## 1 Introduction  
For patients who are suffering from advanced or highly invasive cancer and have lost the opportunity for surgery, chemotherapy remains the best treatment option. One of the biggest limitations to current cancer therapeutics is their lack of a specific targeting mechanism that avoids nonspecific toxicity to healthy tissue [1]. Nanotechnology offers a unique opportunity for overcoming non-specific tissue targeting and the unwanted toxic side effects of current chemotherapeutics [2; 3; 4]. Of the nanopharmaceuticals currently on the market, very few are designed to treat cancer [5; 6]. To decrease the toxic effects associated with paclitaxel, for example, a nanoparticle formulation for paclitaxel was introduced under the trade name Abraxane [5; 6]. A reduction in toxicity was accomplished by binding paclitaxel with albumin in a protein-bound nanoparticle followed by nanoparticle dissolution and release of an albumin-bound drug complex [6; 7; 8]. While this system has been successful and has been on the market since 2005, its major drawback is that it lacks a targeting system [5; 6]. This design limitation has led to intense research directed towards the fabrication of nanoparticles with surface ligands capable of targeting a specific tumor [9; 10; 11]. Furthermore, nanoparticles are being designed that not only deliver a drug to the tumor site but also have a tracking moiety bound to the surface of the nanoparticle itself [5]. With the combination of tracking and targeting moieties, it is expected that cancer treatments will lead to significantly improved patient outcomes [10; 11]. Different types of nanoparticles designed for multi-functionality have been investigated. Some systems are capable of carrying two separate drugs in one nanocarrier [1; 3; 4; 12]. Other nanocarrier systems are bi-functionalized so they are capable of targeting cancerous tissue and delivering a cancer drug [7; 13]. Other nanocarriers contain a third functionality that enables real-time monitoring of the nanoparticle's movement through the body [14]. These systems are of particular interest because they permit monitoring of the effectiveness of the targeting system as well as drug release [2; 9; 11]. One nanocarrier that has potential to become a critical component of bi-functional nanoparticle systems are halloysite clay nanotubes (HNTs). HNTs are naturally occurring clay nanoparticles that have emerged as a potent nanocontainer and nanocarrier for drug delivery [15; 16; 17]. HNTs are formed through strain caused by lattice mismatch between the adjacent silicon dioxide and aluminum oxide layers [15; 16; 17]. HNTs have found numerous commercial applications as additives in polymers and plastics, electronics components, cosmetics and personal care products [17; 18]. HNTs are unique and versatile nanomaterials that are composed of a double layer of aluminum, silicon, hydrogen, and oxygen [15; 16; 17]. HNTs are ultra-thin hollow tubes with diameters typically smaller than 100 nanometers, with lengths typically ranging from 500 nanometers to over 1.2 microns [15; 19]. Due to the chemical makeup of the HNT lumen, it is capable of being doped with a diverse set of substances including antibiotics, chemotherapeutics, growth factors, RNA and DNA, and used as a vehicle for drug transportation and sustained release [20; 21; 22; 23]. Additionally, several recent studies have demonstrated that HNTs are cytocompatible [24; 20; 25; 26]. In one study, HNTs were added to cultures of epithelial adenocarcinoma and human breast cancer cells up to a concentration as high as 75 \(\upmu\)g/mg) and cell proliferation was not affected [24]. In fact, most studies have shown that the HNTs do not produce cytotoxic effects [20; 24; 25; 26]. Recently, [PERSON] et al. in 2012 showed that HNTs also have anti-inflammatory properties [27]. Research interest in the surface modification of HNTs has grown significantly in recent years [28].