Quantum dots' size matters for balancing their quantity and quality in label materials to improve lateral flow immunoassay performance for C-reactive protein determination

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.

In Situ Synthesis of Highly Fluorescent, Phosphorus-Doping Carbon-Dot-Functionalized, Dendritic Silica Nanoparticles Applied for Multi-Component Lateral Flow Immunoassay

The sensitivity of fluorescent lateral flow immunoassay (LFIA) test strips is compromised by the low fluorescence intensity of the signaling molecules. In this study, we synthesized novel phosphorus-doped carbon-dot-based dendritic mesoporous silica nanoparticles (DMSNs-BCDs) with a quantum yield as high as 93.7% to break this bottleneck. Meanwhile, the in situ growth method increased the loading capacity of carbon dots on dendritic mesoporous silica, effectively enhancing the fluorescence intensity of the composite nanospheres. Applied DMSNs-BCDs in LFIA can not only semi-quantitatively detect a single component in a short time frame (procalcitonin (PCT), within 15 min) but also detect the dual components with a low limit of detection (LOD) (carbohydrate antigen 199 (CA199) LOD: 1 U/mL; alpha-fetoprotein (AFP) LOD: 0.01 ng/mL). And the LOD of PCT detection (0.01 ng/mL) is lower by 1.7 orders of magnitude compared to conventional colloidal gold strips. For CA199, the LOD is reduced by a factor of four compared to LFIA using gold nanoparticles as substrates, and for AFP, the LOD is lowered by two orders of magnitude compared to colloidal gold LFIA. Furthermore, the coefficients of variation (CV) for intra-assay and inter-assay measurements are both less than 11%.

Fluorescence-enhanced dual signal lateral flow immunoassay for flexible and ultrasensitive detection of monkeypox virus

The outbreak of the monkeypox virus (MPXV) worldwide in 2022 highlights the need for a rapid and low-cost MPXV detection tool for effectively monitoring and controlling monkeypox disease. In this study, we developed a flexible lateral flow immunoassay (LFIA) with strong colorimetric and enhanced fluorescence dual-signal output for the rapid, on-site, and highly sensitive detection of the MPXV antigen in different scenarios. A multilayered SiO2-Au core dual-quantum dot (QD) shell nanocomposite (named SiO2-Au/DQD), which consists of a large SiO2 core (~ 200 nm), one layer of density-controlled gold nanoparticles (AuNPs, 20 nm), and thousands of small QDs, was fabricated instead of a traditional colorimetric nanotag (i.e., AuNPs) and a fluorescent nanotag (QD nanobead) to simultaneously provide good stability, strong colorimetric ability and superior fluorescence intensity. With the dual-signal output LFIA, we achieved the specific screening of the MPXV antigen (A29L) in 15 min, with detection limits of 0.5 and 0.0021 ng/mL for the colorimetric and fluorometric modes, respectively. Moreover, the colorimetric mode of SiO2-Au/DQD-LFIA exhibits the same sensitivity as the traditional AuNP- LFIA, whereas the overall sensitivity of this method on the basis of the fluorescent signal can achieve 238- and 3.3-fold improvements in sensitivity for MPXV compared with the AuNP-based LFIA and ELISA methods, respectively, indicating the powerful performance and good versatility of the dual-signal method in the point-of-care testing of the MPXV.

Dendritic mesoporous nanoparticles for the detection, adsorption, and degradation of hazardous substances in the environment: State-of-the-art and future prospects

Equipped with hierarchical pores and three-dimensional (3D) center-radial channels, dendritic mesoporous nanoparticles (DMNs) make their pore volumes extremely large, specific surface areas super-high, internal spaces especially accessible, and so on. Other entities (like organic moieties or nanoparticles) can be modified onto the interfaces or skeletons of DMNs, accomplishing their functionalization for desirable applications. This comprehensive review emphasizes on the design and construction of DMNs-based systems which serve as sensors, adsorbents and catalysts for the detection, adsorption, and degradation of hazardous substances, mainly including the construction procedures of brand-new DMNs-based materials and the involved hazardous substances (like industrial chemicals, chemical dyes, heavy metal ions, medicines, pesticides, and harmful gases). The sensitive, adsorptive, or catalytic performances of various DMNs have been compared; correspondingly, the reaction mechanisms have been revealed strictly. It is honestly anticipated that the profound discussion could offer scientists certain enlightenment to design novel DMNs-based systems towards the detection, adsorption, and degradation of hazardous substances, respectively or comprehensively.

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.

SARS-Cov-2 Spike-S1 Antigen Test Strip with High Sensitivity Endowed by High-Affinity Antibodies and Brightly Fluorescent QDs/Silica Nanospheres

The extensive research into developing novel strategies for detecting respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in clinical specimens, especially the sensitive point-of-care testing method, is still urgently needed to reach rapid screening of viral infections. Herein, a new lateral flow immunoassay (LFIA) platform was reported for the detection of SARS-CoV-2 spike-S1 protein antigens, in which four sensitive and specific SARS-CoV-2 mouse monoclonal antibodies (MmAbs) were tailored by using quantum dot (QD)-loaded dendritic mesoporous silica nanoparticles modified further for achieving the -COOH group surface coating (named Q/S-COOH nanospheres). Importantly, compact QD adsorption was achieved in mesoporous channels of silica nanoparticles on account of highly accessible central-radial pores and electrostatic interactions, leading to significant signal amplification. As such, a limit of detection for SARS-CoV-2 spike-S1 testing was found to be 0.03 ng/mL, which is lower compared with those of AuNPs-LFIA (traditional colloidal gold nanoparticles, Au NPs) and enzyme-linked immunosorbent assay methods. These results show that optimizing the affinity of antibody and the intensity of fluorescent nanospheres simultaneously is of great significance to improve the sensitivity of LFIA.

Visual Detection of Chicken Adulteration Based on a Lateral Flow Strip-PCR Strategy

The aim of this study was to develop an accurate, easy-to-use, and cost-effective method for the detection of chicken adulteration based on polymerase chain reaction (PCR) and lateral flow strip (LFS). We compared six DNA extraction methods, namely the cetyltrimethylammonium bromide (CTAB) method, salt method, urea method, SDS method, guanidine isothiocyanate method, and commercial kit method. The chicken cytb gene was used as a target to design specific primers. The specificity and sensitivity of the PCR-LFS system were tested using a self-assembled lateral flow measurement sensor. The results showed that the DNA concentration obtained by salt methods is up to 533 ± 84 ng µL⁻¹, is a suitable replacement for commercial kits. The PCR-LFS method exhibits high specificity at an annealing temperature of 62 °C and does not cross-react with other animal sources. This strategy is also highly sensitive, being able to detect 0.1% of chicken in artificial adulterated meat. The results of the test strips can be observed with the naked eye within 5 min, and this result is consistent with the electrophoresis result, demonstrating its high accuracy. Moreover, the detection system has already been successfully used to detect chicken in commercial samples. Hence, this PCR-LFS strategy provides a potential tool to verify the authenticity of chicken.

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.