Tailoring of hydroxyapatite nanoparticle surfaces of varying morphologies to facilitate counterion diffusion and subsequent protein denaturation.

Rapid advances in nanotechnology have led to the synthesis and development of various nanomaterials with complex structures and appropriate surface functionalization in recent years. Specifically designed and functionalized nanoparticles (NPs) are increasingly researched and hold great potential in biomedical applications (for example, imaging, diagnostics and therapeutics). Yet, the surface functionalization and biodegradability of NPs play a significant role in their application. Understanding the interactions occurring at the interface between the NPs and the biological components is thus crucial for predicting the fate of the NPs. In this work we study the effect of trilithium citrate functionalization of the hydroxyapatite NPs (HAp NPs) with and without cysteamine modification and their subsequent interaction with hen egg white lysozyme and corroborate the conformational changes of the protein with effective diffusion of the lithium (Li+) counter ion.

Solid-Supported Amplification of Aggregation Emission: A Tetraphenylethylene-Cucurbit[6]uril@Hydroxyapatite-Based Supramolecular Sensing Assembly for the Detection of Spermine and Spermidine in Human Urine and Blood.

The development of sensitive and selective tools for the detection and quantification of biomarkers is important in the diagnosis and treatment of clinical diseases. Spermine (SP) and spermidine (SPD) act as biomarkers for early-stage diagnosis of cancer in humans as their increased levels in urine are indicative of abnormal biological processes associated with this fatal disease. In this study, we introduced a strategy for solid-supported amplification of the effective aggregation-induced-emission (AIE) effect of a water-soluble tetraphenylethylene (TPE)-based probe in developing a supramolecular sensing platform for the rapid, sensitive, and selective detection of SP and SPD in water. The nonemissive TPE derivative (TPEHP) forms a less emissive conjugate with hydroxyl cucurbit[6]uril (CB[6]OH) in water, which undergoes several-fold enhancement of effective emission upon electrostatic interaction with the solid surface of hydroxyapatite nanoparticles (HAp NPs), dispersed in the aqueous media. The corresponding three-component supramolecular assembly disrupts by the intrusion of SP and SPD in the CB[6] portal because of the stronger binding ability with CB[6], resulting in a turn-off fluorescence sensor for SP and SPD with enhanced sensitivity. The assembly-disassembly-based sensing mechanism was thoroughly demonstrated by carrying out isothermal titration calorimetry (ITC), spectroscopic, and microscopic experiments. The sensing system showed low limits of detection (LODs) of 1.4 × 10-8 and 3.6 × 10-8 M for SP and SPD, respectively, which are well below the required range for the early diagnosis of cancer. Besides, a good linear relationship was obtained for both SP and SPD. Nominal interference from various metal ions, anions, common chemicals, amino acids, and other biogenic amines makes this sensing platform suitable for the real-time, low-level measurement of spermine (and spermidine) in human urinary and blood samples.

Role of surface charges on interaction of rod-shaped magnetic hydroxyapatite nanoparticles with protein.

Magnetic hydroxyapatite (MHAp) exhibits excellent biocompatibility, making it an ideal candidate as a biomaterial. Recent investigations have shown that the combined effect of magnetite and hydroxyapatite nanostructures provide efficient means for diagnostic and therapeutic applications which can be controlled with an external magnetic field. For these applications an important aspect to be considered is the interaction of the MHAp nanoparticles (NPs) with biomolecules such as protein (P) and the subsequent biological response. The present study involves synthesis and characterization of Fe doped MHAp NPs, surface functionalized with tri-lithium citrate and cetyl pyridinium chloride having Li+ and Cl- as counterions, respectively. The electrostatic interaction of the MHAp NPs (with and without surface functionalization) with proteins such as Hen egg white lysozyme and Pepsin A were investigated to study the P-NP interactions. The crystalline structure and compositions of these NPs were characterized using X-ray diffraction. The size and aspect ratio were measured using transmission electron microscopy. The P-NP interaction was characterized by Dynamic light scattering, Zeta-potential measurements, UV-vis absorption and fluorescence emission spectroscopies. The conformational changes of the protein secondary structures were investigated by circular dichroism spectroscopy. The functionality of the protein after interaction with surface modified MHAp NPs were studied using activity assays.