Optical lateral flow test strip biosensors for pesticides: Recent advances and future trends

Development of a gold nanoparticle-based lateral flow immunochromatographic assay for the rapid and quantitative detection of thymidine kinase 1 in human serum

Thymidine kinase 1 (TK1) is a marker of cell proliferation that can be used for early screening, treatment monitoring, and evaluating the prognosis of patients with tumors. The main purpose of this study was to develop clinically applicable TK1 antibodies, establish an appropriate detection method, and provide material and technical support for the research and clinical application for different types of tumors. Experimental mice were immunized with the C-terminal 31 peptide of human TK1 to screen monoclonal cell lines capable of stably secreting specific antibodies. Monoclonal antibodies were then prepared, purified and screened for optimal pairing following the identification of purity and isotype. Finally, based on the principles adopted by the double-antibody sandwich detection method, we constructed a lateral flow immunochromatographic assay (LFIA) to quantify the concentration of TK1 in serum samples when using a gold nanoparticle-labeled anti-TK1 monoclonal antibody as a probe. The limit of detection for TK1 in serum was 0.31 pmol/L with a detection range of 0.31-50 pmol/L. The spiked recoveries ranged from 97.7% to 109.0% with an analytical precision of 5.7-8.2%; there was no cross-reactivity with common proteins in the serum. The established LFIA also exhibited good consistency with commercially available chemiluminescent immunoassay kits for the detection of clinical samples. The LFIA developed in this study has the advantages of high sensitivity, accuracy, reproducibility and strong specificity, and provides a new technical tool for the quantitative detection of TK1.

Multiplexed Detection Strategies for Biosensors Based on the CRISPR-Cas System

A growing number of applications require simultaneous detection of multiplexed nucleic acid targets in a single reaction, which enables higher information density in combination with reduced assay time and cost. Clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR-Cas system have broad applications for the detection of nucleic acids due to their strong specificity, high sensitivity, and excellent programmability. However, realizing multiplexed detection is still challenging for the CRISPR-Cas system due to the nonspecific collateral cleavage activity, limited signal reporting strategies, and possible cross-reactions. In this review, we summarize the principles, strategies, and features of multiplexed detection based on the CRISPR-Cas system and further discuss the challenges and perspective.

Two swords combination: Smartphone-assisted ratiometric fluorescent and paper sensors for dual-mode detection of glyphosate in edible malt

The long-term and excessive use of glyphosate (GLY) in diverse matrices has caused serious hazard to the human and environment. However, the ultrasensitive detection of GLY still remains challenging. In this study, the smartphone-assisted dual-signal mode ratiometric fluorescent and paper sensors based on the red-emissive gold nanoclusters (R-AuNCs) and blue-emissive carbon dots (B-CDs) were ingeniously designed accurate and sensitive detection of GLY. Upon the presence of GLY, it would quench the fluorescence of B-CDs through dynamic quenching effect, and strengthen the fluorescence response of R-AuNCs due to aggregation-induced enhancement effect. Through calculating the GLY-induced fluorescence intensity ratio of B-CDs to R-AuNCs by using a fluorescence spectrophotometer, low to 0.218 μg/mL of GLY could be detected in lab in a wide concentration range of 0.3-12 μg/mL with high recovery of 94.7-103.1% in the spiked malt samples. The smartphone-assisted ratiometric fluorescent sensor achieved in the 96-well plate could monitor 0-11 μg/mL of GLY with satisfactory recovery of 94.1-107.0% in real edible malt matrices for high-throughput analysis. In addition, a portable smartphone-assisted ratiometric paper sensor established through directly depositing the combined B-CDs/R-AuNCs probes on the test strip could realize on-site measurement of 2-8 μg/mL of GLY with good linear relationship. This study provides new insights into developing the dual-signal ratiometric sensing platforms for the in-lab sensitive detection, high-throughput analysis, and on-site portable measurement of more trace contaminants in foods, clinical and environmental samples.

