polyimide into LIG, which eliminates the need for chemical synthesis of graphene, ink formulation, masks, stencils, pattern rolls, and postprint annealing commonly associated with other printed graphene sensors. The LIG electrodes were capable of monitoring four major neonicotinoids (CLO, IMD, TMX, and DNT) with low detection limits (CLO, 823 nM; IMD, 384 nM; TMX, 338 nM; and DNT, 682 nM) and a rapid response time (∼10 s) using square-wave voltammetry without chemical/biological functionalization. Interference testing exhibited negligible responses from widely used pesticides including the broad-leaf insecticides parathion, paraoxon, and fipronil, as well as systemic herbicides glyphosate (roundup), atrazine, dicamba, and 2,4-dichlorophenoxyacetic acid. These scalable, graphene-based sensors have the potential for wide-scale mapping of neonicotinoids in watersheds and potential use in numerous electrochemical sensor devices.

BRET Q-Body: A Ratiometric Quench-based Bioluminescent Immunosensor Made of Luciferase-Dye-Antibody Fusion with Enhanced Response

A quenchbody (Q-body) is an immunosensor comprising an antibody fragment containing an antigen-binding site that is site-specifically labeled with a fluorescent dye. The fluorescent dye of a Q-body is quenched in the absence of an antigen; however, its fluorescence recovers in the presence of an antigen, offering simple and rapid systems for antigen detection. In this study, we fused luciferase NanoLuc to a Q-body to construct a new immunosensor termed the "BRET Q-body" that can detect antigens based on the bioluminescence resonance energy transfer (BRET) principle. The resulting BRET Q-bodies for an osteocalcin peptide that emit three different emission colors could detect an antigen without the requirement of an external light source, based on ratiometric detection and color change with two wavelengths for the luciferase and fluorophore. Furthermore, the BRET Q-body produced unexpectedly higher responses up to 12-fold because of the increased BRET efficiency, probably associated with antigen-dependent dye movement. Thus, the BRET Q-body is a useful biosensor as a core of point-of-care tests.

Recent Advances in Quenchbody, a Fluorescent Immunosensor

The detection of viruses, disease biomarkers, physiologically active substances, drugs, and chemicals is of great significance in many areas of our lives. Immunodetection technology is based on the specificity and affinity of antigen–antibody reactions. Compared with other analytical methods such as liquid chromatography coupled with mass spectrometry, which requires a large and expensive instrument, immunodetection has the advantages of simplicity and good selectivity and is thus widely used in disease diagnosis and food/environmental monitoring. Quenchbody (Q-body), a new type of fluorescent immunosensor, is an antibody fragment labeled with fluorescent dyes. When the Q-body binds to its antigen, the fluorescence intensity increases. The detection of antigens by changes in fluorescence intensity is simple, easy to operate, and highly sensitive. This review comprehensively discusses the principle, construction, application, and current progress related to Q-bodies.

Creation of a Nanobody-Based Fluorescent Immunosensor Mini Q-body for Rapid Signal-On Detection of Small Hapten Methotrexate

"Quenchbody (Q-body)" is a quench-based fluorescent biosensor labeled with a fluorescent dye near the antigen-binding site of an antibody. Q-bodies can detect a range of target molecules quickly by simply mixing with a sample. However, the development of Q-bodies using V_HH-nanobodies derived from camelid heavy-chain antibodies has not been reported despite their favorable characteristics. Here, we report a "mini Q-body" that can detect the chemotherapy agent methotrexate (MTX) by using anti-MTX nanobody. Three kinds of constructs each encoding an N-terminal Cys-tag and anti-MTX VHH gene with a different length of linker (GGGS)_n (n = 0, 2, and 4) between them were prepared followed by the expression in Escherichia coli and labeling with several dye maleimides. When the fluorescence intensities in the presence of varied MTX concentrations were measured, TAMRA-labeled nanobodies showed a higher response than ATTO520- or R6G-labeled ones. Especially, TAMRA C6-labeled mini Q-body with no linker showed the highest response of ∼6-fold and a low detection limit of 0.56 nM. When each Trp residue in the mini Q-body was mutated to address the quenching mechanism, the major role of Trp34 at CDR1 in quenching was revealed. Furthermore, the mini Q-body could detect MTX in 50% human serum with a low detection limit of 1.72 nM, showing its applicability to therapeutic drug monitoring. This study is expected to become the basis of the construction of highly responsive mini Q-bodies for sensitive detection of many molecules from small haptens to larger proteins, which will lead to broader applications such as point-of-care tests.

