We incorporated a near-infrared (NIR) fluorescent dye, indocyanine green (ICG), in amine-modified layered double hydroxide nanoparticles (LDHs) by electrostatic attractions to render LDHs–ICG as an efficient NIR contrast agent for in vivo optical imaging. The further coating of chitosan on the external surfaces of LDHs–ICG was achieved through the cross-linking of amine-modified LDHs and different amounts of chitosan by using glutaraldehyde (GA) as a cross-linked agent. The hybridization of this organic–inorganic nanocomposite produced an efficient NIR optical contrast agent because the adsorbed ICG molecules were stabilized in the layered structures of LDHs to prevent them from leaching and/or metabolizing in physiological conditions. The cell viability and hemolysis assay also showed low cytotoxicity and low release of hemoglobin from the cell lysis of red blood cells (RBCs). The in vivo biodistribution results demonstrated that the coating of LDHs with different amounts of chitosan can develop organ-specific drug delivery systems, which can efficiently regulate the nanoparticle accumulation in various organs with un-coated LDHs–ICG targeting the liver and spleen, mono-chitosan-coated LDHs–ICG targeting the lungs, double chitosan-coated LDHs–ICG targeting the lungs and liver, and trimethylammonium (TA) modified double chitosan-coated LDHs–ICG samples targeting the liver. In addition to the high potential for the employment of chitosan-coated LDHs–ICG samples for developing contrast agents for in vivo imaging, the LDH nanoparticles can deliver therapeutic drugs to desired target organs by controlling the coating amounts of chitosan. Therefore, this approach can improve efficiency for traditional cancer diagnosis and cancer chemotherapy.

We designed a novel oral colon-specific drug delivery system (OCDDS) using a modification of mesoporous silica nanoparticle (MSN) surfaces with pH-sensitive trimethylammonium (TA) groups through a pH-sensitive hydrazone bond. The pH-sensitive TA groups can efficiently increase the loading amounts of anionic drugs by a strong electrostatic attraction. After oral administration, the acidic pH of gastric juice can fully hydrolyze the TA–hydrazone bonds and further eliminate the positive charges of TA groups from MSN surfaces. When the hydrolyzed complexes were further delivered to the colon's pH of 7–8, a rapid and complete release of adsorbed drugs was observed. From the studies of spectroscopic characterizations, we demonstrated that the combination of pH-sensitive hydrazone–TA groups and nano-sized particles of the MSN carriers took the advantages of increasing the accessible surface areas of drug molecules and varying the charges of MSN surfaces, which can increase dissolution and release rate of hydrophobic drug molecules. In addition, a cell viability assay also indicated that no cytotoxicity of MSN–hydrazone–TA complexes was observed even with treatment in an extremely high nanoparticle concentration. Consequently, our new formulation is highly biocompatible for the OCDDS, and we can completely solve the low stability, low solubility, and low drug bioavailability in the free form of drug molecules for the design of OCDDS.

Intracellular hydrogen peroxide levels have the potential to be exploited in cancer therapy.

To evaluate the role of charge in the nanoparticle distribution we modified the external surface of layered double hydroxide nanoparticles with various organic groups bearing different charges and further a near-infrared (NIR) fluorescent dye (Cy5.5) is conjugated in the layered structure to assess the biodistribution. The functionalized nanocomposites performed as highly efficient contrast agents since Cy5.5 molecule stabilization inside the layered structure can safeguard them from metabolization in the physiological environments. The cell viability, lactate dehydrogenase and hemolytic assays showed no cytotoxicity with an exceptionally low release of both lactate dehydrogenase and hemoglobin from the treated cells. The in vivo biodistribution results disclosed a high accumulation of positive amino-layered double hydroxides (LDHs) in the lungs. In contrast, there is a rapid clearance of negatively charged carboxylate-LDHs from blood flow by liver uptake. Interestingly neutral LDH-PEG5000 showed enhanced blood circulation time, without high fluorescent accumulation in the major organs. In vitro cellular uptake studies from flow cytometry are relevant to the interactions between the nanoparticle surfaces and various cell types and the data are relevant to effects observed for in vivo biodistribution. To further demonstrate that surface functionalization on LDH nanoparticles can promote targeted drug release, we further immobilized hydroxo-substituted cisplatin (CP) on carboxylate-modified LDHs by coordination bonding. Due to the ideal cleaving property of the carboxylate group the coordinated CP can be efficiently released by the increase of acidic proton and Cl⁻ concentration in the endosomal environment. Functionalized LDHs can be successfully employed as targeted drug delivery systems. When the LDH–CP complex accumulate primarily in the targeted organ, the high positive charge on the framework of LDHs cause susceptibility to rapid endocytosis, which facilitates sustained drug release with minimal systemic toxicity providing the apt treatment in the targeted organ.

To develop a carrier for use in enzyme prodrug therapy, Horseradish peroxidase (HRP) was immobilized onto mesoporous silica nanoparticles (IBN-4: Institute of Bioengineering and Nanotechnology), where the nanoparticle surfaces were functionalized with 3-aminopropyltrimethoxysilane and further conjugated with glutaraldehyde. Consequently, the enzymes could be stabilized in nanochannels through the formation of covalent imine bonds. This strategy was used to protect HRP from immune exclusion, degradation and denaturation under biological conditions. Furthermore, immobilization of HRP in the nanochannels of IBN-4 nanomaterials exhibited good functional stability upon repetitive use and long-term storage (60 days) at 4 °C. The generation of functionalized and HRP-immobilized nanomaterials was further verified using various characterization techniques. The possibility of using HRP-encapsulated IBN-4 materials in prodrug cancer therapy was also demonstrated by evaluating their ability to convert a prodrug (indole-3- acetic acid (IAA)) into cytotoxic radicals, which triggered tumor cell apoptosis in human colon carcinoma (HT-29 cell line) cells. A lactate dehydrogenase (LDH) assay revealed that cells could be exposed to the IBN-4 nanocomposites without damaging their membranes, confirming apoptotic cell death. In summary, we demonstrated the potential of utilizing large porous mesoporous silica nanomaterials (IBN-4) as enzyme carriers for prodrug therapy.