Nucleic Acid Amplification Techniques in Immunoassay: An Integrated Approach with Hybrid Performance

High-visual-resolution colorimetric immunoassay with attomolar sensitivity using kinetically controlled growth of Ag in AuAg nanocages and poly-enzyme-boosted tyramide signal amplification

Colorimetric enzyme-linked immunosorbent assays (CELISAs) have long been used for protein biomarker detection in diagnostics. Unfortunately, as confined by the monochromatic nature of detection signals and the limited catalytic activity of enzymes, CELISAs suffer from poor visual resolution and low sensitivity, hindering their effectiveness for early diagnostics in resource-limited settings. Herein, we report an ultrasensitive, high-visual-resolution CELISA (named PE-TSA-AuAg Cage-CELISA) that combines kinetically controlled growth of Ag in AuAg nanocages with poly-enzyme-boosted tyramide signal amplification (PE-TSA), enabling visual semiquantitative detection of protein biomarkers at attomolar levels with the naked eye. Specifically, the assay begins with the formation of sandwich-type immunocomplexes on a microplate in the presence of targets, and the labeled poly-horseradish peroxidases (poly-HRPs) initiate TSA, resulting in attaching numerous alkaline phosphatases (ALPs) on the microplate. The ALPs further catalyze ascorbic acid 2-phosphate to produce ascorbic acid, triggering the kinetically controlled growth of Ag inside AuAg nanocages. This process induces vivid multicolor variations spanning the visible spectrum range of 691∼477 nm, allowing for visual semiquantitation of protein biomarkers at ultralow levels without requiring specialized equipment. Using interleukin-12 as a model protein biomarker, we demonstrate that the PE-TSA-AuAg Cage-CELISA achieves a visual semiquantitative limit of detection (LOD) of 5 fg mL-1 (67 aM) and an instrumental quantitative LOD of 0.71 fg mL-1 (9.5 aM), representing an 853-fold improvement compared to the conventional HRP-based CELISA. Our findings suggest that the PE-TSA-AuAg Cage-CELISA has the potential to serve as an affordable and effective biosensing platform for early diagnostics in resource-limited settings.

Immuno-transcription-amplified single microbead assay for protein and exosome analysis through an S9.6 antibody-nucleic acid recognition strategy

High-sensitive detection of circulating biomarkers is in high demand because many of them are found at low concentrations in bioliquids. Herein, we report an immuno-transcription-amplified single microbead (MB) assay (IT-SMA) based on the specific S9.6 antibody-DNA/RNA hybrid recognition strategy for the sensitive and universal quantification of protein biomarkers. This design rationally converts the immunoreaction events into amplified nucleic acid transcription to produce numerous RNA molecules, which can efficiently enrich fluorescent signals onto a single MB through a specific S9.6 antibody-DNA/RNA hybrid recognition mechanism, enabling sensitive protein analysis. This method exhibits excellent specificity and high sensitivity for protein analysis with a low detection limit at the fg/mL level. Furthermore, the S9.6 antibody-aided IT-SMA allows for universal detection of various proteins and even exosomes, testing target proteins in serum samples, and differentiating cancer patients from healthy individuals by directly analyzing the exosomes in human blood samples. These features make the IT-SMA strategy a promising tool for the quantitative detection of a variety of biomarkers toward precision diagnostics.

The Development Potential of AuNPs-Based Lateral Flow Technology Combined with Other Advanced Technologies in POCT

