Lateral flow immunoassay (LFIA) is extensively utilized for point-of-care testing due to its ease of operation, cost-effectiveness, and swift results. This study investigates the flow dynamics and ...reaction mechanisms in LFIA by developing a three-dimensional model using the Richards equation and porous media transport, and employing numerical simulations through the finite element method. The study delves into the transport and diffusion behaviors of each reaction component in both sandwich LFIA and competitive LFIA under non-uniform flow conditions. Additionally, the impact of various parameters (such as reporter particle concentration, initial capture probe concentrations for the T-line and C-line, and reaction rate constants) on LFIA performance is analyzed. The findings reveal that, in sandwich LFIA, optimizing parameters like increasing reporter particle concentration and initial capture probe concentration for the T-line, as well as adjusting reaction rate constants, can effectively enhance detection sensitivity and broaden the working range. Conversely, in competitive LFIA, the effects are inverse. This model offers valuable insights for the design and enhancement of LFIA assays.
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•A simple sensitive photothermal LFIA platform was demonstrated.•Nanoengineering the GNS morphology enables to achieve LSPR in the NIR-II region.•Our optimized GNS (GNS-3) shows ...excellent photothermal efficiency.•A portable device was developed for the PPh-LFIA assay.•GNS-3 demonstrates remarkable photothermal sensitivity in detecting cTnI.
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.
Immunoassay has been routinely used in hospitals and central labs. Nowadays, to further meet the requirement of widespread applications of immunoassays, it is urgently needed to produce a simplified, ...rapid and low-cost immunoassay to perform tests on site. To this end, paper-based point-of-care (POC) immunoassays have attracted intensive interests in recent years. In this paper, we present a comprehensive review of the recent advances and emerging trends of paper-based POC immunoassays, including the fundamental components and work principles, various detection mechanisms and applications, and existing commercialized devices/products. At last, we envision three promising development directions for paper-based POC immunoassays.
•A SERS-based lateral flow assay for the rapid and sensitive detection of COVID-19 was reported for the first time.•A novel SiO2@Ag nanocomposite labeled with dual layers of DTNB was employed as ...high-performance SERS tags.•The SERS-LFIA enables simultaneous detection of anti-SARS-CoV-2 IgM and IgG with high sensitivity.•The analysis results from 68 clinical serum samples revealed the 100 % accuracy and specificity of the SERS-LFIA.
The accurate and rapid screening of serum antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the key to control the spread of 2019 coronavirus disease (COVID-19). In this study, we reported a surface-enhanced Raman scattering-based lateral flow immunoassay (SERS-LFIA) for the simultaneous detection of anti-SARS-CoV-2 IgM/IgG with high sensitivity. Novel SERS tags labeled with dual layers of Raman dye were fabricated by coating a complete Ag shell on SiO2 core (SiO2@Ag) and exhibited excellent SERS signals, good monodispersity, and high stability. Anti-human IgM and IgG were immobilized onto the two test lines of the strip to capture the formed SiO2@Ag-spike (S) protein-anti-SARS-CoV-2 IgM/IgG immunocomplexes. The SERS signal intensities of the IgM and IgG test zones were easily recorded by a portable Raman instrument and used for the high-sensitivity analysis of target IgM and IgG. The limit of detection of SERS-LFIA was 800 times higher than that of standard Au nanoparticle-based LFIA for target IgM and IgG. The SERS-LFIA biosensor was tested on 19 positive serum samples from COVID-19 patients and 49 negative serum samples from healthy people to demonstrate the clinical feasibility of our proposed assay. The results revealed that the proposed method exhibited high accuracy and specificity for patients with SARS-CoV-2 infection.
