Smartphone-assisted colorimetric detection of Salmonella typhimurium based on the catalytic reduction of 4-nitrophenol by ß-cyclodextrin-capped gold nanoparticles.

Salmonella typhimurium (S. typhimurium) is one of the most common pathogens in the environment, such as in drinking water and soil. Herein, an on-site detection method was developed by combining silver-coated magnetic nanoparticles (Fe3O4@Ag NPs) with the ß-cyclodextrin-capped gold nanoparticles (ß-CD-Au NPs) to achieve sensitive detection of S. typhimurium. After they formed a sandwich structure in the presence of S. typhimurium, the 4-nitrophenol was reduced to 4-aminophenol based on the nitro-reductase activity of ß-CD-Au NPs. The naked eyes were able to observe the color change from yellow to colorless. Under optimal conditions, the detection range of S. typhimurium was 10-107 CFU mL-1, and the limit of detection (LOD) was 10 CFU mL-1. The total detection time was 90 min, showing satisfactory performance in real samples. We combined a smartphone app with the colorimetric method, making it possible to semi-quantitatively detect S. typhimurium by analyzing the grey value. In conclusion, this assay detects S. typhimurium in environmental samples, offering an accurate and sensitive detection method without sophisticated equipment.

On-site colorimetric detection of Salmonella typhimurium.

Rapid qualitative and quantitative detection of Salmonella typhimurium (S. typhimurium) takes an important role in ensuring food safety. Herein, a colorimetric assay aptasensor for S. typhimurium utilizing intrinsic peroxidase-like activity of gold nanoparticles embedded spherical covalent organic framework and the affinity and specificity of S. typhimurium-aptamer has been explored. This aptasensor can capture the S. typhimurium via the selective binding effect of aptamer, and the catalytically active sites were shielded. As a result, the colorimetric signals of the 3,3',5,5'-tetramethylbenzidine-H2O2 system were turned off. Under optimum conditions, the aptasensor gave a linear response over the range of 10 to 107 CFU/mL for S. typhimurium. The detection limit of 7 CFU/mL was obtained within 45 min and was effectively applied to detect S. typhimurium in milk and lake water samples with recoveries in the range from 96.4 to 101.0%. More importantly, combined with a self-developed smartphone-based image analysis system, the proposed aptasensor can be used for point-of-care testing applications.

Colorimetric detection of Salmonella typhimurium based on hexadecyl trimethyl ammonium bromide-induced supramolecular assembly of ß-cyclodextrin-capped gold nanoparticles.

We developed an effective and specific colorimetric strategy to detect Salmonella typhimurium (S. typhimurium) based on hexadecyl trimethyl ammonium bromide (CTAB)-induced supramolecular assembly of ß-cyclodextrin-capped gold nanoparticles (ß-CD-AuNPs). In this study, ssDNA aptamer of S. typhimurium could combine with CTAB to form the supramolecular ssDNA-CTAB composite, so the ssDNA aptamer was applied to control the concentration of CTAB. In the presence of S. typhimurium, ssDNA aptamers selectively bound to S. typhimurium but not to CTAB, leading to the host-guest chemistry reaction of CTAB and ß-CD resulting in ß-CD-AuNP supramolecular assembly aggregation with an obvious color change. The ratio of absorption at 650 and 520 nm (A650nm/A520nm) has a linear correlation to the log scale of the concentration of the bacteria (1 × 102-1 × 107 CFU/mL) with a low limit of detection (LOD) of 13 CFU/mL. In addition, this optical sensor has good selectivity and practicability. In milk samples, the recovery was 93.55-111.32%, which suggested its potential application in real samples.

Promising application of polyoxometalates in the treatment of cancer, infectious diseases and Alzheimer's disease.

As shown in studies conducted in recent decades, polyoxometalates (POMs), as inorganic metal oxides, have promising biological activities, including antitumor, anti-infectious and anti-Alzheimer's activities, due to their special structures and properties. However, some side effects impede their clinical applications to a certain extent. Compared with unmodified POMs, POM-based inorganic-organic hybrids and POM-based nanocomposite structures show significantly enhanced bioactivity and reduced side effects. In this review, we introduce the biological activities of POMs and their derivatives and highlight the side effects of POMs on normal cells and organisms and their possible mechanisms of action. We then propose a development direction for overcoming their side effects. POMs are expected to constitute a new generation of inorganic metal drugs for the treatment of cancer, infectious diseases, and Alzheimer's disease.Graphical abstract.

Multi-functional magnetic molecular imprinting probe for visual detection of IgY antibodies.

Egg yolk antibodies (IgY) are an alternative to mammalian antibodies, which have been successfully applied in treatment of disease, as immunochemical reagents and as food additives. A fast, accurate, and easy-to-operate detection method for IgY antibodies is needed. Herein, we developed a rapid and cost-effective colorimetric assay for the ultrasensitive detection of anti-S. aureus IgY antibodies using multi-functional magnetic molecularly imprinted polymers (MMIPs). The prepared MMIPs can recognize, adsorb, and separate the analyte from the matrix efficiently, and oxidize TMB to generate a colorimetric signal within ~ 60 min. As low as 0.013 mg·mL-1 was able to be detected by using this method. The visual detection limit reached 0.02 mg·mL-1. By testing the IgY in milk samples, the feasibility was verified.