Development of a simple polymer-based sensor for detection of the Pirimicarb pesticide

In this study, a sensitive and selective fluorescent chemosensor was developed for the determination of pirimicarb pesticide by adopting the surface molecular imprinting approach. The magnetic molecularly imprinted polymer (MIP) nanocomposite was prepared using pirimicarb as the template molecule, CuFe2O4 nanoparticles, and graphene quantum dots as a fluorophore (MIP-CuFe2O4/GQDs). It was then characterized using X-ray diffraction (XRD) technique, Fourier transforms infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), and transmission electron microscopy (TEM). The response surface methodology (RSM) was also employed to optimize and estimate the effective parameters of pirimicarb adsorption by this polymer. According to the experimental results, the average particle size and imprinting factor (IF) of this polymer are 53.61 nm and 2.48, respectively. Moreover, this polymer has an excellent ability to adsorb pirimicarb with a removal percentage of 99.92 at pH = 7.54, initial pirimicarb concentration = 10.17 mg/L, polymer dosage = 840 mg/L, and contact time = 6.15 min. The detection of pirimicarb was performed by fluorescence spectroscopy at a concentration range of 0-50 mg/L, and a sensitivity of 15.808 a.u/mg and a limit of detection of 1.79 mg/L were obtained. Real samples with RSD less than 2 were measured using this chemosensor. Besides, the proposed chemosensor demonstrated remarkable selectivity by checking some other insecticides with similar and different molecular structures to pirimicarb, such as diazinon, deltamethrin, and chlorpyrifos.

Self-ratiometric fluorescent platform based on upconversion nanoparticles for on-site detection of chlorpyrifos

Monitoring organophosphorus pesticides is significant for food safety assessment. Herein, we developed upconversion nanoparticles (UCNPs)-based self-ratiometric fluorescent platform for the detection of chlorpyrifos. The UCNPs have the ability to confine the detection and reference functions in one nanoparticle. Specifically, the blue upconversion (UC) emission (448 nm) in the shell layer of UCNPs is quenched by the product of the acetylcholinesterase-mediated reaction, while the red UC emission (652 nm) from the core remains constant as a self-calibrated reference signal. Employing the inhibition property of chlorpyrifos, self-proportional fluorescence is employed to detect chlorpyrifos. As proof-of-concept, test strips are fabricated by loading the UCNPs onto filter paper. Combined with the smartphone and image-processing algorithm, chlorpyrifos quantitative testing is achieved with a detection limit of 14.4843 ng mL-1. This portable platform displays anti-interference capability and high stability in the complicated matrix, making it an effective candidate for on-site application.

Improving design features and air bubble manipulation techniques for a single-step sandwich electrochemical ELISA incorporating commercial electrodes into capillary-flow driven immunoassay devices

Integrating electrochemistry into capillary-flow driven immunoassay devices provides unique opportunities for quantitative point-of-care testing. Although custom electrodes can be inexpensive and are tunable, they require skilled fabrication. Here, we report the incorporation of a commercial electrode into a capillary-flow driven immunoassay (iceCaDI) device for a single end-user step sandwich electrochemical enzyme-linked immunosorbent assay (ELISA). The iceCaDI device is a pump-free portable microfluidic device with an integrated commercial screen-printed electrode and flow driven by capillary action. The iceCaDI device is composed of alternating polyester transparency film and double-sided adhesive film layers that are patterned with a laser cutter. This platform was designed to address known limitations of laminated device fabrication methods and operation. First, we developed a foldable laminated device fabrication using hinges for easy assembly and precise alignment. Second, reagent dispersing was achieved by incorporating a 1 mm wide arrow-shaped notch in the middle of the channel that trapped an air bubble and formed a baffle that facilitated reagent spreading to cover the detection area. Third, small vent holes were added to the top layer of the channels to prevent air bubbles from blocking flow. Finally, we fabricated a CRP immunosensor with a detection range of 0.625 to 10.0 μg mL-1 as a proof-of-concept to demonstrate an automatically driven sandwich electrochemical ELISA using the iceCaDI device. Three concentrations of CRP were successfully measured under flow conditions within 8 min. Our proposed device is a promising approach and a step forward in the development of point-of-care (POC) devices for techniques that traditionally require multiple user steps.

