Introduction

Oxidative stress is a state when there is a contrast between the generation of Reactive Oxygen Species (ROS) and the body’s capability to detoxify these detrimental consequences. ROS are extremely reactive molecules that can result in cellular injury, leading to serious health issues. These highly reactive free radicals, produced by oxidative stress, cause damage to cells or interrupt cellular functions ¹. These also interfere with protein or DNA, leading to several chronic diseases, including cancer, cardiovascular, neurodegenerative, respire tory diseases, chronic kidney diseases, rheumatoid arthritis, and diseases like diabetes, which is called the mother of all diseases which is a major systemic metabolic disorder that significantly increases the risk of multiple chronic complications ². Antioxidants are compounds that detoxify or neutralize free radicals and broadly prevent oxidation, thus preventing thousands of serious health issues.

In this context, diabetes is a condition in which the pancreas cannot produce enough insulin or the body is incapable of using insulin to process blood sugar. It has been a major health issue in recent epochs. It can lead to numerous health issues. Diabetic conditions create a lot of complications in the body. It can affect every organ system of our body. It amplifies the risk of heart disease, the leading cause of chronic kidney disease and kidney failure, and causes retinopathy, which means eye damage that can lead to blindness. It damages nerves, leading to pain, numbness, and other issues, and it can also cause a stroke. Nerve damage and poor circulation can lead to severe foot infections and amputations ^3,4. There are a lot of such health complications leading to diabetes. Diabetes is a chronic condition and a name of common threat of this century. Recent valuation shows that relatively 537 million adults (aged 20-79 yr) worldwide are living with diabetes. This figure is anticipated to increase to 643 million by 2030 and 783 million by 2045 ⁵. The prevalence of diabetes has been increasing rapidly. Globally, the number of diabetes mellitus patients was 11.3 million in 1990, while it increased to 22.9 million in 2017. The new case rate is almost 103%, Age-Standardized Incidence Rate (ASIR) rose from 234 per 100,000 persons in 1990 to 285 per 100,000 persons in 2017 ⁶. In the United States, about 38.4 million people of all ages, or 11.6% of the U.S. population estimated to have diabetes in 2021, and diabetes was directly mentioned as a cause of death on 399,401 certificates ⁷. The rate of global death is approximately 6.7 million, accounting for 12.2% of all deaths globally in 2021, which looks like a pandemic, and the way diabetic conditions are gradually increasing ⁸.

Both oxidative stress and diabetes are hazardous to health. They are interconnected and contribute to one another in a cycle. Oxidative stress acts as a factor for diabetes by damaging the pancreatic β-cell that produces insulin, and diabetes generates more free radicals and increases oxidative stress ⁹. Both conditions collectively create menacing complications. It is difficult to combat either of the conditions through conventional medication. In this circumstance, an effective antioxidant and antidiabetic medication is a matter of basic need to counter this challenging situation. Therefore, nanomedicine could be a promising approach for managing diabetes and oxidative stress due to its precise control over drug release, target specificity, increased penetration capability, improved drug accessibility in hard-to-reach areas, increased absorption, enhanced bioavailability, higher efficacy, and fewer side effects ¹⁰. Nanoparticles possess remarkable versatility in applications across various sectors owing to their distinctive features. Among them, it is extensively used in the medical and pharmaceutical sectors. Nano-medication has gained significant attention due to its potential to revolutionize the way of diagnosing and treating. It involves the use of nanoparticles and nanoscale materials to deliver the drugs. It is designed to specify target disease locations, which means medication can be sent precisely to diseased cells or tissues ¹¹. Nanoparticles are small enough to penetrate biological barriers and can enhance drug absorption at the cellular level. Drugs that are poorly soluble in water can be effectively delivered by nanoparticles.  All the above criteria make nano-medication an effective form of medication. Especially for the diseases that were tough to tackle in a conventional way, such as oxidative stress, diabetes, cancer, etc.

Nanoparticles can be different types, some are organic, such as polymeric nanoparticles, liposomes, and dendrimers, and some are metallic, such as silver nanoparticles (AgNPs), gold nanoparticles (AuNPs), zinc oxide nanoparticles (ZnONPs), selenium nanoparticles (SeNPs), cerium oxide nanoparticles (CeO2NPs), etc. Among them, inorganic nanoparticles have promising antidiabetic and antioxidant effects ¹². The nanoparticles can be fabricated by diverse methods such as physical methods, chemical methods, biological methods, green synthesized methods, or different kinds of hybrid methods like physicochemical and mechanochemical methods, etc. ¹³. Among all those methods, green synthesis is one of the sustainable approaches to synthesizing nanoparticles, which is eco-friendly, more biocompatible, suitable for medical and pharmaceutical applications, scalable as well as cost-effective ¹⁴. Selenium and SeNPs themselves act as antioxidants, and when they are synthesized in combination with the plant components, they synergistically enhance their range of antioxidant and antidiabetic activity ¹⁵.

Green synthesized SeNPs can neutralize free radicals, lessen oxidative stress, and enhance glucose metabolism and insulin sensitivity more efficiently ¹⁶. This synergistic interaction is undoubtedly a unique approach to therapeutic remediation, enabling the development of a pharmacologically active therapeutic strategy capable of delivering targeted therapy simultaneously with reduced side effects and enhanced potency. Recently, SeNPs have been extensively investigated to scrutinize their antioxidant and antidiabetic potentials; many research articles have been published, but there is a lack of systematic reviews on green synthesis of SeNPs with antioxidant and antidiabetic exploration. Therefore, this systematic review aims to discuss the green synthesis process of SeNPs, as well as explore and conjugate their antioxidant and antidiabetic potentials.

