Highly sensitive detection of lipopolysaccharide based on collaborative amplification of dual enzymes

Visual Detection of LPS at the Femtomolar Level Based on Click Chemistry-Induced Gold Nanoparticles Electrokinetic Accumulation

Lipopolysaccharide (LPS) presents a significant threat to human health. Herein, a novel method for detecting LPS was developed by coupling hybridization chain reaction (HCR), gold nanoparticles (AuNPs) agglutination (AA) triggered by a Cu(I)-catalyzed azide-alkyne cycloaddition click chemistry (CuAAC), and electrokinetic accumulation (EA) in a microfluidic chip, termed the HCR-AA-EA method. Thereinto, the LPS-binding aptamer (LBA) was coupled with the AuNP-coated Fe3O4 nanoparticle, which was connected with the polymer of H1 capped on CuO (H1-CuO) and H2-CuO. Upon LPS recognition by LBA, the polymers of H1- and H2-CuO were released into the solution, creating a "one LPS-multiple CuO" effect. Under ascorbic acid reduction, CuAAC was initiated between the alkyne and azide groups on the AuNPs' surface; then, the product was observed visually in the microchannel by EA. Finally, LPS was quantified by the integrated density of AuNP aggregates. The limit of detections were 29.9 and 127.2 fM for water samples and serum samples, respectively. The levels of LPS in the injections and serum samples by our method had a good correlation with those from the limulus amebocyte lysate test (r = 0.99), indicating high accuracy. Remarkably, to popularize our method, a low-cost, wall-power-free portable device was developed, enabling point-of-care testing.

Surface-enhanced fluorescence for lipopolysaccharide analysis based on shell-isolated nanoparticle

Lipopolysaccharide (LPS) as the component of cell membrane on gram-negative bacteria played a central role on inflammatory inducer to stimulate a multi-system host response. Herein, a surface-enhanced fluorescent (SEF) sensor was developed for LPS analysis based on shell-isolated nanoparticles (SHINs). The fluorescent signal of CdTe quantum dots (QDs) was amplified by silica shell-coated Au nanoparticles (Au NPs). The 3D finite-difference time-domain (3D-FDTD) simulation revealed that this enhancement was due to local electric field amplification. This method has a linear detection range of 0.1-20 μg/mL and a detection limit of 64 ng/mL for LPS. Furthermore, the developed method was successfully applied for LPS analysis in milk and human serum sample. The results indicated that the as-prepared sensor has significant potential for selective detection of LPS in biomedical diagnosis and food safety.

Ultramicro and ultrasensitive detection of lipopolysaccharides based on triple-signal amplification via ultrafast ATRP and an ultramicroelectrode

Highly sensitive testing of trace lipopolysaccharides (LPS) is very important due to their high toxicity to the human body. Here, an ultrasensitive electrochemical sensor requiring only 5 μL solution was developed for LPS detection via triple-signal amplification based on ultrafast atom transfer radical polymerization (UATRP) and a Au ultramicroelectrode (UME). Firstly, the Au UME was modified with gold nanoparticles (nAu) and an LPS aptamer (Apt) in turn. When the Apt recognized LPS, the ATRP initiator of 4-(bromomethyl)phenylboronic acid (BPA) could be tethered to the electrode by covalent cross-linking between the phenylboronic acid moiety and the cis-diol site of LPS. Then UATRP was conducted for 2.5 min with nitrogen-doped carbon quantum dots (N-CQDs) as the photocatalyst and methylacrolein (MLA) as the monomer. After the electroactive probes of Ag nanoparticles (AgNPs) were formed on the surface of poly(MLA) by the silver mirror reaction, the electrochemical sensor was successfully prepared. Under the optimal conditions, the sensor exhibited a lower detection limit and a wider linear range when it was compared with a similar assay for LPS. In particular, the LOD of 7.99 × 10-2 pg mL-1 was better than that of the limulus amoebocyte lysate (LAL)-based technique, which is the gold standard for LPS detection. In the end, the sensor reported in this paper showed good selectivity and satisfactory feasibility for LPS detection in real biological samples and food products. The results obtained from the drug, blood and potable water samples laid a strong foundation for its clinical applications and application in other fields.