UiOL@AIEgens-assisted lateral flow immunosensor for the ultrasensitive dual-modal point-of-care detection of aflatoxin B1

Aflatoxin B1 (AFB1) contamination in food has attracted worldwide attention. The sensitive detection of AFB1 is vital for ensuring food quality and safety. This study developed an ultrasensitive signal-enhanced lateral flow immunosensor (LFIS) based on the functionalized zirconium metal-organic framework (MOF) of a UiO linker enriched with abundant aggregation-induced emission luminogen (UiOL@AIEgens) probes for the rapid dual-modal point-of-care (POC) determination of AFB1. Using UiO MOFs with numerous active sites as the carrier facilitated abundant AIEgens enrichment on the surface. After coupling with enough anti-AFB1 monoclonal antibodies (mAbs), the green-emissive UiOL@AIEgens-mAbs probes with high specificity and remarkably-enhanced fluorescence responses were obtained to competitively capture target AFB1 in the standard or sample solution and AFB1 antigen immobilized on the test (T) line of the POC LFIS. Under optimum conditions, the LFIS was capable of visual qualitative and smartphone-assisted dual-modal determination of target AFB1 within 7 min. Detection occurred in a range of 0.01-5 ng/mL at an ultra-low detection limit of 0.003 ng/mL, which was 300- and 600-fold lower than traditional immunoassays and the maximum limit set by the European Union, respectively. Moreover, the feasibility and robustness of the LFIS platform were assessed by detecting AFB1 in maize and lotus seed samples with average recoveries of 94.3-109.0%. The developed UiOL@AIEgens-based POC LFIS can be used for ultrasensitive, reliable, on-site detection in food. This study provides a new method for the real-time monitoring of AFB1 and other harmful contaminants in food and more complex matrices.

Portable sensors equipped with smartphones for organophosphorus pesticides detection

Organophosphorus pesticides (OPs) play an important role in agricultural production and the accurate detection of OP residues is essential to ensure food safety. Portable sensors are expected to be a potential device due to their high detection efficiency, easy-to-use processes and low cost. Due to the widespread popularity and powerful capabilities of smartphones, smartphone-based sensing systems have rapidly developed into ideal tools for portable detection, however, a systematic review on the detection of OPs is still lacking. Therefore, a comprehensive overview of sensors equipped with smartphones for OP detection in recent year is provided; this overview includes their sensing signals (colorimetric, fluorescent, chemiluminescent and electrochemical signals), detection mechanism, analysis applications, advantages/disadvantages and perspectives. Moreover, the progress of sensors equipped with smartphones for the detection of OPs in food is thoroughly summarized. This review contributes to food safety and the development of efficient and reliable methods for smartphone-based OPs detection.

Triple Cascade Quantum-Strip for Heart Failure Point-of-Care Testing

Heart failure (HF) is a life-threatening syndrome. Timely and accurate bedside monitoring of the occurrence and progression of HF via measurements of multiple HF-related biomarkers remains a challenge. Here, we report a triple cascade quantum-strip (TCQS) sensing strategy for the rapid and selective multiplex-tracing of three clinically validated HF biomarkers (BNP/NT-proBNP/ST2) in serum. High selectivity to the three biomarkers is achieved by controlling the individual recognition ability of three target-specific quantum immunoprobes and tuning their simultaneous use to BNP/NT-proBNP/ST2 recognition without mutual interference, which allows the three biomarkers to be directly enriched from serum samples. Benefiting from the fast release-binding kinetics of target-bound immunoprobes on TCQS, recognizable fluorescent signals can be rapidly read out through combining with a self-designed smartphone-based portable reader. This rapid and simple profiling strategy results in good specificity and sensitivity with LODs of 0.097, 0.072, and 0.948 ng/mL for BNP, NT-proBNP, and ST2, respectively, which match the need of clinical applications. Real serum samples are tested with an accuracy of 92.86% for HF diagnosis, validating the capability of the smartphone-read TCQS for practical applications. In particular, the simultaneous detection of the TCQS sensing strategy for BNP/NT-proBNP/ST2 will facilitate the accurate monitoring of HF occurrence, risk stratification, progression, and prognosis as a powerful POCT tool.