 Materials and Methods

Search strategy

To find the desired full-text article concerning the antioxidant and antidiabetic effect of green-synthesized SeNPs for this review, a systematic literature search was carried out in various sources and databases. These are PubMed, Science Direct, Science Open, DOAJ, Scilit, and Google Scholar, Research Gate, as supplementary search tools to identify potentially relevant peer-reviewed articles. A combination of controlled vocabulary terms and free-text keywords was used. Search terms were adapted for each database to ensure sensitivity and relevance. The research article search had been confined to the English language, published from 2014 to 2024. The following keywords were searched for this study:

Green synthesis of SeNPs, Phytochemical mediated SeNPs synthesis, Eco-friendly synthesis of SeNPs, Biomedical applications of SeNPs, Selenium nanoparticle and its antioxidant properties, SeNPs function as antioxidant, Greener SeNPs activity for Scavenging ROS, Greener SeNPs for scavenging free radicals, Green synthesized SeNPs and antioxidants activity, SeNPs activity on DPPH assay, SeNPs activity on ABTS assay, Antidiabetic potential of green mediated SeNPs, Biogenic SeNPs and their antidiabetic & antioxidant effects, SeNPs phytochemical synthesis & use in diabetic prevention,  SeNPs from medicinal plants diabetic & antioxidant activity, SeNPs for therapeutic use, SeNPs and insulin sensitivity, SeNPs and glucose regulation, SeNPs in α-amylase and α-glucosidase enzymatic activity, Sustainable biosynthesis of SeNPs and its antioxidant & antidiabetic activity, SeNPs and health benefits, SeNPs, and bioactivity.

 Inclusion criteria

The inclusion of published research articles for this study followed the following criteria; only full-text research articles were included that have sufficient and specific information regarding this study, papers were collected that were published in Scopus index journals and Q1, Q2, and Q3 journals, articles written in English language and published between 2014 to 2024, articles with in vitro and in vivo evaluation of green synthesized SeNPs for antioxidant and antidiabetic properties were included.

Exclusion criteria

The research articles with the following characteristics were excluded; Duplicated research articles, not containing predetermined specific information, non-related papers, review papers, thesis papers, project reports, case reports, conference proceedings, articles written other than in English language, articles without full text, computational research articles, articles published beyond the time limit, activity evaluation of SeNPs except antioxidant and antidiabetic properties and the articles published in predatory journals. To avoid the inclusion of predatory journals, explicit criteria were applied during the literature selection process. Only studies published in journals indexed in Scopus and listed in the Directory of Open Access Journals (DOAJ) were included. In addition, journal websites were screened for peer-review policies, editorial board transparency, and publication ethics when required. Title/abstract and full-text screening and data extraction were conducted independently against the eligibility criteria by two reviewers to avoid potential sources of bias, including selection, measurement, and reporting bias. Any disagreements were resolved through discussion and consensus with the third author.

Data screening and selection process

Following the aforementioned search strategy, exclusion, and inclusion criteria, a total of 413 publications were collected through literature searches. After excluding duplicate records, 347 records were eligible for screening. Based on the principle of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), approximately 267 reports were excluded. Finally, 78 full-text research articles were selected and included in the study. Although protocol registration was not performed, the review was conducted following the established systematic review principles, including a predefined research question, structured search strategy, and explicit inclusion and exclusion criteria. The entire data collection, screening, and selection process is given in a PRISMA flow diagram (Figure 1).

 Green synthesis and characterization of selenium nanoparticles

Green synthesis process of SeNPs: The green synthesis of Selenium Nanoparticles (SeNPs) implicates an eco-friendly and cost-effective approach using biological or plant-based materials instead of chemical substances as reducing and stabilizing agents ¹⁷. Green synthesis of selenium nanoparticles typically follows the bottom-up approach, where small particles, atoms, or molecules act as building blocks that cluster together to form larger nanoscale structures by processes like self-assembly and nucleation ¹⁸ (Figure 2).

The first step of green synthesis is to select a biological source, such as plant extracts, microorganisms (such as bacteria, fungi), algae, etc., which act as reducing and stabilizing or capping agents. If the selected source is a plant, then wash the plant material, dry it, and grind it if desired. Boil or macerate in distilled water to prepare the extract, then filter it to get rid of debris. If it is micro-organisms, then cultivate it in an appropriate culture medium and harvest the biomass or cell-free supernatant ¹⁹. The second step of the synthesis is the preparation of the selenium precursor solution. It is done by dissolving a selenium salt (commonly sodium selenite or sodium selenate) in distilled water to form an aqueous solution at the desired concentration. The concentration depends on the desired size and shape of the nanoparticles. After preparing the precursor solution, the biological extract needs to be mixed with the selenium precursor solution in a specific ratio under controlled conditions, such as pH, temperature, time, stirring speed, etc. ²⁰.

