Development of an immunochromatographic strip for rapid detection of Pantoea stewartii subsp. stewartii

Nanomaterial-based biosensors: a new frontier in plant pathogen detection and plant disease management

Nanotechnology has significantly advanced the detection of plant diseases by introducing nano-inspired biosensors that offer distinct advantages over traditional diagnostic methods. These biosensors, enhanced with novel nanomaterials, exhibit increased sensitivity, catalytic activity, and faster response times, resulting in improved diagnostic efficiency. The increasing impact of climate-induced stress and emerging plant pathogens have created an urgent demand for real-time monitoring systems in agriculture. Nanobiosensors are revolutionizing plant disease management by enabling on-site detection of pests and weeds, facilitating precise pesticide applications. This article provides a comprehensive overview of the development and application of nanobiosensors in real-time plant disease diagnosis. It highlights key innovations, such as smartphone-integrated nanozyme biosensing and lab-on-a-chip technologies. Special emphasis is placed on the detection of molecular biomarkers, demonstrating the critical role of nanobiosensors in addressing the evolving challenges of plant disease management and agricultural sustainability.

Microbial Nanoparticles in Biological Plant Protection

Nanoparticles are small structures that differ in terms of their shape and composition; their high surface-to-volume ratio is responsible for their unique properties that make them perfect mediators for the delivery of substances. Nanoparticles do not only include metallic spheres but also complex polysaccharides capsule viruses or bacterial protein complexes (which can be considered bionanoparticles), which are 1-100 nm in size. Although nanoparticles are most widely studied from medical perspectives, their potential applications are almost limitless. One such promising use of functional nanoparticles is for plant protection against diseases. Although the precise use of nanoparticles decreases the need for the use of other chemical compounds, thanks to their increased product stability and delivery to a target site, the production of nanoparticles is often burdened by large quantities of toxic wastes. This problem can be limited if we apply the bioreactor green synthesis method, which includes the production of nanoparticles with the use of microorganisms. Bacteria can produce nanoparticles internally, externally, by only producing metabolites used for nanoparticle production directly, e.g., polysaccharides or surfactants, or indirectly as reducing agents for metal nanoparticle production. Regardless of the source of the nanoparticles, they can be widely used in processes from plant disease/pathogen detection to disease suppression. The endless variety of materials for nanoparticle production and the possible modifications that nanoparticles can be subjected to makes it impossible to predict how their structures will be used in the future. Nevertheless, in this study, we would like to turn attention to the fact that although nanoparticles are viewed as synthetic structures, they are ever-present in the microbial world and play an important part in intermicrobial interactions. As nanoparticle usefulness has been tested over years of co-evolution, it may be useful to look for potential future directions for this fascinating technology.

A gold nanoparticle-based lateral flow immunoassay for atrazine point-of-care detection using a handhold scanning device as reader

A method is described to achieve accurate quantitative detection of atrazine (ATZ) in maize by using lateral flow strips based on gold nanoparticles (GNPs) and a handheld scanning reader. GNPs of 15 nm in diameter were applied as label, and a lateral flow immune assay strip was prepared. The linear range was 5.01-95.86 ng mL^-1 with a detection limit of 4.92 ng mL^-1 in phosphate buffer, 4 times better than the readout by the naked eye. ATZ-spiked corn samples were also analysed. The accuracy of results of spiked samples was confirmed by ELISA and liquid chromatography-tandem mass spectrometry (HPLC), which proved the reliability of the proposed method. A handhold device with an optical scanning system was designed for on-site quantitative detection. Combined with the pretreatment, the assay could be completed in less than 20 min.

