Hybrid Metallic Nanostructures for Bio and Analytical Applications

Different hybrid nanoparticles (NPs), including FeM (M=Ni, Au, Pt, Pd) and Fe-biomolecules (biomolecule=glucose oxidase, p53p protein), have been synthesized by a surfactant-free, single-step electrochemical method. FeNi bimetallic NP systems have been chosen as the starting point of the present study. Shape evolution and phase transformation of FeNi NPs obtained by changing their composition is demonstrated. It has been shown that the shape evolution of NPs from concave cube to truncated sphere occurs concurrently with the phase transformation from bcc to fcc. In-situ formation of a very thin Ni-doped FeOOH outer layer and NiFe2O4 intermediate layer on the skin of the NPs is observed, the latter of which passivates the surface and dramatically enhances the air stability. Furthermore, bimetallic FeNi concave nanocubes with high Miller index planes have been obtained through controlled triggering of the different growth modes of Fe and Ni. Taking advantage of the higher activity of the high-index planes, mono-dispersed concave nanocages have been fabricated by introducing a material-independent electroleaching process. With the high-index facets exposed, these concave nanocubes and nanocages are found to be 10 and 100-fold, respectively, more active toward electrochemical detection of 4-aminophenol than cuboctahedrons which provides a label-free sensing approach to monitoring toxins in water and pharmaceutical wastes. In addition, the shape-dependent magnetic properties of a bimetallic system have been studied for FeNi NPs with well-defined concave cubic and octahedron shapes. The alloy composition was chosen to be close to that of Invar FeNi alloys (35% Ni content) but with concurrent presence of both bcc and fcc phases, in order to investigate the role of phase combination in controlling the magnetic properties. The role of the two phases in governing the magnetic properties has also been studied for both bulk and nanoalloys by large-scale density function theory (DFT) calculations using Vienna Ab-initio Simulation Package (VASP, Version 5.2), which provides a new complementary approach to understanding the magnetic properties of alloy materials. To extend the aforementioned method to other hybrid and bimetallic systems, FePt NPs with different compositions (Fe25Pt75, Fe30Pt70, Fe35Pt65) have been synthesized and their chemical sensing investigated for the electro-oxidation of vitamin C. The FePt alloy NPs are found to be superior catalysts for vitamin C electro-oxidation than Pt NPs and are significantly more selective for the detection of vitamin C against other common interference species, including dopamine, citric acid, uric acid, glucose, and NaCl. Enhancement in sensor performance can be attributed to the increase in specific surface area due to reduction of nanocrystallite size and to modification in the Pt electronic structure as a result of nanoalloying. We also synthesize bimetallic FeAu, FePd, and AuPt NPs and investigate their electrochemical properties for As(III) detection. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, Pd) than pristine noble metal NPs (without Fe alloying), with the best performance found for FePt NPs. The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), acting as the most detrimental interfering ion for As detection. The versatility of the method for hybridization of different components is demonstrated by synthesizing size-specific hybrid NPs based on Fe-biomolecules. We have chosen an anticancer peptide (p53p, MW 1.8 kDa) and an common enzyme (glucose oxidase, MW 160 kDa) as model molecules to illustrate the versatility of the method towards different types of molecules over a large size range. We show that the electrostatic interaction for complex formation of metal hydroxide ion with the partially charged side of the biomolecule in the solution is the key to hybridization of metal-biomolecule materials to form complexes as the building blocks. These hybrid NPs with controllable sizes ranging from 30 nm to 3.5 μm are found to exhibit superparamagnetic behavior, which is a big challenge for particles in this size regime. As an example of greatly improved properties and functionality of the new hybrid material, in-vitro toxicity assessment of Fe-glucose oxidase hybrid NPs shows no adverse effect, while the Fe-p53p hybrid NPs are found to selectively bind to cancer cells. The present work therefore definitely demonstrates the general applicability of the hybridization method for synthesis of metallic hybrid NPs with magnetic properties for different applications, including chemical sensing, magnetic resonance imaging contrast agents, and targeted drug delivery carriers

Hydrogel porosity controlling DNA-directed immobilization of gold nanoparticles revealed by DNA melting and scanning helium ion microscopy