Single-molecule lipopolysaccharides identification and the interplay with biomolecules via nanopore readout

Lipopolysaccharides (LPS) are the major constituent on the cell envelope of all gram-negative bacteria. They are ubiquitous in air, and are toxic inflammatory stimulators for urinary disorders and sepsis. The reported optical, thermal, and electrochemical sensors via the intermolecular interplay of LPS with proteins and aptamers are generally complicated methods. We demonstrate the single-molecule nanopore approach for LPS identification in distinct bacteria as well as the serotypes discrimination. With a 4 nm nanopore, we achieve a detection limit of 10 ng/mL. Both the antibiotic polymyxin B (PMB) and DNA aptamer display specific binding to LPS. The identification of LPS in both human serum and tap water show good performance with nanopore platforms. Our work shows a highly-sensitive and easy-to-handle scheme for clinical and environmental biomarkers determination and provides a promising screening tool for early warning of contamination in water and medical supplies.

Applications of Terminal Deoxynucleotidyl Transferase Enzyme in Biotechnology

The use of polymerase enzymes in biotechnology has allowed us to gain unprecedented control over the manipulation of DNA, opening up new and exciting applications in areas such as biosensing, polynucleotide synthesis, and DNA storage, aptamer development and DNA-nanotechnology. One of the most intriguing enzymes which has gained prominence in the last decade is terminal deoxynucleotidyl transferase (TdT), which is one of the only polymerase enzymes capable of catalysing the template independent stepwise addition of nucleotides onto an oligonucleotide chain. This unique enzyme has seen a significant increase in a variety of different applications. In this review, we give a comprehensive discussion of the unique properties and applications of TdT as a biotechnology tool, and the application in the enzymatic synthesis of poly/oligonucleotides. Finally, we look at the increasing role of TdT enzyme in biosensing, DNA storage, synthesis of DNA nanostructures and aptamer development, and give a future outlook for this technology.

Ratiometric fluorescence probe integrated with smartphone for visually detecting lipopolysaccharide

A portable instrument-free detection method for lipopolysaccharide (LPS) analysis was developed based on dual-emission ratiometric fluorescence sensing system. Herein, red-emitting Au nanoclusters (Au NCs) were as reference probe, while blue-emitting fluorescent silica quantum dots (Si QDs) were as response probe. Additionally, the aptamer of LPS was covalently grafted to the surface of Si QDs in order to specific recognize the LPS. According to the changes of fluorescence intensityratio (FL ratio, I_{461 nm}/I_{643 nm}) with the concentrations of LPS, the linear equation was fitted with the range of 50-3000 ng/mL, and the limit of detection (LOD) was 29.3 ng/mL. As a practical application, this method was employed to analyze LPS in normal saline with the recovery rate of 97.7-103.8 %. The color picker platform in the smartphone was used to transform the detection picture to the process of Red, Green and Blue (RGB) for visual detection of LPS. The low-cost and easy-carry method reported here presents broad merits for the visually quantitative detection of LPS.

Simple and fast colorimetric detection of lipopolysaccharide based on aptamer and SYBR Green I mediated aggregation of gold nanoparticles

Lipopolysaccharide (LPS) poses a considerable threat to food safety and human health. A colorimetric assay for LPS detection based on LPS binding aptamer (LBA) and SYBR Green I (SG) mediated aggregation of gold nanoparticles (AuNPs) was established. In the absence of LPS, the LBA was absorbed onto the AuNPs surface which prevented SG-induced aggregation of AuNPs, and the sensing system exhibited red color. When LPS was added, it interacted with the LBA, forming a complex. At higher LPS concentration, many LBAs were exhausted resulting in SG-induced aggregation of AuNPs, and color change from red to blue. The range of colorimetric detection of LPS was linear in 0-12 EU/mL, with a limit of detection of 0.1698 EU/mL. Spiked LPS in real samples and interfering substances were also identified. This assay ingeniously using the fluorescent dye SG as an effective trigger of AuNPs aggregation, is rapid and facile than most of those earlier reported LBA-based LPS assays, and there is potential to be modified to construct assays for other targets.

