Gold-silver alloy hollow nanoshells-based lateral flow immunoassay for colorimetric, photothermal, and SERS tri-mode detection of SARS-CoV-2 neutralizing antibody.

Although many approaches have been developed for the quick assessment of SARS-CoV-2 infection, few of them are devoted to the detection of the neutralizing antibody, which is essential for assessing the effectiveness of vaccines. Herein, we developed a tri-mode lateral flow immunoassay (LFIA) platform based on gold-silver alloy hollow nanoshells (Au-Ag HNSs) for the sensitive and accurate quantification of neutralizing antibodies. By tuning the shell-to-core ratio, the surface plasmon resonance (SPR) absorption band of the Au-Ag HNSs is located within the near infrared (NIR) region, endowing them with an excellent photothermal effect under the irradiation of optical maser at 808 nm. Further, the Raman reporter molecule 4-mercaptobenzoic acid (MBA) was immobilized on the gold-silver alloy nanoshell to obtain an enhanced SERS signal. Thus, these Au-Ag HNSs could provide colorimetric, photothermal and SERS signals, with which, tri-mode strips for SARS-CoV-2 neutralizing antibody detection were constructed by competitive immunoassay. Since these three kinds of signals could complement one another, a more accurate detection was achieved. The tri-mode LFIA achieved a quantitative detection with detection limit of 20 ng/mL. Moreover, it also successfully detected the serum samples from 98 vaccinated volunteers with 79 positive results, exhibiting great application value in neutralizing antibody detection.

Colorimetric and Raman dual-mode lateral flow immunoassay detection of SARS-CoV-2 N protein antibody based on Ag nanoparticles with ultrathin Au shell assembled onto Fe3O4 nanoparticles.

Serological antibody tests are useful complements of nuclei acid detection for SARS-CoV-2 diagnosis, which can significantly improve diagnostic accuracy. However, antibody detection in serum or plasma remains challenging to do with high sensitivity. In this study, Ag nanoparticles with ultra-thin Au shells embedded with 4-mercaptobenzoic acid (MBA) (AgMBA@Au) were manufactured and then assembled onto Fe3O4 surface by electrostatic interaction to construct the Fe3O4-AgMBA@Au nanoparticles (NPs) with magnetic-Raman-colorimetric properties. Based on the composite nanoparticles, a colorimetric and Raman dual-mode lateral flow immunoassay (LFIA) for ultrasensitive identification of SARS-CoV-2 nucleocapsid (N) protein antibody was constructed. The magnetic nanoparticles (Fe3O4 NPs) were acted as the core and coated a layer of AgMBA@Au particles on the surface by electrostatic interaction to prepare Fe3O4-AgMBA@Au NPs, which can amplify the SERS signal due to multiple AgMBA@Au particles concentrated on a single magnetic nanoparticle. Moreover, the Fe3O4-AgMBA@Au NPs facilitated pre-purifying sample using magnetic separation, and complex matrix interference would be greatly decreased in the detection. The Fe3O4-AgMBA@Au NPs modified with N protein recognized and bound with N protein antibodies, which were trapped on the T-line, forming color band for observing detection. Under optimal conditions, the N protein antibodies could be qualitatively detected in colorimetric mode with the visual limit of 10-8 mg/mL and quantitatively detected by SERS signals between 10-6 and 10-10 mg /mL with 0.08 pg/mL detection limit. The coefficients variations (CV) of intra-assay was 8.0%, whereas of inter-assay was 11.7%, confirming of good reproducibility. Finally, this approach was able to discriminate between positive, negative, and weakly positive samples when detecting 107 clinical serum samples. The process enables highly sensitive quantitative assays that are valuable for evaluating disease processes and guiding treatment. Colorimetric and Raman dual-mode LFIA detection of SARS-CoV-2 N protein antibody based on Fe3O4-AgMBA@Au nanoparticles.

Ag Nanoparticles with Ultrathin Au Shell-Based Lateral Flow Immunoassay for Colorimetric and SERS Dual-Mode Detection of SARS-CoV-2 IgG.

