Plasmonic active film integrating gold/silver nanostructures for H2O2 readout

Combining plasmonic and electrochemical biosensing methods

The idea of combining electrochemical (EC) and plasmonic biosensor methods was introduced almost thirty years ago and the potential of electrochemical-plasmonic (EC-P) biosensors has been highlighted ever since. Despite that, the use of EC-P biosensors in analytics has been rather limited so far and the search for unique applications of the EC-P method continues. In this paper, we review the advances in the field of EC-P biosensors and discuss the features and benefits they can provide. In addition, we identify the main challenges for the development of EC-P biosensors and the limitations that prevent EC-P biosensors from more widespread use. Finally, we review applications of EC-P biosensors for the investigation and quantification of biomolecules, and for the study of biomolecular and cellular processes.

A colorimetric assay for H2O2 and glucose based on the morphology transformation of Au/Ag nanocages to nanoboxes

Herein, we introduced a sensitive colorimetric platform for hydrogen peroxide (H2O2) assay based on gold/silver (Au/Ag) nanocages with porous structure. In the presence of H2O2, the morphology of hollow Au/Ag nanocages was converted to closed nanoboxes, altering their localized surface plasmon resonance (LSPR) peak position and the solution color from light blue to deep blue. The morphology transformation and LSPR peak position of Au/Ag nanocages were proportional to H2O2 concentration at the range of 0.1 to 50 µM. The limit of detection (LOD) was obtained to be 0.02 µM, and the relative standard deviation (RSD, for 0.2, 2.0, and 20 µM) was 2.7, 2.3, and 2.9%, respectively. Moreover, a smartphone-based colorimetric sensor was developed for H2O2 assay at the concentration range of 0.25-4.0 µM, with LOD of 0.2 µM and RSD of 3.2, 2.5, and 2.9% (for 0.5, 1.0, and 3.0 µM, respectively). We exploited the established sensor for glucose assay by measuring the generated H2O2 from the enzymatic reaction between glucose and glucose oxidase. There was a linear relationship between LSPR peak wavelength variations and the amount of glucose from 1.0 to 50 µM, with LOD of 0.4 µM and RSD of 3.2, 3.1, and 3.8% (for 2.0, 10, and 30 µM, respectively). The sensor was successfully applied to determine H2O2 and glucose in food and human serum samples, respectively.

Plasmonic nanoparticle etching-based optical sensors: current status and future prospects

Plasmonic nanoparticles are an emerging tool for developing label-free multicolorimetric sensors for biosensing and chemosensing applications. The color absorbed by nanoparticles from visible light is influenced by their size, shape, orientation, and interparticle distance. Differently sized and shaped gold and silver nanoparticles exhibit a wide range of colors, aiding in the development of label-free sensors. Etching is the process of oxidizing nanoparticles, which alters their aspect ratio, shape, plasmonic peak, and outward appearance. It is typically used to create sensitive sensing platforms. Through etching, analytes could be detected in a simple, sensitive, and selective manner. The multicolor readout of nanoparticle etching-based multicolorimetric sensors can overcome the limitations of conventional colorimetric assays and improve the accuracy of visual inspection. This review discusses different approaches for target sensing using nanoparticle etching strategies like direct etching, enzyme-mediated etching, chemical reaction-driven etching, and anti-etching-based sensors and their mechanisms. In the future, etching strategies could be modified into portable sensing devices to detect a variety of analytes, which will aid in the development of on-time, in situ, and point-of-care sensing systems.

