Compact Magneto-Fluorescent Colloids by Hierarchical Assembly of Dual-Components in Radial Channels for Sensitive Point-of-Care Immunoassay

Integration of a biocompatible metal-phenolic network and fluorescence microspheres as labels for sensitive and stable detection of carbendazim with a lateral flow immunoassay

High fluorescence intensity microspheres such as aggregation-induced emission fluorescence microspheres (AIEFM) have improved the sensitivity of lateral flow immunoassay (LFIA). The preparation of immune probes in LFIA usually adopts the chemical coupling strategy with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide for antibody coupling, which has the problems of low coupling efficiency, tedious coupling process, and poor repeatability. A biocompatible metal-phenolic network (MPN), which contains large amounts of phenols and galloyl groups, could easily, quickly, and stably couple with antibodies. Herein, we proposed a strategy based on MPN modification on ultrabright AIEFM surface as a novel label for the rapid detection of carbendazim. The limit of detection of AIEFM@MPN-LFIA was 0.019 ng/mL, which was 4.9 times lower than that of AIEFM-LFIA. In spiked samples, the average recoveries of AIEFM@MPN-LFIA ranged from 80% to 118% (coefficient of variation <13.45%). Therefore, AIEFM@MPN was a promising signal label that could improve the detection performance of LFIA.

Hierarchical magneto-colorimetric labels for immediate lateral flow immunoassay of chlorothalonil residues

Quantitative detection of pesticide residues in food and environmental samples using an improved lateral flow immunoassay (LFIA) is of considerable importance for real-time analysis. This paper proposes a highly sensitive LFIA platform based on a hierarchical magneto-colorimetric compact. This compact serves as both the target magnetic enrichment substrate and a photosensitive label. Initially, a large porous dendritic silica template is prepared and doped with superparamagnetic ferric oxide nanoparticles (Fe3O4 NPs) and colloidal gold nanoparticles (AuNPs) at high densities within its vertical channels. The sequential assembly of central-radial channels allow for the three-dimensional integration of these two components, enabling independent control of their discrete functions without mutual interference. Following alkyl organosilicon encapsulation and silica sealing, the composite spheres are then applied in LFIA to detect chlorothalonil residues. Fe3O4 NPs enhance the binding efficiency to target analytes, while AuNPs amplify the signal, leveraging their high loading densities and robust optical properties. The developed LFIA platform exhibited a detection limit of 0.34 ng/mL for chlorothalonil and a linear range of 0.0085-824 ng/mL. The recoveries varied between 85.1 % and 103.1 %, and the relative standard deviations were 1.25%-8.84 %. This LFIA approach demonstrates high sensitivity, specificity, reproducibility and flexible detection modes, making it highly suitable for the on-site monitoring of pesticide residues.

"Three-in-One": Ultrasensitive Lateral Flow Immunoassay Driven by Magnetic Enrichment and Photothermal Signal Amplification

Conventional lateral flow immunoassay (LFIA) usually suffers from poor antimatrix interference, unsatisfactory sensitivity, and lack of quantitative ability for target analyte detection in food matrices. In response to these limits, here, multifunctional nanomaterial ZnFe2O4 nanoparticles (ZFOs) were developed and integrated into LFIA for powerful magnetic separation/enrichment and colorimetric/photothermal target sensing. Under optimum conditions, the detection for clenbuterol (CL) with magnetic enrichment achieves 9-fold higher sensitivity compared to that without enrichment and 162-fold higher sensitivity compared to that based on traditional colloidal golds. Attributing the improved performances of ZFOs, CL can be detected at ultralow levels in pork and milk with 10 min of immunoreaction time. The vLODs were 0.01 μg kg-1 for two modes, and the cutoff values of CL were about 5 and 3 μg kg-1, respectively. More importantly, the enrichment ZFO-mediated LFIA (ZE-LFIA) exhibits a similar limit of detection (LOD) in both buffer solution and food matrix, demonstrating a universal resistance to the food matrix. The multitudinous performance merits of this ZE-LFIA with high sensitivity, matrix tolerance, accuracy, and specificity have ensured a broad application potential for target detection of clenbuterol and can serve as an experience for other veterinary drug residues' detection.