Simultaneous determination of acetamiprid and 6-chloronicotinic acid in environmental samples by using ion chromatography hyphenated to online photoinduced fluorescence detector

This study aims to introduce a simple, sensitive, and cost-effective method for the simultaneous determination of acetamiprid and its main metabolite 6-chloronicotinic acid in environmental samples by using a nonsuppressed ion chromatography hyphenated with an online postcolumn photoinduced fluorescence detection system. The fluorescence detector wavelengths λ_ex /λ_em  = 257/382 nm was set for up to 6.0 min for acetamiprid, while λ_ex /λ_em  = 231/370 nm programmed for 6-chloronicotinic acid for the rest of the analysis time. Both samples were treated by applying miniaturized quick, easy, cheap, effective, rugged, and safe method before the separation of analytes on an IonPac^® AS11-HC column by pumping 40 mM NaOH having minuscule content of acetonitrile (5%, v/v) as an eluent. Both intrinsically nonfluorescent analytes were turned-on by online postcolumn photoinduced derivatization, avoiding the need for complex chemical derivatization or addition of a postcolumn extra pump. The developed method was appraised for the analysis of environmental samples, exhibiting excellent linearity (0.050-10 μg/mL) with a correlation coefficient greater than 0.9993 for both analytes. Whereas, obtained limit of detection (0.025-0.0072 μg/mL), recoveries (98.02-116.00%), and inter- and intraday precision (≤3.02 %) were satisfactory for both compounds in environmental samples.

Development of a fluorescent probe for the detection of hPD-L1

Interaction of human programmed death factor-1 (hPD-1) of T cells and one of its ligands hPD-L1 which is expressed on cancer cells suppresses effector T cell functions. Studies showed that the hPD-1/hPD-L1 pathway is associated with killing mechanisms of tumor cells evading the immune system. Immunotherapy based on the checkpoint inhibitor on hPD-1 has been an important approach to treat cancer; however, not all cancer cells over-express hPD-L1. Detection of hPD-L1 over-expression in cancer cells may be a key factor for deciding on whether immunotherapy should be conducted. In the present study, we produced recombinant hPD-1 using Escherichia coli, and created a fluorescent probe termed quenched hPD-1 (QPD-1) for the detection of hPD-L1. We found that hPD-1 can quench fluorescence of carboxytetramethylrhodamine labeled on its N-terminal and QPD-1 is a convenient tool to rapidly detect hPD-L1 with a limit of detection of 10 nM and detectable range of 10 nM-1000 nM. QPD-1 may also function as a probe to screen for hPD-L1 over-expressing tumor cells and promote appropriate medical procedure through tumor immunotherapy.

Detection and destruction of HER2-positive cancer cells by Ultra Quenchbody-siRNA complex

Ultra Quenchbody (UQ-body) is a biosensor that utilizes the quenching behavior of the fluorescent dye linked to the antibody V region. When the corresponding antigen is bound to the UQ-body, the fluorescence is restored and allows the detection of target molecules easily and sensitively. In this paper, we constructed UQ-bodies to sensitively detect the human epidermal growth factor receptor 2 (HER2) cancer marker in solution or on cancer cells, which was further used to kill the cancer cells. A synthetic Fab fragment of anti-HER2 antibody Fab37 with many Trp residues at hypervariable region was prepared and labeled with fluorescent dyes to obtain the UQ-bodies. The UQ-body could detect HER2 in solution at concentrations as low as 20 pM with an EC₅₀ of 0.3 nM with a fourfold response. Fluorescence imaging of HER2-positive cells was successfully performed without any washing steps. To deliver small interfering RNA (siRNA) to cancer cells, a modified UQ-body with C-terminal 9R sequence was also prepared. HER2-positive cancer cells were effectively killed by polo-like kinase 1 siRNA intracellularly delivered by the UQ-body-9R. The novel approach employing siRNA-empowered UQ-body could detect and image the HER2 antigen easily and sensitively, and effectively kill the HER2-positive cancer cells.