Genomics-Informed Multiplex PCR Scheme for Rapid Identification of Rice-Associated Bacteria of the Genus Pantoea

The genus Pantoea forms a complex of more than 25 species, among which several cause diseases of various crop plants, including rice. Notably, strains of Pantoea ananatis and P. stewartii have been repeatedly reported to cause bacterial leaf blight of rice, whereas other authors have observed that P. agglomerans can also cause bacterial leaf blight of rice. The contribution of these and perhaps other species of Pantoea to plant diseases and yield losses of crop plants is currently not well documented, partly due to the lack of efficient diagnostic tools. Using 32 whole-genome sequences of the three major plant-pathogenic Pantoea spp., a set of PCR primers that detect each of the three species P. agglomerans, P. ananatis, and P. stewartii was designed. A multiplex PCR scheme which can distinguish these three species and also detects members of other Pantoea spp. was further developed. Upon validation on a set of reference strains, 607 suspected Pantoea strains that were isolated from rice leaves or seed originating from 11 African countries were screened. In total, 41 P. agglomerans strains from 8 countries, 79 P. ananatis strains from 9 countries, 269 P. stewartii strains from 9 countries, and 218 unresolved Pantoea strains from 10 countries were identified. The PCR protocol allowed detection of Pantoea bacteria grown in vitro, in planta, and in rice seed. The detection threshold was estimated as total genomic DNA at 0.5 ng/µl and heated cells at 1 × 10⁴ CFU/ml. This new molecular diagnostic tool will help to accurately diagnose major plant-pathogenic species of Pantoea. Due to its robustness, specificity, sensitivity, and cost efficiency, it will be very useful for plant protection services and for the epidemiological surveillance of these important crop-threatening bacteria.

Biosensor Technologies for Early Detection and Quantification of Plant Pathogens

Plant pathogens are a major reason of reduced crop productivity and may lead to a shortage of food for both human and animal consumption. Although chemical control remains the main method to reduce foliar fungal disease incidence, frequent use can lead to loss of susceptibility in the fungal population. Furthermore, over-spraying can cause environmental contamination and poses a heavy financial burden on growers. To prevent or control disease epidemics, it is important for growers to be able to detect causal pathogen accurately, sensitively, and rapidly, so that the best practice disease management strategies can be chosen and enacted. To reach this goal, many culture-dependent, biochemical, and molecular methods have been developed for plant pathogen detection. However, these methods lack accuracy, specificity, reliability, and rapidity, and they are generally not suitable for in-situ analysis. Accordingly, there is strong interest in developing biosensing systems for early and accurate pathogen detection. There is also great scope to translate innovative nanoparticle-based biosensor approaches developed initially for human disease diagnostics for early detection of plant disease-causing pathogens. In this review, we compare conventional methods used in plant disease diagnostics with new sensing technologies in particular with deeper focus on electrochemical and optical biosensors that may be applied for plant pathogen detection and management. In addition, we discuss challenges facing biosensors and new capability the technology provides to informing disease management strategies.

Development of an ic-ELISA and Immunochromatographic Strip Assay for the Detection of Diacetoxyscirpenol in Rice

Diacetoxyscirpenol (DAS) is a highly toxic type A trichothecene, a natural contaminant in food and animal feed, which is a serious hazard to human and animal health. An anti-DAS mAb, 3H10, with high sensitivity and specificity, was prepared, and an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and a lateral-flow immunochromatographic strip (ICA strip) were developed for rapid testing of DAS in rice samples. The 50% inhibitory concentration and limit of detection of ic-ELISA were 5.97 and 0.78 ng/mL, respectively. The recovery of rice samples ranged from 99.4 to 110.7%, demonstrating that the analytical method can be used to detect rice samples. The cutoff value of the lateral-flow ICA strip to DAS was 500 ng/g. The developed immunoassay method can provide an effective method of initially detecting and screening DAS in food and feed samples.