A nanoparticle-assisted signal-enhancement technique for lateral flow immunoassays

Lateral flow immunoassay (LFIA), an affordable and rapid paper-based detection technology, is employed extensively in clinical diagnosis, environmental monitoring, and food safety analysis. The COVID-19 pandemic underscored the validity and adoption of LFIA in performing large-scale clinical and public health testing. The unprecedented demand for prompt diagnostic responses and advances in nanotechnology have fueled the rise of next-generation LFIA technologies. The utilization of nanoparticles to amplify signals represents an innovative approach aimed at augmenting LFIA sensitivity. This review probes the nanoparticle-assisted amplification strategies in LFIA applications to secure low detection limits and expedited response rates. Emphasis is placed on comprehending the correlation between the physicochemical properties of nanoparticles and LFIA performance. Lastly, we shed light on the challenges and opportunities in this prolific field.

Electrochemical Lateral Flow Immunoassay with Built-In Electrodes for Ultrasensitive and Wireless Detection of Inflammatory Biomarkers

Paper-based lateral flow immunoassays (LFIAs) are cost-effective, portable, and simple methods for detection of diverse analytes, which however only provide qualitative or semiquantitative results and lack sufficient sensitivity. A combination of LFIA and electrochemical detection, namely, electrochemical lateral flow immunoassay (eLFIA), enables quantitative detection of analytes with high sensitivity, but the integration of external electrodes makes the system relatively expensive and unstable. Herein, the working, counter, and reference electrodes were prepared directly on the nitrocellulose membrane using screen printing, which remarkably simplified the structure of eLFIA and decreased the cost. Moreover, a horseradish peroxidase (HRP)-based electrochemical signal amplification strategy was used for further increasing the analytical sensitivity. HRP captured on the working electrode can catalyze the oxidation of tetramethylbenzidine (TMB) to form the TMB-TMBox precipitate on the electrode surface, which as an electrochemically active product can output an amplified current for quantification. We demonstrated that the eLFIA could detect low-abundant inflammatory biomarkers in human plasma samples with limits of detection of 0.17 and 0.54 pg mL-1 for interleukin-6 and C-reactive protein, respectively. Finally, a fully portable system was fabricated by integrating eLFIA with a flexible and wireless electrochemical workstation, realizing the point-of-care detection of interleukin-6.

Ultrasensitive Fluorescence Detection of Ascorbic Acid Using Silver Ion-Modulated High-Quality CdSe/CdS/ZnS Quantum Dots

Improving the sensitivity of the fluorescence method for the detection of bioactive molecules is crucial in biochemical analysis. In this work, an ultrasensitive sensing strategy was constructed for the detection of ascorbic acid (AA) using high-quality 3-mercaptopropionic acid-capped CdSe/CdS/ZnS quantum dots (MPA-CdSe/CdS/ZnS QDs) as the fluorescent probe. The prepared water-soluble QDs exhibited a high photoluminescence quantum yield (PL QY) of up to 96%. Further, the fluorescence intensity of the QDs was intensively quenched through the dynamic quenching of Ag+ ions due to an efficient photoinduced electron transfer progress. While the existence of AA before adding Ag+ ions, Ag+ ions were reduced. Thus, the interaction of the QDs and Ag+ ions was destroyed, which led to the fluorescence distinct recovery. The detection limit of AA could be as low as 0.2 nM using this sensing system. Additionally, most relevant small molecules and physiological ions had no influence on the analysis of AA. Satisfactory results were obtained in orange beverages, showing its great potential as a meaningful platform for highly sensitive and selective AA sensing for clinical analysis.

Recent advances in SERS-based immunochromatographic assay for pathogenic microorganism diagnosis: A review

Infectious diseases caused by bacteria, viruses, fungi, and other pathogenic microorganisms are among the most harmful public health problems in the world, causing tens of millions of deaths and incalculable economic losses every year. The establishment of rapid, simple, and highly sensitive diagnostic methods for pathogenic microorganisms is important for the prevention and control of infectious diseases, guidance of timely treatment, and the reduction of public safety risks. Lateral flow immunoassay (LFA) based on the colorimetric signal of colloidal gold is the most popular point-of-care testing technology at present, but it is limited by poor sensitivity and low throughput and hardly meets the needs of the highly sensitive screening of pathogenic microorganisms. In recent years, the combination of surface-enhanced Raman scattering (SERS) and LFA technology has developed into a novel analytical platform with high sensitivity and multiple detection capabilities and has shown great advantages in the detection of pathogenic microorganisms and infectious diseases. This review summarizes the working principle, design ideas, and application of the existing SERS-based LFA methods in pathogenic microorganism detection and further introduces the effect of new technologies such as Raman signal encoding, magnetic enrichment, novel membrane nanotags, and integrated Raman reading equipment on the performance of SERS-LFA. Finally, the main challenges and the future direction of development in this field of SERS-LFA are discussed.

