Lateral Flow Immunoassay Platform Research Articles

Polydopamine modified colloidal gold nanotag-based lateral flow immunoassay platform for highly sensitive detection of pathogenic bacteria and fast evaluation of antibacterial agents

Bacterial infection is a great threat to human health. Lateral flow immunoassays (LFIAs) with the merits of low cost, quick screening, and on-site detection are competitive technologies for bacteria detection, but their detection limits depend on the optical performance of the adopted nanotags. Herein, we presented a LFIA platform for bacteria detection using polydopamine (PDA) functionalized Au nanoparticles (denoted as Au@PDA) as the nanotag. The introduction of PDA could provide enhanced light absorption of Au, as well as numerous functional groups for conjugation. Small recognition molecules i.e. vancomycin (Van) and p-mercaptophenylboronic acid (PMBA) were covalently anchored to Au@PDA, and selected as the specific probes towards Gram-positive (G+) and Gram-negative (G—) bacteria, respectively. Taken Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) as the representative targets of G+ and G— bacteria, two LFA strips were successfully constructed based on the immuno-sandwich principle. They could quantitatively detect S. aureus and E. coli both down to 102 cfu/mL, a very competitive detection limit in comparison with other colorimetric or luminescent probes-based LFIAs. Furthermore, the proposed two strips were applied for the quantitative, accurate, and rapid detection of S. aureus and E. coli in food and human urine samples with good analytical results obtained. In addition, they were integrated as a screening platform for quick evaluation of diverse antibacterial agents within 3 h, which is remarkably shortened compared with that of the two traditional methods i.e. bacterial culture and plate-counting.

Multiple-readout lateral flow immunoassay for the sensitive detection of nitrofurazone metabolites through ultrabright AIE-MOF coupled in-situ growth strategy

The multiple-readout capability of multimodal detection enhances the flexibility, reliability, and accuracy of lateral flow immunoassay (LFIA). The conjugation of two different metal-organic frameworks (MOFs) as a new-generation composite material offers extraordinary opportunities for developing multimodal LFIA. It is anticipated to compensate limitations of traditional single colorimetric signal LFIA and improve the analysis performance. Herein, an ultra-bright fluorescent AIE-MOF was proposed and coupled with an in-situ growth of Prussian blue (PB) nanoparticles strategy to obtain a novel multimodal signal tracer (AIE-MOF@PB). Thereafter, it was successfully applied to develop the multimodal LFIA platform for the detection of nitrofurazone metabolites. The synergy of AIE-MOF and PB endows AIE-MOF@PB with superb water dispersibility, robust fluorescence emission, brilliant colorimetric signal, marvelous photothermal conversion, and enhanced antibody coupling efficiency, all of which facilitate a highly sensitive triple-readout LFIA platform. The detection sensitivity improved by at least 5-fold compared with the colloidal gold-based LFIA. This work not only inspires the rational design of aggregation-induced emission luminogens (AIEgen)-based complex materials but also highlights the promising potential in flexible point-of-care applications.

Nanoengineered plasmonics-enhanced photothermal tags for sensitive detection of cardiac biomarker troponin I using lateral flow immunoassay

In recent years, photothermal lateral flow immunoassay (LFIA) has gained widespread use as a point-of-care testing (POCT) technique because of its cost-effective portable instrumentation and easy-to-handle procedures. However, developing a highly sensitive photothermal LFIA platform with high photothermal efficiency remains challenging. In this study, we developed a portable smartphone-based plasmonics-enhanced photothermal LFIA (PPh-LFIA) platform to improve the photothermal LFIA sensitivity by engineering plasmonic-active gold nanostars (GNS) having large-sized sharp branches. We investigated the photothermal effect using various GNS engineered to have different sizes and spike lengths of GNSs (GNS-1, GNS-2, GNS-3, and GNS-4) in order to exhibit optimal plasmonics properties. The results showed that the GNS-3 having a broad plasmon band with a plasmon maximum band at 995 nm exhibited the strongest photothermal efficiency (80 %). As a proof-of demonstration, we have employed GNS-3 for the detection of the cardiac biomarker, troponin I (cTnI), used as the model system. The results show high sensitivity with a detection limit (LOD) of 5.5 pg/mL, which was around 1000 times more sensitive than traditional colorimetric LFIA based on gold nanospheres (GNSP). To verify the applicability of the PPh-LFIA platform, cTnI was spiked into human blood serum samples, enabling the detection of cTnI with an LOD of 6.7 pg/mL. Overall, this study offers insights for nanoengineering and fine-tuning the GNS morphology to increase the photothermal efficiency, consequently improving the PPh-LFIA detection sensitivity, which makes it suitable for use as a sensitive and portable POCT tool.