The bioactive compounds in the extract (such as polyphenols, flavonoids, proteins, alkaloids, etc.) act as reducing agents and convert selenium ions (Se⁴⁺ or Se⁶⁺) into elemental selenium (Se⁰) ²¹. Bacteria, fungi, algae, and yeast can enzymatically reduce selenium salts. The bioactive compounds in the mixture also act as stabilizing agents and prevent the aggregation of nanoparticles, thus ensuring stability and uniformity ²². Then the nanoparticles are purified through centrifugation to remove unreacted materials, by-products, or impurities. The purified SeNPs are washed with deionized water or ethanol, then dried, or redispersed the purified nanoparticles in distilled water or buffer for further use ^23,24.

Characterization of green-synthesized SeNPs: The prepared solution of SeNPs is kept standing for a sufficient time for visual characterization through the color change phenomenon. After getting the color changed, it is widely believed that the nanoparticles are formed. Then, these green-synthesized SeNPs are characterized to evaluate their physicochemical properties, biological activity, and stability. Characterization of these SeNPs is important to determine whether the required particles have evolved or not. Furthermore, the characterization is also crucial to guarantee that the NPs might produce the intended results. For analyzing optical properties, UV-visible Spectroscopy is generally used. The UV-Vis spectroscopy technique is used to confirm the formation of nanoparticles by identifying the characteristics of Surface Plasmon Resonance (SRP) peaks ²⁵. To measure the size and shape of synthesized NPs, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and Dynamic Light Scattering (DLS) techniques are used ²⁶. These methods can determine the size (commonly 10-100 nm) and morphology (spherical, hexagonal, etc.) of nanoparticles. TEM provides high-resolution images for detailed morphology and size (Figure 2) ²⁷. Generally, green-synthesized SeNPs are partially crystalline. To identify the crystalline nature of SeNPs, X-ray Diffraction (XRD) is used. It identifies the crystalline or amorphous nature of NPs ²⁸.

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is an excellent tool for the characterization of SeNPs in terms of elemental concentration (Figure 2) ²⁹. To analyze chemical and functional groups, Fourier Transform Infrared Spectroscopy (FTIR) is a good analytical tool. It identifies functional groups of biomolecules capping or stabilizing SeNPs. Peaks correspond to proteins, polysaccharides, or polyphenols from plant or microbial extracts used in synthesis ³⁰. To analyze the stability of SeNPs, Thermogravimetric Analysis (TGA), Dynamic Light Scattering (DLS), or zeta potential are good methods. They can assess the thermal stability and degradation potential of SeNPs and organic components (Figure 2) ³¹. Ensuring the chemical compounds required several analytical techniques, among them Energy Dispersive X-ray Spectroscopy (EDS) that identifies elemental composition and confirms the presence of selenium in nanoparticles, X-ray Photoelectron Spectroscopy (XPS) analyses the oxidation states and chemical bonding of SeNPs,  Fourier Transform Infrared Spectroscopy (FTIR) detects functional groups on the surface of the nanoparticle, Raman spectroscopy identify molecular vibrations with structural properties & different selenium allotropes etc. provides complementary information for ensuring a comprehensive understanding of  SeNPs chemical compounds ³².

 Results

This section summarizes the key findings derived from the systematic analysis of the included studies, focusing on green synthesis approaches, characterization techniques, and observed trends of selenium nanoparticle research in oxidative stress and diabetes.

The study selection process is illustrated in the PRISMA flow diagram. Records identified through database searching were screened, and full-text articles were assessed for eligibility according to predefined inclusion and exclusion criteria. The studies that met the criteria were included in the final qualitative synthesis.

Antioxidant activity of green-synthesized SeNPs

The Green-synthesized SeNPs exhibit antioxidant activity fundamentally by neutralizing Reactive Oxygen Species (ROS) and preventing oxidative stress that can damage cellular components like lipids, proteins, and DNA ³³. SeNPs are well-acting antioxidant components for their scavenging activity of free radicals. It can donate electrons to neutralize free radicals, such as hydroxyl, peroxyl, superoxide radicals, etc., and convert them into less harmful molecules like water or hydrogen peroxide etc. ^34,35. Also, SeNPs can mimic the activity of antioxidant enzymes such as glutathione peroxidase, superoxide dismutase, catalase, etc. ³⁶. Nanoparticles modulate endogenous antioxidant defense pathways by regulating key antioxidant enzymes such as Superoxide Dismutase (SOD), Catalase (CAT), and Glutathione peroxidase (GPx). This regulation is largely mediated through activation of the Nrf2-Keap1 signaling pathway, where nanoparticles promote nuclear translocation of Nrf2, leading to increased expression of antioxidant response element-driven genes ³⁷. SeNPs can chelate transition metal ions like iron and copper, thus reducing their participation in Fenton and Haber-Weiss reactions that produce harmful hydroxyl radicals and therefore prevent free radical production ^38,39. The bioactive compounds used in green synthesis (e.g., polyphenols, flavonoids) frequently remain on the surface of SeNPs and enhance their ROS scavenging activity by directly interacting and counteracting oxidizing agents. These several antioxidant mechanisms make green-synthesized SeNPs highly effective in reducing oxidative stress and defending biological systems ⁴⁰. These antioxidant methods for evaluating green-mediated SeNPs generally involve their ability to neutralize ROS and free radicals. The commonly used methods for the evaluation are the DPPH assay, which measures the ability of SeNPs to donate electrons or hydrogen to neutralize DPPH radicals, which are confirmed by a color change that indicates antioxidant activity ABTS assay ⁴¹, which estimates the ability of SeNPs to eradicate  ABTS radicals ⁴², Ferric Reducing Antioxidant Power (FRAP) determines the reducing potential of SeNPs by converting ferric ions (Fe³⁺) to ferrous ions (Fe²⁺) in a reaction that produces a colored complex ⁴³. Superoxide Radical Scavenging assay tests the ability of SeNPs to neutralize superoxide anions that are generated in a specific chemical reaction, and the Hydroxyl Radical Scavenging assay evaluates the ability of SeNPs to scavenge highly reactive hydroxyl radicals. Hydrogen peroxide Scavenging measures the ability of SeNPs to decompose hydrogen peroxide into water and oxygen, and reduce oxidative stress ⁴⁴, a lipid peroxidation inhibition assay that helps to test the ability to prevent lipid peroxidation in the cell membrane by neutralizing free radicals ⁴⁵. The above method defines the antioxidant potential of SeNPs and their effectiveness in alleviating oxidative stress (Figure 3).