Immobilization of nanomaterials is important for many applications, including sensor development, biomaterials design and catalysis. DNA-directed immobilization has been widely used because of its high specificity and programmability. While most previous work has been carried out using inorganic surfaces such as gold, silica, and carbon, we recently found that hydrogels are also useful for immobilization. For non-porous inorganic surfaces, DNA-directed immobilization is governed mainly by probe density, while porosity might play a major role for hydrogels. Herein, we test the effect of gel porosity on DNA-directed immobilization of gold nanoparticles (AuNPs). Porosity was varied by changing the hydrogel percentage and crosslinker density. The number of immobilized AuNPs and its binding strength were characterized by DNA melting experiments. Using scanning helium ion microscopy, the AuNP density on hydrogel was studied. The number of AuNP binding sites decreased with decreasing gel porosity or increasing AuNP size, implying that the associated AuNPs were inside the gel pores. Polyvalent binding is a key feature for nanoparticle immobilization. For a non-porous surface, polyvalent binding occurs only at one small spot. We found that hydrogels take advantage of its porous nature to establish 3-dimensional polyvalent binding. Even with a very low surface DNA density, effective AuNP immobilization can still be achieved.University of Waterloo || Canada Foundation for Innovation || Ontario Ministry of Research and Innovation || Natural Sciences and Engineering Research Council || Ministry of Higher Education of Saudi Arabia |

The Effect of Resilience Education by the Teach-back Method on the Stress of Mothers of Educable Mentally Retarded Children: A Field Trial Study

Background: The presence of a mentally retarded child is a stressful experience for the family, especially mothers. The present study aimed to determine the effect of resilience education by the teach-back method on the stress of mothers of educable mentally retarded children. Materials and Methods In this field trial study, 70 mothers of educable mentally retarded children were selected as the sample using convenience sampling method and then assigned to the intervention (n=35) and control groups (n=35) based on block random allocation. Each mother in the intervention group participated in 8 sessions of resilience education by the teach-back method (each session lasted 30-45 minutes) in a period of 30 days. The Parenting Stress Index of Abidin and Connor-Davidson Resilience Scale were filled out by mothers of the intervention (teach-back) and control groups in pretest and posttest. The obtained data were analyzed using SPSS version 16.0 software. Results: The mean score of maternal stress before the intervention was 127.94 ± 22.35 in the intervention group, and 129.31±21.82 in the control group. These values after the intervention were 88.6±17.98 and 135.23±23.08 in the intervention and control groups, respectively. In addition, the mean score of resilience before the intervention was 29.17±11.95 in the intervention group, and 25.89±10.3 in the control group. These values after the intervention were obtained 58.94±9.43 and 22.2±8.17 in the intervention and control groups, respectively. There was a significant difference between the intervention and control groups in the mean score of stress and resilience one month after the completion of intervention (p

Bimetallic Nanoparticles for Arsenic Detection

Effective and sensitive monitoring of heavy metal ions, particularly arsenic, in drinking water is very important to risk management of public health. Arsenic is one of the most serious natural pollutants in soil and water in more than 70 countries in the world. The need for very sensitive sensors to detect ultralow amounts of arsenic has attracted great research interest. Here, bimetallic FePt, FeAu, FePd, and AuPt nanoparticles (NPs) are electrochemically deposited on the Si(100) substrate, and their electrochemical properties are studied for As­(III) detection. We show that trace amounts of As­(III) in neutral pH could be determined by using anodic stripping voltammetry. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, and Pd) than pristine noble metal NPs (without Fe alloying). Limit of detection and linear range are obtained for FePt, FeAu, and FePd NPs. The best performance is found for FePt NPs with a limit of detection of 0.8 ppb and a sensitivity of 0.42 μA ppb^–1. The selectivity of the sensor has also been tested in the presence of a large amount of Cu­(II), as the most detrimental interferer ion for As detection. The bimetallic NPs therefore promise to be an effective, high-performance electrochemical sensor for the detection of ultratrace quantities of arsenic