A handheld fluorescent lateral flow immunoassay platform for highly sensitive point-of-care detection of methamphetamine and tramadol

The escalating issue of drug abuse poses a significant threat to public health and societal stability worldwide. An on-site drug detection platform is vital for combating drug abuse and trafficking, as it eliminates the need for additional tools, extensive processes, or specialized training. Therefore, it is imperative to develop a fast, sensitive, non-invasive, and reliable multiplex drug testing platform. In this study, we have presented a silica core@dual quantum dot-shell nanocomposite (SI/DQD)-based fluorescent lateral flow immunoassay (LFIA) platform for the highly sensitive and simultaneous point-of-care (POC) detection of methamphetamine (MET) and tramadol (TR). A 3D-printed attachment was designed to integrate optical and electrical components, facilitating the miniaturization of the instrument and reducing both cost and complexity. The device's advanced hardware and effective fluorescence extraction algorithm with waveform reconstruction enable swift, automatic noise reduction and data analysis. SI/DQD nanocomposites were utilized as fluorescent nanotags in the LFIA strips due to their outstanding luminous efficiency and robustness. This LFIA platform achieves impressive detection limits (LODs) of 0.11 ng mL−1 for MET and 0.017 ng mL−1 for TR. The method has also successfully detected MET and TR in complex biological samples, demonstrating its practical application capabilities. The proposed fluorescent LFIA platform, based on SI/DQD technology, holds significant promise for the swift and accurate POC detection of these substances. Its affordability, compact size, and excellent analytical performance make it suitable for on-site drug testing, including at borders and roadside checks, and open up new possibilities for the design and implementation of drug testing methods.

A novel integrated lateral flow immunoassay platform for the detection of cardiac troponin I using hierarchical dendritic copper-nickel nanostructures

Cardiac troponin I (cTnI) is a critical biomarker for the diagnosis of acute myocardial infarction (AMI). Herein, we report a novel integrated lateral flow immunoassay (LFIA) platform for highly sensitive point-of-care testing (POCT) of cTnI using hierarchical dendritic copper-nickel (HD-nanoCu-Ni) nanostructures. The electrodeposited HD-nanoCu-Ni film (∼22 μm thick) on an ITO-coated glass substrate exhibits superior capillary action and structural integrity. These properties enable efficient sample transport and antibody immobilization, making it a compelling alternative to conventional multi-component paper-based LFIA test strips, which are often plagued by structural fragility and susceptibility to moisture damage. The biofunctionalized HD-nanoCu-Ni substrates were laser-etched with lateral flow channels, including a sample loading/conjugate release zone, a test zone, and a control zone. Numerical simulations were used to further optimize the design of these channels to achieve optimal fluid flow and target capture. The HD-nanoCu-Ni LFIA device utilizes a fluorescence quenching based sandwich immunoassay format using antibody-labeled gold nanoparticles (AuNPs) as quenchers. Two different fluorescent materials, fluorescein isothiocyanate (FITC) and CdSe@ZnS quantum dots (QDs), were used as background fluorophores in the device. Upon the formation of a sandwich immunocomplex with cTnI on the HD-nanoCu-Ni device, introduced AuNPs led to the fluorescence quenching of the background fluorophores. The total assay time was approximately 15 min, demonstrating the rapid and efficient nature of the HD-nanoCu-Ni LFIA platform. For FITC, both inner filter effect (IFE) and fluorescence resonance energy transfer (FRET) contributed to the AuNP-mediated quenching. In the case of CdSe@ZnS QDs, IFE dominated the AuNP-induced quenching. Calibration curves were established based on the relationship between the fluorescence quenching intensity and cTnI concentration in human serum samples, ranging from 0.5 to 128 ng/mL. The limits of detection (LODs) were determined to be 0.27 ng/mL and 0.40 ng/mL for FITC and CdSe@ZnS QDs, respectively. A method comparison study using Passing-Bablok regression analysis on varying cTnI concentrations in human serum samples confirmed the equivalence of the HD-nanoCu-Ni LFIA platform to a commercial fluorescence cTnI LFIA assay kit, with no significant systematic or proportional bias observed.