Green-synthesized SeNPs cross the cell membrane and show their antioxidant activity by directly donating electrons to free radicals, mimicking antioxidant enzymes, and chelating metals. Antioxidant activities of different plant mediated SeNPs are descriptively represented in table 1. Among the various plants, some plant mediated SeNPs showed remarkable antioxidant activities. The most promising anti-oxidant activities of few plants mediated SeNPs in DPPH and ABTS assays are represented in the below diagram (Figures 4 and 5).

Table 1. Antioxidant activity of green-synthesized SeNPs

  Contd. Table 1. Antioxidant activity of green-synthesized SeNPs

 Contd. Table 1. Antioxidant activity of green-synthesized SeNPs 

 Contd. Table 1. Antioxidant activity of green-synthesized SeNPs 

 Contd. Table 1. Antioxidant activity of green-synthesized SeNPs 

This summary represents the more potent plant-based greener SeNPs, which exhibited excellent antioxidant activity in the DPPH assay. The potentiality of antioxidant activity was evaluated by analyzing their IC₅₀ values. Here, we can observe a gradual growth of the IC₅₀ value, which represents the gradual decrease in antioxidant activity. The first three plants mediated SeNPs; Waltheria indica (W. indica) (0.00692) to Citrus sinensis (C. sinensis) (0.00849) exhibited the most potent effect, as their IC₅₀ values are lower than others. It shows a little increase for Withania somnifera (W. somnifera) (0.014181). On the next plants, it shows a little variation with growing IC₅₀ value from Azadirachta indica (A. indica) (0.02393) to Tinospora cordifolia (0.02862). Then it shows a gradual, rapid increase from Terminalia arjuna (0.04518) to Goniothalamus wightii (G. wightii) (0.07562). In this rapidly growing stage, the plants Acai Berry and Cymbopogon citratus (C. citratus) with Syzgium aromaticum give the same IC₅₀ value of 0.05.  Here, in the DPPH assay, the plant W. indica (IC₅₀ value 0.00692) has the lowest IC₅₀ value, which represents the highest antioxidant capacity, and G. wightii (IC₅₀ value 0.07562) has the highest IC₅₀ value among these plants based SeNPs, which indicates its lowest antioxidant capacity (Figure 4 and Table 1).

In this review, it was found that four plant-mediated green SeNPs showed more potent antioxidant activity in the ABTS assay. The potentiality of the SeNPs was also evaluated by their IC₅₀ values. Here, W. indica (0.01685) and Calluna vulgaris (C. vulgaris) (0.01687) exhibited more promising activities as their IC₅₀ value are the lowest. The Annona muricata (A. muricata) (0.0661) and G. wightii (0.07412) have had decreasing activities than the first couple, as their IC₅₀ value is comparatively higher (Figure 5 and Table 1).

 Meta-analysis of Antioxidant Activity of SeNPs

 Forest Plot and Funnel Plot Analysis of IC₅₀ Values for Different Plant-Based SeNPs

DPPH Assay: In this analysis, the forest plot represents IC₅₀ values of plant-mediated SeNPs, which are used in biological research. The IC₅₀ value is a critical parameter, representing the concentration of a substance required to inhibit 50% of scavenging activity. Lower IC₅₀ values indicate higher potency, as smaller concentrations are needed for inhibition, whereas higher IC₅₀ values suggest weaker activity. The accompanying error bars represent the Standard Deviation (SD) for each IC₅₀ value, indicating the variability or precision of the IC₅₀ measurement for each plant-mediated SeNPs. For example, Bixa orellana (B. orellana) mediated SeNPs have a low SD of 0.006, indicating high precision in their IC₅₀ measurement. In contrast, Holarrhena antidysenterica has a higher SD of 0.022, reflecting more variability in its inhibitory activity. B. orellana (IC₅₀ =0.00538) exhibited extremely strong inhibitory activity, requiring a very low concentration to achieve 50% inhibition. This suggests that B. orellana could be a highly effective candidate for further research in medicinal applications. Acai Berry (IC₅₀ = 0.05) and Allium sativum (A. sativum) (IC₅₀ = 0.05898) also exhibit strong potency, as their IC₅₀ values are well below the threshold of 1, indicating that these plant-based SeNPs have significant inhibitory effects at relatively low concentrations. C. citratus (IC₅₀ = 0.23) and Cassia siamea (C. siamea) (IC₅₀ = 0.1239) exhibited moderate inhibitory effects, with IC₅₀ values above 0.1, yet still demonstrating potential for effective inhibition in certain contexts. The logarithmic scale on the x-axis enhances the clarity of the plot by compressing a wide range of IC₅₀ values, making it easier to compare plants with both low and high values on the same plot. The scale spans from 0.01 to 100, with values greater than 1 showing a shift towards weaker potency (to the right of the vertical reference line at IC₅₀ = 1) (Figure 6 and Table 2).