Currently, there is a demand for rapid, sensitive, low-cost, portable, and visualized testing technologies for point-of-care testing (POCT). However, most traditional testing methods face challenges such as long testing times, complicated operations, and high costs, limiting their implementation in resource-limited areas and hindering the fulfillment of POCT demands. Lateral flow assay (LFA) has emerged as an ideal detection technique for POCT, particularly when utilizing gold nanoparticles (AuNPs) as labels. This approach not only enables visualization with the naked eye but also reduces the need for expensive reading instruments. The technologies reviewed in this paper encompass integrated detection technology utilizing amplification technique and LFA, integrated detection technology utilizing clustered regularly interspaced short palindromic repeats (CRISPR) system and LFA, the utilization of surface-enhanced Raman spectroscopy (SERS) in LFA detection technique, the utilization of aptamers in LFA detection technique, and the utilization of DNA barcodes in LFA detection technique. By integrating these advanced techniques, there is significant potential to overcome the limitations of LFA, including low sensitivity, poor specificity, inability to quantify, and false positives, thereby enabling broader applications in resource-constrained settings. Additionally, this article comprehensively evaluates the strengths and weaknesses of each approach, underscoring the immense developmental potential of AuNPs-based LFA in point-of-care testing (POCT).

DNA circuit-based immunoassay for ultrasensitive protein pattern classification

Cytokines are important immune modulators, and pivotal biomarkers for the diagnostic of various diseases. In standard analytical procedure, each protein is detected individually, using for instance gold standard ELISA protocols or nucleic acid amplification-based immunoassays. In recent years, DNA nanotechnology has been employed for creating sophisticated biomolecular systems that perform neuromorphic computing on molecular inputs, opening the door to concentration pattern recognition for biomedical applications. This work introduces immuno-PUMA (i-PUMA), an isothermal amplification-based immunoassay for ultrasensitive protein detection. The assay couples the convenience of supported format of an ELISA protocol with the computing capabilities of a DNA/enzyme circuit. We demonstrate a limit of detection of 2.1 fM, 8.7 fM and 450 aM for IL12, IL4 and IFNγ cytokines, respectively, outperforming the traditional ELISA format. i-PUMA's versatility extends to molecular computation, allowing the creation of 2-input perceptron-like classifiers for IL12 and IL4, with tunable weight sign and amplitude. Overall, i-PUMA represents a sensitive, low-cost, and versatile immunoassay with potential applications in multimarker-based sample classification, complementing existing molecular profiling techniques.

Isothermal Nucleic Acid Amplification-Based Lateral Flow Testing for the Detection of Plant Viruses

Isothermal nucleic acid amplification-based lateral flow testing (INAA-LFT) has emerged as a robust technique for on-site pathogen detection, providing a visible indication of pathogen nucleic acid amplification that rivals or even surpasses the sensitivity of real-time quantitative PCR. The isothermal nature of INAA-LFT ensures consistent conditions for nucleic acid amplification, establishing it as a crucial technology for rapid on-site pathogen detection. However, despite its considerable promise, the widespread application of isothermal INAA amplification-based lateral flow testing faces several challenges. This review provides an overview of the INAA-LFT procedure, highlighting its advancements in detecting plant viruses. Moreover, the review underscores the imperative of addressing the existing limitations and emphasizes ongoing research efforts dedicated to enhancing the applicability and performance of this technology in the realm of rapid on-site testing.

Development of a highly sensitive colloidal gold semiquantitative method for the determination of difenoconazole residues in citrus

Introduction

Difenoconazole (DIFE) is a common pesticide used in citrus cultivation; excessive intake can cause neurological damage to the organism, and the existing colloidal gold immunochromatographic test strips cannot meet the requirements for the detection of citrus samples.

Methods

Difenoconazole test strip was prepared based on the colloidal gold immunochromatographic technique (GICT), and its application in citrus samples was investigated; with colloidal gold (CG) as the probe, the optimization of GICT parameters, and the determination of reaction method, the immunochromatographic test strips for the detection of DIFE in citrus was developed, and the limit of detection (LOD), specificity, accuracy, and stability of the test strips were verified.

Results

The results showed that the visual detection limit of the prepared colloidal gold immunochromatographic test strips was 0.2 mg/kg and the quantitative range was 0.06-0.6 mg/kg, and the test strips could specifically identify DIFE and have no cross-reaction with other common triazole pesticides. The detection method established in this study was verified by the GC-MS method, and the detection results achieved good consistency (R2 > 0.98).

