Silver Nanoparticles for Hydrogen Peroxide Sensors

the Roman Empire, including Egypt, Mesopotamia, and Greece, Egyptian blue for decorative purposes has been observed during archaeological excavations. Natural or synthetic ways can synthesize NPs by two basic approaches, including various sub-preparation methods. The first approach is called the “top to bottom” method, including breaking down bulk solid materials into smaller pieces by applying external energy from physical, chemical, and thermal techniques [11]. The second approach, called “from the bottom up, “brings together and combines atoms or molecules of gases or liquids. The top-down approach is expensive. However, it is impossible to obtain perfect surfaces and edges due to the cavities and roughness in NPs, while a bottom-up approach can get excellent results of nanoparticle synthesis. In addition, with the bottom-up approach, no waste is Silver Nanoparticles for Hydrogen Peroxide Silver nanoparticles (AgNPs) are currently increasingly synthesized for their superior physicochemical and electronic properties. Good knowledge of these characteristics allows the development of applications in all sensitive and essential fields in the service of humans and the environment. This review aims to summarize the Ag NPs synthesis methods, properties, and applications in hydrogen peroxide sensors. Generally, Ag NPs can be synthesized using physical, chemical, and biological routes. Studies of Ag NPs have increased after clear and substantial support from governments to develop nanotechnology. Ag NPs are the most widely due to their various potent properties. Thus, this review discusses some different synthesis procedures and hydrogen peroxide applications of Ag NPs.

formed to be eliminated, and the smaller NPs can be obtained with better control of the sizes [12][13][14][15][16]. However, adapting the production of large quantities of powders on an industrial scale is not simple.
A significant advantage of treatment in solution is the possibility of generating encapsulated NPs using surfactants as a protective shell, which makes it possible to obtain very homogeneous and well dispersed NPs [17].
The main bottom-up approaches are the supercritical fluid synthesis, the use of the template, the spinning, the synthesis by plasma or flame projection, the green synthesis, the sol-gel process, the laser pyrolysis, the aerosol-based process, the chemical vapor deposition, and the atomic or molecular condensation. The main top-down approaches are the mechanical milling, the etching (chemical), the electro-explosion (thermal/chemical), the spraying (kinetics), and the laser ablation (thermal). The green synthesis approach is based on biological methods (accommodating plants, algae, the mushrooms, yeasts, actinomycetes and bacteria).

Types and Synthesis of Silver Nanoparticles
Among the various types of NPs, Ag NPs have been widely developed to be utilized in various applications due to their outstanding properties. Typical applications of Ag NPs include clothing and textiles, medical devices, food storage, cosmetics, sunscreens, laundry detergents [18], bandages [19], and sensors [20]. Some studies have found that Ag NPs have cytotoxicity that can induce ROS formation in cells [21]. Therefore, many products such as detergents, toiletries, etc. In addition, their synthetic or in-use personal care, whether industrial or household, produces a release of NPs, which ultimately ends up in the sewer. This untreated wastewater affects aquatic ecosystems and thus microorganisms.
Recently, Ag NPs had great concerns regarding aquatic toxicology due to the difficulty of tracking these particles in the environment and accessing their effects on living organisms [22]. The fate of NPs in the aquatic environment and their interactions, the interactions between NPs with biological and abiotic components, and their potential for damage are not well understood, and these uncertainties raise concerns about related risks. These molecules impose on humans on health and the environment [23]. Based on the Scopus database [24], the publications on Ag NPs increase with time, where it started in 1990 (two reports) and reached 7105 reports in 2020.
Colloidal Ag NPs are molecules with an average diameter of 20-40 nm and comprise 80% silver atoms and 20% silver ions. They are the best-selling nanoparticles ahead of carbon nanotubes and titanium nanoparticles and are released into the environment.
The demand for Ag NPs has increased due to their applicability in multiple fields. Over the years, various synthesis techniques have been developed, and procedures have been improved to prepare small and uniform Ag NPs. Ag NPs were prepared by a chemical reduction technique, where the silver ions are reduced by sodium citrate [25]. As referenced, various kinds of Ag NPs have been utilized in various applications [26]. Specifically, Ag NPs of differing sizes and shapes have been used in a broad scope of uses and clinical gear, such as electronic gadgets, coatings, cleansers, swathes, etc. [27]. Explicit physical a nd optical properties of Ag The physical technique usually utilized to prepare Ag NPs is the evaporation-condensation method. It is commonly performed using a tube furnace at atmospheric pressure, synthesizing various sizes [28]. Several attempts have been made. For instance, Tsuji, et al. [29] proposed a new method for synthesizing Ag NPs by a laser ablation technique with focused and unfocused laser beam irradiation carried out at 12 and 900 mJ cm −2 intensities, respectively. The radiation wavelengths used were 355, 532, and 1064 nm. This study revealed that the surface plasmon wavelength of Ag NPs irradiated using 355, 532, and 1064 nm is ~400 nm for focused and unfocused beams. The famous chemical method for Ag NPs synthesis is a reduction by natural and inorganic reducing agents. By and large, unique reducing agents, for example, sodium citrate, ascorbate, sodium borohydride, essential hydrogen, polyol measure, Tollen's reagent, N, N-dimethylformamide (DMF), and poly (ethylene glycol)-block copolymers are utilized for the reduction of silver particles (Ag + ) in aqueous or non-aqueous arrangements.
These reducing agents decrease Ag + and lead to metallic silver (Ag0), trailed by agglomeration into oligomeric clusters. These clusters ultimately arrange the metallic colloidal silver particles [30]. It is critical to utilize defensive agents to stabilize dispersive NPs during metal nanoparticle planning and ensure that the NPs consumed or tied onto nanoparticle surfaces stay away from their agglomeration [31]. Green synthesis methodologies dependent on natural reducing agents rely on different reaction parameters such as solvent, temperature, pressing, and pH conditions (acidic, fundamental, or impartial). For the union of metal oxide nanoparticles, plant biodiversity has been extensively viewed as the accessibility of successful phytochemicals in different plant separates, particularly in leaves such as ketones and aldehydes flavones, amides, terpenoids, carboxylic acids, phenols, and ascorbic acids [32,33]. These parts are fit for decreasing metal salts into MNPs [34]. The fundamental focus of such nanomaterials has been researched for biomedical diagnostics, antimicrobials, catalysis, atomic detecting, optical imaging, and marking of natural frameworks.

