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

Multifunctional metal-organic frameworks-mediated colorimetric/photothermal immunosensor for highly sensitivity detection of dibutyl phthalate

Dibutyl phthalate (DBP), a priority pollutant among phthalic acid esters (PAEs) exhibits significant reproductive and respiratory toxicity. In this study, a multifunctional metal-organic frameworks-mediated colorimetric/photothermal immunosensor was established for the quantitative detection of DBP. Firstly, a highly sensitive and specific monoclonal antibody (mAb), designated 3A5, was prepared with a sensitivity IC50 value of 16.29 ng/mL. Secondly, a metal-organic framework material (ZrO₂@C) was synthesized via a two-step pyrolysis process of UiO-66. Subsequently, a multifunctional immunoprobe was prepared for the detection of DBP. Using ZrO₂@C-based colorimetric and photothermal dual-signal immunosensor ensured the accuracy of the detection results, as the multiple of these signals effectively guaranteed the reliability of the results. The limit of detection (LOD) for the dual signal was 0.766 ng/mL (colorimetric signal) and 0.465 ng/mL (photothermal signal). In conclusion, this work presented a novel and feasible approach for the development of multifunctional nanomaterials for the fabrication of immunosensors.

Ultrasensitive Love-SAW Biosensor Based on Self-Assembled DMSN@AuNPs with In Situ Amplification for Detecting Biomarker Procalcitonin in Exhaled Breath Condensate

The COVID-19 pandemic has highlighted the importance of early screening and pathogen identification for the effective treatment of pneumonia. Exhaled breath condensate (EBC) provides a noninvasive and easily accessible method for early diagnosis of respiratory diseases, as it captures biomarkers from the airway lining fluid, offering a timely and reliable reflection of respiratory inflammation. Procalcitonin (PCT) is a biomarker widely used to assess infection type and severity, particularly for distinguishing between bacterial and nonbacterial pneumonia. However, detecting PCT especially in EBC is challenging due to its extremely low concentrations. In this work, we developed an ultrasensitive Love-type surface acoustic wave (Love-SAW) biosensor based on self-assembled gold nanoparticles on dendritic mesoporous silica nanoparticles (DMSN@AuNPs) with in situ amplification for PCT detection in EBC. Dendritic mesoporous silica nanoparticles (DMSNs), an emerging porous material with features of large surface area, high thermal stability, and ease of functionalization were employed to load a large amount of AuNPs that can spontaneously grow in situ to further enhance the sensing performance. An automatic detection system was also developed to integrate with the Love-SAW biosensor for multichannel detection of PCT in EBC for pneumonia screening. The DMSN@AuNPs based Love-SAW biosensor demonstrates remarkable performance with a detection range of 0.01-10 ng/mL and detection limit of 3.7 pg/mL, which is about 350 times higher than conventional AuNPs-based methods. These results validate the potential of DMSN@AuNPs based Love-SAW biosensors for ultrasensitive detection of low-concentration biomarkers, providing a promising platform for in vitro diagnostics.

Enhancing lateral flow immunoassay performance for cardiac troponin I detection with pore-size tailored silica nanoparticles and smartphone-based "AdaptiScan" analysis

The accurate and rapid detection of cardiac troponin I (cTnI) at the point of care is crucial for the timely diagnosis of myocardial infarction (MI). This study introduces an advanced lateral flow immunoassay (LFIA) platform for cTnI detection. We employed small-sized, large-pore dendritic mesoporous silica nanoparticles (DMSN-2) to encapsulate quantum dots (QDs), achieving an enhanced QD loading capacity of 1.427 g QD/g silica, compared to 0.881 g QD/g silica for smaller pore counterparts (DMSN-1). This nano-LFIA was further integrated with "AdaptiScan", a smartphone-based detection system that uses adaptive detection algorithms to automatically extract and analyze fluorescence signals from LFIA strips. This integration of pore-size tailored DMSNs and "AdaptiScan" resulted in a limit of detection for cTnI of 42.6 ng/L, which meets clinical diagnostic requirements. The platform offers a sensitive, cost-effective, and portable solution for rapid detection of MI, potentially transforming point-of-care testing in resource-limited settings.

AIE nanoparticle with enhanced fluorescence for ultrasensitive lateral flow immunoassays and point-of-care diagnosis of interstitial lung disease

Krebs von den Lungen-6 (KL-6) has been recognized as an effective serum biomarker for interstitial lung disease (ILD). The KL-6 accurate detection is of great significance for evaluating the severity of ILD and the prognosis of patients. In this study, a bright aggregation-induced emission luminogen (AIEgen) N, N'-((1,2-diphenylethene-1,2-diyl)bis(4,1-phenylene))bis(N-phenylnaphthalen-1-amine) (TPETN) with a high quantum yield of 87.57% was designed and synthesized, which was subsequently encapsulated into polystyrene nanoparticles (PSNPs) for construction of ultrahigh fluorescent nanoparticle (TPNPs). The obtained TPNPs was found to be 128 times and 16 times higher sensitivity than traditional gold nanoparticles (AuNPs) and tetramethyl 4',4''',4''''',4'''''''-(ethene-1,1,2,2-tetrayl) tetrakis([1,1'-biphenyl]-4-carboxylate) (TCBPE) embedded nanoparticles (TCNPs), respectively. Then, TPNPs were employed as signal output to construct a lateral flow immunoassay platform (TPNP-LFIA) for KL-6 detection. TPNP-LFIA achieved a limit of detection (LOD) of 0.0534 ng/mL, which was 77.15 times and 7.69 times lower than those of AuNP- and TCNP- based LFIA, respectively. The dynamic linearity of TPNP-LFIA for detecting KL-6 ranged from 0.15 to 333.33 ng/mL. The recovery rates of TPNP-LFIA in serum samples varied from 99.96% to 108.13%, with coefficients of variation ≤6.24%. Hence, TPNP-LFIA has promising potential as a rapid and quantitative method for detecting KL-6.