Boronate Affinity-Amplified Electrochemical Aptasensing of Lipopolysaccharide

As lipopolysaccharide (LPS) is closely associated with sepsis and other life-threatening conditions, the point-of-care (POC) detection of LPS is of significant importance to human health. In this work, we illustrate an electrochemical aptasensor for the POC detection of low-abundance LPS by utilizing boronate affinity (BA) as a simple, efficient, and cost-effective amplification strategy. Briefly, the BA-amplified electrochemical aptasensing of LPS involves the tethering of the aptamer receptors and the BA-mediated direct decoration of LPS with redox signal tags. As the polysaccharide chain of LPS contains hundreds of cis-diol sites, the covalent crosslinking between the phenylboronic acid group and cis-diol sites can be harnessed for the site-specific decoration of each LPS with hundreds of redox signal tags, thereby enabling amplified detection. As it involves only a single-step operation (∼15 min), the BA-mediated signal amplification holds the significant advantages of unrivaled simplicity, rapidness, and cost-effectiveness over the conventional nanomaterial- and enzyme-based strategies. The BA-amplified electrochemical aptasensor has been successfully applied to specifically detect LPS within 45 min, with a detection limit of 0.34 pg/mL. Moreover, the clinical utility has been validated based on LPS detection in complex serum samples. As a proof of concept, a portable device has been developed to showcase the potential applicability of the BA-amplified electrochemical LPS aptasensor in the POC testing. In view of its simplicity, rapidness, and cost-effectiveness, the BA-amplified electrochemical LPS aptasensor holds broad application prospects in the POC testing.

Environmental protection based on the nanobiosensing of bacterial lipopolysaccharides (LPSs): material and method overview

Lipopolysaccharide (LPS) or endotoxin control is critical for environmental and healthcare issues. LPSs are responsible for several infections, including septic and shock sepsis, and are found in water samples. Accurate and specific diagnosis of endotoxin is one of the most challenging issues in medical bacteriology. Enzyme-linked immunosorbent assay (ELISA), plating and culture-based methods, and Limulus amebocyte lysate (LAL) assay are the conventional techniques in quantifying LPS in research and medical laboratories. However, these methods have been restricted due to their disadvantages, such as low sensitivity and time-consuming and complicated procedures. Therefore, the development of new and advanced methods is demanding, particularly in the biological and medical fields. Biosensor technology is an innovative method that developed extensively in the past decade. Biosensors are classified based on the type of transducer and bioreceptor. So in this review, various types of biosensors, such as optical (fluorescence, SERS, FRET, and SPR), electrochemical, photoelectrochemical, and electrochemiluminescence, on the biosensing of LPs were investigated. Also, the critical role of advanced nanomaterials on the performance of the above-mentioned biosensors is discussed. In addition, the application of different labels on the efficient usage of biosensors for LPS is surveyed comprehensively. Also, various bio-elements (aptamer, DNA, miRNA, peptide, enzyme, antibody, etc.) on the structure of the LPS biosensor are investigated. Finally, bio-analytical parameters that affect the performance of LPS biosensors are surveyed.

Biosensor-based assay of exosome biomarker for early diagnosis of cancer

Cancer imposes a severe threat to people's health and lives, thus pressing a huge medical and economic burden on individuals and communities. Therefore, early diagnosis of cancer is indispensable in the timely prevention and effective treatment for patients. Exosome has recently become an attractive cancer biomarker in noninvasive early diagnosis because of the unique physiology and pathology functions, which reflects remarkable information regarding the cancer microenvironment, and plays an important role in the occurrence and evolution of cancer. Meanwhile, biosensors have gained great attention for the detection of exosomes due to their superior properties, such as convenient operation, real-time readout, high sensitivity, and remarkable specificity, suggesting promising biomedical applications in the early diagnosis of cancer. In this review, the latest advances of biosensors regarding the assay of exosomes were summarized, and the superiorities of exosomes as markers for the early diagnosis of cancer were evaluated. Moreover, the recent challenges and further opportunities of developing effective biosensors for the early diagnosis of cancer were discussed.