Bimetallic Nanozyme: A Credible Tag for In Situ-Catalyzed Reporter Deposition in the Lateral Flow Immunoassay for Ultrasensitive Cancer Diagnosis

The lateral flow immunoassay (LFIA) is a sought-after point-of-care testing platform, yet the insufficient sensitivity of the LFIA limits its application in the detection of tumor biomarkers. Here, a colorimetric signal amplification method, bimetallic nanozyme-mediated in situ-catalyzed reporter deposition (BN-ISCRD), was designed for ultrasensitive cancer diagnosis. The bimetallic nanozyme used, palladium@iridium core-shell nanoparticles (Pd@Ir NPs), had ultrahigh enzyme-like activity, which was further explained by the electron transfer of Pd@Ir NPs and the change in the Gibbs free energy during catalysis through density functional theory calculations. With gastric cancer biomarkers pepsinogen I and pepsinogen II as model targets, this assay could achieve a cutoff value of 10 pg/mL, which was 200-fold lower than that without signal enhancement. The assay was applied to correctly identify 8 positive and 28 negative clinical samples. Overall, this BN-ISCRD-based LFIA showed great merits and potential in the application of ultrasensitive disease diagnosis.

Molybdenum disulfide-loaded multilayer AuNPs with colorimetric-SERS dual-signal enhancement activities for flexible immunochromatographic diagnosis of monkeypox virus

The sudden outbreak of monkeypox in 2022 suggests the importance of developing a rapid but sensitive virus detection technology. Herein, we report a colorimetric/surface-enhanced Raman scattering (SERS) dual-signal co-enhanced immunochromatographic assay (ICA) for the flexible, ultrasensitive, and accurate detection of monkeypox virus (MPXV) in various complex samples. A thickness-controlled polyethyleneimine interlayer (1 nm) is coated onto two-dimensional molybdenum disulfide (MoS2) nanosheet to enable the electrostatic adsorption of two layers of dense 30 nm AuNPs, which not only improves colorimetric ability but also creates numerous efficient SERS hotspots. Moreover, the SERS activity of film-like dual-signal tag (MoS2@Au-Au) is drastically enhanced by combining the chemical enhancement effect of MoS2 sheets and the electromagnetic enhancement effect of Au-Au hotspots. The introduction of MoS2@Au-Au greatly broadens the application range of existing ICA methods, in which the colorimetric signal supports the quick identification of the target virus and the SERS signal allows the quantitative detection of MPXV with detection limits of as low as 0.2 and 0.002 ng/mL. Given its rapid detection ability (< 20 min), high accuracy in real samples (RSD < 9.89 %), and superior sensitivity than traditional AuNP-based colorimetric ICA (> 500 times), the proposed assay has great potential for field application.

Engineered Collaborative Size Regulation and Shape Engineering of Tremella-Like Au-MnOx for Highly Sensitive Bimodal-Type Lateral Flow Immunoassays

Engineered collaborative size regulation and shape engineering of multi-functional nanomaterials (NPs) offer extraordinary opportunities for improving the analysis performance. It is anticipated to address the difficulty in distinguishing color changes caused by subtle variations in target concentrations, thereby facilitating the highly sensitive analysis of lateral flow immunoassays (LFIAs). Herein, tremella-like gold-manganese oxide (Au-MnOx ) nanoparticles with precise MnCl2 regulation are synthesized as immuno signal tracers via a facile one-step redox reaction in alkaline condition at ambient temperature. Avail of the tunable elemental composition and anisotropy in morphology, black-colored tremella-like Au-MnOx exhibits superb colorimetric signal brightness, enhanced antibody coupling efficiency, marvelous photothermal performance, and unrestricted immunological recognition affinity, all of which facilitate highly sensitive multi-signal transduction patterns. In conjunction with the handheld thermal reader device, a bimodal-type LFIA that combines size-regulation- and shape-engineering-mediated colorimetric-photothermal dual-response assay (coined as the SSCPD assay) with a limit of detection of 0.012 ng mL-1 for ractopamine (RAC) monitoring is achieved by integrating Au-MnOx with the competitive-type immunoreaction. This work illustrates the effectiveness of this strategy for establishing high-performance sensing, and the SSCPD assay may be extended to a wide spectrum of future point-of-care (POC) diagnostic applications.