Development of a gold nanoparticle-based lateral-flow strip for the detection of dinitolmide in chicken tissue

Dinitolmide is a nitro amide coccidiostat used in poultry feed, and is a potential threat to the environment and human health. In this study, a monoclonal antibody (mAb) against dinitolmide was prepared and an immunochromatographic assay (ICA) was developed to detect residual dinitolmide in chicken tissue. The results show that the mAb exhibited high sensitivity, with a limit of detection as low as 9.01 ng mL-1. A cross reactivity test revealed that the mAb also had good specificity for dinitolmide. This ICA method showed a visible limit of detection of 2.5 μg kg-1, and a cut-off value of 25 μg kg-1 for testing dinitolmide in chicken sample extract by using the naked eye. Importantly, these observations using our ICA, were comparable to other methods of detection such as liquid chromatography, tandem mass spectrometry and indirect competitive enzyme-linked immunosorbent assays (IC-ELISA). These data suggest that our ICA method is a reliable, portable, and high-throughput method for the detection of dinitolmide residues in chicken tissue.

Preparing monoclonal antibodies and developing immunochromatographic strips for paraquat determination in water

Paraquat (PQ) poisoning is a serious threat to human health that leads to pulmonary toxicity, neurotoxicity, and inflammation. Protecting humans from PQ exposure requires the development of rapid analytical methods for on-site detection. Here, two monoclonal antibodies against PQ were generated and an immunochromatographic assay (ICA) was exploited to determine PQ concentrations in water samples. The results showed that the monoclonal antibody 1D6 exhibited higher affinity and sensitivity, with an affinity constant of 5.4 × 10⁸ mol/L and a limit of detection as low as 0.02 ng/mL. Without sample pretreatment, the developed ICA method provided visible limits of detection ranging from 0.25 to 1 ng/mL, and cut-off limits ranging from 1 to 5 ng/mL, where average recoveries were between 83.15% ± 1.9% and 94.49% ± 2.45% with a coefficient of variation ranging from 1.40% to 7.37%. Importantly, these observations were consistent with liquid chromatography tandem mass spectrometry. These data and results suggested that the ICA method was a reliable, portable, and high-throughput method for determining PQ residues in water samples.

Rapid and sensitive detection of Shigella flexneri using fluorescent microspheres as label for immunochromatographic test strip

Background

Bacillary dysentery caused by Shigella genus is a major cause of morbidity and mortality worldwide. In China, the popular strain was mainly Shigella flexneri (S. flexneri). Therefore, fluorescent microspheres (FMs)-based immunochromatographic test strip (ICTS), as a novel, reliable, sensitive and uncomplicated method, was evaluated to detect S. flexneri.

Methods

Sixty-three clinical samples of S. flexneri were collected in this paper. Polymerase chain reaction (PCR) combined with FMs-ICTS based on magnetic purification assay was developed for the quantitative detection of Shigella. And the genus-specific gene of ipaH and drug resistant gene of CTX-M-9 from Shigella were selected to investigate the potential of this new method. The sensitivity and specificity of this method were demonstrated by classical microbiological methods (API Coryne System), PCR assay based on agarose gel electrophoresis (PCR-GE) and the real-time fluorescent quantitative PCR (RTFQ-PCR) method.

Results

Under optimized conditions, the lower detection limits of PCR-ICTS, PCR-GE and RTFQ-PCR were 2.5×10^-7, 2.5×10^-5 and the 3.2×10^-7 ng/µL, respectively. Experiments demonstrated the PCR-ICTS has a diagnostic agreement of 100% with conventional PCR and RTFQ-PCR on detection of clinical samples and could correctly recognize Shigella and non-Shigella from different microbial samples. After the purification of PCR products with Silicon coated magnetic nanoparticles (Si-MNPs), the false positive results were removed because of the strong screening ability of the purification process. Our results showed that FM-based ICTS was promising for measurable and sensitive detection of S. flexneri within 3 h.

Conclusions

The results from immunochromatographic test were agreement with those from API Coryne system and RTFQ-PCR. Hence, this developed method might be useful for screening and monitoring clinical sample of S. flexneri, due to its speed, non-poisonous, simplicity and low-cost and helpful for promoting the prevention and control of communicable diseases caused by enteric pathogens such as S. flexneri.