Microfluidic-assisted integrated nucleic acid test strips for POCT

Numerous diseases have posed significant threats to public health, notably the global pandemic of COVID-19, resulting in widespread devastation due to its high infectivity and severity. The nucleic acid lateral flow assay (NALFA) addresses challenges of complexity, cost, and time associated with traditional assays, offering a reliable platform for rapid and precise nucleic acid target detection. NALFA is gaining prominence as a point-of-care testing (POCT) technique, thanks to its user-friendly operation and rapid results. Nevertheless, conventional NALFA relies on specialized technicians and involves labor-intensive steps like DNA extraction and PCR processes, impeding its efficiency. To overcome these limitations, integrating NALFA with microfluidic technology, widely employed in rapid field detection, holds promise. This review comprehensively outlines prevailing strategies for integrating NALFA, encompassing both research initiatives and commercial applications. Addressing the bottleneck of nucleic acid amplification as a rate-limiting step, the review delves into progress in amplification-free NALFA and highlights prevalent signal amplification techniques. Ultimately, the review outlines the future prospect of integrated NALFA development, capturing the technology's evolution and providing valuable insights for academic and commercial endeavors.

Recent advances in aptamer-based biosensors for potassium detection

Maintaining a stable level of potassium is crucial for proper bodily function because even a slight imbalance can result in serious disorders like hyperkalemia and hypokalemia. Therefore, detecting and monitoring potassium ion (K+) levels are of utmost importance. Various biosensors have been developed for rapid K+ detection, with aptamer-based biosensors garnering significant attention due to their high sensitivity and specificity. This review focuses on aptamer-based biosensors for K+ detection, providing an overview of their signal generation strategies, including electrochemical, field-effect transistor, nanopore, colorimetric, and fluorescent systems. The analytical performance of these biosensors is evaluated comprehensively. In addition, factors that affect their efficiency, such as their physicochemical properties, regeneration for reusability, and linkers/spacers, are listed. Lastly, this review examines the major challenges faced by aptamer-based biosensors in K+ detection and discusses potential future developments.

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

Enhanced sensitivity and accuracy via gold nanoparticles based multi-line lateral flow immunoassay strip for Salmonella typhimurium detection in milk and orange juice

Food borne pathogens threaten food safety and affect human health. The lateral flow immunoassays (LFIAs) are widely concerned because of simplicity, low cost and user friendliness, and have broad application prospects in pathogen detection. However, the sensitivity of LFIAs is limited. Herein, multi-line LFIAs are introduced into pathogen detection for the first time. Compared with traditional single-line LFIAs, the overall signal strength of multi-line LFIAs has been significantly improved. It is particularly noteworthy that multi-line LFIAs detection accuracy of 10³ CFU/mL pathogen has been improved by about 55%. The proposed multi-line LFIAs reduce the possibility of judging a positive result as a false negative result. The LFIAs strip was validated in real samples of milk and orange juice. This strategy has great potential for rapid detection of pathogens in real samples, and provides new insights for improving the accuracy and sensitivity of LFIAs strips.

CRISPR/Cas9-based point-of-care lateral flow biosensor with improved performance for rapid and robust detection of Mycoplasma pneumonia