Conclusion

The test strips developed in this study have good performance and can be used for highly sensitive detection of citrus samples.

A Rapid and Sensitive Gold Nanoparticle-Based Lateral Flow Immunoassay for Chlorantraniliprole in Agricultural and Environmental Samples

Chlorantraniliprole (CAP) is a new type of diamide insecticide that is mainly used to control lepidopteran pests. However, it has been proven to be hazardous to nontarget organisms, and the effects of its residues need to be monitored. In this study, five hybridoma cell lines were developed that produced anti-CAP monoclonal antibodies (mAbs), of which the mAb originating from the cell line 5C5B9 showed the highest sensitivity and was used to develop a gold nanoparticle-based lateral flow immunoassay (AuNP-LFIA) for CAP. The visible limit of detection of the AuNP-LFIA was 1.25 ng/mL, and the detection results were obtained in less than 10 min. The AuNP-LFIA showed no cross-reactivity for CAP analogs, except for tetraniliprole (50%) and cyclaniliprole (5%). In the detection of spiked and blind samples, the accuracy and reliability of the AuNP-LFIA were confirmed by a comparison with spiked concentrations and verified by ultra-performance liquid chromatography-tandem mass spectrometry. Thus, this study provides the core reagents for establishing CAP immunoassays and a AuNP-LFIA for the detection of residual CAP.

RNA-cleaving deoxyribozyme-linked immunosorbent assay for the ultrasensitive detection of chloramphenicol in milk

In this presented work, an artificial deoxyribozyme was employed as the substitute for horseradish peroxidase (or alkaline phosphatase) in ELISA for generating amplified signals. The feasibility of the proposed deoxyribozyme-based ELISA (DLISA) was demonstrated in the detection of a forbidden veterinary drug, chloramphenicol. And its efficiency was praised since that ultrahigh sensitivity was accomplished with a detection limit of 0.1 ng/L. The wide linear range from 0.000001 μg/mL to 1.0 μg/mL, as well as good recoveries from 86 % to 104 % in whole milk samples showed its excellent practical performances. Besides, the DLISA was worth popularizing due to the easy connection of antibody and DNAzyme through a facile functionalization process of gold nanoparticles. These advantages showed the possibility of DLISA for developing commercial kits, and the utilization of flexible DNA fluorescent probes in DLISA would inspire more work on innovations.

Fluorescent aptasensor for the ultrasensitive detection of antibiotic residue in food samples based on dumbbell DNA-mediated signal amplification

Sensitive and reliable detection of antibiotics is of great significance for environmental and food safety due to its high risk in trace concentrations. Herein, we developed a fluorescence sensing system for chloramphenicol (CAP) detection based on dumbbell DNA-mediated signal amplification. Two hairpin dimers (2H1 and 2H2) were employed as the building blocks to construct the sensing scaffolds. The CAP-aptamer binding in another hairpin H0 can liberate the trigger DNA, which then activates the cyclic assembly reaction between 2H1 and 2H2. The separation of FAM and BHQ in the formed product of cascaded DNA ladder yields a high fluorescence signal for CAP monitoring. Compared with the monomer hairpin assembly between H1 and H2, the dimer hairpin assembly between 2H1 and 2H2 exhibits enhanced signal amplification efficiency and reduced reaction time. The developed CAP sensor showed a wide linear range from 10 fM to 10 nM with a detection limit of 2 fM. Importantly, this sensing platform has been successfully applied to the determination of CAP in fish, milk, and water samples with satisfactory recovery and accuracy. With the advantages of high sensitivity, mix-and-read pattern, and robustness, our proposed CAP sensor can be used as a simple and routine tool for the detection of trace amounts of antibiotic residues.

