# Copper- and Iron-Based Nanoflowers in Cancer Theranostics
## 1 Introduction  
Despite various advancements and the introduction of cutting-edge technologies in medical sciences, cancer remains a significant global public health concern [1]. It accounted for an estimated 9.6 million deaths in 2018. Projections suggest that cancer could soon surpass heart disease as the leading common cause of death [2]. Typical treatments are often less effective and can cause serious damage to healthy cells, worsening patients' condition [3, 4]. Consequently, there is a constant global demand for more effective cancer treatments [4]. In this regard, the rise of nanotechnology offers new avenues for early cancer diagnosis and treatment. Nanotechnology, particularly through the modification of various nanoparticles (NPs), has been extensively utilized in biomedical research [5]. NPs offer several unique advantages: their small size allows for easy metabolism by the body, and their large surface area enables them to carry therapeutic drugs, prolong drug action, enhance efficacy at lower doses, and reduce side effects [6, 7, 8, 9, 10]. Nano-PROTAC offers solutions to challenges such as poor water solubility, limited cell permeability, off-target effects, and metabolic instability [11]. [PERSON] et al., introduced a nanoengineering approach (Nano-PROTACs) by encapsulating ARV-771 within glutathione (GSH)-responsive polydithamide polymer (PDSA) nanoparticles, which enhanced BRD4 protein degradation and suppressed downstream oncogene c-Myc expression [12]. In another study, a homogeneous anti-MHC-II nanobody-drug conjugate (VHH7-DM1) was developed using Sortase A (StrA)-mediated protein conjugation. This conjugate demonstrated efficacy in both in vitro and in vivo models for treating aggressive murine B-cell lymphoma. With superior pharmacokinetics, VHH conjugates surpassed commercial monoclonal antibodies (mAbs) in terms of internalizationand clearance, offering reduced systemic toxicity and enabling convenient non-invasive imaging [13]. As a result, NPs are considered powerful theranostic tools with multiple biomedical applications [14; 15]. Theranostics is a cutting-edge strategy that integrates therapy and diagnosis into a single platform for accurate cancer detection. It is considered a promising advancement in addressing the challenges of conventional cancer treatments. Nanoparticles (NPs) are especially effective as carriers for theranostic agents due to their exceptional physicochemical properties [16]. Previous applications have imposed varied requirements on nanostructures, leading to the development of a wide array of nanoparticle types. Among these, metal nanoparticles, particularly copper [17; 18] and iron [19; 20], have become indispensable in biomedicine due to their tunable properties and biocompatibility [21; 22], establishing them as a promising category. For instance, copper is present in many proteins and enzyme catalytic sites [23], and its oxides offer a multitude of advantages, such as inducing oxidative stress for tumor destruction and catalyzing oxygen production from endogenous hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) to alleviate tumor hypoxia [24]. Similarly, transition metals like iron (Fe) enhance the fundamental properties of nanomaterials, increasing their functionality and offering flexibility to meet the specific requirements of various applications [25]. The performance of metal oxides can be precisely adjusted by controlling factors like size, shape, composition, and structure, rather than relying solely on their chemical composition [26; 27]. With this level of precision, the use of metal oxides reaches new heights, where their performance can be significantly impacted by slight manipulations, sometimes making it challenging to select the most suitable candidate for a given application. In addition to other nanostructures, a new category of NPs owing structural parts smaller than 100 nm [28] known as nanoflowers (NFs), has recently captured extensive attention.