Screening of acute respiratory infections causes serious challenges in urgent point-of-care scenarios where conventional methods are impractical and alternative techniques suffer from low accuracy, poor robustness, and reliance on sophisticated instruments. As an improvement to this paradigm, we report a point-of-care lateral flow biosensor (LFB) based on the recognition property of clustered regularly interspaced short palindromic repeats (CRISPR)/associated protein 9 (Cas9) and apply it to the detection of Mycoplasma pneumoniae (M. pneumoniae). The designed biosensor employs CRISPR/Cas9 for secondary recognition after preamplification of target gene using specific primer set, avoiding false positives caused by nontarget factors. The high amplification efficiency and low applicable temperatures of recombinase polymerase amplification brings the detection limit of the biosensor to 3 copies even at a preamplification temperature of 25 °C. Its practical application is further demonstrated with 100% accuracy by testing with 43 M. pneumoniae-infected specimens and 80 uninfected specimens. Additionally, the entire detection, including pretreatment, preamplification, CRISPR/Cas9 recognition, and visual analysis, can be completed in 30 min. Featured with the combination of CRISPR/Cas9 and LFB, the biosensor we developed herein ensures excellent convenience, accuracy, and robustness, which endows promising point-of-care screening potential for infectious pathogens.

Lateral Flow Immunoassay for Proteins

Protein biomarkers are useful for disease diagnosis. Identification thereof using in vitro diagnostics such as lateral flow immunoassays (LFIAs) has attracted considerable attention due to their low cost and ease of use especially in the point of care setting. Current challenges, however, do remain with respect to material selection for each component in the device and the synergistic integration of these components to display detectable signals. This review explores the principle of LFIA for protein biomarkers, device components including biomaterials and labeling methods. Medical applications and commercial status are examined as well. This review highlights critical methodologies in the development of new LFIAs and their role in advancing healthcare worldwide.

Multiplex Detection of Infectious Diseases on Microfluidic Platforms

Infectious diseases contribute significantly to the global disease burden. Sensitive and accurate screening methods are some of the most effective means of identifying sources of infection and controlling infectivity. Conventional detecting strategies such as quantitative polymerase chain reaction (qPCR), DNA sequencing, and mass spectrometry typically require bulky equipment and well-trained personnel. Therefore, mass screening of a large population using conventional strategies during pandemic periods often requires additional manpower, resources, and time, which cannot be guaranteed in resource-limited settings. Recently, emerging microfluidic technologies have shown the potential to replace conventional methods in performing point-of-care detection because they are automated, miniaturized, and integrated. By exploiting the spatial separation of detection sites, microfluidic platforms can enable the multiplex detection of infectious diseases to reduce the possibility of misdiagnosis and incomplete diagnosis of infectious diseases with similar symptoms. This review presents the recent advances in microfluidic platforms used for multiplex detection of infectious diseases, including microfluidic immunosensors and microfluidic nucleic acid sensors. As representative microfluidic platforms, lateral flow immunoassay (LFIA) platforms, polymer-based chips, paper-based devices, and droplet-based devices will be discussed in detail. In addition, the current challenges, commercialization, and prospects are proposed to promote the application of microfluidic platforms in infectious disease detection.

Simultaneous, Label-Free and High-throughput SERS Detection of Multiple Pesticides on Ag@Three-Dimensional Silica Photonic Microsphere Array

Rapid identification and quantitative simultaneous analysis for multiple pesticide in real samples based on surface-enhanced Raman spectroscopy (SERS) is still a challenge because of sample complexity, reproducibility, and stability of SERS substrate. With use of colloidal silver nanoparticles loaded three-dimensional (3D) silica photonic microspheres (SPMs) array as the analytical platform, a SERS-based array assay for multiple pesticides was developed in this work. The silver nanoparticles were fixed into the gaps formed by the self-assembled nanospheres of the 3D SPMs to produce "hot spots", on which the Raman enhanced effect was up to 9.86 × 10⁷ and the maximum electric field enhancement effect reached to 9.75 times, ensuring the target pesticides on the surface of the SERS-substrate integrated SPM can be detected sensitively. Using 2,4-dichlorophenoxyacetic acid (2,4-D), glyphosate, and imidacloprid as the testing pesticides, the label-free and high-throughput SERS assay for simultaneous detection of the pesticides was established, giving good linear detection ranges (0.1-204.8 μg/mL for 2,4-D, 0.3-247.9 μg/mL for glyphosate, and 0.2-204.8 μg/mL for imidacloprid) and low detection limits (3.03 ng/mL for 2,4-D, 3.14 ng/mL for glyphosate, and 8.82 ng/mL for imidacloprid). The spiked recovery rates in the real samples were measured in the range of 82-112%, which was consistent with that of the classical standard methods. The label-free 3D SERS array analytical platform provides a powerful tool for high-throughput and low-cost screening of multiple pesticide residues in real samples.