Table 2. Antidiabetic activity of green-synthesized SeNPs 

A funnel plot is made of selected plant extracts-based SeNPs, approximately 13 plants, with IC₅₀ values ranging from 0.12 mg/ml (Aloe vera) to 2.37 mg/ml [Polygala tenuifolia (P. tenuifolia)]. The overall mean IC₅₀ was approximately 0.47 mg/ml. Most SeNPs clustered around this mean with relatively small variability, for example, A. sativum (IC₅₀=0.16±0.007) and C. siamea (IC₅₀=1.50±0.011). More precise estimates with lower SD values (e.g., A. sativum, A. indica) feel closer to the mean, while SeNPs with larger IC₅₀ values [e.g., Moringa oleifera (M. oleifera), IC₅₀=0.46±0.010, and P. tenuifolia, IC₅₀=2.37±0.012] lie toward the edges of the funnel. Most points were located within the 95%CI boundaries, with no extreme outliers observed. The funnel plot (Table 2) demonstrated a generally symmetrical distribution of IC₅₀ values around the pooled mean of 0.47 mg/ml. Lower IC₅₀ values, such as Aloe vera (0.12±0.020 mg/ml) and A. indica (0.124±0.014 mg/ml), were balanced by higher IC₅₀ values, including C. siamea (1.50±0.011 mg/ml) and P. tenuifolia (2.37± 0.012 mg/ml). The absence of strong asymmetry suggests limited evidence of publication bias. As expected, studies with smaller SDs (more precise estimates, e.g., A. sativum at 0.16± 0.007 mg/ml) appear near the top of the funnel and cluster closely around the mean, while those with higher variability spread more widely. Although the plot is consistent with unbiased reporting, it should be noted that the use of SD instead of SE may underestimate or overestimate the actual confidence intervals. Moreover, the relatively small number of included SeNPs (n=13) reduces the sensitivity of the funnel plot to detect subtle asymmetries.

ABTS assay: The forest plot generated using the provided data shows the IC₅₀ values for different plant-based green SeNPs and their SDs. The IC₅₀ values are plotted on a logarithmic scale with error bars representing the 95% Confidence Intervals (CIs). The confidence intervals are calculated as the range within which the true IC₅₀ value lies with 95% certainty. IC₅₀ denotes the concentration at which 50% of the free radicals are inhibited. Standard Deviation (SD): Represents the variability of the IC₅₀ value for each plant. 95%CI: The confidence interval for the IC₅₀, typically calculated as IC₅₀±(1.96×SD), where 1.96 is the Z-value for a 95% confidence level.

SeNPs with smaller IC₅₀ values (indicating stronger inhibitory capacity) tend to have higher precision, as indicated by the tight clustering of data points at the top of the funnel. For example, A. sativum (IC₅₀ = 0.0661) and Aloe vera (IC⁵⁰=0.01687) are located near the top, suggesting strong inhibitory effects with low variability in the estimates. SeNPs with larger IC₅₀ values (indicating weaker inhibitory capacity) show a wider spread on the funnel plot, representing lower precision and larger uncertainty in their inhibitory effects. For instance, G. wightii (IC₅₀= 0.07412) and Morinda citrifolia (IC₅₀=0.01) show increased variability in their IC₅₀ measurements, as evidenced by the larger spread toward the bottom. The symmetry of the funnel plot is important. A symmetric funnel indicates that the data is reliable and unbiased. As seen in this plot, the data follow a symmetrical funnel shape, suggesting that there is no significant publication bias or distortion in the data. This indicates that the IC₅₀ estimates for plant extracts are generally consistent across studies. The funnel plot appears symmetric, which suggests that the IC₅₀ values for these plant-based SeNPs are reliable and consistent for antioxidant activity in the ABTS assay, with no significant bias or outliers in the data (Table 2).

 Antidiabetic effect of SeNPs

Diabetes is a rapidly growing global health concern, and diabetic patients has been rapidly increasing in recent times. Most synthetic conventional medicines are about to be botched to treat this condition.  Moreover, this conventional medicine has a lot of side effects like hypoglycemia, weight gain, gastrointestinal issues (nausea, diarrhea, abdominal pain, bloating), vitamin B12 deficiency, lactic acidosis, urinary tract infections, fluid retention (edema), etc. ¹¹¹. In this condition, nanomedicines could be a promising option as it has some extraordinary capabilities of enhancing drug delivery, drug solubility, stability, selective targeting, and the ability to reduce side effects ¹¹².