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•Using gold nanoparticles as gold seeds, a new type of nanomaterial, gold nanostar, was prepared by seed growth. The dendritic structure on the surface of gold nanostars can produce ...stronger Raman signal intensity than gold nanoparticles.•A new type of test strip was developed by combining SERS technology with LFA technology to give full play to their unique advantages, such as high sensitivity, no water interference, strong specificity, obvious Raman characteristic peak, simple operation, stable performance and low cost.•The limit of detection for glycinin was 0.23 ng/mL on immunostrips using gold nanostars as immunoprobes..
Glycinin is one of the most nutritious ingredients in soybean, but it is also an allergen that can cause allergic reactions in humans and animals, and even endanger life in severe cases. Therefore, it is imperative to develop a rapid and ultrasensitive detection method for glycinin. In order to achieve this goal, this experiment combined surface-enhanced Raman spectroscopy (SERS) technology with an economical, simple, fast and easy-to-carry immunochromatographic test strip, and successfully constructed an efficient sandwich immunochromatographic test strip. The immunoprobe of the test strip was covalently coupled by gold nanostars (AuNSs), Raman molecule 4-aminothiophenol (4-PATP) and rabbit polyclonal antibody. In this experiment, a gold nanostar immunochromatographic test strip for detecting glycinin was established. The detection limit of the test strip was 0.23 ng / mL, the recovery rate was 91.5–96.6 %, and the coefficient of variation was 1.61–6.15 %. In addition, the test strip had no cross reaction with whey protein, wheat protein, peanut protein, sesame protein and β-conglycinin, indicating that the detection method had good specificity and the ability to avoid false positive results. Hence, this experiment successfully prepared a rapid and sensitive test strip for glycinin.
Lateral flow immunoassays (LFIAs) have been developed rapidly in recent years and used in a wide range of application at point-of-care-testing (POCT), where small biomolecules can be conveniently ...examined on a test strip. Compared with other biochemical detection methods such as ELISA (enzyme linked immunosorbent assay) or mass spectrometry method, LFIAs have the advantages of low cost, easy operation and short time-consuming. However, it suffers from low sensitivity since conventional LFIA can only realize qualitative detection based on colorimetric signals. With the increasing demand for more accurate and sensitive determination, novel nanomaterials have been used as labels in LFIAs due to their unique advantages in physical and chemical properties. Colloidal gold, fluorescent nanoparticles, SERS-active nanomaterials, magnetic nanoparticles and carbon nanomaterials are utilized in LFIAs to produce different kinds of signals for quantitative or semi-quantitative detection. This review paper first gives a description of the LFIA principles, and then focuses on the state-of-the-art nanomaterial labelling technology in LFIAs. At last, the conclusion and outlook are given to inspire exploration of more advanced nanomaterials for the development of future LFIAs.
A portable surface-enhanced Raman scattering (SERS)-based lateral flow immunoassay (LFIA) reader with multiplexed detection was developed using an integrated LFIA reaction column. The proposed LFIA ...reader was designed to simultaneously detect multiple samples or samples with multiple biomarkers. With the integrated LFIA reaction column, we achieved the specific detection of alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), and prostate-specific antigen (PSA) with a detection limit of 0.01 ng/mL, which was three orders of magnitude lower than that of the visual signal. We also investigated the uniformity of channels based on an eight-channel integrated LFIA reaction column. The relative standard deviation values of the SERS intensity of the eight-channel for measuring the AFP, CEA, and PSA antigens at 1323 cm−1 were 13%, 4.8%, and 5%, respectively. We detected 45 clinical serum samples of the three antigens using the proposed portable SERS-based LFIA reader to further confirm its applicability to clinical samples. The SERS signals of the positive sera were higher than those of the negative sera and their thrice standard deviation. This result indicated the practicality of the developed integrated reaction column and the proposed portable and multiplexed Raman reader. This work provides a new high-sensitivity, multiplexed, and automated SERS-based LFIA detector for use in the point-of-care setting.
