**1. Introduction**

Nanomaterials exhibit chemical, physical, and biological features that are not found in other materials. In the food industry, electrical and chemistry industry, and cosmetics industry metal nanostructures have unique applications. In medicinal and industrial uses, Ag and Au nanoparticles comprise the backbone. The food sector [1, 2], catheters [3], dressings of wound [4], surgery equipment [5], synthetics [6], and optical limiter applications [7] all use silver nanostructures. Sensors [8], catalytic [9], and electrical applications [10] are only a few of the applications for gold nanoparticles. The usage of Au and Ag nanostructures as drug delivery systems demonstrated as bactericidal against Gram-positive and negative [11].

By-products from traditional synthesis techniques can be hazardous [12]. As a result, a variety of environmental and green synthesis strategies are being researched [7, 13]. Nanomedicine has had a huge influence as a result of these biosynthesized nanomaterials, and they have become the elementary units for upcoming medications to treat many ailments [14]. Plant extracts, enzymes, fungi, bacteria, and other ecofriendly synthesis processes have been using to synthesize Ag NSa and Au NSs [7, 15, 16]. Papaya, tansy, and citrus fruits are antioxidants found in fruit extracts that are used as stabilizers in the production of Ag and Au NPs [17].

Pomegranate is the scientific name for *Punica granatum*, it related to the Lythraceae's family. Polyphenol, anthocyanidins, glucose, ellagic acids, cyanidin 3-glucose, and 3,5-diglucose, hydrolysable tannins, and gall tannins, are all found in pomegranate extract [18]. Anthocyanins, which are found in abundance in pomegranates, are responsible for forming, reducing, and stabilizing of nanostructures [19]. The orange, *Citrus reticulata*, is high in phytochemicals, flavonoids, phenols, vitamins, folic acids, essential oils, and pectin [20]. Flavonoids aid in the removal of metallic ions from the body.

Ag NSs have exceptional antibacterial action, which explains why so much work is being put into developing these nanostructures. The use of Ag NPs in medicine is becoming more common. Various investigations have found that Ag NPs significantly reduce mitochondrial activity, resulting in cell apoptosis or necrosis in a variety of cells [21–23]. Interactions between Ag NPs and cells, on the other hand, have been limited. The surfaces of Au NPs are modified by DNA and amino acids when they are coupled with thiol and amine groups [24, 25]. The biocompatibility of Au NPs in therapeutic applications is critical. The size, shape, and surface modification of Au NPs determine whether they are hazardous or benign to cells [26].

Due to larger Stokes shift, narrower bandwidth of emission, and longer lifetimes emission, lanthanide ions have attracted for various applications like bio-labeling and optical amplification [27], solar cells [28], light-emitting diode (LED) [29], cancer photodynamic therapy [30], and fluoroimmunoassay [31].

Many scientists are interested in the metal enhanced fluorescence (MEF) of metal NSs and rare-earth ions because they need significantly low input intensities, and hence their applications in diagnostics have increased [32, 33]. The fluorophore's emission intensity is increased by 10–103 when it is near metal particles with subwavelength sizes [34]. The MEF is caused by two methods: (1) fluorophores' coupling with SPR, and (2) fluorophores' coupling to the SPR. The influence of a local electric field [35]. Fluorophores with metal particles at 10 nm spacing are acted on by increasing electric fields surrounded the particles, increasing their absorption cross-section and, ultimately, enhanced radiation. The energy transmits from surface plasmonic resonance to the rare-earth ion, and vice versa, results in either enhanced reduction or reabsorption in emission in the other mechanism. The fluorescence increase is primarily influenced by the shape and diameter of nanostructures, fluorophore's dipole orientations, and the overlap of the fluorophore luminescence intensity and absorption with the plasmonic band of nanostructures [36]. Because of the rivalry of the highly enhanced field surrounding nanoparticles and nonradiative transition due to the dampening of dipole oscillators by metal surfaces, MEF is mostly dependent on the spacing among metal structures and fluorophores [37].

The SPR value is altered by different shapes, various sizes, and dielectric functions of NSs as well as the host [38]. The optimal spacing between fluorophore ions and NPS for emission enhancement exists. Based on the different energy between the rare-earth ions and the metal SPR, quenching of luminescence may occur even at relatively short distances. The number of NSs, SPR, and number of phonon states of fluorophores all affect the luminescence efficiency. The plasmon-mediated augmentation of luminescence-based on the antenna effect has been found, it boosts the excitation effect and emission rate [39]. Metal nanoparticles (donor) absorb energy, which is subsequently transferred nonradiatively to rare-earth ions (acceptor) in the Forster process [40]. One group concluded that energy transmit is the primary cause of emission amplification near metal objects [41]. Other research has found that nanoparticles can stop rare-earth ions from transferring non-radiative energy to metal nanostructures [42, 43]. These are dependent on the luminophore-nanoparticle distance, nanoparticle size, and metal particle concentration.

The goal of this research is to investigate the binding of enhanced fluorescence from Eu(TTFA)3 and Sm(TTFA)3 complexes to metal nanostructures such as silver and gold NSs in greater detail. We discovered a robust link among SPR of NSs and rare-earth molecules, as well as metal nanoparticle reabsorption by the SPR. The MTT assay is being used to investigate the cytotoxicity of metal NSs on cancer cell lines. The findings could aid in the development of biomedication delivery systems that are less hazardous than toxic ones.