Simultaneous Determination of Antibiotics, Mycotoxins, and Hormones in Milk by an 8-17 DNAzyme-Based Enzyme-Linked Immunosorbent Assay

The simultaneous detection of three kinds of small-molecule contaminants (antibiotics, mycotoxins, and hormones) in milk was realized by using an 8-17 DNAzyme-based fluorescent enzyme-linked immunosorbent assay (ELISA), in which 8-17 DNAzyme was utilized as the catalytic enzyme for amplifying the signal. Compared with the conventional ELISA in which horseradish peroxidase is used as the catalyzing factor, this 8-17 DNAzyme-based ELISA could achieve multicolor signal output with lower detection limits. The linearities for chloramphenicol, 17β-estradiol, and aflatoxin M₁ were in the range of 0.3 ng/mL-3 μg/mL, 3 ng/mL-3 μg/mL, and 3 pg/mL-3 ng/mL with quantitation limits of 0.3, 3, and 0.003 ng/mL, respectively. This proposed scheme demonstrated that the 8-17 DNAzyme might be an effective substitute for horseradish peroxidase in ELISA for the development of ultrasensitive and multicolor fluorescence immunoassay, which would stimulate the development of ELISA in a new orientation.

Hapten-labeled fusion-polymerase chain reaction of multiple marker genes for the application of immunochromatographic test

A variety of methods have been reported using polymerase chain reaction (PCR)-based nucleic acid testing (NAT) because of its potential to be used in highly sensitive inspection systems. Among these NATs, fusion-PCR (also called as overlap-extension-PCR) has been focused on this study and adopted to generate the fused amplicon composed of plural marker gene fragments for detection. Generally, conventional agarose gel electrophoresis followed by gel staining is employed to check the PCR results. However, these are time-consuming processes that use specific equipment. To overcome these disadvantages, the immunochromatographic test (ICT) for the detection of PCR amplicons with hapten-labels that were generated by PCR using hapten-labeled primers was also adopted in this study. Based on these concepts, we constructed the systems of hapten-labeled fusion-PCR (HL-FuPCR) followed by ICT (HL-FuPCR-ICT) for the two and three marker genes derived from pathogenic microbe. As a result, we successfully developed a two marker genes system for the pathogenic influenza A virus and a three marker genes system for the penicillin-resistant Streptococcus pneumoniae. These detection systems of HL-FuPCR-ICT are characterized by simple handling and rapid detection within few minutes, and also showed the results as clear lines. Thus, the HL-FuPCR-ICT system introduced in this study has potential for use as a user-friendly inspection tool with the advantages especially in the detection of specific strains or groups expressing the characteristic phenotype(s) such as antibiotic resistance and/or high pathogenicity even in the same species.

CRISPR/Cas12a-based fluorescence immunoassay: combination of efficient signal generation with specific molecule recognition

The sensing strategy ingeniously combines the efficient signal generation of the CRISPR/Cas12a system with antigen–antibody-specific recognition.

Recombinase Polymerase Amplification Assay with and without Nuclease-Dependent-Labeled Oligonucleotide Probe

The combination of recombinase polymerase amplification (RPA) and lateral flow test (LFT) is a strong diagnostic tool for rapid pathogen detection in resource-limited conditions. Here, we compared two methods generating labeled RPA amplicons following their detection by LFT: (1) the basic one with primers modified with different tags at the terminals and (2) the nuclease-dependent one with the primers and labeled oligonucleotide probe for nuclease digestion that was recommended for the high specificity of the assay. Using both methods, we developed an RPA-LFT assay for the detection of worldwide distributed phytopathogen-alfalfa mosaic virus (AMV). A forward primer modified with fluorescein and a reverse primer with biotin and fluorescein-labeled oligonucleotide probe were designed and verified by RPA. Both labeling approaches and their related assays were characterized using the in vitro-transcribed mRNA of AMV and reverse transcription reaction. The results demonstrated that the RPA-LFT assay based on primers-labeling detected 103 copies of RNA in reaction during 30 min and had a half-maximal binding concentration 22 times lower than probe-dependent RPA-LFT. The developed RPA-LFT was successfully applied for the detection of AMV-infected plants. The results can be the main reason for choosing simple labeling with primers for RPA-LFT for the detection of other pathogens.