One-step silver coating of polypropylene surgical mask with antibacterial and antiviral properties

Face masks can filter droplets containing viruses and bacteria minimizing the transmission and spread of respiratory pathogens but are also an indirect source of microbes transmission. A novel antibacterial and antiviral Ag-coated polypropylene surgical mask obtained through the in situ and one-step deposition of metallic silver nanoparticles, synthesized by silver mirror reaction combined with sonication or agitation methods, is proposed in this study. SEM analysis shows Ag nanoparticles fused together in a continuous and dense layer for the coating obtained by sonication, whereas individual Ag nanoparticles around 150 nm were obtained combining the silver mirror reaction with agitation. EDX, XRD and XPS confirm the presence of metallic Ag in both coatings and also oxidized Ag in samples by agitation. A higher amount of Ag nanoparticles is deposited on samples by sonication, as calculated by TGA. Further, both coatings are biocompatible and show antibacterial properties: coating by sonication caused 24 % and 40 % of bacterial reduction while coating by agitation 48 % and 96 % against S. aureus and E. coli, respectively. At 1 min of contact with SARS-CoV-2, the coating by agitation has an antiviral capacity of 75 % against 24 % of the one by sonication. At 1 h, both coatings achieve 100 % of viral inhibition. Nonetheless, larger samples could be produced only through the silver mirror reaction combined with agitation, preserving the integrity of the mask. In conclusion, the silver-coated mask produced by silver mirror reaction combined with agitation is scalable, has excellent physico-chemical characteristics as well as significant biological properties, with higher antimicrobial activities, providing additional protection and preventing the indirect transmission of pathogens.

The Development of the Fluorescence-based Portable Device for Lead (II) and Formalin Determination in Food Samples by Using Nitrogen-Doped Carbon Dots (N-CDs)

The fluorescence-based portable device for the determination of lead (Pb²⁺) and formalin (FA) in food samples by using Nitrogen-doped carbon dots (N-CDs) as a fluorescence probe was developed. The proposed approach, Pb^2+, and FA were determined based on the photo-induced electron transfer (PET) mechanism and the silver mirror reaction. The fluorescence intensity of the N-CDs decreased with the increase of Pb²⁺ concentration and increased with the increasing FA concentration. The fluorescence intensity of N-CDs after the reactions were measured by a filter-free fluorometer platform using a commercial camera module and a Raspberry Pi, a compact computer, as a detector and processor. The experimental results were obtained using control samples with known Pb²⁺ and FA concentrations in the 0.01-10 mg L^- 1 and 25-150 mg L^- 1, respectively. The proposed approach is simple, low-cost, and accurate for the on-site monitoring of Pb²⁺ and FA in various food samples. Of utmost importance, the proposed approach is expected to be a pioneering model for the future development of other analytes with a broad range of practical applications.

Old silver mirror in qualitative analysis with new shoots in quantification: Nitrogen-doped carbon dots (N-CDs) as fluorescent probes for "off-on" sensing of formalin in food samples

A novel fluorometric assay for selective and sensitive determination of formalin (FA) was developed based on nitrogen-doped carbon dots (N-CDs) coupled with silver mirror reaction. N-CDs was synthesized using the hydrothermal method with the ethylene glycol and ammonia solution as carbon and nitrogen precursors, respectively. The detection principle was based on "off-on" fluorescence switching. Specifically, the fluorescence signal of N-CDs was first turned off after incorporating the Ag⁺ and Tollens' reagents. Then, in the presence of FA, the Ag⁺ species on the N-CDs surface were reduced to Ag⁰ species and the fluorescence signal of N-CDs was switched back on. The fluorescence intensity due to the N-CDs signal linearly increased with the increasing FA concentrations in the range of 5-100 mg L^-1, with the detection limit of 1.5 mg L^-1. The proposed approach provides rapid, simple, sensitive, and selective detection of FA in various food samples.

Plasmonic sensing of β-glucuronidase activity via silver mirror reaction on gold nanostars

We outline a novel approach for the plasmonic detection of β-glucuronidase activity by modulating the silver mirror reaction at the nanoscale on gold nanostars. β-glucuronidase catalyzes the hydrolysis of a non-reducing substrate to generate reducing products that trigger the silver mirror reaction on gold nanostars to alter their surface plasmon resonance. By modulating the silver deposition on gold nanostars, the unique plasmonic property of silver-coated gold nanostars enables a significant change in the surface plasmon resonance that allows for a plasmonic readout for detecting the enzymatic activity. This plasmonic nanosensor enables a detection of the β-glucuronidase activity as low as 0.1 U/L, showing great promise as a plasmonic approach for enzyme detection.