As a part of nanomedicine therapy, green-synthesized SeNPs can be a good choice. The antidiabetic effects of green-synthesized SeNPs are mostly owing to their capacity to improve insulin sensitivity. SeNPs enhance glucose uptake by cells and improve insulin signaling pathways ¹¹³. It protects pancreatic β-cells from oxidative damage and conserves their activity of insulin production and secretion ¹¹⁴. It inhibits the enzymes α-Glucosidase and α-Amylase, which help in breaking down carbohydrates to glucose. SeNPs can inhibit these enzymes and reduce blood glucose levels ¹¹⁵. Their suppression contributes to lower postprandial blood glucose levels ¹¹⁶. It can also control oxidative stress and inflammation, lowering the levels of ROS and inflammatory cytokines, which are elevated in diabetes ¹¹³. Moreover, green SeNPs were reported to lower fasting blood glucose by decreasing albumin and creatinine in the liver and kidneys. It helps to restore blood glucose, as glycogen consequently reduces the glucose level in the blood (Figure 6) ¹¹⁷.

Green SeNPs show their antidiabetic potentials by pancreatic beta cells reformation, scavenging beta cell’s reactive oxygen species, blocking the breakdown of complex carbohydrates in GIT and, and regulating glucose metabolism.

In this review, various studies were scrutinized to identify anti-diabetic potentials of green synthesized SeNPs in both α-glucosidase and α-amylase inhibition assays. Antidiabetic effects were measured based on the IC₅₀ value in both assays. Different plant-based SeNPs exhibited different extents of activities, where some plant-mediated SeNPs showed more promising activities.

Here, among the various plants, two plants were found those mediate SeNPs exhibited potent antidiabetic effects in the α-glucosidase inhibition assay. One of them is Fagonia cretica (F. cretica) (0.1) and the other is Ribes nigrum L. (4.484). F. cretica gives the most promising antidiabetic effects when used to mediate SeNPs, as it has exhibited the lowest IC₅₀ value. Ribes nigrum L. also showed encouraging activities, but comparatively less than F. cretica (Table 1).

In the α-amylase inhibition assay, the effects of the plant-based SeNPs were also evaluated by their IC₅₀ value. Two plants that mediate the SeNPs showed the most propitious antidiabetic effects among all the plants reviewed. The SeNPs fabricated using Solanum lycopersicum (S. lycopersicum) (IC₅₀ 0.0244642) showed the lowest IC₅₀ value in the inhibition assay, and showed the most promising antidiabetic activity. The second one, which mediated the SeNPs, is F. cretica (0.092), having a slightly increased IC₅₀ value between the two plants, indicating its decreased activity in the α-amylase inhibition assay (Table 1).

 Meta-analysis of Antidiabetic Activity of SeNPs

 Forest Plot and Funnel Plot Analysis of IC₅₀ Values for Different Plant-Based SeNPs

Alpha amylase assay: The forest plot highlights marked variability in α-amylase inhibitory activity among the tested plant extract-mediated SeNPs. The most potent inhibitors, S. lycopersicum and F. cretica, have IC₅₀ values well below 1 mg/ml, indicating strong enzyme inhibition. Zea mays shows intermediate inhibition, while Ribes nigrum L is comparatively weak. The 95% confidence intervals are narrow for the most potent extracts mediated SeNPs, reflecting relatively precise estimates, whereas they widen with higher IC₅₀ values. Overall, the plot demonstrates a clear gradient of inhibitory potency, with S. lycopersicum and F. cretica being the most promising candidates for α-amylase inhibition.

The funnel plot presented below visualizes the relationship between the log-transformed IC₅₀ values (on the x-axis) and the standard deviations (SDs) (on the y-axis) for various plant extract-mediated SeNPs. This log transformation is typically used in meta-analysis to compress the wide range of IC₅₀ values and allow for more meaningful comparisons. The log-transformed IC₅₀ values give insight into the inhibitory potency of the SeNPs. A lower IC₅₀ corresponds to stronger inhibitory activity (requiring lower concentrations), while a higher IC₅₀ indicates weaker activity (requiring higher concentrations). The SDs on the y-axis represent the uncertainty or variability in the IC₅₀ estimates. Larger SD values correspond to less precision in the IC₅₀ estimates, while smaller SD values reflect more reliable and precise measurements. Data points at the top of the funnel indicate high precision, while those at the bottom reflect low precision.

 Discussion

The present study provides a comprehensive synthesis of existing evidence on the antioxidant potential of nanoparticles and their relevance in oxidative stress-mediated pathologies. The findings indicate that nanoparticle-based systems consistently exhibit significant antioxidant and antidiabetic activity, primarily through modulation of intracellular redox balance and related cellular pathways. In this study authors found some plant mediated SeNPs those give promising antioxidant and antidiabetic activities. In DPPH assay, Aloe vera mediated SeNPs show scavenging activity near to 90% at 0.6 mg/ml concentration. Annona muricata NPs exhibit 90% scavenging at 0.1 mg/ml concentration. Camellia sinensis NPs show close to 100% scavenging at 0.091 mg/ml concentration. W. indica NPs show the lowest IC₅₀ value (IC₅₀-0.00692) and scavenging capacity 81.12±0.76% at 0.010-0.050 mg/ml concentration represent its promising activity. Citrus sinensis NPs (IC₅₀-0.00849) exhibit scavenging capacity 83.7% at 0.050 mg/ml concentration. The plant W. somnifera NPs (IC₅₀-0.014181) activity rises to 80% at 100 mg/ml concentration. In ABTS assay Annona muricata NPs (IC₅₀-0.0661) show almost 90% scavenging at 0.1 mg/ml concentration. C. vulgaris NPs (IC₅₀-0.016.87) exhibit 99.7% scavenging activity at 1.5 mg/ml concentration. Echinacea purpurea NPs exhibit 93.40% scavenging activity at 5 mg/ml concentration. In the FRAP assay, A. sativum NPs exhibit more than 80% inhibition at 0.5-0.6 mg/ml concentration. Aloe vera NPs scavenge nearly 90% at 0.5 mg/ml concentration. Blighia sapida NPs, scavenging capacity 200% at 10 mg/ml concentration and its ABTS scavenging capacity is 570.2%.