Sandwich mode lateral flow assay for point-of-care detecting SARS-CoV-2

The global corona virus disease 2019 (COVID-19) has been announced a pandemic outbreak, and has threatened human life and health seriously. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as its causative pathogen, is widely detected in the screening of COVID-19 patients, infected people and contaminated substances. Lateral flow assay (LFA) is a popular point-of-care detection method, possesses advantages of quick response, simple operation mode, portable device, and low cost. Based on the above advantages, LFA has been widely developed for detecting SARS-CoV-2. In this review, we summarized the articles about the sandwich mode LFA detecting SARS-CoV-2, classified according to the target detection objects indicating genes, nucleocapsid protein, spike protein, and specific antibodies of SARS-CoV-2. In each part, LFA is further classified and summarized according to different signal detection types. Additionally, the properties of the targets were introduced to clarify their detection significance. The review is expected to provide a helpful guide for LFA sensitization and marker selection of SARS-CoV-2.

Functional Micro-/Nanostructures in Agrofood Science: Precise Inspection, Hazard Elimination, and Potential Health Risks

Nanotechnology, biotechniques, and chemical engineering have arisen as new trends with significant impacts on agrofood science development. Advanced analytical techniques with high sensitivity, specificity, and automation based on micro-/nanomaterials for food hazard elimination have become leading research hotspots in agrofood science. Research progress in micro-/nanomaterials has provided a solid theoretical basis and technical support to solve problems in the industry. However, the rapid development of micro-/nanostructures has also raised concerns regarding potential risks to human health. This review presents the latest advances in the precise inspection and elimination of food hazards from micro-/nanomaterials and discusses the potential threats to human health posed by nanomaterials. The theoretical reference was provided for the application trend of micro-/nanomaterials in the field of agrofood science in the future.

Carbon Dot-Anchored Cobalt Oxyhydroxide Composite-Based Hydrogel Sensor for On-Site Monitoring of Organophosphorus Pesticides

The development of a portable, quantitative, and user-friendly sensor for on-site monitoring of organophosphorus pesticides (OPs) is significantly urgent to guarantee food safety. Herein, a carbon dot/cobalt oxyhydroxide composite (CD/CoOOH)-based fluorescent hydrogel sensor is constructed for precisely quantifying OPs using a homemade portable auxiliary device. As a fluorescence signal indicator, the orange-emissive CD/CoOOH composite is encapsulated into an agarose hydrogel kit for amplifying the detection signals, shielding background interference, and enhancing stability. Acetylcholinesterase (AChE) catalyzes the hydrolysis of the substrate to produce thiocholine, which induces the decomposition of CoOOH and makes the fluorescence enhancement of the hydrogel platform possible. OPs can specifically block the AChE activity to limit thiocholine production, resulting in a decrease in platform fluorescence. The image color of the fluorescent hydrogel kit is transformed into digital information using a homemade auxiliary device, achieving on-site quantitative detection of paraoxon (model target) with a detection limit of 10 ng mL^-1. Harnessing CD/CoOOH composite signatures, hydrogel encapsulation, and portable optical devices, the proposed fluorescence hydrogel platform demonstrated high sensitivity and good anti-interference performance in agricultural sample analysis, indicating considerable potential in the on-site application.