Introduction of multilayered quantum dot nanobeads into competitive lateral flow assays for ultrasensitive and quantitative monitoring of pesticides in complex samples

A competitive fluorescent lateral flow assay (CFLFA) is proposed for direct, ultrasensitive, quantitative detection of common pesticides imidacloprid (IMI) and carbendazim (CBZ) in complex food samples by using silica-core multilayered quantum dot nanobeads (SiO2-MQB) as liquid fluorescent tags. The SiO2-MQB nanostructure comprises a 200-nm SiO2 core and a shell of hundreds of carboxylated QDs (excitation/emission maxima ~365/631 nm), and can generate better stability, superior dispersibility, and higher luminescence than traditional fluorescent beads, greatly improving the sensitivity of current LFA methods for pesticides. Moreover, using liquid SiO2-MQB directly instead of via the conjugate pad both simplifies the structure of LFA system and improves the efficiency of immunobinding reactions between nanotags and the targets. Applying these methods, the established CFLFA realized the stable and accurate detection of IMI and CBZ in 12 min, with detection limits down to 1.94 and 14.79 pg/mL, respectively. The SiO2-MQB-CFLFA is practicable for application to real food samples (corn, apple, cucumber, and cabbage), and undoubtedly a promising and low-cost tool for on-site monitoring of trace pesticide residues.

Introduction of a multilayered fluorescent nanofilm into lateral flow immunoassay for ultrasensitive detection of Salmonella typhimurium in food samples

Fast and sensitive identification of foodborne bacteria in complex samples is the key to the prevention and control of microbial infections. Herein, an ultrasensitive lateral flow assay (LFIA) based on multilayered fluorescent nanofilm (GO/DQD)-guided signal amplification was developed for the rapid and quantitative determination of Salmonella typhimurium (S. typhi). The film-like GO/DQD was prepared through the electrostatic mediated layer-by-layer assembly of numerous carboxylated CdSe/ZnS quantum dots (QDs) onto an ultrathin graphene oxide (GO) nanosheet, which possessed advantages including higher QD loading, larger surface areas, superior luminescence, and better stability, than traditional spherical nanomaterials. The antibody-modified GO/DQD can effectively attach onto a target bacterial cell to form a GO/DQD-bacteria immunocomplex containing almost ten thousand QDs, thus greatly improving the detection sensitivity of LFIA. The constructed GO/DQD-LFIA biosensor achieved the rapid and sensitive detection of S. typhi in 14 min with detection limits of as low as 9 cells/mL. Moreover, compared with traditional LFIA techniques for bacteria detection, the proposed assay exhibited excellent stability and accuracy in real food samples and enormously improved sensitivity (2-3 orders of magnitude), demonstrating its great potential in the field of rapid diagnosis.

Ultrasensitive and simultaneous monitoring of multiple small-molecule pollutants on an immunochromatographic strip with multilayered film-like fluorescent tags

A wide variety of small-molecule pollutants is harmful to human health, and their highly sensitive universal and rapid detection in complex environments remains a challenge. Herein, a multiplexed and ultrasensitive immunochromatographic strip (ICS) was developed for the universal analysis of three kinds of different pollutants based on multilayered fluorescent nanofilm-guided signal amplification. Flexible three-dimensional nanofilms (GO-MQD) with large surface areas, high quantum dot (QD) loading, superior luminescence, and good stability were synthesized through the electrostatic adsorption-mediated layer-by-layer assembly of three layers of small QDs onto two-dimensional graphene oxide (GO) nanosheets, modified with specific antibodies, and utilized as enhanced fluorescent tags in the ICS method for quantitative target detection. By combining the GO-MQD nanofilms and multiplexed ICS, the proposed assay can rapidly and sensitively detect aflatoxin B1, clenbuterol, and kanamycin in actual samples/environmental samples (pork extract, milk, river water, and lake water) with low detection limit (0.87, 2.04, and 0.81 pg/mL), fast testing time (15 min), good stability and high reproducibility (RSD < 8.71 %). The GO-MQD-ICS method developed here exhibits great potential to meet the demands of the on-site and practical detection of small-molecule pollutants.