Jeger M, Bragard C, Candresse T, Chatzivassiliou E, Dehnen-Schmutz K, Gilioli G, Grégoire JC, Jaques Miret JA, MacLeod A, Navajas Navarro M, Niere B, Parnell S, Potting R, Rafoss T, Rossi V, Urek G, Van Bruggen A, Van der Werf W, West J, Winter S, Manceau C, Pautasso M, Caffier D. Pest categorisation of Pantoea stewartii subsp. stewartii

Following a request from the European Commission, the EFSA Plant Health Panel performed a pest categorisation of Pantoea stewartii subsp. stewartii (hereafter P. s. subsp. stewartii). P. s. subsp. stewartii is a Gram-negative bacterium that causes Stewart's vascular wilt and leaf blight of sweet corn and maize, a disease responsible for serious crop losses throughout the world. The bacterium is endemic to the USA and is now present in Africa, North, Central and South America, Asia and Ukraine. In the EU, it is reported from Italy with a restricted distribution and under eradication. The bacterium is regulated according to Council Directive 2000/29/EC (Annex IIAI) as a harmful organism whose introduction and spread in the EU is banned on seeds of Zea mays. Other reported potential host plants include various species of the family Poaceae, including weeds, rice (Oryza sativa), oat (Avena sativa) and common wheat (Triticum aestivum), as well as jackfruit (Artocarpus heterophyllus), the ornamental Dracaena sanderiana and the palm Bactris gasipaes, but there is uncertainty about whether these are hosts of P. s. subsp. stewartii or of the other subspecies. The pest could enter the EU via host plants for planting (including seed) and via insect vectors from neighbouring countries. Host plants are widely distributed and climatic conditions are conducive in the EU. P. s. subsp. stewartii could spread by movement of host plants for planting (including seeds) and insect vectors. Impacts could occur on maize and rice. Methods to certify pest freedom of maize seeds are available. The main knowledge gaps concern the availability of vectors in the EU, the level of susceptibility of the maize cultivars grown in the EU, the virulence of strains in recent outbreaks, and the host range of the bacterium. The criteria assessed by the Panel for consideration as a potential quarantine pest are met.

Fluorescein Isothiocyanate Labeling Antigen-Based Immunoassay Strip for Rapid Detection of Acidovorax citrulli

A simple and fast immunoassay strip to detect Acidovorax citrulli (Ac) using fluorescein isothiocyanate as a marker was developed. Fluorescein isothiocyanate (FITC) was added to sample culture medium for bacteria incubation, and the bacteria could emit a yellow-green fluorescence under ultraviolet light and become a fluorescent probe. This immunofluorescence strip (IFS) was based on the binding between fluorescent bacteria and the unlabeled monoclonal antibody (McAb) immobilized on the test area in nitrocellulose membrane. The detection limit of the strip was 10⁶ CFU/ml with a result that could be observed within 10 min. The IFS could detect eight strains of Ac and display no cross-reactions with 30 other pathogenic strains. The detection results would not be affected by impurities in plant or unknown microorganisms in natural field samples and were consistent with PCR results, indicating that the IFS has high accuracy. This is the first report of using only one unlabeled McAb to develop a direct-type immunofluorescence strip for the rapid detection of Ac. The IFS reduced detection time and simplified operation procedures compared with the traditional enzyme-linked immunosorbent assay (ELISA) and PCR methods. In addition, this simple and inexpensive method will play a significant role in monitoring plant pathogens on field detection.