Fluorescence turn-on and turn-off sensing of pesticides by carbon dot-based sensor

Green chemistry C-Dot-based ‘turn-on’ and ‘turn-off’ fluorescence sensor for pesticides [imidacloprid (LOD ∼ 0.013 μM) and tetradifon (LOD ∼ 0.04 μM)] in aqueous solution.

Single-Step Detection of the Influenza Virus Hemagglutinin Using Bacterially-Produced Quenchbodies

We have successfully generated a Quenchbody that enables the detection of the influenza virus hemagglutinin (HA), in a simple and convenient manner. By two-site labeling of the bacterially-produced anti-HA Fab with ATTO520, its fluorescence intensity was increased to 4.4-fold, in the presence of a nanomolar concentration of H1N1 HA. Our results indicate the potential use of this Quenchbody, as a sensor for the simple in situ detection of influenza A virus.

Competitive and noncompetitive immunoassays for the detection of benzothiostrobin using magnetic nanoparticles and fluorescein isothiocyanate-labeled peptides

Phage-displayed peptides have been proven to be powerful reagents for competitive and noncompetitive immunoassays. However, they are unconventional reagents, which greatly limit their analytical commercial applications and require additional reagents for detection. In this work, the peptides that specifically bind with anti-benzothiostrobin monoclonal antibody (mAb) or benzothiostrobin-mAb immunocomplex were synthesized and conjugated with fluorescein isothiocyanate (FITC) as substitutes of the phage-displayed peptides to avoid their shortcomings and extend their applications. Competitive and noncompetitive fluorescence immunoassays (FIAs) for benzothiostrobin were developed by mAb coupling with magnetic nanoparticles as concentration elements and peptides conjugated with FITC as tracers. Compared with enzyme-linked immunosorbent assays, the FIAs reduced the number of steps from 6 to 2 and analysis time from more than 5 to 1.2 h. The competitive FIA showed the half-maximal inhibition concentration (IC₅₀) of 16.8 ng mL^-1 and detection range (IC₁₀-IC₉₀) of 1.0-759.9 ng mL^-1, while the concentration of analyte producing 50% saturation of the signal (SC₅₀) and detection range (SC₁₀-SC₉₀) of noncompetitive FIA were 93.4 and 5.9-788.2 ng mL^-1, respectively. The average spiked recoveries were 68.33-98.50% and 73.33-96.67% for competitive and noncompetitive FIAs, respectively. The FIAs showed good correlation with high-performance liquid chromatography for the detection of benzothiostrobin in authentic samples. Graphical abstract Development of competitive and noncompetitive fluorescence immunoassays for benzothiostrobin by using monoclonal antibody coupling with magnetic nanoparticles as concentration elements and peptides conjugated with fluorescein isothiocyanate as tracers.

Construction of Quenchbodies to detect and image amyloid β oligomers

A quenchbody (Q-body) is an antibody-based biosensor that employs fluorescence quenching of the dye(s) attached to the antibody fragment, which are de-quenched upon antigen binding. In this study, we aimed to develop Fab type Q-bodies (UQ-bodies) to aid the diagnosis of Alzheimer's disease (AD). Characteristic senile plaques in AD consist of amyloid-β peptide (Aβ) generated from the amyloid precursor protein. Aβ42, one of the major peptide forms, aggregates fast and manifests higher neurotoxicity. Recent studies showed that Aβ oligomers, such as Aβ-derived diffusible ligand (ADDL), are more toxic than fibrils. Thus, detection of Aβ and its oligomers in body fluid might help detect deterioration caused by the disease. To this end, the Fab fragment of the anti-Aβ antibody h12A11, which binds preferentially to ADDL, was expressed in Escherichia coli, and labeled with a fluorescent dye at the N terminus of either the heavy chain, or the heavy and light chains, via Cys-containing tag(s) to prepare UQ-bodies. As a result, the double-labeled UQ-bodies detected ADDL with higher sensitivity than that for the Aβ peptide. In addition, the UQ-body could be used to image aggregated Aβ with a low background, which suggested the potential of UQ-bodies as a fast bioimaging tool.