A Portable Fluorescent Lateral Flow Immunoassay Platform for Rapid Detection of FluA.

The spread of the FluA virus poses significant public health concerns worldwide. Fluorescent lateral flow immunoassay (LFIA) test strips have emerged as vital tools for the early detection and monitoring of influenza infections. However, existing quantitative virus-detection methods, particularly those utilizing smartphone-based sensing platforms, encounter accessibility challenges in resource-limited areas and among the elderly population. Despite their advantages in speed and portability, these platforms often lack user-friendliness for these demographics, impeding their widespread utilization. To address these challenges, this study proposes leveraging the optical pick-up unit (OPU) sourced from commercial optical drives as a readily available fluorescence excitation module for the quantitative detection of antibodies labeled with quantum-dot fluorescent microspheres. Additionally, we utilize miniaturized and high-performance optical components and 3D-printed parts, along with a customized control system, to develop an affordable point-of-care testing (POCT) device. Within the system, a stepping motor scans the test strip from the T-line to the C-line, enabling the calculation of the fluorescence-intensity ratio between the two lines. This simple yet effective design facilitates rapid and straightforward field or at-home testing for FluA. The proposed prototype platform demonstrates promising performance, achieving a limit of detection (LOD) of 2.91 ng/mL, a total detection time of no more than 15 min, and dimensions of 151 mm × 11.2 mm × 10.8 mm3. We believe that the proposed approach holds great potential for improving access to an accurate influenza diagnosis.

Ultrabright NIR AIEgen nanoparticles‐enhanced lateral flow immunoassay platform for accurate diagnostics of complex samples

AbstractAccurate and sensitive near‐infrared (NIR) luminescent lateral flow immunoassay (LFIA) has attracted considerable attention in the field of point‐of‐care testing (POCT). However, the detection accuracy and sensitivity are often compromised by the low fluorescence quantum efficiency (<10%) of the NIR fluorescent probe. Herein, ultrabright NIR AIEgen nanoparticles (PS@AIE830NPs) composed of polystyrene (PS) nanoparticles and NIR aggregation‐induced emission luminogen (AIEgen) with the maximum emission at 830 nm (AIE830) is reported, and its potential to promote an accurate and sensitive detection of complex samples by LFIA is described. The relative quantum yield (QY) of the PS@AIE830NPs was 14.76%, which was superior to that of the polymer embedding method and indocyanine green (ICG)‐based NIR nanoparticles. The PS@AIE830NPs immunolabeled‐LFIA combined with laboratory‐built NIR‐LFIA portable quantitative instruments (detected light range > 800 nm) completely eliminated background interference and allowed highly accurate and sensitive detection without any pre‐treatment steps. The limits of detection (LODs) for aflatoxin B1 (AFB1) in soy sauce, alpha hemolysin (Hla) of Staphylococcus aureus biomarker in joint fluid, and C‐reactive protein (CRP) in human haemolysed samples were 0.01 ng mL−1, 0.02 µg mL−1, and 0.156 mg L−1, respectively, commensurating with those of the corresponding gold standard assays and covering the detection range of interests. It is anticipated that the ultrabright NIR AIEgen nanoparticles will serve as a universally applicable signal probe for NIR‐LFIA diagnostics, promising to expand the range of applications for quantitative detection of complex samples.

Molecular Engineering and Confinement Effect Powered Ultrabright Nanoparticles for Improving Sensitivity of Lateral Flow Immunoassay.

The application of traditional lateral flow immunoassay (LFIA)-based gold nanoparticles (AuNPs) to measure traces of target chemicals is usually challenging. In this study, we developed an integrated strategy based on molecular engineering and the spatial confinement of nanoparticles (NPs) to obtain ultrahigh quantum yields (QYs) of aggregation-induced emission (AIE) fluorescence NPs and employed them for the highly sensitive detection of T-2 toxin on the LFIA platform. Tetraethyl-4,4',4″,4‴-(ethene-1,1,2,2-tetrayl)tetrabenzoate (TCPEME), an AIE luminogen, was designed using molecular engineering to lower the energy gap, achieving higher QYs (26.26%) than previous AIEgens (13.02%). Subsequently, TCPEME-doped fluorescence NPs (TFNPs) achieved ultrahigh QYs, up to 84.55%, which were generated from the strong restriction of the NP state, efficiently suppressing nonradiative relaxation channels verified by ultrafast electron dynamics. On the LFIA platform, the sensitivity of the designed TFNP-based LFIA (TFNP-LFIA) was 10.4-fold and 4.3-fold more sensitive than that of the AuNP-LFIA and TPENP-LFIA for detecting the T-2 toxin, respectively. In addition, TFNP-LFIA was used for detecting T-2 toxin in samples and showed satisfactory recoveries (79.5 to 122.0%) with CV (1.49 to 11.75%), which implied excellent application potential for TFNP-LFIA. Overall, dual improvement of the molecule in fluorescence performance originating from the molecular engineering and spatial confinement of NPs could be an efficient tool for promoting the development of high-performance reporters in LFIA.