Template-free multiple signal amplification for highly sensitive detection of cancer cell-derived exosomes

In this work, we have designed a template-free multiple signal amplification method for the highly sensitive detection of cancer cell-derived exosomes. In this design, DNase I serves as a bridge to link the DNA-based amplification approach and terminal deoxynucleotidyl transferase (TdT)-mediated polymerization reaction. Consequently, a detection limit of 10 particles per μL can be achieved, while a complex nucleic acid sequence design can be avoided. This method also exhibits good performance in a complicated matrix and enables the differentiation of healthy individuals from colorectal cancer (CRC) patients.

Spherical nucleic acids-based cascade signal amplification for highly sensitive detection of exosomes

Exosomes are regarded as a promising biomarker in the diagnosis of disease due to their close relationship with the change of physiology and pathology. However, it is still a hard challenge to come up with a highly sensitive method for the exosomes detection. Herein, we propose a spherical nucleic acids (SNAs)-based cascade signal amplification strategy for the exosomes detection with high sensitivity. In this method, SNAs anchoring on exosomes membrane can be extended to form polyT sequence by terminal deoxynucleotidyl transferase (TdT), generating a template strand for the Exo III-catalyzed excision of the designed signal probe (probe A), which may finally induce significant decrease of electrochemical signal due to the consumption of probe A. Benefiting from the SNAs-based cascade signal amplification, this fabricated biosensor achieves a limit of detection for exosomes as low as 44 particles/μL. Moreover, this method shows good performance in the differentiation of healthy and malignancy colorectal cancer patients. Therefore, without complicated nucleic acids sequences design, our approach provides a cascade signal amplification strategy for the highly sensitive detection of exosomes and shows the potential applications in clinical diagnosis.

Hydrazone ligation assisted DNAzyme walking nanomachine coupled with CRISPR-Cas12a for lipopolysaccharide analysis

In this work, hydrazone ligation assisted DNAzyme walking nanomachine is explored to couple with CRISPR-Cas12a trans-cleavage. Hydrazone ligation with high efficiency can mediate signal input which can be induced by target binding, thereby regulating the performance of DNAzyme walking nanomachine. The product strand from DNAzyme walking nanomachine can further activate the trans-cleavage of Cas12a. So, cascade signal amplification can be achieved to enhance the sensitivity for target detection. Subsequently, hydrazone ligation assisted DNAzyme walking nanomachine coupled with CRISPR-Cas12a has been further developed as a biosensor to analyze lipopolysaccharides. The developed biosensor exhibits a linear range from 0.05 ng/mL to 10⁶ ng/mL and a lowest limit of detection of 7.31 fg/mL. This research provides a new mode for the signal output of DNAzyme walking nanomachine, so as to sensitively analyze different biomolecules.

Layer-by-Layer Assembly of Polycations and Polyanions for the Sensitive Detection of Endotoxin

Bacterial endotoxin detection is an essential safety requisite in biomedical, food, and pharmaceutical industries. Endotoxin in a sufficient concentration on entering the human bloodstream causes detrimental effects such as septic shock, which can lead to death. Hence, the sensitive and selective detection of endotoxin also known as lipopolysaccharide (LPS) is of paramount importance. Herein, a layer-by-layer (LBL) assembly of gold-chitosan nanocomposite (CGNC)-poly(acrylic acid) (PAA)-polymyxin B (PmB) on gold (Au) electrode is employed for the sensitive and selective detection of endotoxin. The surface electric charge studies using dynamic contact mode electrostatic force microscopy (DC-EFM) revealed the successful formation of each layer on the Au electrode. The polycationic PmB is a specific bioreceptor of LPS, which binds with high affinity to the anionic groups of the carbohydrate portions of LPS molecules and facilitates the selective electrochemical detection. This surface modification method presented a sensitive and selective detection of endotoxin down to the attogram level.