Surface-Mediated Hydrogen Bonding of Proteinogenic α‑Amino Acids on Silicon

ConspectusUnderstanding the adsorption, film growth mechanisms, and hydrogen bonding interactions of biological molecules on semiconductor surfaces has attracted much recent attention because of their applications in biosensors, biocompatible materials, and biomolecule-based electronic devices. One of the most challenging questions when studying the behavior of biomolecules on a metal or semiconductor surface is “What are the driving forces and film growth mechanisms for biomolecular adsorption on these surfaces?” Despite a large volume of work on self-assembly of amino acids on single-crystal metal surfaces, semiconductor surfaces offer more direct surface-mediated interactions and processes with biomolecules. This is due to their directional surface dangling bonds that could significantly perturb hydrogen bonding arrangements.For all the proteinogenic biomolecules studied to date, our group has observed that they generally follow a “universal” three-stage growth process on Si(111)­7×7 surface. This is supported by corroborating data obtained from a three-pronged approach of combining chemical-state information provided by X-ray photoelectron spectroscopy (XPS) and the site-specific local density-of-state images obtained by scanning tunneling microscopy (STM) with large-scale quantum mechanical modeling based on the density functional theory with van der Waals corrections (DFT-D2). Indeed, this three-stage growth process on the 7×7 surface has been observed for small benchmark biomolecules, including glycine (the simplest nonchiral amino acid), alanine (the simplest chiral amino acid), cysteine (the smallest amino acid with a thiol group), and glycylglycine (the smallest (di)­peptide of glycine). Its universality is further validated here for the other sulfur-containing proteinogenic amino acid, methionine. We use methionine as an example of prototypical proteinogenic amino acids to illustrate this surface-mediated process. This type of growth begins with the formation of a covalent-bond driven interfacial layer (first adlayer), followed by that of a transitional layer driven by interlayer and intralayer hydrogen bonding (second adlayer), and then finally the zwitterionic multilayers (with intralayer hydrogen bonding). The important role of surface-mediated hydrogen bonding as the key for this universal three-stage growth process is demonstrated. This finding provides new insight into biomolecule–semiconductor surface interactions often found in biosensors and biomolecular electronic devices. We also establish the trends in the H-bond length among different types of the hydrogen bonding for dimolecular structures in the gas phase and on the Si(111)­7×7 surface, the latter of which could be validated by their STM images. Finally, five simple rules of thumb are developed to summarize the adsorption properties of these proteinogenic biomolecules as mediated by hydrogen bonding, and they are expected to provide a helpful guide to future studies of larger biomolecules and their potential applications

Predicting and elucidating the post-printing behavior of 3D printed cancer cells in hydrogel structures by integrating in-vitro and in-silico experiments

Abstract A key feature distinguishing 3D bioprinting from other 3D cell culture techniques is its precise control over created structures. This property allows for the high-resolution fabrication of biomimetic structures with controlled structural and mechanical properties such as porosity, permeability, and stiffness. However, analyzing post-printing cellular dynamics and optimizing their functions within the 3D fabricated environment is only possible through trial and error and replicating several experiments. This issue motivated the development of a cellular automata model for the first time to simulate post-printing cell behaviour within the 3D bioprinted construct. To improve our model, we bioprinted a 3D construct using MDA-MB-231 cell-laden hydrogel and evaluated cellular functions, including viability and proliferation in 11 days. The results showed that our model successfully simulated the 3D bioprinted structure and captured in-vitro observations. We demonstrated that in-silico model could predict and elucidate post-printing biological functions for different initial cell numbers in bioink and different bioink formulations with gelatine and alginate, without replicating several costly and time-consuming in-vitro measurements. We believe such a computational framework will substantially impact 3D bioprinting's future application. We hope this study inspires researchers to further realize how an in-silico model might be utilized to advance in-vitro 3D bioprinting research

Controlled tumor heterogeneity in a co-culture system by 3D bio-printed tumor-on-chip model

Abstract Cancer treatment resistance is a caused by presence of various types of cells and heterogeneity within the tumor. Tumor cell–cell and cell-microenvironment interactions play a significant role in the tumor progression and invasion, which have important implications for diagnosis, and resistance to chemotherapy. In this study, we develop 3D bioprinted in vitro models of the breast cancer tumor microenvironment made of co-cultured cells distributed in a hydrogel matrix with controlled architecture to model tumor heterogeneity. We hypothesize that the tumor could be represented by a cancer cell-laden co-culture hydrogel construct, whereas its microenvironment can be modeled in a microfluidic chip capable of producing a chemical gradient. Breast cancer cells (MCF7 and MDA-MB-231) and non-tumorigenic mammary epithelial cells (MCF10A) were embedded in the alginate-gelatine hydrogels and printed using a multi-cartridge extrusion bioprinter. Our approach allows for precise control over position and arrangements of cells in a co-culture system, enabling the design of various tumor architectures. We created samples with two different types of cells at specific initial locations, where the density of each cell type was carefully controlled. The cells were either randomly mixed or positioned in sequential layers to create cellular heterogeneity. To study cell migration toward chemoattractant, we developed a chemical microenvironment in a chamber with a gradual chemical gradient. As a proof of concept, we studied different migration patterns of MDA-MB-231 cells toward the epithelial growth factor gradient in presence of MCF10A cells in different ratios using this device. Our approach involves the integration of 3D bioprinting and microfluidic devices to create diverse tumor architectures that are representative of those found in various patients. This provides an excellent tool for studying the behavior of cancer cells with high spatial and temporal resolution