NIR-II fluorescent Ag2Se polystyrene beads in a lateral flow immunoassay to detect biomarkers for breast cancer.

Fluorescent lateral flow immunoassay (LFA), one tool in point of care testing (POCT) systemsfor breast cancer, has attracted attention because it is quick, simple, and convenient. However, samples and the constituent material exhibit autofluorescence in the visible region, which is a very large obstacle in the development of fluorescent LFAs. The autofluorescence of biological samples is scarcely found in the second near-infrared (NIR-II) range and samples scatter and absorb less NIR-II light than visible light. Here, we report an NIR-II QD-LFA platform using the NIR-II fluorescent Ag2Se quantum dots (QDs) with 1020nm emission encapsulated into polystyrene beads as fluorescent probes. The NIR-II LFA platform was established to detect breast cancer tumour markers (CEA and CA153) within 15min with a low limit of detection (CEA: 0.768ngmL-1, CA153: 1.192 U mL-1), high recoveries (93.7% ~ 108.8%), and relative standard deviations (RSDs) of less than 10%. This study demonstrated the potential of NIR-II Ag2Se polystyrene beads as a fluorescent probe in LFA for rapid and accurate identification of biomarkers. They are suited for use in professional situations.

Enhanced NIR-II Fluorescent Lateral Flow Biosensing Platform Based on Supramolecular Host-Guest Self-Assembly for Point-of-Care Testing of Tumor Biomarkers.

Point-of-care detection of tumor biomarkers with high sensitivity remains an enormous challenge in the early diagnosis and mass screening of cancer. Fluorescent lateral flow immunoassay (LFA) is an attractive platform for point-of-care testing due to its inherent advantages. Particularly, a fluorescent probe is crucial to improving the analytical performance of the LFA platform. Herein, we developed an enhanced second near-infrared (NIR-II) LFA (ENIR-II LFA) platform based on supramolecular host-guest self-assembly for detection of the prostate-specific antigen (PSA) as a model analyte. In this platform, depending on the effective supramolecular surface modification strategy, cucurbit[7]uril (CB[7])-covered rare-earth nanoparticles (RENPs) emitting in the NIR-II (1000-1700 nm) window were prepared and employed as an efficient fluorescent probe (RENPs-CB[7]). Benefiting from its superior optical properties, such as low autofluorescence, excellent photostability, enhanced fluorescence intensity, and increased antibody-conjugation efficiency, the ENIR-II LFA platform displayed a wide linear detection range from 0.65 to 120 ng mL-1, and the limit of detection was down to 0.22 ng mL-1 for PSA, which was 18.2 times lower than the clinical cutoff value. Moreover, the testing time was also shortened to 6 min. Compared with the commercial visible fluorescence LFA kit (VIS LFA) and the previously reported NIR-II LFA based on a RENPs-PAA probe, this ENIR-II LFA demonstrated more competitive advantages in analytical sensitivity, detection range, testing time, and production cost. Overall, the ENIR-II LFA platform offers great potential for the highly sensitive, rapid, and convenient detection of tumor biomarkers and is expected to serve as a useful technique in the general population screening of the high-incidence cancer region.

Plasmonic Approach to Fluorescence Enhancement of Mesoporous Silica-Coated Gold Nanorods for Highly Sensitive Influenza A Virus Detection Using Lateral Flow Immunosensor.