Metal Nanoparticle-Flavonoid Connections: Synthesis, Physicochemical and Biological Properties, as Well as Potential Applications in Medicine

Flavonoids are polyphenolic compounds widely occurring throughout the plant kingdom. They are biologically active and have many medical applications. Flavonoids reveal chemopreventive, anticarcinogenic, and antioxidant properties, as well as being able to modulate the immune system response and inhibit inflammation, angiogenesis, and metastasis. Polyphenols are also believed to reverse multidrug resistance via various mechanisms, induce apoptosis, and activate cell death signals in tumor cells by modulating cell signaling pathways. The main limitation to the broader usage of flavonoids is their low solubility, poor absorption, and rapid metabolism. To tackle this, the combining of flavonoids with nanocarriers could improve their bioavailability and create systems of wider functionalities. Recently, interest in hybrid materials based on combinations of metal nanoparticles with flavonoids has increased due to their unique physicochemical and biological properties, including improved selectivity toward target sites. In addition, flavonoids have further utilities, even in the initial step of preparation of metal nanomaterials. The review offers knowledge on multiple possibilities of the synthesis of flavonoid-metal nanoparticle conjugates, as well as presents some of their features such as size, shape, surface charge, and stability. The flavonoid-metal nanoparticles are also discussed regarding their biological properties and potential medical applications.

Fabrication of localized surface plasmon resonance sensors with scalable polyvinyltetrazole/copper cluster hybrid ring-array for Cu(II) detection

The bottom of a hole-array photoresist template deposited with a hydrophobic atom-transfer radical polymerization (ATRP) initiator was wetted by treatment with oxygen plasma. After the removal of the photoresist template, ring patterns of the ATRP initiator were formed at the interface between the hydrophobic and wetting regions. Polyacrylonitrile (PAN) was grafted from the initiator ring array to covert to polyvinyltetrazole (PVT) rings via a cyano-to-tetrazole reaction, which could adsorb Cu(II) at various concentrations. The Cu(II) ions within the PVT rings were reduced to form a PVT-copper hybrid ring (VCHR), resulting in a blue-shift of the localized surface plasmon resonance (LSPR) peak as the Cu(II) was adsorbed by the PVT rings. The blue-shift and Cu(II) concentration were linearly correlated, with a detection limit of ∼25 pg mL^-1 and a linear range of 25-400 pg mL^-1 for Cu(II) detection. Although the PVT rings also chelated Pb(II) and Cr(III), these ions did not exhibit obvious LSPR peaks. The VCHR LSPR sensor exhibited excellent selectivity for Cu(II) detection. Combining lithography and plasma technology provides a versatile platform for developing the scalable ring structure of copper for highly sensitive and selective Cu(II) sensing.

Iron/iron oxide-based magneto-electrochemical sensors/biosensors for ensuring food safety: recent progress and challenges in environmental protection

Foodborne diseases have arisen due to the globalization of industry and the increase in urban population, which has led to increased demand for food and has ultimately endangered the quality of food. Foodborne diseases have caused some of the most common public health problems and led to significant social and economic issues worldwide. Food quality and safety are affected by microbial contaminants, growth-promoting feed additives (β-agonists and antibiotics), food allergens, and toxins in different stages from harvesting to storage and marketing of products. Electrochemical biosensors, due to their reduced size and portability, low cost, and low consumption of reagents and samples, can quickly provide valuable quantitative and qualitative information about food contamination. In this regard, using nanomaterials can increase the sensitivity of the assessment. Magnetic nanoparticle (MNP)-based biosensors, especially, are receiving significant attention due to their low-cost production, physicochemical stability, biocompatibility, and eco-friendly catalytic characteristics, along with magnetic, biological, chemical and electronic sensing features. Here, we provide a review on the application of iron-based magnetic nanoparticles in the electrochemical sensing of food contamination. The types of nanomaterials used in order to improve the methods and increase the sensitivity of the methods have been discussed. Then, we stated the advantages and limitations of each method and tried to state the research gaps for each platform/method. Finally, the role of microfluidic and smartphone-based methods in the rapid detection of food contamination is stated. Then, various techniques like label-free and labelled regimes for the sensitive monitoring of food contamination were surveyed. Next, the critical role of antibody, aptamer, peptide, enzyme, DNA, cells and so on for the construction of specific bioreceptors for individual and simultaneous recognition by electrochemical methods for food contamination were discussed. Finally, integration of novel technologies such as microfluidic and smartphones for the identification of food contaminations were investigated. It is important to point out that, in the last part of each sub-section, attained results of different reports for each strategy were compared and advantages/limitations were mentioned.

