Bappaditya Samanta

Magnetic assembly of colloidal superstructures with multipole symmetry

The assembly of complex structures out of simple colloidal building blocks is of practical interest for building materials with unique optical properties (for example photonic crystals and DNA biosensors) and is of fundamental importance in improving our understanding of self-assembly processes occurring on molecular to macroscopic length scales. Here we demonstrate a self-assembly principle that is capable of organizing a diverse set of colloidal particles into highly reproducible, rotationally symmetric arrangements. The structures are assembled using the magnetostatic interaction between effectively diamagnetic and paramagnetic particles within a magnetized ferrofluid. The resulting multipolar geometries resemble electrostatic charge configurations such as axial quadrupoles (‘Saturn rings’), axial octupoles (‘flowers’), linear quadrupoles (poles) and mixed multipole arrangements (‘two tone’), which represent just a few examples of the type of structure that can be built using this technique.

Polymer and biopolymer mediated self-assembly of gold nanoparticles

Gold nanoparticle-polymer composites are versatile and diverse functional materials, with applications in optical, electronic and sensing devices. This tutorial review focuses on the use of polymers to control the assembly of gold nanoparticles. Examples of synthetic polymers and biopolymers are provided, as well as applications of the composite materials in sensing and memory devices.

Drug delivery using nanoparticle-stabilized nanocapsules.

Microcapsules (MCs) are versatile systems with applications in areas as diverse as microreactors, catalysis,[1] diagnostics and drug delivery.[2] In these systems self-assembly of lipids and/or polymers can be used to generate several types of nano- and micro- capsules. These include vesicular structures such as liposomes,[3] polymerosomes,[4] colloidosomes,[5] and polyelectrolyte capsules that feature aqueous interiors and exteriors.[6] An alternate motif is provided by emulsions, where additives are used to stabilize the interface between immiscible fluids to produce e.g. oil-in-water emulsions.[7] Through tailoring of the composition and structure of the building blocks MCs of both types can be engineered with well-defined structures, functions and stability.[8] MCs provide excellent delivery vehicles for biomedical applications, featuring high payload-to-carrier ratios and protection of encapsulated materials from degradation.

Formation of Ordered Cellular Structures in Suspension via Label-Free Negative Magnetophoresis

The creation of ordered cellular structures is important for tissue engineering research. Here, we present a novel strategy for the assembly of cells into linear arrangements by negative magnetophoresis using inert, cytocompatible magnetic nanoparticles. In this approach, magnetic nanoparticles dictate the cellular assembly without relying on cell binding or uptake. The linear cell structures are stable and can be further cultured without the magnetic field or nanoparticles, making this an attractive tool for tissue engineering.

Self-assembly and cross-linking of FePt nanoparticles at planar and colloidal liquid-liquid interfaces

Terpyridine thiol functionalized FePt and Au NPs were self-assembled and cross-linked at the liquid-liquid interfaces using Fe(II) metal ion. Complexation of terpyridine with Fe(II) metal ion leads to NP network and affords stable membranes and colloidal shells at the liquid-liquid interfaces.

Stability, toxicity and differential cellular uptake of protein passivated-Fe3O4 nanoparticles

We have explored the mechanism and differential uptake of BSA coated Fe3O4nanoparticles (NPs) by different cancerous and isogenic cell types.

Catalytic Microcapsules Assembled from Enzyme–Nanoparticle Conjugates at Oil–Water Interfaces

Involuntary association: Anionic beta-galactosidase enzymes associate with positively charged Au nanoparticles to produce reduced-charge conjugates, which assemble at oil-water interfaces to result in stable microcapsules (see picture). The microcapsules were formed quickly and showed high enzymatic activity, which makes them promising materials for biotechnology applications.

Stable Magnetic Colloidosomes via Click-Mediated Crosslinking of Nanoparticles at Water-Oil Interfaces

Alkyne- and azide-functionalized iron oxide nanoparticles are co-assembled at the water-oil interface and covalently linked using click chemistry under ambient conditions to create magnetic colloidosomes (see image). These colloidosomes possess high stability, size-selective permeability, and are responsive toward external magnetic stimuli.

Nano-Conjugate Fluorescence Probe for the Discrimination of Phosphate and Pyrophosphate

We describe a pyrophosphate (PPi) probe that is based on a fluorescent dicarboxylate-substituted poly(para-phenyleneethynylene) (PPE) and 10 nm cobalt-iron spinel nanoparticles (NPs) in aqueous media. The spinel NPs efficiently quench the fluorescence of the PPE at a concentration of 20-30 pmol. Addition of phosphate anions to the PPE-NP construct displaces the quenched PPE to give rise to a fluorescent response; we found that PPi and phosphate (Pi) have significantly different binding affinities for the self-assembled materials. We can discern >40 nM PPi in the presence of 0.1 mM Pi at pH 7, which suggests that these assemblies may be useful in bio-analytical applications. This displacement assay was used to effectively determine the ability of pyrophosphatase to hydrolyze PPi to Pi.

DNA-mediated assembly of iron platinum (FePt) nanoparticles

Nanocomposite materials consisting of FePt nanoparticles and DNA were constructed via DNA-mediated “bricks and mortar” self-assembly. Electrostatic interaction between the cationic nanoparticles and the DNA through surface recognition led to the formation of extended composite aggregates. These DNA-assembled aggregates feature increased interparticle spacing arising from the DNA “mortar”. The enhanced structure and increased spacing in the bio-nanocomposite assembly was found to alter the magnetic properties of the assemblies, as demonstrated by a 54 K change in blocking temperature (TB).