Rapid diagnostic tests based on the lateral flow immunoassay (LFI) enable early identification of viral infection, owing to simple interpretation, short turnaround time, and timely isolation of patients to minimize viral transmission among communities. However, the LFI system requires improvement in the detection sensitivity to match the accuracy of nucleic acid amplification tests. Fluorescence-based LFIs are more sensitive and specific than absorption-based LFIs, but their performance is significantly affected by fundamental issues related to the quantum yield and photobleaching of fluorophores. Metal-enhanced fluorescence (MEF), which is a plasmonic effect in the vicinity of metallic nanoparticles, can be an effective strategy to improve the detection sensitivity of fluorescence-based LFIs. The key factors for obtaining a strong plasmonic effect include the distance and spectral overlap of the metal and fluorophore in the MEF system. In this study, MEF probes were designed based on core-shell nanostructures employing a gold nanorod core, mesoporous silica shell, and cyanine 5 fluorophore. To optimize the efficiency of MEF probes incorporated on the LFI platform (MEF-LFI), we experimentally and theoretically investigated the distance dependence of plasmonic coupling between cyanine 5 and gold nanorods by adjusting the shell thickness, resulting in significant fluorescence enhancement. The proposed MEF-LFI enabled highly sensitive detection of influenza A virus (IAV) nucleocapsid protein with a detection limit of 0.52 pg mL-1 within 20 min and showed high specificity and accuracy for determining IAV clinical samples. Overall, our findings demonstrate the potential of this method as an effective tool for molecular diagnosis under emergency conditions.

Polydopamine Nanoparticles-Based Three-Line Lateral Flow Immunoassay for COVID-19 Detection.

Currently, the global trend of several hundred thousand new confirmed COVID-19 patients per day has not abated significantly. Serological antibody detection has become an important tool for the self-screening of people. While the most commonly used colorimetric lateral flow immunoassay (LFIA) methods for the detection of COVID-19 antibodies are limited by low sensitivity and a lack of quantification ability. This leads to poor accuracy in the screening of early COVID-19 patients. Therefore, it is necessary to develop an accurate and sensitive autonomous antibody detection technique that will effectively reduce the COVID-19 infection rate. Here, we developed a three-line LFIA immunoassay based on polydopamine (PDA) nanoparticles for COVID-19 IgG and IgM antibodies detection to determine the degree of infection. The PDA-based three-line LFIA has a detection limit of 1.51 and 2.34 ng/mL for IgM and IgG, respectively. This assay reveals a good linearity for both IgM and IgG antibodies detection and is also able to achieve quantitative detection by measuring the optical density of test lines. In comparison, the commercial AuNP-based LFIA showed worse quantification results than the developed PDA-based LFIA for low-concentration COVID-19 antibody samples, making it difficult to distinguish between negative and positive samples. Therefore, the developed PDA-based three-line LFIA platform has the accurate quantitative capability and high sensitivity, which could be a powerful tool for the large-scale self-screening of people.

Sharp Branched Gold Nanostar-Based Lateral-Flow Immunoassay for Detection of Yersinia pestis

Over the past few decades, colorimetric paper-based lateral flow immunoassay (LFIA) has emerged as a versatile analytical tool for rapid point-of-care detection of infectious diseases with high simplicity and flexibility. The LFIA sensitivity is based on color visualization of the antibody-labeled nanoparticles bound with the target analytes at the test line. Therefore, the nanoparticle design is crucial for LFIA sensitivity. The traditional LFIA is based on spherical gold nanoparticles, which usually suffer from poor sensitivity because of very low optical contrast at the test line. To improve the LFIA sensitivity, we have developed an LFIA based on gold nanostars (GNSs) with different branch lengths and sharpness (GNS-1, GNS-2, and GNS-3), which possess higher optical contrast than conventional gold nanospheres (GNSPs). We have selected the bacterium Yersinia pestis as a model analyte system. The effective affinity of GNSPs and GNSs with the Y. pestis fraction 1 (F1) protein was quantitively investigated by colorimetric and optical density measurements of the test line. The results show that GNS-3, which has maximum spike length and branch sharpness, exhibits the highest analytical sensitivity based on the limit of detection of the LFIA readout compared to other GNSs and GNSPs. The detection limit of the Y. pestis F1 antigen was achieved up to 0.1 ng/mL for GNS-3, which is 100 times lower than that for the GNSP at a 1 pmol/L concentration and 10 times lower than that for the reported procedure based on traditional gold nanoparticles. Overall, our prototype LFIA platform based on a highly spiked GNS (GNS-3) exhibits high analytical sensitivity, indicating it to be a promising candidate for routine LFIA application to detect infectious diseases.

High-performance green-emitting AIE nanoparticles for lateral flow immunoassay applications.