Greener SeNPs, which exhibited potent antidiabetic effects in α-glucosidase inhibition assay are, F. cretica NPs (IC₅₀-0.1) showed inhibitory activity of 79.56% at 1 mg/ml concentration, Cassica auriculata (C. auriculata) NPs inhibition capacity greater than 97% at 0.1 mg/ml concentration, M. oleifera NPs show 66.2% inhibition at 0.1 mg/ml concentration, Caralluma tuberculate (C. tuberculate) NPs show 71.55% inhibition at 0.8 mg/ml concentration. In the α-amylase inhibition assay, F. cretica NPs show 79.56% inhibition at 1 mg/ml concentration. C. auriculata NPs display 95% inhibition at 0.1 mg/ml concentration, M. oleifera NPs show 82.8% inhibition at 0.025 mg/ml concentration, C. tuberculata NPs exhibit 78.24% inhibition at 0.8 mg/ml concentration and Broccoli florets NPs exhibit 78.4% inhibition at 0.05 mg/ml concentration.

The effects of the plant-based SeNPs were also evaluated by their IC₅₀ value. Two plants that mediate the SeNPs showed the most propitious antidiabetic effects among all the plants reviewed. The SeNPs fabricated using S. lycopersicum (IC₅₀ 0.0244642) showed the lowest IC₅₀ value in the inhibition assay, and showed the most promising antidiabetic activity. The second one, which mediated the SeNPs, is F. cretica (0.092) 78.13±0.69%, having a slightly increased IC₅₀ value between the two plants, indicating its decreased activity in the α-amylase inhibition assay.

Greener SeNPs exhibit some potential activity both as antioxidant and antidiabetic agents. M. oleifera-mediated SeNPs (MO-SeNPs) suggestively increased the activities of hepatic antioxidant enzymes such as GSH-Px, CAT, and SOD in diabetic rat models, while reducing malondialdehyde levels, a marker of lipid peroxidation and oxidative damage. Thus, it works as both an antioxidant and an antidiabetic agent ¹²⁵. Additionally, SeNPs modulated inflammatory responses by lowering pro-inflammatory cytokines and reducing the accumulation of advanced glycation end products, thereby lessening oxidative stress-induced tissue damage. These findings suggest that SeNPs provide a dual protective mechanism by scavenging ROS and enhancing endogenous antioxidant defenses. Beyond this antioxidant role, SeNPs directly influence glucose homeostasis. In an in vivo study, MO-SeNPs reduced fasting blood glucose levels, enhanced insulin sensitivity, and restored pancreatic β-cell function ¹²⁶. Furthermore, SeNPs improve glucose uptake by increasing the expression of glucose transporter-4 in muscle cells and facilitate efficient glucose utilization. All this evidence suggests that SeNPs may act as a remarkable antioxidant and antidiabetic candidate.

The green biosynthesis method is an environmentally benign process using natural and biological resources like plant parts to synthesize NPs and evaluate biological (antioxidants and antidiabetic) activities. The green NPs are more suitable for antioxidant and enzymatic functions in diabetes. A lot of free radicals are generated in the body by biological mechanisms. These free radicals (oxygen free radical, methyl or ethyl free radical, and chlorine free radical) are more reactive and interfere with normal body mechanisms as well. Green synthesized SeNPs can scavenge these free radicals by their natural antioxidant potentials and functionally reduce oxidative stress. Various methods and assays like DPPH, ABTS, FRAP, etc., are used to estimate the scavenging capacity of free radicals. The measure of scavenging free radicals represents the high neutralization capacity of an antioxidant agent.

In this review, it was observed that the biogenic SeNPs showed concentration-dependent free radical scavenging activity. The green SeNPs with high concentration have a better scavenging capacity of free radicals. For example, among 10, 100, 200, and 400 mg/ml, the 400 mg/ml concentration showed better antioxidant capacity than the others. The free radical scavenging capacity is simply represented by the IC₅₀ values. The agents with lower IC₅₀ values represented the higher neutralizing capacity.

This study also scrutinized and conjugated the anti-diabetic capacity of green-synthesized SeNPs. Diabetes is a metabolic disorder that raises blood glucose levels due to low insulin production in the Islets of Langerhans of the pancreas, specifically in the β-cell. Green SeNPs are more effective for diabetic treatment.  Green-mediated SeNPs exhibit a concentration-dependent antidiabetic action. The overall functions of SeNPs have been shown on insulin hormone and blood glucose levels. Some enzymes are interrelated to maintain blood glucose levels by controlling carbohydrate digestion. Various in vitro and in vivo models suggested that the green synthesized SeNPs dose-dependently induce insulin sensitivity and inhibit the α-amylase and α-glucosidase enzymes (enzymes responsible for carbohydrate digestion), thus aiding in maintaining the blood glucose level and showing antidiabetic potential.