Development of a colloidal gold immunochromatographic test strip for the rapid detection of iprodione

Iprodione is a dicarboximide fungicide that is widely used in agriculture around the world. A reliable and rapid detection method is needed for the on-site monitoring of iprodione residues in a variety of agricultural products. Herein, a colloidal gold immunochromatographic test strip was developed based on a selected coating antigen and a specific monoclonal antibody against iprodione. The particle size of colloidal gold, the preparation technique of the conjugate pad, the composition of the loading buffer, and the extraction solvent were comprehensively optimized for the test strip. A cut-off value of 0.9 mg kg^-1 (50 ng mL^-1) and a visual limit of detection of 0.09 mg kg^-1 (5 ng mL^-1) were achieved in a complex matrix of tobacco. No cross-reactivity was observed for iprodione metabolite and four other widely used pesticides during tobacco growth. Furthermore, the developed colloidal gold immunochromatographic test strip was applied to determine iprodione residues in tobacco samples, and the obtained results were in good agreement with those obtained by liquid chromatography tandem mass spectrometry. Additionally, the test strip was found to be stable afterlong-term storage at 37 °C for two months. The developed colloidal gold immunochromatographic test strip showed excellent accuracy, sensitivity, specificity, and stability, therefore, it is suitable for the rapid detection of iprodione residues in complex matrices.

Biosensing Chlorpyrifos in Environmental Water Samples by a Newly Developed Carbon Nanoparticle-Based Indirect Lateral Flow Assay

Pesticides are used in agriculture to prevent pests. Chlorpyrifos (CHLP) is an insecticide with potentially detrimental effects on humans, bees, and the aquatic environment. Its effects have led to a total ban by the European Union (EU), but outside the EU, CHLP is still produced and used. An indirect lateral flow immunoassay (LFIA) for the detection of CHLP was developed and integrated into a cassette to create a lateral flow device (LFD). Species-specific reporter antibodies were coupled to carbon nanoparticles to create a detector conjugate. Water samples were mixed with a specific CHLP monoclonal antibody and detector conjugate and applied to the LFD. Dose-response curves elicited the detection of low concentrations of CHLP (<1 µg/L). This sensitivity was recorded through a rapid handheld digital imaging device but also visually by naked eye. The CHLP LFD was applied to a range of European surface water samples, fortified with CHLP, revealing a sensitivity in these matrices of 2 µg/L, both by digital and visual analysis. To improve the simplicity of the CHLP LFIA, the assay reagents were dried in tubes, enabling to carry out the test by simply adding water samples and inserting the LFIA strips. This CHLP LFIA is thus suited for the on-site screening of surface waters.

General Method for Pesticide Recognition Using Albumin-Based Host-Guest Ensembles

The massive use of pesticides nowadays has led to serious consequences for the environment and public health. Fluorescence analytical methods for pesticides are particularly advantageous with respect to simplicity and portability; however, currently available fluorescence methods (enzyme-based assays and indicator displacement assays) with poor universality are only able to detect few specific pesticides (e.g., organophosphorus). Making use of the multiple flexible and asymmetrical binding sites in albumin, we herein report a set of multicolor albumin-based host-guest ensembles. These ensembles exhibit a universal but distinctive fluorescent response to most of the common pesticides and allow array-based identification of pesticides with high accuracy. Furthermore, the simplicity, portability, and visualization of this method enable on-site determination of pesticides in a practical setting. This albumin host strategy largely expands the toolbox of traditional indicator displacement assays (synthetic macrocycles as hosts), and we expect it to inspire a series of sensor designs for pesticide detection.

Immunoprofiling of Severity and Stage of Bacterial Infectious Diseases by Ultrabright Fluorescent Nanosphere-Based Dyad Test Strips