One-step synthesis of nanosilver embedding laser-induced graphene for H2O2 sensor

During the novel coronavirus pandemic, hydrogen peroxide (H₂O₂) played an important role as a disinfectant. However, high concentrations of H₂O₂ can also cause damage to the skin and eyes. Therefore, the quantitative and qualitative detection of H₂O₂ is an important research direction. In this work, we report a one-step laser-induced synthesis of graphene doped with Ag NPs composites. It directly trims screen printed electrodes (SPE). Firstly, we did the timekeeping current method (CA) test on H₂O₂ using a conventional platinum sheet as the counter electrode, and obtained linear ranges of 1-110 μM and 110-800 μM with a sensitivity of 118.7 and 96.3 μAmM^-1cm^-2 and a low detection limit of (LOD) 0.24 μM and 0.31 μM. On this basis we have also achieved a good result in CA testing using Screen printed carbon electrodes (SPCE), laying the foundation for portable testing. The sensor has excellent interference immunity and high selectivity.

Catechin versus MoS2 Nanoflakes Functionalized with Catechin: Improving the Sperm Fertilizing Ability-An In Vitro Study in a Swine Model

Nowadays, the adoption of In Vitro Fertilization (IVF) techniques is undergoing an impressive increase. In light of this, one of the most promising strategies is the novel use of non-physiological materials and naturally derived compounds for advanced sperm preparation methods. Here, sperm cells were exposed during capacitation to MoS₂/Catechin nanoflakes and catechin (CT), a flavonoid with antioxidant properties, at concentrations of 10, 1, 0.1 ppm. The results showed no significant differences in terms of sperm membrane modifications or biochemical pathways among the groups, allowing the hypothesis that MoS₂/CT nanoflakes do not induce any negative effect on the parameters evaluated related to sperm capacitation. Moreover, the addition of CT alone at a specific concentration (0.1 ppm) increased the spermatozoa fertilizing ability in an IVF assay by increasing the number of fertilized oocytes with respect to the control group. Our findings open interesting new perspectives regarding the use of catechins and new materials obtained using natural or bio compounds, which could be used to implement the current strategies for sperm capacitation.

Green synthesis of silver nanoparticles using the extract of spent coffee used for paper-based hydrogen peroxide sensing device

Hydrogen peroxide (H₂O₂) has attracted considerable attention for use as a disinfectant ingredient for various applications over the decades. The use of H₂O₂ within the safety regulations can avoid its toxicity to human health and the environment. In this study, a paper-based sensor containing green-synthesized silver nanoparticles (P-AgNPs) was developed for use in a smartphone in the determination of the H₂O₂ concentration. In the synthesis process, an extract of spent coffee grounds was used as a bioreducing agent. The effects of reaction time and silver nitrate (AgNO₃) concentration on the green synthesis of silver nanoparticles (AgNPs) were investigated. The optimum conditions for the preparation of P-AgNPs were determined to be 100 mM AgNO₃ (P-AgNPs-100) and 15 h synthesis time. The P-AgNPs-100 sensor exhibited high sensitivity with a detection limit of 1.26 mM H₂O₂, which might be suitable for the detection of H₂O₂-based household and beverage sanitizers. The H₂O₂ detection capability of P-AgNPs-100 was comparable to that of a commercial strip sensor. Furthermore, P-AgNPs-100 had a detection efficiency of more than 95% after long-term storage for 100 days.

