Lateral flow immunoassay (LFIA) based on color enzymes can amplify the color signal after catalyzing the substrate. In an article published in the journal Analytical Chemistry, researchers applied vanadium disulfide nanosheet (VS2NS) as a label for the LFIA enzyme to detect 17β-estradiol (E2) and improve LFIA testing.
Study: Vanadium disulfide nanosheet increases the brightness of the optical signal as a superior enzymatic label to improve the sensitivity of the lateral flow immunoassay. Image credit: Ian Gessey / Shutterstock.com
They observed more outstanding enzymatic catalytic yield in VS2NS than natural horseradish peroxidase (HRP).
Nanomaterials at LFIA
LFIA is widely used in the food industry, medical diagnosis, genotype analysis and environmental monitoring. Although colloidal nanoparticles (NPs) are widely used in LFIAs, further exploration is required to address the need for rapid signal detection and amplification. To this end, enzyme-catalyzed LFIA offers great potential to extend the detection range and amplify the color signal. However, natural enzymes are colorless, so they require a nanocarrier to serve as a signal tag.
Layered transition metal dicalcogenide (TMD) materials have recently gained considerable interest in the nonlinear optical field due to their broadband gap, ultrafast carrier dynamics, and third-order optical nonlinear polarization. . TMD can also serve as two-dimensional (2D) nanozymes due to its unique surface and exposed active sites, which enhances its catalytic activity. VS2NS is a common TMD material with peroxidase-like activity and a higher adsorption capacity than HRP.
Double signal LFIA for E2 detection
In the present study, researchers addressed bottleneck problems in natural enzyme-based LFIAs. They introduced VS2NS as an enzymatic label to obtain a dual LFIA signal. E2 is widely used in poultry farming and livestock and its residual amounts in the environment enter the food chain, eventually affecting the male reproductive system.
In this work, the researchers chose E2 as the model analyte for accurate detection. In addition, VS2NS with all favorable properties was expected to have high performance as an LFIA enzyme tag. Aggregation of VS2NS-labeled probes induced a different optical signal due to their movement toward the immobilized antigen at the test line (T). In addition, the addition of 3.3 ‘, 5,5’-tetramethylbenzidine (TMB) hydrogen peroxide (H2O2) solution induced peroxidase-like activity in VS2NS, which caused oxidation. of the TMB substrate and the production of blue enzyme catalysis signals.
Research results
VS2NS was prepared by a modified thermothermal method. The team used a green liquid exfoliation method to make an ultra-thin VS2NS. Scanning electron microscopy (SEM) images revealed that the precursor, VS2 · NH3 had a laminar morphology, and was exfoliated in VS2NS less than 1 micrometer in size after being subjected to ultrasound for half an hour and a size less than of 200 nanometers after submitting them. on ultrasound for 2 hours, suggesting the suitability of VS2NS for hair strength. Tapping mode atomic force microscopy (AFM) revealed the thickness of VS2NS, which was less than 5 nanometers.
The X-ray diffraction (XRD) spectrum obtained for VS2NS showed characteristic peaks that matched standard VS2NS. Ultraviolet-visible (UV-vis) absorption showed that VS2NS oxidized TMB in a blue oxidation product with an absorption peak at 650 nanometers in the presence of hydrogen peroxide (H2O2). In contrast, TMB did not oxidize in the absence of VS2NS, as can be deduced from the solution which remained colorless, suggesting VS2NS peroxidase-like activity. VS2NS-catalyzed H2O2 decomposition results in the generation of hydroxyl (• OH) free radicals that oxidize the TMB substrate to a blue product. The researchers showed that low-dimensional VS2NS had higher catalytic activity than bulk VS2. Enhanced catalytic activity of VS2NS is attributed to reduced screening effects in single-layer monolayer structures leading to enhanced Coulomb interactions.
E2-BSA captured the VS2 monoclonal antibody (mAb) probes, after adding them to the solution, resulting in black formation at the T line, which was derived from the captured VS2-mAb probes. by the T line due to specific interactions. between E2-BSA and antibodies. However, the addition of VS2NS did not show the black color in the LFIA. VS2NS-mAb probes were formed by modifying the purified anti-E2 mAb on the VS2NS surface by electrostatic interactions.
The infrared Fourier transform (FTIR) spectra of the VS2NS showed characteristic peaks between 400-1000 centimeters inverse and peaks between 500−690 and 978 centimeters inverse corroborate the VSV and VS stretching vibrations. In addition, the peaks corresponding to amide I and amide II of the antibody polypeptide chain appeared at 1500 and 1700 cm inverse, respectively.
In summary, the researchers exploited a low-layer VS2NS-based LFIA with strong adsorption capacity and a large surface-to-volume ratio. These VS2NS properties illuminated the signal and improved detection sensitivity. Thus, VS2NS peroxidase-like higher activity helps amplify the label signal.
Reference
Chen, Y., Ren, J., Yin, X., Li, Y., Shu, R., Wang, J. and Zhang, D., (2022) Vanadium disulfide nanosheet increases the brightness of the optical signal as to top enzyme label to improve the sensitivity of the lateral flow immunoassay. Analytical Chemistry,. https://pubs.acs.org/doi/10.1021/acs.analchem.2c01008
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