Recent advances in quantum dot-based fluorescence-linked immunosorbent assays

Fluorescence immunoassays have been given considerable attention among the quantitative detection methods in the clinical medicine and food safety testing fields. In particular, semiconductor quantum dots (QDs) have become ideal fluorescent probes for highly sensitive and multiplexed detection due to their unique photophysical properties, and the QD fluorescence-linked immunosorbent assay (FLISA) with high sensitivity, high accuracy, and high throughput has been greatly developed recently. In this manuscript, the advantages of applying QDs to FLISA platforms and some strategies for their application to in vitro diagnostics and food safety are discussed. Given the rapid development of this field, we classify these strategies based on the combination of QD types and detection targets, including traditional QDs or QD micro/nano-spheres-FLISA, and multiple FLISA platforms. In addition, some new sensors based on the QD-FLISA are introduced; this is one of the hot spots in this field. The current focus and future direction of QD-FLISA are also discussed, which provides important guidance for the further development of FLISA.

Introduction of Multilayered Dual-Signal Nanotags into a Colorimetric-Fluorescent Coenhanced Immunochromatographic Assay for Ultrasensitive and Flexible Monitoring of SARS-CoV-2

Timely, accurate, and rapid diagnosis of SARS-CoV-2 is a key factor in controlling the spread of the epidemic and guiding treatments. Herein, a flexible and ultrasensitive immunochromatographic assay (ICA) was proposed based on a colorimetric/fluorescent dual-signal enhancement strategy. We first fabricated a highly stable dual-signal nanocomposite (SADQD) by continuously coating one layer of 20 nm AuNPs and two layers of quantum dots onto a 200 nm SiO2 nanosphere to provide strong colorimetric signals and enhanced fluorescence signals. Two kinds of SADQD with red and green fluorescence were conjugated with spike (S) antibody and nucleocapsid (N) antibody, respectively, and used as dual-fluorescence/colorimetric tags for the simultaneous detection of S and N proteins on one test line of ICA strip, which can not only greatly reduce the background interference and improve the detection accuracy but also achieve a higher colorimetric sensitivity. The detection limits of the method for target antigens via colorimetric and fluorescence modes were as low as 50 and 2.2 pg/mL, respectively, which were 5 and 113 times more sensitive than those from the standard AuNP-ICA strips, respectively. This biosensor will provide a more accurate and convenient way to diagnose COVID-19 in different application scenarios.

Colorimetric-photothermal-magnetic three-in-one lateral flow immunoassay for two formats of biogenic amines sensitive and reliable quantification

Rapid, simple, sensitive and reliable approaches for biogenic amines quantification in various food samples are essential to food safety. Lateral flow immunoassay (LFIA) has been wildly utilized in point-of-care testing (POCT) owing to its advantage of flexibility and feasibility. Here, we reported a Fe₃O₄@Au nanoparticles (NPs) (Fe₃O₄@AuNPs) based multimodal readout LFIA for rapid putrescine (Put) and histamine (His) quantification with a LOD down to 10 and 10 ng/mL in naked eye mode, 2.31 and 4.39 ng/mL in photothermal mode, 0.17 and 0.31 ng/mL in magnetic mode, respectively. Such multi-mode assay has been successfully used to detect Biogenic amines (BAs) in raw aquatic foods, including fish, prawns, beef, and pork, with overall recoveries ranging from 93.68 to 109.34%. Meanwhile, it is easily expanded to detect other typical BAs with high sensitivity by simply replacing antibodies. In view of the multi-signal reading, two quantitative formats, and high sensitivity, it may greatly widen the application of lateral flow detection in food safety.