Nanolabels for biosensors based on lateral flow immunoassays

The COVID-19 outbreak was an important turning point in the development of a new generation of biosensing technologies. The synergistic combination of an immunochromatographic test (lateral flow immunoassays, LFIA) and signal transducers provides enhanced sensitivity and the ability to quantify in the rapid tests. This is possible due to the variety of nanoparticles that can be used as reporter labels. In this review, we first present an overview on the principles of a LFIA and its different formats. We analyze cutting-edge work on these platforms based on different types of nanoparticles used as labels and on the highly sensitive transducers to which they can be coupled. The works discussed herein have a beneficial impact on the fields of clinical analysis, food safety or environmental control, thus highlighting the relevance of the biosensors. Last, we provide insights into the barriers that need to be overcome when designing laboratory prototypes accessible to the society.

One-step copper deposition-induced signal amplification for multiplex bacterial infection diagnosis on a lateral flow immunoassay device

The lateral flow immunoassay (LFIA) is predominant in rapid diagnostic tests owing to its cost-effectiveness and operational simplicity. However, the conventional LFIA exhibits limited sensitivity and is susceptible to human variance for the result readout, impacting result interpretation. In this study, we introduced a novel one-step copper deposition-induced signal amplification lateral flow immunoassay (osa-LFIA) that markedly enhances the detection sensitivity for Staphylococcus aureus (protein A) and Pseudomonas aeruginosa (exotoxin A). Utilizing gold nanoparticles (AuNPs) as a catalyst, this approach employs ascorbic acid to reduce Cu2+ to Cu0, depositing on AuNPs at the test line and amplifying the signal. A user-friendly design features a three-dimensional paper structure incorporating pre-dried reagents, enabling a streamlined, efficient testing process. The osa-LFIA significantly lowers detection limits to 3 ng mL-1 for protein A and 10 ng mL-1 for exotoxin A, offering a tenfold improvement over conventional LFIA. Additionally, we developed a portable grayscale detection device, achieving less than 10% error in quantitative analysis compared to the data acquired and analyzed in the lab. This entire process, from detection to signal amplification, is completed in just 20 min. For the clinical trial, we utilized the osa-LFIA to test synovial fluid samples infected with Staphylococcus aureus. We also successfully detected different concentrations of the exotoxin A in parallel, with a recovery value of 96%-110%. Our findings demonstrate the osa-LFIA's potential as a rapid, highly sensitive, and simple-to-use diagnostic tool for detecting various pathogens, significantly advancing the field of rapid diagnostic testing.

Dendritic mesoporous silica loaded with gold nanoclusters and their application in immunochromatographic assay

Novel green-emitting fluorescent microspheres (GreFMPs) were assembled by loading highly luminescent gold nanoclusters (Arg/ATT/AuNCs) on dendritic mesoporous silica nanoparticles (DMSNs) via PEI-mediated electrostatic adsorption. The fluorescence microspheres  exhibit excellent monodispersion with average diameters about (254.5 ± 34.6 nm). Compared with free Arg/ATT/AuNCs, the GreFMPs have similar fluorescent properties and biocompatibility but superior environmental tolerance. Subsequently, an immunochromatographic assay based on GreFMPs (GreFMP-ICA) has been successfully developed, which is highly selective toward alpha fetoprotein (AFP) in human serum. Under the optimal parameters, there is a good linear range between 0.5 and 160.0 ng/mL, the limit of detection was found to be about 0.5 ng/mL, and the recovery and relative standard deviation are 81.0 ~ 100.6% and 3.5 ~ 16.6%, respectively. These results manifested that the GreFMPs are beneficial for the rational design of the ICA platform, and the proposed GreFMP-ICA has the potential to screen AFP in clinical applications.

Signal-Boosted Electrochemical Lateral Flow Immunoassay for Early Point-of-Care Detection of Liver Cancer Biomarker

The early diagnosis of cancer in a point-of-need manner is of great significance, yet it remains challenging to achieve the necessary sensitivity and speed. Traditional lateral flow immunoassay (LFIA) methods are limited in accuracy and quantification, restricting their suitability for home-based applications. Thus, we explored a new and user-friendly electrochemical LFIA (e-LFIA) test strip to detect α-fetoprotein (AFP), a diagnostic marker for liver cancer. The specific electrochemical immunoprobe utilized in this e-LFIA test strip is characterized by significant signal boosting, resulted from the loading Ag shell into a gold nanoparticle (AuNP)-coated dendritic mesoporous silica nanoscaffold (DMSN). Leveraging the distinct electrochemical characteristics of Ag anodic stripping and the high volume-to-surface area ratio of DMSNs, the developed DMSNs/AuNPs@Ag-based e-LFIA test strip is capable of detecting AFP at a low concentration of 0.85 ng/mL within a rapid 20 min timespan, both of these values are smaller than those in current clinical testing. Furthermore, we utilized homemade screen-printed electrodes in this sensing prototype and demonstrated the high versatility and reliability of this e-LFIA device. We envision that this DMSNs/AuNPs@Ag-based e-LFIA holds substantial potential for the early diagnosis of liver cancer and household health monitoring.

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.