The biological effects of SeNPs depend significantly on their size and shape. Smaller and rod-shaped SeNPs are more reactive and potentially more toxic, but larger and spherical SeNPs are more stable and less toxic. High doses or prolonged exposure to SeNPs can lead to organ-specific toxicity, especially in the liver, kidneys, heart, and lungs, while low doses are generally safe and beneficial. SeNPs exhibit various side effects beyond their well-known antioxidant and antidiabetic properties. At high doses, it induces oxidative stress instead of reducing, leading to DNA damage, lipid peroxidation, mitochondrial dysfunction, cell apoptosis, etc. It can cause neurotoxicity, hepatotoxicity, and immunotoxicity at high doses ^127,128. So, the uses of nanoparticles for specific conditions require careful consideration to avoid toxicities.

Future perspective & limitations

Green synthesis is an eco-friendly process that presently reduces the need for toxic chemicals during nanoparticle synthesis, and shortly it will limit the large-scale use of hazardous chemicals in synthetic chemistry. Thus, this is an innocuous process both for environmental and biological health. Green-mediated SeNPs have been promisingly used in medical fields, and recently, nanotechnology has expanded its dimensions of use in the medical detection and care of diseases through treatment ^129,130. It enables targeted drug delivery, increases bioavailability by enhancing the solubility of poorly water-soluble drugs, enables sustained and controlled drug release, and reduces the side effects of drugs ¹³¹. Due to its comprehensive benefits, it may serve as an ideal antioxidant and antidiabetic agent. Except for their antioxidants and antidiabetic potentials, SeNPs exhibit strong antibacterial, antifungal, and antiviral properties, which makes them ideal for treating microbial infections ¹³². Their unique mechanisms can encounter drug-resistant pathogens. SeNPs are also good for cancer therapy because of their targeted drug delivery and for decreasing the side effects of cancer therapy. As SeNPs have potent antioxidant properties that can help in managing oxidative stress-related diseases like neurodegenerative disorders ¹³³. They show promise in modulating immune responses, which could aid in therapies for autoimmune diseases and inflammatory conditions. It can also be used for the diagnosis of disease ¹³⁴. These particles may produce other better effects of Integration with Other Technologies. Combining SeNPs with other nanomaterials (like graphene or gold nanoparticles) could enhance their properties for medical use, or SeNPs might assist in delivering CRISPR/Cas9 systems for targeted gene therapy ¹³⁵.

Although this systematic review offers a comprehensive outline of the antioxidant and antidiabetic potential of green-synthesized selenium nanoparticles (SeNPs), but the main limitation of this review was the protocol non-registration. There are some other limitations should be considered when interpreting the findings as review was mostly carried out based on in vitro assays. Thus, the translational relevance of these findings to human populations remains uncertain. Another significant limitation is the degree of heterogeneity among the included studies in terms of plant sources, synthesis methods, characterization techniques, particle size, and assay protocols. This variability makes direct comparisons perplexing and challenging; it also complicates the performance of a robust quantitative meta-analysis. In addition, the probability of publication bias cannot be omitted, as studies reporting optimistic outcomes are more likely to be published compared to those with undesirable or inconclusive results. Future research should focus on well-designed, standardized preclinical and clinical studies that will investigate the optimal dosing, safety profiles, and mechanistic pathways of SeNPs as antioxidants and in diabetes management. Multi-center randomized controlled trials and meta-analyses will be necessary to confirm the therapeutic potential observed in preclinical studies and to establish clear clinical guidelines for the use of green-synthesized SeNPs. By addressing these gaps, future studies can strengthen the evidence, facilitate clinical translation, and pave the way for the potential development of SeNPs-based therapeutic agents for oxidative stress and diabetes management.

 Conclusion

The remarkable potential of green-synthesized SeNPs as a sustainable and eco-friendly nanotechnology approach for biomedical applications is highlighted by this study. Nowadays, nanomedicines are better known for their effectiveness than conventional drugs. The use of nanoparticles in conjunction with biological extracts to improve disease management is a relatively recent breakthrough in modern research. It is impactful than any other conventional idea. Green synthesis is non-toxic, cost-effective, and environmentally amicable, in contrast to conventional chemical and physical processes causes which use biological elements such as plant extracts, microorganisms, and biomolecules. In this review, it was noticed that SeNPs may be used as a viable alternative to conventional medications, exhi-biting enhanced therapeutic efficacy with reduced toxicity in antioxidant and antidiabetic assays, as well as reducing environmental impact. Their effectiveness will be promising in treating conditions like oxidative stress or diabetes. Now, further studies should focus on optimizing synthesis protocols to enhance SeNPs stability and scalability, and it’s a need to conduct in-depth preclinical and clinical trials to validate their safety and efficacy, and ascertain the synergistic effects with other bioactive compounds to extend their therapeutic applications. SeNPs themselves have antioxidant properties. When it is synthesized with another biological extract that also has antioxidant properties, hypothetically, the result will be better than the previous one. These SeNPs, made with environmentally safe approaches, also have excellent antidiabetic properties due to their high surface reactivity and bioavailability. Additionally, SeNPs can transport medications with precision, release them in a controlled manner, and produce minimal side effects. Due to these attributes, green-synthesized SeNPs may act as promising therapeutic candidates, particularly for the treatment of diabetes and oxidative stress-related ailments. Thus, the green-synthesized selenium nanoparticles have acquired the potential to revolutionize the medical field due to their affordable and multifunctional nature.

Acknowledgement

The authors would like to thank their colleagues who read and helped refine the scope of this review.

Funding: The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

 Conflict of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.