Applications of Silver Nanoparticles
Over the last decades, the production of NPs has been increasing rapidly for applications in electronics, chemistry, biology, and almost all our daily life applications [35]. This is mainly due to their mainly for the excellent physico-chemical properties, will be reviewed here. Developing fast, sensitive and selective gas sensors has received great attention in environmental monitoring, national security, and food safety applications [42]. Typically, the total performance of gas sensors strongly depends on the specific area surface of the materials utilized for detection gas. Thus nano-scale sensing is predictable to display improved sensing performance [20]. Typically, semi-conductive nano metal oxides such as ZnO and SnO 2 exhibit high sensitivity and fast responses to some gases [43].
A relatively higher temperature (150-600 • C) required for maximum response is a big problem that restricts the practical applications in most areas [44]. Therefore, developing suitable nanomaterials to enhance the sensor response is highly recommended. Noble There are many published articles on the use of LSPR sensing applications in the liquid phase to detect organic phosphorous pesticides [47] and ammonia [48]. Generally, SPR absorption of noble metal NPs is strong in the visible to near-infrared (IR) region. Moreover, SPR is particularly sensitive to its size, shape, composition, distance, and surroundings. Therefore, it displays a promising ability for various sensors. However, Ag NPs have higher extinction coefficients than gold nanoparticles (Au NPs) of the same size [49]. Due to this feature and high specific surface area, high catalytic, high crystallinity, and their electrical and optical properties, Ag NPs have been widely investigated as gas sensor applications [41,50]. This section will present the recent progress on Ag NPs as gas sensors for ammonia, methane, and hydrogen peroxide. Despite the wide use in industry, such as fertilizers, animal feed production, and manufacturing of paper and plastics, ammonia is a toxic material with a harmful effect on the human body as it can harm tissues and the immune system [51]. Ammonia is largely produced in deteriorating food and fruitbodies by various micro/macrofungi [52]. Thus, monitoring the concentration showed an average size of ~22 nm, showing a conductive and metallic nature. As ammonium gas sensing, the synthesized NPs thin films showed the maximum sensitivity towards ammonia gas.

Hydrogen Peroxide Sensing
In the last decade, hydrogen peroxide (H 2 O 2 ) monitoring has gained importance due to its widely employed in many industrial, atomic power stations, medical sectors and its application as a disinfecting agent for water pools [56][57][58]. However, the high presence of H 2 O 2 can cause various biological damages, leading to aging, neurodegeneration, and cancer [59,60]. Therefore, developing a high-response, cheap method is highly recommended for medical, pharmaceutical security, and environmental protection [59]. Various techniques, such as spectrophotometry [60,61], chemiluminescence [62], and electrochemistry [63], have been utilized to detect H 2 O 2 . These methods are categorized as enzymatic and non-enzymatic methods. In the case of enzymatic, the peroxidase is an illustrative enzyme for H 2 O 2 exposure; however, both pH and temperature are limited.
As mentioned above, noble metal NPs display strong SPR absorption with extreme sensitivity to the size, shape, composition, and surroundings suitable for colorimetric sensors in the range of visible to near-infrared region. For colorimetric assays, Ag NPs have a high ability toward the decay of H 2 O 2 [64]. This reaction can mainly be sensed by colorimetric principles, as the colloidal Ag NPs exhibit a characteristic color from the LSPR. The alteration in both

Conflict of Interest
No conflict of interest with any institution/organization.