Green Synthesis of Molecularly Imprinted Polymers for Dispersive Magnetic Solid-Phase Extraction of Erythrosine B Associated with Smartphone Detection in Food Samples

Monitoring synthetic colorants in foods is important due to their potential toxicity and pathogenicity. We propose here a new and simple method for the extraction and determination of erythrosine B (ERT-B) in food samples. A composite of polydopamine-based molecularly imprinted polymers coating magnetic nanoparticles (Fe₃O₄@PDA@MIP) was synthesized using a green approach and exploited for the magnetic dispersive solid-phase extraction (MDSPE) of ERT-B. Fe₃O₄@PDA@MIP provides a rapid extraction of ERT-B, exhibiting good reusability and preconcentration ability. Moreover, the MIP showed a relatively good imprinting factor (3.0 ± 0.05), demonstrating excellent selectivity against patent blue (an interfering dye) and other food matrix components. The proposed MDSPE was coupled to colorimetric smartphone-based detection that allowed us to obtain similar performances of UV-Vis spectroscopy detection. The smartphone-based optical detection facilitated the determination of ERT-B in the 0.5-10 mg/L range, with a limit of detection of 0.04 mg/L. The developed method was successfully employed to determine ERT-B in food samples (juice, candy, and candied cherries) with good recovery values (82-97%).

Colorimetric/SERS dual-channel nanoprobe for reactive oxygen species monitoring in elucidating the mechanism of chemotherapeutic drugs action on cancer cells

Reactive oxygen species (ROS) are involved in drug-induced cytotoxicity by regulating cell signaling, inducing oxidative stress, and damaging the DNA and proteins. Examining ROS production in cells under the stimulation of chemotherapeutic drugs is of great importance for understanding the ROS roles and identifying the mechanism of drug-induced cytotoxicity. Here, a silver/gold (Ag/Au) nanoshell-based colorimetric and surface-enhanced Raman spectroscopy (SERS) dual-response nanoprobe was proposed for ROS sensing on the basis of Ag etching. In this study, as a kind of ROS, hydrogen peroxide (H₂O₂) was detected by the prepared nanoprobe. The linear ranges of 0.5-100 μM with a limit of detection (LOD) of 0.343 μM for the colorimetric determination and 1-50 μM with LOD of 0.294 μM for SERS determination were achieved. The detection of cellular ROS concentration after stimulation by cisplatin, paclitaxel, doxorubicin, and 5-fluorouracil was validated by the nanoprobe. The nanoprobe could also be used to detect the signal pathway of ROS production by cisplatin stimulation. This study provided a simple and novel dual-response nanoplatform for detecting and monitoring ROS in cells, which holds great potential for elucidating the mechanism of occurrence and treatment of ROS-involved diseases.

Silver nanoflowers coupled with low dose antibiotics enable the highly effective eradication of drug-resistant bacteria

Due to the global overuse of antibiotics, the issue of multidrug-resistant bacteria (MDR) continuously calls for effective strategies to tackle the antibiotic resistance crisis. Here, we develop a silver nanomaterial with a petal-like structure (namely Ag Nano Flowers, AgNFs). AgNFs are synthesized in an eco-friendly way with bovine serum albumin as an assisting template and stabilizing agent under mild conditions. These AgNFs have desired physical properties, including good dispersion, high stability, and large surface area with an average size in the range of 700-800 nm. We demonstrate AgNFs as a highly effective drug carrier and an adjuvant to restore the susceptibility of drug-resistant E. coli towards standard antibiotics such as norfloxacin and streptomycin. The doses of AgNFs and norfloxacin are reduced by 80% and 90%, respectively, in the combined treatment compared to those used individually. The dose reductions of AgNFs and streptomycin are 80% and 50% in the combined treatment of streptomycin and AgNFs. Through further analysis of the metabolomics and activities of bacteria, we speculate that the synergistic antibacterial efficacy between AgNFs and antibiotics could be explained by the enhanced respiration of bacteria and the up-regulation of the tricarboxylic acid cycle, which in turn increase the release of reactive oxygen species and promote the uptake of antibiotics, thereby eventually eradicating the drug-resistant bacteria.