Introduction of graphene oxide-supported multilayer-quantum dots nanofilm into multiplex lateral flow immunoassay: A rapid and ultrasensitive point-of-care testing technique for multiple respiratory viruses

A lateral flow immunoassay (LFA) biosensor that allows the sensitive and accurate identification of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other common respiratory viruses remains highly desired in the face of the coronavirus disease 2019 pandemic. Here, we propose a multiplex LFA method for the on-site, rapid, and highly sensitive screening of multiple respiratory viruses, using a multilayered film-like fluorescent tag as the performance enhancement and signal amplification tool. This film-like three-dimensional (3D) tag was prepared through the layer-by-layer assembly of highly photostable CdSe@ZnS-COOH quantum dots (QDs) onto the surfaces of monolayer graphene oxide nanosheets, which can provide larger reaction interfaces and specific active surface areas, higher QD loads, and better luminescence and dispersibility than traditional spherical fluorescent microspheres for LFA applications. The constructed fluorescent LFA biosensor can simultaneously and sensitively quantify SARS-CoV-2, influenza A virus, and human adenovirus with low detection limits (8 pg/mL, 488 copies/mL, and 471 copies/mL), short assay time (15 min), good reproducibility, and high accuracy. Moreover, our proposed assay has great potential for the early diagnosis of respiratory virus infections given its robustness when validated in real saliva samples.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (Section S1 Experimental section, Section S2 Calculation of the maximum number of QDs on the GO@TQD nanofilm, Section S3 Optimization of the LFA method, and Figs. S1-S17 mentioned in the main text) is available in the online version of this article at 10.1007/s12274-022-5043-6.

Recent Advances in Silica-Nanomaterial-Assisted Lateral Flow Assay

Lateral flow assays (LFAs) have attracted much attention as rapid and affordable point-of-care devices for medical diagnostics. The global SARS-CoV-2 pandemic has further highlighted the importance of LFAs. Many efforts have been made to enhance the sensitivity of LFAs. In recent years, silica nanomaterials have been used to either amplify the signal of label materials or provide stability, resulting in better detection performance. In this review, the recent progress of silica-nanomaterial-assisted LFAs is summarized. The impact of the structure of silica nanomaterials on LFA performance, the challenges and prospects in this research area are also discussed.

Magnetic Fluorescent Quantum Dots Nanocomposites in Food Contaminants Analysis: Current Challenges and Opportunities

The presence of food contaminants can cause foodborne illnesses, posing a severe threat to human health. Therefore, a rapid, sensitive, and convenient method for monitoring food contaminants is eagerly needed. The complex matrix interferences of food samples and poor performance of existing sensing probes bring significant challenges to improving detection performances. Nanocomposites with multifunctional features provide a solution to these problems. The combination of the superior characteristics of magnetic nanoparticles (MNPs) and quantum dots (QDs) to fabricate magnetic fluorescent quantum dots (MNPs@QDs) nanocomposites are regarded as an ideal multifunctional probe for food contaminants analysis. The high-efficiency pretreatment and rapid fluorescence detection are concurrently integrated into one sensing platform using MNPs@QDs nanocomposites. In this review, the contemporary synthetic strategies to fabricate MNPs@QDs, including hetero-crystalline growth, template embedding, layer-by-layer assembly, microemulsion technique, and one-pot method, are described in detail, and their advantages and limitations are discussed. The recent advances of MNPs@QDs nanocomposites in detecting metal ions, foodborne pathogens, toxins, pesticides, antibiotics, and illegal additives are comprehensively introduced from the perspectives of modes and detection performances. The review ends with current challenges and opportunities in practical applications and prospects in food contaminants analysis, aiming to promote the enthusiasm for multifunctional sensing platform research.