Bacterial infectious diseases are common clinical diseases that seriously threaten human health, especially in countries and regions with poor environmental hygiene. Due to the lack of characteristic clinical symptoms and signs, it is a challenge to distinguish a bacterial infection from other infections, leading to misdiagnosis and antibiotic overuse. Therefore, there is an urgent need to develop a specific method for detection of bacterial infections. Herein, utilizing ultrabright fluorescent nanospheres (FNs) as reporters, immunochromatographic dyad test strips are developed for the early detection of bacterial infections and distinction of different stages of bacterial infectious diseases in clinical samples. C-reactive protein (CRP) and heparin-binding protein (HBP) are quantified and assayed because their levels in plasma are varied dynamically and asynchronously during the progression of the disease. The detection limits of CRP and HBP can reach as low as 0.51 and 0.65 ng/mL, respectively, due to the superior fluorescence intensity of each FN, which is 570 times stronger than that of a single quantum dot. The assay procedure can be achieved in 22 min, fully meeting the needs of rapid and ultrasensitive detection in the field. This constructed strip has been successfully used to profile the stage and severity of bacterial infections by monitoring the levels of CRP and HBP in human plasma samples, showing great potential as a point-of-care biosensor for clinical diagnosis. In addition to bacterial infections, the developed ultrabright FN-based point-of-care testing can be readily expanded for rapid, quantitative, and ultrasensitive detection of other trace substances in complex systems.

Non-thiolated nucleic acid functionalized gold nanoparticle-based aptamer lateral flow assay for rapid detection of kanamycin

A novel Apt-LFA has been established for kanamycin based on non-thiolated nucleic acid-modified colloidal gold nanoprobe (AuNPs@polyA-DNA). The improvement in nucleic acid hybridization speed and efficiency was verified by modifying AuNPs with polyA-DNA strands instead of thiolated oligonucleotides (SH-DNA) strands. Moreover, the AuNPs@polyA-DNA was explored to apply in an Apt-LFA. The experimental factors including the concentration of the aptamer, the concentration of SA-DNA_T conjugate, the incubation time, and temperature were carefully investigated. In addition, the kanamycin aptamer was modified by extending several bases at its end to modulate the hybridization complementary strand, which was found to significantly improve the performance of Apt-LFA. Under optimal experimental conditions, the Apt-LFA can detect kanamycin in honey with a LOD of 250 ng mL^-1 by the naked eyes. A linear range of 50-1250 ng mL^-1 was obtained with a LOD of 15 ng mL^-1 in honey by a portable reader. The Apt-LFA was successfully applied to the detection of kanamycin in honey with recoveries of 95.1-105.2%.

A Universal Bacterial Catcher Au-PMBA-Nanocrab-Based Lateral Flow Immunoassay for Rapid Pathogens Detection

In traditional lateral flow immunoassays (LFIA) for pathogens detection, capture antibody (CA) is necessary and usually conjugated to Au nanoparticles (NPs) in order to label the target analyte. However, the acquisition process of the Au-CA nanoprobe is relatively complicated and costly, which will limit the application of LFIA. Herein, p-mercaptophenylboronic acid-modified Au NPs (namely Au-PMBA nanocrabs), were synthesized and applied for a new CA-independent LFIA method. The stable Au-PMBA nanocrabs showed outstanding capability to capture both Gram-negative bacteria and Gram-positive bacteria through covalent bonding. The acquired Au-PMBA-bacteria complexes were dropped onto the strip, and then captured by the detection antibody on the test line (T-line). Take Escherichia coli O157:H7 as an example, the gray value of T-line was proportional to the bacteria concentration and the linear range was 10³-10⁷ cfu·mL^-1. This CA-independent strategy exhibited higher sensitivity than the traditional CA-dependent double antibody sandwich method, because detection limit of the former one was 10³ cfu·mL^-1 only by visual observation, which was reduced by 3 orders of magnitude. Besides, this platform successfully screened E. coli O157:H7 in four food samples with recoveries ranging from 90.25% to 107.25%. This CA-independent LFIA showed great advantages and satisfactory potential for rapid foodborne pathogens detection in real samples.

Ultrasensitive detection of multiple Alzheimer's disease biomarkers by SERS-LFA

A lateral flow assay, based on Surface-enhanced Raman scattering nanotags (SERS-LFA), is proposed for simultaneous quantification of multiple AD biomarkers with high sensitivity.

Sensitive and rapid determination of heat shock protein 70 using lateral flow immunostrips and upconversion nanoparticle fluorescence probes

Heat shock protein 70 (Hsp70), belonging to the heat shock protein (HSP) family, is reported to be a potential diagnostic biomarker.