Metal nanoparticles based lab-on-paper for phenolic compounds evaluation with no sample pretreatment. Application to extra virgin olive oil samples

In this work, a low-cost, disposable, and portable lab-on-paper device is proposed to simultaneously quantify total polyphenol content (TPC) and antioxidant capacity (AOC) in 15 min; the assay requires no pre-treatment of the samples. The lab-on-paper device fabrication has been carried out employing a xurography-based benchtop microfabrication technology using low-cost materials as chromatography paper and polymeric sheets. Extra virgin olive oil (EVOO) phenolic compounds' represents a nutritional added value, nevertheless, the high lipidic content hinders their direct and rapid analysis, resulting in an extremely challenging sample. The realized lab-on-paper allows to perform the dual TPC and AOC determination in three simple steps: (i) sample loading, (ii) analytes transport to the analysis spot, and (iii) double colorimetric analysis exploiting the growth of AuNPs and AgNPs on paper mediated by phenolic compounds. Signal acquisition is achieved using a standard digital camera. The dual colorimetric assay is able to detect phenolic compounds in the 25-500 mg L^-1 range with limits of detection ≤6 mg L^-1 and good reproducibility (RSDs ≤11%). Direct analysis of EVOO samples (n = 30) correlated well (r > 0.92) with conventional spectrophotometric methods for TPC and AOC determination.

Molecularly Imprinted Polymers Combined with Electrochemical Sensors for Food Contaminants Analysis

Detection of relevant contaminants using screening approaches is a key issue to ensure food safety and respect for the regulatory limits established. Electrochemical sensors present several advantages such as rapidity; ease of use; possibility of on-site analysis and low cost. The lack of selectivity for electrochemical sensors working in complex samples as food may be overcome by coupling them with molecularly imprinted polymers (MIPs). MIPs are synthetic materials that mimic biological receptors and are produced by the polymerization of functional monomers in presence of a target analyte. This paper critically reviews and discusses the recent progress in MIP-based electrochemical sensors for food safety. A brief introduction on MIPs and electrochemical sensors is given; followed by a discussion of the recent achievements for various MIPs-based electrochemical sensors for food contaminants analysis. Both electropolymerization and chemical synthesis of MIP-based electrochemical sensing are discussed as well as the relevant applications of MIPs used in sample preparation and then coupled to electrochemical analysis. Future perspectives and challenges have been eventually given.

Effect of phenolic compounds-capped AgNPs on growth inhibition of Aspergillus niger

An exponential increase of scientific works dealing with the use of polyphenol-rich 'natural products' for the synthesis of bioactive AgNPs is in progress. However, a lack of fundamental studies on phytochemical compounds involved, and their role is evident. In this work, a comprehensive study of the antifungal performances of silver nanoparticles (AgNPs) synthesized exclusively with phenolic compounds (PCs) with different structures and different antioxidant capacity is presented. The experimental hypothesis is that AgNPs@PCs produced with different PCs can exert different toxicity. In particular, di-hydroxylic and tri-hydroxylic phenolic acids (caffeic acid and gallic acid) and flavonoids (catechin and myricetin) were compared. A room temperature rapid and simple AgNPs synthesis was carefully optimized, obtaining stable and reproducible colloids. AgNPs@PCs suspensions were characterized by UV-vis spectroscopy, ς-potential, dynamic light scattering and transmission electron microscopy. AgNPs@PCs radical scavenging capacity was also assessed. Finally, the AgNPs@PCs antifungal effect was tested against Aspergillus niger, particularly on spore germination and mycelial growth. The different antifungal activity was attributed to the different PCs' ability to generate/stabilize AgNPs with different shells, residual antioxidant capacity, and capacity to interact and aggregate during their 'attack' to A. niger hyphae. This work paves the way for the rational use of PCs and PCs rich-products for AgNPs-based applications.