Colorful Luminescent Magnetic Supraparticles: Expanding the Applicability, Information Capacity, and Security of Micrometer-Scaled Identification Taggants by Dual-Spectral Encoding

(Sub)micrometer-scaled identification (ID) taggants enable direct identification of arbitrary goods, thereby opening up application fields based on the possibility of tracking, tracing, and anti-counterfeiting. Due to their small dimensions, these taggants can equip in principle even the smallest subcomponents or raw materials with information. To achieve the demanded applicability, the mostly used optically encoded ID taggants must be further improved. Here, micrometer-scaled supraparticles with spectrally encoded luminescent and magnetically encoded signal characteristics are reported. They are produced in a readily customizable bottom-up fabrication procedure that enables precise adjustment of luminescent and magnetic properties on multiple hierarchy levels. The incorporation of commonly used magnetic nanoparticles and fluorescent dyes, respectively, into polymer nanocomposite particles, establishes a convenient toolbox of magnetic and luminescent building blocks. The subsequent assembly of selected building blocks in the desired ratios into supraparticles grants for all the flexibility to freely adjust both signal characteristics. The obtained spectrally resolved visible luminescent and invisible magnetic ID signatures are complementary in nature, thus expanding applicability and information security compared to recently reported optical- or magnetic-encoded taggants. Additionally, the introduced ID taggant supraparticles can significantly enhance the coding capacity. Therefore, the introduced supraparticles are considered as next-generation ID taggants.

Quantum dots assembly enhanced and dual-antigen sandwich structured lateral flow immunoassay of SARS-CoV-2 antibody with simultaneously high sensitivity and specificity

Exploring reliable and highly-sensitive SARS-CoV-2 antibody diagnosis by point-of-care (POC) manner, holds great public health significance for extensive COVID-19 screening and controlling. Unfortunately, the currently applied gold based lateral flow immunoassay (GLFIA) may expose both false-negative and false-positive interpretations owing to the sensitivity and specificity limitations, which may cause significant risk and waste of public resources for large population screening. To simultaneously overcome the drawbacks of GLFIA, a novel fluorescent LFIA based on signal amplification and dual-antigen sandwich structure was established with largely improved sensitivity and specificity. The compact three-dimensional incorporation of hydrophobic quantum dots within dendritic affinity templates and multilayer surface derivation guaranteed a high and robust fluorescence of single label, which lowered the false negative rate of GLFIA prominently. A dual-antigen sandwich structure using labeled/immobilized SARS-CoV-2 spike receptor binding domain antigen for capturing total human SARS-CoV-2 antibody was developed, instead of general indirect antibody capturing approach, to reduce the false positive rate of GLFIA. Over 300 cases of COVID-19 negative and 97 cases of COVID-19 positive samples, the current assay revealed a 100% sensitivity and 100% specificity confirmed by both polymerase chain reaction (PCR) and chemiluminescence immunoassay (CLIA), compared with the considerable misinterpretation cases by currently applied GLFIA. The quantitative results verified by receiver operating characteristic curve and other statistical analysis indicated a well-distinguished positive/negative sample groups. The proposed strategy is highly sensitive towards low concentrated SARS-CoV-2 antibody serums and highly specific towards serums from COVID-19 negative persons and patients infected by other viruses.

Ultrasensitive Competitive Lateral Flow Immunoassay with Visual Semiquantitative Inspection and Flexible Quantification Capabilities

Antibiotics abuse has caused various problems threatening human health and ecological environment. Monitoring antibiotics residual levels is of great significance, yet still challenging for quantitative point-of-need testing with high-sensitivity and visual capability. Here we developed a competitive lateral flow immunoassay (CLFIA) platform with flexible readout for enrofloxacin (ENR), a regularly added antibiotic. To overcome the limitation of low sensitivity of traditional colloidal gold-based CLFIA, the three-dimensionally assembled gold nanoparticles (AuNPs) within dendritic silica scaffold were fabricated as signal reporters. The assembly structure effectively retained the intrinsic absorption features of hydrophobic AuNPs and greatly enhanced the light extinction ability of a single label for signal amplification. The obtained CLFIA strips can not only achieve qualitative screening of ENR at a very low concentration by naked eye (cutoff value: 0.125 ng/mL), but also enable ultrasensitive quantification of ENR by an optical scanner (limit of detection: 0.00195 ng/mL) or a smartphone (limit of detection: 0.0078 ng/mL). Moreover, to elaborate the visual inspection degree of CLFIA against traditional yes/no interpretation, a novel multirange gradient CLFIA strip was prepared for visually semiquantitative identification of ENR with four concentration ranges. The novel CLFIA platform demonstrated sensitive, specific, and reliable determination of ENR with flexible signal readout and provides a potential and invigorating pathway to point-of-need immunoassay of antibiotics.