A dual signal amplification strategy combining thermally initiated SI-RAFT polymerization and DNA-templated silver nanoparticles for electrochemical determination of DNA

A highly sensitive method is described for determination of DNA. It is based on dual signal amplification, viz. (a)DNA-templated metal deposition, and (b) thermally initiated surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization. A peptide nucleic acid (PNA) with a terminal thiol group was grasped onto a gold electrode by self-assembly. The modified electrode serves as a probe to selectively capture target DNA (tDNA). In the next step, Zr(IV) ions are bound to the phosphate groups of the tDNA. A chain-transfer agent (CTA) for thermally initiated SI-RAFT polymerization, 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPAD), was immobilized on tDNA by conjugation of the carboxy group to Zr(IV) ions. Subsequently, numerous monomers of glycosyloxyethyl methacrylate (GEMA) were connected to the CPAD by thermally initiated SI-RAFT polymerization with azobisisobutyronitrile (AIBN) serving as the free-radical thermal initiator. Afterwards, hydroxyl groups of the GEMA were oxidized to aldehyde groups reacting with sodium periodate, and silver nanoparticles were further introduced on the surface of electrode via "silver mirror reaction". This results in a large electrochemical signal amplification. Under optimized conditions, the electrochemical signal (best measured at a working potential of 0 V vs. SCE (KCl; 3 M)) increases linearly with the logarithm of tDNA concentration in the 10 to 10⁶ aM concentration range. The detection limit is as low as 5.6 aM (~34 molecules in a 10 μL sample). This is lower by factors between 2 and 1800 times than detection limits of most other ultra-sensitive electrochemical DNA assays. Graphical abstractSchematic representation of a dual signal amplification strategy combining thermally initiated surface-initiated reversible addition-fragmentation chain transfer polymerization (SI-RAFT) and DNA-templated silver nanoparticles for electrochemical determination of DNA.

Development of silver nanoparticle-doped adsorbents for the separation and recovery of radioactive iodine from alkaline solutions

Removing radioactive iodine from solutions containing fission products is essential for nuclear facility decontamination, radioactive waste treatment, and medical isotope production. For example, the production of high-purity fission ⁹⁹Mo by irradiation of ²³⁵U with neutrons involves the removal of iodine from an alkaline solution of the irradiated target (which contains numerous fission products and a large quantity of aluminate ions) using silver-based materials or anion-exchange resins. To be practically applicable, the utilized iodine adsorbent should exhibit a decontamination factor of at least 200. Herein, the separation of radioactive iodine from alkaline solutions was achieved using alumina doped with silver nanoparticles (Ag NPs). Ag NPs have a larger surface area than Ag powder/wires and can thus adsorb iodine more effectively and economically, whereas alumina is a suitable inert support that does not adsorb ⁹⁹Mo and is stable under basic conditions. The developed adsorbents with less impurities achieved iodine removal and recovery efficiencies of 99.7 and 62%, respectively, thus being useful for the production of ¹³¹I, a useful medical isotope.

A three-dimensional silver nanoparticles decorated plasmonic paper strip for SERS detection of low-abundance molecules

The fabrication of SERS substrates, which can offer the advantages of strong Raman signal enhancement with good reproducibility and low cost, is still a challenge for practical applications. In this work, a simple three-dimensional (3D) paper-based SERS substrate, which contains plasmonic silver-nanoparticles (AgNPs), has been developed by the silver mirror reaction. This paper strip was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), etc. Pretreatment of the paper as well as the reaction time, temperature, and reagent concentrations for the silver mirror reaction were varied for further studies. With the optimized experimental parameters, the AgNPs synthesized and distributed in-situ on the paper strip could give more favorable SERS performance. The limit of detection (LOD) as low as 10(-11)M for Rhodamine 6G (R6G) and 10(-9)M for p-aminothiophenol (p-ATP) plus wide linear range for the log-log plot of Raman intensity versus analyte concentration were achieved. The detection of R6G in rain water was also carried out successfully. The merits of this protocol include low cost, easy operation, high sensitivity and acceptable stability, which make it ideal for the detection of environmental samples in trace amounts.