Bimetallic FeNi Concave Nanocubes and Nanocages

Concave nanostructures are rare because of their thermodynamically unfavorable shapes. We prepared bimetallic FeNi concave nanocubes with high Miller index planes through controlled triggering of the different growth kinetics of Fe and Ni. Taking advantage of the higher activity of the high-index planes, we then fabricated monodispersed concave nanocages via a material-independent electroleaching process. With the high-index facets exposed, these concave nanocubes and nanocages are 10- and 100-fold more active, respectively, toward electrodetection of 4-aminophenol than cuboctahedrons, providing a label-free sensing approach for monitoring toxins in water and pharmaceutical wastes

<i>In Situ</i> Hybridization of Superparamagnetic Iron-Biomolecule Nanoparticles

The increase in interest in the integration of organic–inorganic nanostructures in recent years has promoted the use of hybrid nanoparticles (HNPs) in medicine, energy conversion, and other applications. Conventional hybridization methods are, however, often long, complicated, and multistepped, and they involve biomolecules and discrete nanostructures as separate entities, all of which hinder the practical use of the resulting HNPs. Here, we present a novel, in situ approach to synthesizing size-specific HNPs using Fe-biomolecule complexes as the building blocks. We choose an anticancer peptide (p53p, MW 1.8 kDa) and an enzyme (GOx, MW 160 kDa) as model molecules to demonstrate the versatility of the method toward different types of molecules over a large size range. We show that electrostatic interaction for complex formation of metal hydroxide ion with the partially charged side of biomolecule in the solution is the key to hybridization of metal-biomolecule materials. Electrochemical deposition is then used to produce hybrid NPs from these complexes. These HNPs with controllable sizes ranging from 30 nm to 3.5 μm are found to exhibit superparamagnetic behavior, which is a big challenge for particles in this size regime. As an example of greatly improved properties and functionality of the new hybrid material, <i>in vitro</i> toxicity assessment of Fe-GOx HNPs shows no adverse effect, and the Fe-p53p HNPs are found to selectively bind to cancer cells. The superparamagnetic nature of these HNPs (superparamagnetic even above the size regime of 15–20 nm!), their biocompatibility, and the direct integration approach are fundamentally important to biomineralization and general synthesis strategy for bioinspired functional materials

Effect of Electrolyte Conductivity on Controlled Electrochemical Synthesis of Zinc Oxide Nanotubes and Nanorods

A one-step, catalyst- and seed-layer-free growth process is used to control the morphology of ZnO nanotubes and nanorods by modifying the electrolyte conductivity in an amperometric electrodeposition technique. This method does not require the use of O₂ bubbling or any etching step. ZnO nanotubes with high surface areas are found to form in less conductive electrolytes with monovalent anions (Cl^–, NO₃^–, ClO₄^–), and nanorods with smaller surface areas are produced in more conductive electrolytes with divalent anions (SO₄^2–, C₂O₄^2–), all mixed with ZnCl₂ at 80 °C. Our conductance measurements of the electrolytes confirm the important effect of the supporting electrolyte on controlling the observed morphologies and further suggest that ion diffusion in the electrolyte plays a key role in the growth mechanism of ZnO nanotubes and nanorods. In particular, ion diffusion in a more conducting electrolyte supported by divalent anions facilitates growth in the [0001] and [10–11] directions, with preferential growth in the [0001] direction therefore favoring one-dimensional or nanorod growth. On the other hand, in a less conducting electrolyte supported by monovalent anions, ion diffusion is sufficiently slow, which facilitates growth in the [0001] and [10–11] directions but with a higher contribution in the [10–11] direction due to termination of the (0001) plane by anion adsorption, leading to growth of the perimeter walls of the nanotubes. Furthermore, we demonstrate that the as-prepared ZnO nanotubes can be used as an effective photoanode material in a typical dye-sensitized solar cell application