Ultrabright green-emissive AIE nanoparticles (AIENPs) were used as signal-amplification probes to enhance the detectability of lateral flow immunoassay (LFIA). The detection performances of the green-emissive AIENP probes in both sandwich and competitive LFIA formats were systematically evaluated. Benefiting from its remarkable fluorescent brightness, the developed AIENP-LFIA showed versatile applicability for the detection of small molecules and macromolecules by using ochratoxin A (OTA) and procalcitonin (PCT) as model analytes, respectively. Under the optimum conditions, the detection limits (LODs) of the fabricated AIENP-LFIA for OTA and PCT were 0.043 ng mL-1 and 0.019 ng mL-1, respectively. These LOD values are significantly lower than those of conventional LFIA methods using gold nanoparticles as signal reporters. In addition, we demonstrated the practical application potential of AIENP-LFIA for the detection of OTA in real maize samples and PCT in real serum samples. These results indicated that the ultrabright green-emissive AIENPs were promising as signal output materials for building high-performance LFIA platform and broadening the application scenarios of LFIA.

Eu-Chelate Polystyrene Microsphere-Based Lateral Flow Immunoassay Platform for hs-CRP Detection.

Inflammation caused by viral or bacterial infection is a major threat to human health globally. Blood C-reactive protein (CRP) has been proven to be a sensitive indicator for the occurrence and development of inflammation. Furthermore, a tiny change of blood CRP concentration may portend chronic diseases; therefore, high-sensitivity CRP (hs-CRP) detection in a quantitative, rapid, user-friendly, and low-cost manner is highly demanded. In this paper, we developed a europium-chelate polystyrene microsphere (EuPSM)-based lateral flow immunoassay (LFIA) integrating with a benchtop fluorescence analyzer for hs-CRP detection. The optimization of the EuPSM-based LFIA was implemented through adjusting the antibody density on EuPSM from 100% to 60% of the saturated density. Finally, the limit of detection of 0.76 pg/mL and detection range of 0.025-250 ng/mL were obtained. Moreover, the clinical application capability of the proposed platform was validated through detecting CRP in clinical serum samples, showing high consistency with the results obtained from the clinical standard method. Hence, the proposed EuPSM-based LFIA has been verified to be well suitable for hs-CRP detection, while also showing great applicability for sensitively and rapidly detecting other biomarkers.

Development of fluorescent lateral flow immunoassay for SARS-CoV-2-specific IgM and IgG based on aggregation-induced emission carbon dots.

Understanding the dynamic changes in antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential for evaluating the effectiveness of the vaccine and the stage for the recovery of the COVID-19 disease. A rapid and accurate method for the detection of SARS-CoV-2-specific antibodies is still urgently needed. Here, we developed a novel fluorescent lateral flow immunoassay (LFA) platform for the detection of SARS-CoV-2-specific IgM and IgG by the aggregation-induced emission carbon dots conjugated with the SARS-CoV-2 spike protein (SSP). The aggregation-induced emission carbon dots (AIE-CDs) are one of the best prospect fluorescent probe materials for exhibiting high emission efficiency in both aggregate and solid states. The AIE-CDs were synthesized and displayed dual fluorescence emission, which provides a new perspective for the design of a high sensitivity testing system. In this work, the novel LFA platform adopted the AIE carbon dots, which are used to detect SARS-CoV-2-specific IgM and IgG conveniently. Furthermore, this sensor had a low LOD of 100 pg/ml. Therefore, this newly developed strategy has potential applications in the areas of public health for the advancement of clinical research.

A novel delayed lateral flow immunoassay for enhanced detection of SARS-CoV-2 spike antigen.

A new detection strategy was developed to improve the sensitivity of a lateral flow immunoassay platform utilizing a delayed hydrophobic barrier fabricated with trimethylsilyl cellulose (TMSC). The SARS-CoV-2 spike receptor-binding domain (SARS-CoV-2 SP RBD) antigen was chosen as a model analyte to demonstrate the superior detectability of this scheme. The novel device consists of 2 separate layers, so-called delayed lateral flow immunoassay (d-LFIA). The upper layer is intended for the analyte or sample flow path, where the test solution flows freely straight to the detection zone to bind with the primary antibody. The lower layer, located just underneath, is designed for the SARS-CoV-2 spike receptor-binding domain-conjugated gold nanoparticles (SARS-CoV-2 SP RBD-AuNPs) used for producing a colorimetric signal. This layer is fabricated with a TMSC barrier to time-delay the movement of SARS-CoV-2 SP RBD-AuNPs, thus allowing the antigen to bind with the primary antibody more efficiently. This platform exhibited a 2.6-fold enhancement in the sensitivity and 9.1-fold improvement in the limit of detection (LOD) as compared with the conventional LFIA. In addition, this d-LFIA device was satisfactorily applied to accurate screening of COVID-19 patients.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s00604-022-05467-3.

