Highly uniform self-assembled monolayers of silver nanospheres for the sensitive and quantitative detection of glutathione by SERS

Effects on molecular interactions of hollow gold nanoparticles and antibody for sensitizing P24 antigen determination

In recent years, with the rapid development of point-of-care testing, the application of lateral flow immunochromatography assay (LFIA) has become increasingly widespread. The key to the success of these detection technologies is the effective binding with diagnostic materials and detection antibody proteins. Although many researchers have tried to optimize antibody binding, a universally accepted strategy that can provide maximum performance has not been determined. In this study, the HIV infection P24 antigen was selected as the detection biomarker. Then the binding mechanism between hollow gold nanoparticles as diagnostic materials and detection antibodies was explored through dynamic light scattering, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, and other methods. It was found that the binding efficiency is related to the change in protein secondary conformation during binding, hydrogen bonding, and van der Waals force maintain the binding mechanism between antibodies and nanoparticles. The main forces of particle complexation and the main binding site of the antibody were discussed and analyzed. Finally, an immunochromatographic system was constructed to evaluate the significant advantages of this platform compared to the common colloidal gold immunochromatographic system.

Multicolor detection of glutathione by manganese dioxide nanosheets and gold nanotetrapods based on an anti-etching mechanism

Glutathione (GSH) is a crucial non-protein thiol and an indispensable endogenous antioxidant. The aberrant expression of GSH in plasma and cytosol is closely related to numerous diseases, including cancer. Therefore, establishing a sensitive method for analyzing GSH has important application value for biomedical research and clinical medical detection. Herein, A method for the rapid and simple detection of GSH was proposed, which is based on an anti-etching mechanism by utilizing gold nanotetrapods (Au NTPs) and manganese dioxide nanosheets (MnO2 NSs). In the absence of GSH, Au NTPs solution can cause a distinct color change from gray-green to red through the etching effect of MnO2 NSs. However, in the presence of GSH, the redox reaction between GSH and MnO2 NSs inhibits the etching of Au NTPs by MnO2 NSs, and Au NTPs solution maintains persistent gray-green color. The colorimetric probe exhibited excellent selectivity for GSH. The limits of detection for GSH were 43.5 nM (UV-vis spectrum) and 0.25 μM (naked eyes). The sensing technique exhibited excellent linearity between wavelength shift and GSH concentration within the range of 0.25 μM-1.5 μM. The outcomes of GSH detection in actual biological samples demonstrate that this probe has the potential to be applied to GSH detection in intricate biological samples.

SERS Determination of Oxidative Stress Markers in Saliva Using Substrates with Silver Nanoparticle-Decorated Silicon Nanowires

Glutathione and malondialdehyde are two compounds commonly used to evaluate the oxidative stress status of an organism. Although their determination is usually performed in blood serum, saliva is gaining ground as the biological fluid of choice for oxidative stress determination at the point of need. For this purpose, surface-enhanced Raman spectroscopy (SERS), which is a highly sensitive method for the detection of biomolecules, could offer additional advantages regarding the analysis of biological fluids at the point of need. In this work, silicon nanowires decorated with silver nanoparticles made by metal-assisted chemical etching were evaluated as substrates for the SERS determination of glutathione and malondialdehyde in water and saliva. In particular, glutathione was determined by monitoring the reduction in the Raman signal obtained from substrates modified with crystal violet upon incubation with aqueous glutathione solutions. On the other hand, malondialdehyde was detected after a reaction with thiobarbituric acid to produce a derivative with a strong Raman signal. The detection limits achieved after optimization of several assay parameters were 50 and 3.2 nM for aqueous solutions of glutathione and malondialdehyde, respectively. In artificial saliva, however, the detection limits were 2.0 and 0.32 μM for glutathione and malondialdehyde, respectively, which are, nonetheless, adequate for the determination of these two markers in saliva.

Surface Filtration in Mesoporous Au Films Decorated by Ag Nanoparticles for Solving SERS Sensing Small Molecules in Living Cells

For surface-enhanced Raman spectroscopy (SERS) sensing of small molecules in the presence of living cells, biofouling and blocking of plasmonic centers are key challenges. Here, we have developed a mesoporous Au (AuM) film coated with a Ag nanoparticles (NPs) as a plasmonic sensor (AuM@Ag) to analyze aromatic thiols, which is an example of a small molecule, in the presence of a living cell strain (e.g., MDA-MB-231) as a model living system. The resulting AuM@Ag provides 0.1 nM sensitivity and high reproducibility for thiols sensing. Simultaneously, the AuM@Ag film filters large biomolecules, preventing Raman signals from overlapping produced by large biomolecules. After analysis, the AuM@Ag film undergoes recycling by the full dissolution of the Ag-thiol layer and removal of thiols from AuM. Furthermore, fresh AgNPs are formed for further SERS analysis, which circumvents the Ag oxidation issue. The ease of the AgNPs deposition allows up to 12 cycles of on-demand recycling and sensing even after utilization as a sensor in multicomponent media without enhancement and sensitivity loss. The reported mesoporous film with surface filtering ability and prominent recycling procedure promises to offer a new strategy for the detection of various small molecules in the presence of living cells.