Immunoglobulin detection is essential for diagnosing progression of SARS-CoV-2 infection, for which SARS-CoV-2 IgG is one of the most important indexes. In this paper, Ag nanoparticles with ultrathin Au shells (∼2 nm) embedded with 4-mercaptobenzoic acid (MBA) (AgMBA@Au) were manufactured via a ligand-assisted epitaxial growth method and integrated into lateral flow immunoassay (LFIA) for colorimetric and SERS dual-mode detection of SARS-CoV-2 IgG. AgMBA@Au possessed not only the surface chemistry advantages of Au but also the superior optical characteristics of Ag. Moreover, the nanogap between the Ag core and the Au shell also greatly enhanced the Raman signal. After being modified with anti-human antibodies, AgMBA@Au recognized and combined with SARS-CoV-2 IgG, which was captured by the SARS-CoV-2 spike protein on the T line. Qualitative analysis was achieved by visually observing the color of the T line, and quantitative analysis was conducted by measuring the SERS signal with a sensitivity four orders of magnitude higher (detection limit: 0.22 pg/mL). The intra-assay and inter-assay variation coefficients were 7.7 and 10.3%, respectively, and other proteins at concentrations of 10 to 20 times higher than those of SARS-CoV-2 IgG could hardly produce distinguishable signals, confirming good reproducibility and specificity. Finally, this method was used to detect 107 clinical serum samples. The results agreed well with those obtained from enzyme-linked immunosorbent assay kits and were significantly better than those of the colloidal gold test strips. Therefore, this dual-mode LFIA has great potential in clinical practical applications and can be used to screen and trace the early immune response of SARS-CoV-2.

Au-Fe3O4 heterodimer multifunctional nanoparticles-based platform for ultrasensitive naked-eye detection of Salmonella typhimurium.

In this work, we developed an ultrasensitive colorimetry for Salmonella typhimurium detection with multifunctional Au-Fe3O4 dumbbell-like nanoparticles (DBNPs) which possessed easy bio-modifiability, excellent LSPR characteristics, superparamagnetic properties and super peroxidase-like activity. In the detection, the anti-S. typhimurium antibody modified DBNPs (IDBNPs) bound with S. typhimurium and aggregated on their surfaces in a large number, which showed much quicker magnetic response than free IDBNPs. By controlling appropriate separation conditions, IDBNPs@S. typhimurium composites were captured, while free IDBNPs were remained in the supernatant. Therefore, by detecting the absorbance of the supernatant, quantitative detection was achieved from 10 to 1000 CFU/mL. Moreover, utilizing the peroxidase-like activity of IDBNPs, we further realized semi-quantitative naked-eye detection. By adding ABTS into the above supernatant, which was oxidized to green chelate (OxABTS), colorimetric signal was amplified significantly, and meanwhile, the green chelates and the wine-red IDBNPs engendered mixed color, enhancing the range of color gradation and greatly improving the visual resolution. Finally, a detection limit (10 CFU/mL) comparable with that of above spectrum measurement was achieved. Besides, our method exhibited efficient capture capability (nearly 100% even for rare S. typhimurium), and had good stability and specificity, and acceptable anti-interference ability in fetal bovine serum and milk samples.

Risk Assessment of Deep Venous Thrombosis and Its Influencing Factors in Burn Patients.

The objective of this study is to explore the relevant risk factors of deep venous thrombosis (DVT) in burn patients. A retrospective analysis was conducted for the medical records of 845 hospitalized burn patients from September 2012 to August 2017. Caprini thrombosis risk assessment scale (CTRAS) was employed for evaluating the risks of DVT. Based upon whether or not DVT occurred, they were divided into non-DVT group (n = 830) and DVT group (n = 15). Among 360 (42.7%) patients with high-risk Caprini scores, only 30 patients received color Doppler examination of lower limb veins, and 15 patients were diagnosed as DVT with a diagnostic rate of 1.8%. Caprini scores of non-DVT and DVT groups were 4.30 ± 2.71 and 9.87 ± 1.46 points, respectively. There was statistically significant difference (P < .05). As revealed by stepwise Logistic regression analysis, age, lower limb burn, wound infection, femoral vein catheterization, and long bedriddening time (>40 days) were independent risk factors for DVT. Burn patients are particularly prone to develop DVT. Age, wound infection, femoral vein catheterization, and long bedriddening time (>40 days) are risk factors. Aggressive preventive measures of DVT should be implemented.