Thiolated AuNP probes and multiplex PCR for molecular detection of Staphylococcus epidermidis

The emergence of nanotechnology in biology helps to apply the gold nanoparticle probes for fast and accurate identification of pathogens compared to the time-consuming and non-precise phenotypic methods. In this study, two molecular methods have been established for the accurate identification of staphylococcus epidermidis from other coagulase-negative staphylococci. Multiplex PCR was performed using designed primers for Gmk2 and pta housekeeping genes, and SESB specific gene of S. epidermidis. Colorimetric detection by gold nanoparticle probes was carried out using two 20-base thiolated probes designed based on the sequence of pta housekeeping gene of S. epidermidis. The specificity of multiplex PCR and colorimetric assays were determined using genomic DNA of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii as negative controls and no alteration was detected. To investigate the sensitivity of the primers and gold nanoparticle probes, different concentrations of the extracted DNA from S. epidermidis were used. Based on the results, the minimum required quantity of target DNA for multiplex PCR amplification was 1 ng/μL and for color and absorption alteration of solution in colorimetric assay was 20 ng/μL. Our results revealed that both methods were sufficiently specific and sensitive to detect S. epidermidis.

Biosensors for plant pathogen detection

Infectious plant diseases are caused by pathogenic microorganisms such as fungi, bacteria, viruses, viroids, phytoplasma and nematodes. Worldwide, plant pathogen infections are among main factors limiting crop productivity and increasing economic losses. Plant pathogen detection is important as first step to manage a plant disease in greenhouses, field conditions and at the country boarders. Current immunological techniques used to detect pathogens in plant include enzyme-linked immunosorbent assays (ELISA) and direct tissue blot immunoassays (DTBIA). DNA-based techniques such as polymerase chain reaction (PCR), real time PCR (RT-PCR) and dot blot hybridization have also been proposed for pathogen identification and detection. However these methodologies are time-consuming and require complex instruments, being not suitable for in-situ analysis. Consequently, there is strong interest for developing new biosensing systems for early detection of plant diseases with high sensitivity and specificity at the point-of-care. In this context, we revise here the recent advancement in the development of advantageous biosensing systems for plant pathogen detection based on both antibody and DNA receptors. The use of different nanomaterials such as nanochannels and metallic nanoparticles for the development of innovative and sensitive biosensing systems for the detection of pathogens (i.e. bacteria and viruses) at the point-of-care is also shown. Plastic and paper-based platforms have been used for this purpose, offering cheap and easy-to-use really integrated sensing systems for rapid on-site detection. Beside devices developed at research and development level a brief revision of commercially available kits is also included in this review.

A gold nanoparticle-based semi-quantitative and quantitative ultrasensitive paper sensor for the detection of twenty mycotoxins

A semi-quantitative and quantitative multi-immunochromatographic (ICA) strip detection assay was developed for the simultaneous detection of twenty types of mycotoxins from five classes, including zearalenones (ZEAs), deoxynivalenols (DONs), T-2 toxins (T-2s), aflatoxins (AFs), and fumonisins (FBs), in cereal food samples. Sensitive and specific monoclonal antibodies were selected for this assay. The semi-quantitative results were obtained within 20 min by the naked eye, with visual limits of detection for ZEAs, DONs, T-2s, AFs and FBs of 0.1-0.5, 2.5-250, 0.5-1, 0.25-1 and 2.5-10 μg kg(-1), and cut-off values of 0.25-1, 5-500, 1-10, 0.5-2.5 and 5-25 μg kg(-1), respectively. The quantitative results were obtained using a hand-held strip scan reader, with the calculated limits of detection for ZEAs, DONs, T-2s, AFs and FBs of 0.04-0.17, 0.06-49, 0.15-0.22, 0.056-0.49 and 0.53-1.05 μg kg(-1), respectively. The analytical results of spiked samples were in accordance with the accurate content in the simultaneous detection analysis. This newly developed ICA strip assay is suitable for the on-site detection and rapid initial screening of mycotoxins in cereal samples, facilitating both semi-quantitative and quantitative determination.

Effect of different-sized spherical gold nanoparticles grown layer by layer on the sensitivity of an immunochromatographic assay

Effect of different-sized spherical gold nanoparticles grown layer by layer on the sensitivity of immunochromatographic assay.