An ultrasensitive lateral flow immunoassay platform for foodborne biotoxins and pathogenic bacteria based on carbon-dots embedded mesoporous silicon nanoparticles fluorescent reporter probes

Lateral flow immunoassays (LFIAs) are routine methods for rapid foodborne pollutants screening, with detection limits that are closely associated with the label probes used. The exploitation of high performance and robust probe is highly desirable, and remains a great challenge. Herein, we reported an emerging fluorescent nanobeads i.e. carbon-dots (CD) covalently incorporated mesoporous silicon nanoparticles (CD-MSNs) for LFIAs. CD-MSNs revealed brighter fluorescence, larger particle size and more modification sites in comparison with those of single CD. After bio-functionalisation, CD-MSNs probes were introduced to construct LFIA test strips, and designed for ultrasensitive detection of aflatoxin B1 (AFB1) and Staphylococcus aureus (S. aureus), two representative foodborne pollutants, based on the competitive and sandwich models, respectively. Very competitive quantitative detection limits i.e. 0.05 ng/mL and 102 cfu/mL were correspondingly obtained. Additionally, the test strips were successfully applied to rapidly and accurately screen AFB1 and S. aureus in food samples, highlighting their practicality.

Artificial intelligence-assisted colorimetric lateral flow immunoassay for sensitive and quantitative detection of COVID-19 neutralizing antibody

Currently, vaccination is the most effective medical measure to improve group immunity and prevent the rapid spread of COVID-19. Since the individual difference of vaccine effectiveness is inevitable, it is necessary to evaluate the vaccine effectiveness of every vaccinated person to ensure the appearance of herd immunity. Here, we developed an artificial intelligent (AI)-assisted colorimetric polydopamine nanoparticle (PDA)-based lateral flow immunoassay (LFIA) platform for the sensitive and accurate quantification of neutralizing antibodies produced from vaccinations. The platform integrates PDA-based LFIA and a smartphone-based reader to test the neutralizing antibodies in serum, where an AI algorithm is also developed to accurately and quantitatively analyze the results. The developed platform achieved a quantitative detection with 160 ng/mL of detection limit and 625–10000 ng/mL of detection range. Moreover, it also successfully detected totally 50 clinical serum samples, revealing a great consistency with the commercial ELISA kit. Comparing with commercial gold nanoparticle-based LFIA, our PDA-based LFIA platform showed more accurate quantification ability for the clinical serum. Therefore, we envision that the AI-assisted PDA-based LFIA platform with sensitive and accurate quantification ability is of great significance for large-scale evaluation of vaccine effectiveness and other point-of-care immunoassays.

Engineering light-initiated afterglow lateral flow immunoassay for infectious disease diagnostics

The pandemic of highly contagious diseases has put forward urgent requirements for high sensitivity and adaptive capacity of point-of-care testing (POCT). Herein, for the first time, we report an aggregation-induced emission (AIE) dye-energized light-initiated afterglow nanoprobes (named LiAGNPs), implemented onto a lateral flow immunoassay (LFIA) test strip, for diagnosis of two highly contagious diseases, human immunodeficiency virus (HIV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as model validation. The primary working mechanism relies on the cyclically generated singlet oxygen (1O2)-triggered time-resolved luminescent signals of LiAGNPs in which AIE dyes (TTMN) and chemiluminescent substrates (SO) are loaded. The designed LiAGNPs were found 2-fold and 32-fold sensitive than the currently used Eu(III)-based time-resolved fluorescent nanoparticles and gold nanoparticles in lateral flow immunoassay (LFIA), respectively. In addition, the extra optical behaviors of nude color and fluorescence of LiAGNPs enable the LFIA platform with the capability of the naked eye and fluorescent detection to satisfy the applications under varying scenarios. In short, the versatile LiAGNPs have great potential as a novel time-resolved reporter in enhancing detection sensitivity and application flexibility with LFIA platform for rapid but sensitive infectious disease diagnostics.