•A portable and multiplexed SERS-based lateral flow immunoassay (LFIA) reader integrated with a multichannel LFIA reaction column is developed.•The proposed reader can detect multiple samples or samples with multiple biomarkers and features automation, high sensitivity, and portability.•The sensitivity, specificity and the uniformity of the developed SERS-based LFIA system were investigated in the detection of three cancer markers (AFP, CEA and PSA).•To further confirm its applicability to clinical samples, clinical serum samples of the three cancer markers were detected.•Our work solves the problems encountered in SERS-based LFIA, including the expensive detecting equipment and complicated operation. The results also pave the way for the multiplexed, automated, and high-sensitivity application of the proposed SERS-based LFIA to POCT.
The rapid and accurate diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the early stage of virus infection can effectively prevent the spread of the virus and control the ...epidemic. Here, a colorimetric and fluorescent dual-functional lateral flow immunoassay (LFIA) biosensor was developed for the rapid and sensitive detection of spike 1 (S1) protein of SARS-CoV-2. A novel dual-functional immune label was fabricated by coating a single-layer shell formed by mixing 20 nm Au nanoparticles (Au NPs) and quantum dots (QDs) on SiO2 core to produce strong colorimetric and fluorescence signals and ensure good monodispersity and high stability. The colorimetric signal was used for visual detection and rapid screening of suspected SARS-CoV-2 infection on sites. The fluorescence signal was utilized for sensitive and quantitative detection of virus infection at the early stage. The detection limits of detecting S1 protein via colorimetric and fluorescence functions of the biosensor were 1 and 0.033 ng/mL, respectively. Furthermore, we evaluated the performance of the biosensor for analyzing real samples. The novel biosensor developed herein had good repeatability, specificity and accuracy, which showed great potential as a tool for rapidly detecting SARS-CoV-2.
•The composite nanospheres with colorimetric and fluorescent dual-functional and excellent stability was synthesized.•The sensitivity of the colorimetric signal and the fluorescence signal of the SiO2@Au/QDs-based LFIA strip was 10-fold and 300-fold higher than those of Au-based LFIA strip, respectively.•The novel biosensor for rapid antigen detection demonstrated excellent specificity and reproducibility, RSD< 7.16%.•The LOD of the novel LFIA biosensor for the inactivated SARS-CoV-2 virus could reach 1.02 × 104 copies/mL.•A dual-functional platform for rapid and sensitive detection of SARS-CoV-2 spike 1 protein in the field was established. The proposed LFIA system could be applied to detect other pathogens.
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•A lateral flow immunoassay (LFIA) was developed based on the obtained specific paraquat monoclonal antibody.•Herbicide products were tested after PBS dilution without other sample ...pretreatments.•Dipstick has been used to screen the illegal usage of paraquat in adulterated herbicides on-site.
The use of the herbicide paraquat has been banned in many countries due to its high toxicity. However, there is an issue that illegal addition of paraquat in herbicide products. Therefore, a rapid, sensitive, and portable method will be useful to detect paraquat in adulterated herbicides for regulation purpose.
In the present study, an indirect competition enzyme-linked immunosorbent assay (icELISA) was developed with a new paraquat-specific monoclonal antibody (mAb) for paraquat detection. The icELISA results showed a 50% inhibitory concentration (IC50) of 7.63 ng/mL with a working range (IC20-IC80) of 1.68–33.1 ng/mL. In addition, a lateral flow immunoassay (LFIA) with a cut-off value of 20.0 ng/mL was also developed. The LFIA showed no detection of the herbicides diquat, glyphosate and glufosinate up to 50 µg/mL. Nine herbicide samples were collected across Hainan province, China and analyzed by the LFIA dipsticks. One out of the nine samples was tested positive, which was confirmed with icELISA and HPLC. The accuracy of the LFIA was further verified through onsite tests in different places in China. Forty-seven commercial herbicide products were tested via the LFIA dipsticks, of which 9 samples were positive and confirmed with HPLC analysis.
The paraquat LFIA exhibited the most promising potential as the point of care (POC) device for the rapid screening of paraquat in adulterated herbicide products.
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